This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Lötsch, J.
Right arrow Articles by von Hentig, N.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Lötsch, J.
Right arrow Articles by von Hentig, N.

 Previous Article  |  Next Article 

Antimicrobial Agents and Chemotherapy, September 2007, p. 3264-3272, Vol. 51, No. 9
0066-4804/07/$08.00+0     doi:10.1128/AAC.00036-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Association of Saquinavir Plasma Concentrations with Side Effects but Not with Antiretroviral Outcome in Patients Infected with Protease Inhibitor-Susceptible Human Immunodeficiency Virus Type 1{triangledown}

Jörn Lötsch,1* Sebastian Harder,1 Martin Stürmer,2 Hans-Wilhelm Doerr,2 Gerd Geisslinger,1 Schlomo Staszewski,3 and Nils von Hentig1

pharmazentrum frankfurt/ZAFES, Institute of Clinical Pharmacology, Johann Wolfgang Goeth University, Theodor Stern Kai 7, D-60590 Frankfurt, Germany,1 Institute of Medical Virology/ZAFES, Johann Wolfgang Goethe University, Theodor Stern Kai 7, 60590 Frankfurt, Germany,2 Medical HIV Research and Treatment Unit, Johann Wolfgang Goethe University, Theodor Stern Kai 7, 60590 Frankfurt am Main, Germany3

Received 11 January 2007/ Returned for modification 27 April 2007/ Accepted 11 June 2007


arrow
ABSTRACT
 
The objective of this study was to identify parameters among saquinavir pharmacokinetics, patients' demographics or comedications, to be addressed for improved personalized therapy. The presence of human immunodeficiency virus type 1 (HIV-1) RNA at therapy week 48 (principal target parameter), CD4 cell count at week 48, infections and side effects during 48 weeks, indicators of liver toxicity and lipid abnormalities at week 48, and a 12-h saquinavir plasma concentration-versus-time profile were assessed in 56 patients receiving saquinavir-ritonavir (1,000 and 100 mg, respectively) twice daily (44 therapy-naïve and 12 antiretrovirally pretreated patients) for association with saquinavir plasma concentrations, demographics, baseline values of target parameters, and coadministered antiretrovirals. Antiretroviral failure was observed in 8 of the 56 patients in whom HIV-1 RNA was detectable at week 48. This therapeutic failure was not associated with individual saquinavir pharmacokinetics. More likely, therapeutic failure was related to incidences interfering with antiretroviral therapy, causing therapy interruptions or incompliance. Weak associations were, however, seen between high maximum saquinavir plasma concentrations and both CD4 counts of ≥200 cells µl–1 at week 48 (P = 0.014) and constitutional side effects during 48 weeks (P = 0.002). However, patients with high CD4 counts and constitutional side effects were not identical (P = 0.53). Saquinavir therapeutic drug monitoring in patients infected with protease inhibitor-susceptible HIV-1 taking saquinavir-ritonavir (1,000 and 100 mg, respectively) is not demanded for improving the antiretroviral effect. It may be contemplated in cases with constitutional side effects or low CD4 counts with weak immune responses.


arrow
INTRODUCTION
 
The human immunodeficiency virus type 1 (HIV-1) protease inhibitor saquinavir at a twice-daily oral dose of 1,000 mg is a well-established component of antiretroviral therapy (2, 8, 10, 20). It is combined with 100 mg ritonavir, which blocks cytochrome P450 3A4/5 (CYP3A4/5) (8, 10), ensuring antiretrovirally effective saquinavir plasma concentrations.

However, antiretroviral therapy that includes saquinavir-ritonavir is still associated with therapeutic failure and side effects, and saquinavir plasma concentrations display high interindividual variability (15). This is a therapeutic setting that suggests that personalized dosing regimens should be established to tailor saquinavir plasma concentrations with the intention to maximize therapy success while minimizing side effects. In fact, therapeutic drug monitoring of antiretroviral drugs has been suggested previously by various authors (1, 18).

However, a modification of the dosing regimen bears the danger of losing therapeutic efficacy or increasing side effects. Therefore, it is good clinical pharmacological practice to base personalized dosing on quantitative information about the relationship between a patient's individual variables, coadministered drugs and plasma concentrations, and between plasma concentrations and therapeutic effects. Once an effect-versus-plasma concentration relationship has been established, methods such as therapeutic drug monitoring up to population pharmacokinetics are available to individually adapt the dosing regimen.

The present study explored the quantitative relationship of plasma concentrations of saquinavir with its clinical wanted and unwanted effects in 56 HIV-1-infected patients taking saquinavir-ritonavir (1,000 and 100 mg, respectively). On the basis of a positive finding, the possibility of establishing personalized dosing regimens for saquinavir to increase therapeutic efficacy and/or decrease side effects was to be explored.


arrow
MATERIALS AND METHODS
 
Study design. The main goal of antiretroviral therapy is the suppression of HIV. Therefore, the principal target parameter of this investigation was the detection of HIV-1 RNA at the 48th week of therapy. Since the study's focus was on saquinavir dose personalization, pharmacokinetic parameters of saquinavir were assessed for their predictive value for the main target parameter. However, having in mind therapy optimization by any means, additional potential predictors of antiretroviral therapy success, such as individual antiretroviral comedications, were included in the search for predictive factors of HIV suppression.

As second target parameters, the patients' immune status was assessed by analyzing the CD4 cell count at week 48 and the occurrence of infections during the observation period for associations with saquinavir pharmacokinetics or antiretroviral comedications.

When the main goal of antiretroviral therapy is achieved, when HIV is successfully suppressed and the patient's immune status is stable, therapy personalization can address improving the subject's quality of life. Therefore, tertiary target parameters were unwanted effects such as laboratory biochemical indicators of liver toxicity and lipid abnormalities at week 48 and side effects over the entire observation period with their association to saquinavir pharmacokinetics and antiretroviral comedications.

In the case of a positive finding of an association of saquinavir pharmacokinetics with target parameters, its correlations with the subjects' demographics were analyzed to obtain a personalized dosing recommendation. In addition, correlations between ritonavir and saquinavir plasma concentrations were analyzed because of a possibility to tailor saquinavir plasma concentrations by modifying ritonavir dosing. Moreover, since dose personalization may be jeopardized by high intraindividual variability of the target pharmacokinetic parameter, a second pharmacokinetic assessment was performed using 14 consenting patients.

The study protocol adhered to the Declaration of Helsinki on Biomedical Research Involving Human Subjects. It was approved by the Medical Faculty Ethics Review Board of the Johann Wolfgang Goethe University of Frankfurt, and informed consent was obtained.

Patients. Between March 2002 and June 2005, 46 men and 10 women with HIV-1 infection aged 25 to 60 years (median, 40 years) and weighing 44 to 98 kg (median, 69.5 kg) were enrolled. They took 1,000 mg saquinavir mesylate (corresponding to 10.2 to 22.2 mg/kg of body weight [median, 14.4 mg/kg]) two times a day either as saquinavir soft gel capsules (Fortovase, 200 mg saquinavir mesylate; Hoffmann-La Roche, Basel, Switzerland) (n = 37) or as saquinavir hard gel capsules (Invirase, 200 mg saquinavir mesylate; Hoffmann-La Roche, Basel, Switzerland) (n = 19). During the study period, the formulation was not switched in an individual patient. Assignment of the pharmaceutical formulation to an individual patient was not controlled by protocol, although a temporal bias was avoided (P = 1.0 for soft gel/hard gel versus first/second half of the study period [Fisher's exact test]). All patients took 100 mg ritonavir twice daily (Norvir; Abbot GmbH, Wiesbaden, Germany), whereas reverse transcriptase inhibitors were administered as part of highly active antiretroviral therapy independent of the actual study protocol (Table 1).


View this table:
[in this window]
[in a new window]

  		TABLE 1. Measures of antiretroviral success, immune status, and side effects in 56 patients treated with saquinavir separately for antiretroviral comedication

Forty-four patients were naïve with respect to specific antiretroviral therapy, 12 had previously taken antiretroviral therapy (5 to 94 months; median, 42.5 months), and 8 of them had taken protease inhibitors including saquinavir (n = 5). Baseline genotypic HIV resistance testing using the ViroSeq HIV-1 Genotyping System V2 (Abbott, Wiesbaden, Germany) (22) was negative in all patients with respect to viral mutations conferring resistance against protease inhibitors. Therefore, all patients were eligible for the present analysis, and the exclusion of nonnaïve subjects with respect to therapy as a possible confounder was unnecessary. The two women who were treated during pregnancy according to their immune status and in accordance with actual guidelines (16) finished the entire period of 48 therapy weeks with saquinavir-ritonavir. Patients with liver function impairment corresponding to a Child-Pugh classification of B or C (17) and patients taking CYP3A4-modulating cotherapies other than antiretrovirals were not enrolled.

Patients at any CD4 cell count or viral load at baseline of therapy were included. Baseline viral load ranged between "below the lower limit of quantification," i.e., <50 copies/ml (n = 4) to 106 copies/ml (median, 234,000 copies/ml), and the baseline CD4 cell count ranged from 1 to 514 cells µl–1 (median, 56 cells µl–1), with 44 patients having a baseline CD4 cell count of <200 cells µl–1.

Pharmacokinetic assessments. (i) Drug administration and blood sampling. A 12-h plasma concentration-versus-time profile was taken once for each patient between the 9th and 1,913th saquinavir-ritonavir dose (median, 184th dose), i.e., between the end of week 1 and week 137 (median, week 14). After an overnight fast, saquinavir and ritonavir were administered, followed by a standard breakfast of about 595 kcal, 21% fat, composed of 20 g butter, 50 g bread, 20 g marmalade, 40 g cornflakes, 150 ml milk, 200 ml apple juice, and 400 ml tea. Venous blood was drawn into potassium EDTA tubes before dosing and at 1, 2, 4, 6, 9, and 12 h after dosing. The blood was centrifuged for 10 min at 4,000 min–1; plasma was separated within 20 min and stored at –20°C with quality control samples until testing. For 14 patients taking saquinavir soft gel capsules, the intraindividual variability of saquinavir pharmacokinetics was studied by taking an additional 12-h plasma concentration-versus-time profile between weeks 1 and 68. A sufficiently sized group of patients taking hard gel capsules could not be gathered.

(ii) Analytics of saquinavir and ritonavir plasma concentrations. Saquinavir and ritonavir plasma concentrations were assayed by high-performance liquid chromatography-tandem mass spectrometry methods (Therapia GmbH, Berlin, Germany) (equipment from Merck-Hitachi, Darmstadt, Germany, and Applied Biosystems, Streetsville, Canada). The validation of the assay used internal standards for saquinavir and ritonavir (provided by Hoffmann-LaRoche, Basel, Switzerland, and Abbott Laboratories Ltd., Queenborough, United Kingdom), and the reliable lower limit of quantification for both saquinavir and ritonavir was 20 ng/ml; linearity of the calibration curve was proven up to 20,000 ng/ml (11). Ritonavir is antiretrovirally inactive at the given dose (12) but was assayed because a possible association with saquinavir plasma concentrations provided an additional possibility to therapeutically optimize saquinavir plasma concentrations by modifying ritonavir dosing rather than saquinavir dosing. Interday and intraday coefficients of variation for ritonavir and saquinavir were <8% and <7%, respectively, at concentrations of 2,500 ng/ml and <10% and <9%, respectively, at concentrations of 250 ng/ml. Mean deviations from nominal concentrations were below 5% for all analytes and concentrations throughout the entire analysis. External quality control was performed by frequent participation in an interlaboratory quality assurance program (INSTAND eV, Düsseldorf, Germany).

Pharmacodynamic measurements. The study focused on the status of therapy at week 48 after the start of therapy. Wanted and unwanted therapeutic effects of antiretroviral therapy were assessed through this time.

(i) Antiretroviral activity and patients' immune status. The viral load was measured using a COBAS AmpliPrep/COBAS TaqMan HIV-1 test (Roche Diagnostics, Mannheim, Germany) with a quantification range of 50 to 10,000,000 copies/ml. CD4 cells were counted, and all infections were recorded with additional consideration of AIDS-related diagnoses (category C according to Centers for Disease Control and Prevention [CDC] criteria [www.cdc.gov, accessed 3 November 2006]).

(ii) Unwanted effects. Laboratory indicators of liver function (aspartate transaminase [AST], alanine amino transferase [ALT], gamma glutamyl transferase [{gamma}-GT]) and plasma lipids (cholesterol and triglycerides) were assessed at the scheduled times. Values threefold higher than the upper limit of the normal laboratory range were taken as indicators of liver toxicity (AST level of >105 IU, ALT level of >105 IU, and {gamma}-GT level of >117 IU, grade 2 or more according to the Common Toxicity Criteria [CTC v3.0] [http://www.fda.gov/cder/cancer/toxicityframe.htm, accessed 3 November 2006]), or lipid abnormalities were assessed (plasma cholesterol and triglyceride levels >250 mg/dl). In addition, all drug-related adverse events during the first 48 therapy weeks were recorded and grouped into gastrointestinal, constitutional (e.g., asthenia and sleepiness, lymphadenoma, or fever of unknown genesis), or neurological side effects; psychiatric or dermatological symptoms; lipodystrophy; or hematological abnormalities.

Data analysis. (i) Pharmacokinetic analyses. The maximum and minimum plasma concentrations, Cmax and Cmin, respectively, and the time from dosing to Cmax, Tmax, were taken directly from the data. The absorption lag time, Tlag, was defined as the time of the last sampling point at which the saquinavir plasma concentrations were not higher than those at baseline. The area under the plasma concentration-versus-time curves (AUC) was calculated using the log-linear trapezoidal rule, and the saquinavir clearance, CL/F, was obtained from dose/AUC. The apparent elimination half-life, t1/2, was obtained by dividing ln2 by the slope of a regression line through the terminal linear segment of the log-transformed saquinavir concentration-versus-time curve. Pharmacokinetic parameters were log transformed for analysis according to the outcome of normality testing and in accordance with FDA guidelines for pharmacokinetic parameter assessments (http://www.fda.gov/cber/gdlns/pedphrm.htm).

The pharmacokinetic parameters of saquinavir that had been identified as being associated with effects were analyzed for correlations with demographic parameters of the patients or with ritonavir pharmacokinetics, with the latter being obtained in a manner similar to that of saquinavir. The intraindividual and interindividual variabilities of pharmacokinetic parameters of saquinavir that had been identified to be associated with effects were compared by means of analysis of variance in order to judge whether these parameters can be addressed at some precision for personalized therapy.

(ii) Principal target parameter: HIV-1 RNA at week 48. The viral load at therapy week 48 was dichotomized into 0 or 1 for <50 copies/ml (the lower limit of detection of HIV-1 RNA) or ≥50 copies/ml, respectively. It was submitted to binary logistic regression with regressors being saquinavir pharmacokinetic parameters (log Cmax, log Cmin, Tmax, Tlag, and log AUC, obtained during the first occasion of pharmacokinetic assessment in all patients), with the Cmin for saquinavir (Cmin,saquinavir) being below the upper limit of 53.7 ng/ml of the in vitro 90% inhibitory concentration (IC90) range (19) or below the proposed in vivo protein-binding corrected IC95 of 278 ng/ml (3, 24), both dichotomized for "yes" or "no"; ritonavir pharmacokinetic parameters; the patients' demographic parameters (age and sex); the log viral load at baseline; coadministered antiretrovirals (dichotomized into 0 or 1 for absent or present); the total number of antiretrovirals given to the patient (i.e., three or four); previously taken antiretroviral therapy (dichotomized for "yes" or "no"); and previously taken protease inhibitors (dichotomized for "yes" or "no"). Variables were included "stepwise forward" into the logistic regression, and the likelihood ratio was used as a statistical criterion. Subsequently, chi-square statistics, Fisher's exact tests, or Wilcoxon/Kruskal-Wallis rank sum tests were applied to significant regressors; odds ratios were calculated; and analyses were performed when appropriate. In principle, results are reported only when they passed the post hoc steps after logistic regression.

(iii) Secondary target parameters: CD4 cell count at week 48 and infections during 48 weeks. A cutoff of 200 CD4 cells/µl at week 48 was taken as a pharmacodynamic indicator of the patient's immune status as an accepted parameter guiding antiretroviral therapy; that is, patients with less than 200 CD4 cells (i) are recommended to take prophylaxis for Pneumocystis carinii pneumonia, (ii) should be treated if they are therapy naïve (www.aidsinfo.nih.gov/guidelines/), and (iii) are classified as grade 3 in the CDC classification of HIV and AIDS (www.cdc.gov). The CD4 cell count at week 48, dichotomized for <200 cells µl–1 or ≥200 cells µl–1, was submitted to logistic regression including the same regressors and procedures as those used for the detection of HIV-1 RNA at week 48. The occurrence of infections during the 48 weeks was similarly analyzed for "all infections" and again for AIDS-related infectious diseases.

(iv) Tertiary target parameters: laboratory biochemical indicators of liver toxicity and lipid abnormalities at week 48 and unwanted effects during 48 weeks. The presence or absence of laboratory indicators of drug toxicity at week 48, separately dichotomized for "yes" or "no" and again dichotomized for the presence of any indicator of liver toxicity (i.e., AST level of >105 IU, ALT level of >105 IU, or {gamma}-GT level of >117 IU) or of any indicator of lipid abnormalities (plasma cholesterol or triglyceride level of >250 mg/dl), was submitted to logistic regression as described above.


arrow
RESULTS
 
The therapeutic status at week 48 is summarized in Table 1, and pharmacokinetic parameters of saquinavir and ritonavir are summarized in Table 2. HIV-1 RNA was undetectable in both women at the time of labor (between the 37th and 38th weeks of pregnancy). HIV therapy was continued for 3 and 32 weeks, respectively, in the mothers after giving birth by caesarean section to two HIV-1-negative children.


View this table:
[in this window]
[in a new window]

  		TABLE 2. Noncompartmental pharmacokinetic parameters of saquinavir and ritonavir after twice-daily oral administration of 1,000 mg saquinavir and 100 mg ritonavir in 56 HIV-1-infected patients

Predictors of HIV-1 RNA detection at therapy week 48. At week 48, HIV-1 RNA in plasma was undetectable in 48 of the 56 patients (Fig. 1). Cmin,saquinavir (Fig. 2) was above the upper limit of 53.7 ng/ml of the in vitro IC90 range (19) in all patients except for one, with a Cmin of 50 ng/ml. Cmin,saquinavir was below the proposed in vivo protein-binding corrected IC95 of 278 ng/ml (3, 24), but this was not predictive of the antiretroviral outcome. Although the plasma concentration-versus-time curves suggested a later Tmax in patients with therapy failure (Fig. 3), none of the pharmacokinetic parameters (log Cmax, log Cmin, log AUC, Tlag, and Tmax) was identified by logistic regression to predict this therapeutic outcome. Moreover, none of the parameters [plus the concentration range, log(Cmax – Cmin)], differed statistically significantly between patients with and without HIV-1 RNA at week 48 when multiple non-{alpha}-corrected tests were applied (P = 0.22 for Tmax and P < 0.68 for all other parameters [Wilcoxon tests]) (Fig. 2). These results did not change when the 12 monotherapy-naïve patients were excluded from the analysis, nor did they change when the five saquinavir-pretreated patients were excluded from the analysis.


Figure 1
View larger version (11K):
[in this window]
[in a new window]

  		FIG. 1. Incidence of detection of HIV-1 RNA after 1 year of therapy in relation to the patients' sex and antiretroviral comedications. *, P < 0.05; (*), P = 0.089 (multiple, non-{alpha}-corrected Fisher's exact tests). The results did not pass the logistic regression analysis step and are therefore to be regarded only as a tendency. ART, antiretroviral therapy; PI, protease inhibitors.


Figure 2
View larger version (16K):
[in this window]
[in a new window]

  		FIG. 2. Main noncompartmental pharmacokinetic parameters of saquinavir obtained from 12-h pharmacokinetic profiles of 56 patients with HIV-1 infection. The parameter values found for patients who had no detectable HIV-1 RNA after 48 weeks of therapy did not significantly differ from those found for patients who had detectable levels of HIV-1 RNA after 48 weeks. Single values and box plots showing the median (horizontal solid line), the mean line (horizontal dotted line), and the lower boundary of the box indicate the 25th percentile; the upper boundary indicates the 75th percentile; and whiskers above and below the box indicate the 90th and 10th percentiles.


Figure 3
View larger version (11K):
[in this window]
[in a new window]

  		FIG. 3. Steady-state saquinavir plasma concentration-versus-time profiles (median and interquartile range) obtained from 56 HIV-1-infected patients treated with 1,000 mg oral saquinavir plus 100 mg ritonavir separately for patients in whom HIV-1 RNA was detected in plasma after 48 weeks of therapy or not. Pharmacokinetic parameters Cmax, Cmin, AUC, Tlag, and Tmax did not differ statistically significantly between outcome groups (Fig. 2).

Thus, reasons other than saquinavir pharmacokinetics were more likely to have caused the antiretroviral therapy failure. Specifically, hospitalizations for therapy of tuberculosis (n = 1), Kaposi's sarcoma (n = 1), or severe anemia (n = 1) and occurrences of serious depression (n = 1), severe tiredness and asthenia (n = 1), and acknowledged incompliance (n = 2) were likely to have caused interruptions of antiretroviral therapy. There was only one patient with detectable HIV-1 RNA for whom no incident was recorded that could explain therapeutic failure.

Predictors of CD4 cell count at week 48 and of infections during 48 weeks. Log Cmax,saquinavir was significantly associated with a CD4 cell count at week 48 above or below 200 cells µl–1 (P < 0.001 [chi-square statistics after significant logistic regression]). In patients with CD4 cell counts of ≥200 cells µl–1, the median Cmax,saquinavir was 3,270 ng/ml (range, 484 to 6,390 ng/ml), whereas it was 2,195 ng/ml (range, 674 to 4290 ng/ml) in patients with CD4 cell counts of <200 cells µl–1 (P = 0.014 [Wilcoxon test]) (Fig. 1). In addition, lower baseline CD4 cells numbers were predictive for CD4 cell counts of <200 cells µl–1 at week 48 (P < 0.001 [chi-square statistics after logistic regression]).

CD4 cell counts of <200 cells µl–1 were not identified by logistic regression to be associated with the occurrence of infections, both "all infections" such as candidosis (n = 5), bacterial pneumonia (n = 2), varicella zoster virus infections (n = 4), and syphilis (n = 2) and infections associated with AIDS such as tuberculosis (n = 1), Pneumocystis carinii pneumonia (n = 1), and cytomegalovirus pneumonia (n = 1) and also Kaposi's sarcoma (n = 2). However, single testing performed despite the negative result of logistic regression showed a tendency towards more frequent infections in patients with CD4 cell counts of <200 cells µl–1; that is, "all infections" occurred in 10 of 20 patients with CD4 cell counts of <200 cells µl–1 but in only 8 of 36 patients with CD4 cell counts of ≥200 cells µl–1 (P = 0.042 [Fisher's exact test]), and opportunistic infections occurred in 4 of 20 patients with CD4 cell counts of <200 cells µl–1 but in only 1 of 36 patients with CD4 cell counts of ≥200 cells µl–1 (P = 0.05 [Fisher's exact test]). These results did not change when the 12 non-therapy-naïve patients were excluded from the analysis, nor did they change when the five saquinavir-pretreated patients were excluded from the analysis.

After Cmax,saquinavir (Table 2) had been identified as somewhat predicting the patients' immune statuses, its correlation with other parameters and its intraindividual variability were analyzed. Not surprisingly, log Cmax was strongly correlated with log Cmin,saquinavir (r2 = 0.72; P < 0.001) (Fig. 4). Jeopardizing body weight-based dose personalization, log Cmax was only very weakly correlated with the patients' weights (r2 = 0.09; P = 0.023) (Fig. 4). Further jeopardizing dose personalization, the interindividual and intraindividual variances of Cmax ({sigma}2 = 2,066,000 and 1,254,000 mg/ml2, respectively) (Fig. 5) did not differ statistically significantly (P = 0.18 [analysis of variance]). Cmax,saquinavir was also very weakly correlated with the minimum and maximum plasma concentrations (Table 2) of ritonavir (r2 = 0.08 and P = 0.033 for a correlation with Cmin,ritonavir and r2 = 0.09 and P = 0.026 for a correlation with Cmax,ritonavir) (Fig. 4) as previously reported (9). In addition, log Cmax,ritonavir and log Cmin,ritonavir were negatively correlated with log CL/Fsaquinavir (r2 = 0.14; P < 0.01) and positively correlated with t1/2,saquinavir (r2 = 0.11 and P = 0.012 and r2 = 0.13 and P < 0.01 for correlations with log Cmax,ritonavir and log Cmin,ritonavir, respectively).


Figure 4
View larger version (7K):
[in this window]
[in a new window]

  		FIG. 4. Correlations of maximum saquinavir plasma concentrations, Cmax, with patients' weights and with minimum and maximum plasma concentrations of ritonavir. All correlations were weak except for the correlation between Cmax,saquinavir and Cmin,saquinavir, for which the equation of linear regression is also given to provide a basis to estimate Cmax when only trough plasma concentrations of saquinavir (Cmin) are clinically available.


Figure 5
View larger version (15K):
[in this window]
[in a new window]

  		FIG. 5. Interindividual variability of Cmax in 56 patients (left, closed symbols) taking 1,000 mg saquinavir plus 100 mg ritonavir twice daily and inter- and intraindividual variabilities for 14 patients (right, open symbols [one symbol per occasion]) who participated on two occasions of pharmacokinetic assessments. The intraindividual variabilities of Cmax were as high as their interindividual variabilities (P = 0.18). The values of individual patients are displayed with different symbols and are connected by dotted lines for better visibility.

Predictors of unwanted effects. Log Cmax,saquinavir was predictive (P = 0.001 [chi-square statistics after significant logistic regression]) of constitutional side effects such as asthenia and sleepiness (n = 7), lymphadenopathy (n = 2), orthostatic dizziness (n = 2), fever without infection (n = 1), weight gain (n = 1), peripheral edema (n = 1), and spontaneous pneumothorax (n = 1). Patients with these side effects had median maximum saquinavir plasma concentrations of 3,810 ng/ml (range, 1,810 to 6,140 ng/ml), whereas patients without constitutional side effects had a median Cmax,saquinavir of 2,300 ng/ml (range, 484 to 6,390 ng/ml; P = 0.002 [Wilcoxon test]) (Fig. 6). Moreover, one patient with severe asthenia and tiredness jeopardizing his compliance and in whom the antiretroviral therapy was ineffective had a Cmax,saquinavir of 4,600 ng/ml.


Figure 6
View larger version (20K):
[in this window]
[in a new window]

  		FIG. 6. Saquinavir maximum plasma concentrations, Cmax, compared between patients with CD4 counts of <200 cells µl–1 and patients with CD4 counts of ≥200 cells µl–1 at week 48 and compared between patients with and without constitutional side effects. (A) Single values and box plots show the median (horizontal solid line) and the mean (horizontal dotted line), the lower boundary of the box indicates the 25th percentile, the upper boundary indicates the 75th percentile, and whiskers above and below the box indicate the 90th and 10th percentiles. The significance levels (*, P < 0.05; **, P < 0.01) have been obtained by pairwise comparisons with Wilcoxon tests. (B) Presence or absence of CD4 cell counts of <200 and constitutional side effects on an individual level. All 56 patients are sorted for saquinavir Cmax, shown in the left column (the minimum is at the bottom, in white; the maximum is at the top, in black; and intermediate values are in gray, darkening with increasing Cmax). Each individual has a separate line connecting their individual values of Cmax (grayscale) with those of the presence (black) or absence (white) of a CD4 cell count of <200 cells µl–1 after 48 weeks (middle column) and the presence (black) or absence (white) of constitutional symptoms through week 48 (right column). The figure shows that with increasing Cmax from bottom to top, the frequency of CD4 cell counts of <200 cells µl–1 decreases and the frequency of constitutional side effects increases, however, without a statistically significant association (P = 0.533).

Although Cmax,saquinavir was associated with both constitutional side effects and high CD4 cell counts (see above), a tendency that fewer occurrences of CD4 counts of <200 cells µl–1 with increasing Cmax,saquinavir were associated with more constitutional symptoms (Fig. 6, right) was not statistically significant. Specifically, among patients with CD4 cell counts of ≥200 cells µl–1 at week 48, 11 had constitutional symptoms, and 25 did not, and among patients with CD4 cell counts of <200 cells µl–1, 4 had constitutional symptoms, whereas 16 did not (P = 0.533 [Fisher's exact test]). Further contradicting that a high CD4 cell count is unavoidably associated with constitutional side effects was the observation that patients with constitutional symptoms had almost the same CD4 cell counts at week 48 as patients without these side effects (median CD4 cell counts of 226 cells µl–1 [range, 54 to 773 µl–1] and 268 cells µl–1 [range, 73 to 1,264 µl–1], respectively; P = 0.77 [Wilcoxon test]).

Saquinavir pharmacokinetics were not associated with any side effects other than constitutional side effects. Associations of antiretroviral therapy with side effects were (i) more frequent high triglycerides at week 48 in patients taking abacavir (P < 0.001 by chi-square statistics after logistic regression; odds ratio, 7.3; 95% confidence interval [CI], 1.6 to 33.3; P = 0.019 by Fisher's exact test), (ii) more frequent lipid abnormalities (plasma cholesterol or triglyceride levels of >250 mg/dl) at week 48 in patients on a quadruple regimen than in patients on a triple regimen (P = 0.002 by chi-square statistics after logistic regression; odds ratio, 4.2; 95% CI, 1.05 to 16.7; P = 0.047 by Fisher's exact test), (iii) more frequent lipodystrophy in patients taking stavudine (odds ratio, 51; 95% CI, 3.1 to 826.5; P = 0.011 by Fisher's exact test), and (iv) more gastrointestinal side effects in patients on abacavir (odds ratio, 6.2; 95% CI; 1.4 to 26.6; P = 0.016 by Fisher's exact test). High laboratory values of cholesterol, ALT, and {gamma}-GT at week 48 were predicted by the respective high baseline values (data not shown).


arrow
DISCUSSION
 
In one-seventh of the patients, HIV was detectable at the end of the 48-week observation period. However, this therapeutic failure could not be associated with individual saquinavir pharmacokinetics. Saquinavir plasma concentrations neither were lower nor fluctuated more or peaked significantly later or earlier in these patients than in those with undetectable levels HIV-1 RNA. Although zidovudine administration was associated with fewer incidences of HIV-1 RNA at week 48, this observation did not pass the main statistical analysis and neither did a tendency toward better antiretroviral efficacy of quadruple therapy than of triple therapy (P = 0.089) (Fig. 1).

More likely, the therapeutic failure in seven of the eight patients was related to incidences that interfered with antiretroviral therapy, causing therapy interruptions or incompliance. For only one patient, an explanation for therapy failure was found neither in the patient's records nor by genotypic HIV resistance testing (ViroSeq TM HIV-1 Genotyping System V2; Abbott, Wiesbaden, Germany) or saquinavir pharmacokinetics. Thus, from the present data, routine monitoring of saquinavir plasma concentrations for personalizing the dosing regimen cannot be advised, and a particular antiretroviral regimen cannot be favored. Only in suspicious cases may plasma concentrations serve to prove incompliance.

The relatively small fraction of subjects with therapy failure corresponding to previous reports (4) is nevertheless a potentially limiting aspect of the present study with respect to the detection of pharmacokinetic-related causes of therapy failure. However, the pharmacokinetic parameters of subjects with therapy failures completely overlapped with those from subjects with successful therapy (Fig. 2), suggesting that a larger case number would not have rendered the difference significant. This supports our general conclusion of an only modest benefit of therapeutic drug monitoring of saquinavir in patients with HIV-1 strains that are fully susceptible to saquinavir.

While the observed plasma concentration range of saquinavir (Fig. 2 and Table 2) was not associated with therapeutic outcome in these patients, who either were antiretrovirally naïve or had a protease inhibitor-susceptible virus at baseline genotypic resistance testing, a poorer antiretroviral response with lower trough saquinavir concentrations was reported for patients who already had one failed protease inhibitor-containing therapy regimen (3). In that study, the values of Cmin were divided by the proposed protein-binding corrected "wild-type" IC95 of saquinavir of 278 ng/ml (3, 24), i.e., all values of Cmin by the same number, and the resulting ratio ranged from 0.12 to 3.24 (3), which agrees with the present range of this ratio of 0.18 to 7.91 (interquartile range, 0.83 to 3.1). This complements our advice to not monitor saquinavir plasma concentrations for antiretroviral efficacy in patients at the beginning of therapy with previously reported advice to do so in patients at later therapy stages (3).

Although saquinavir plasma concentration monitoring and subsequent dosing personalization do not appear to improve the antiretroviral therapeutic success in patients infected with protease inhibitor-susceptible HIV-1, saquinavir dose personalization based on individual pharmacokinetic parameters could nevertheless be contemplated for improving the patient's immune status. Indeed, the present association of higher Cmax,saquinavir with CD4 cell counts of ≥200 cells µl–1 at week 48 suggests that increasing Cmax,saquinavir could serve to increase the CD4 cell count. Moreover, considering the tendency towards more infectious diseases with CD4 cell counts of <200 cells µl–1, a dose adaptation to increase Cmax,saquinavir may be justified. Unfortunately, this may be clinically difficult because of (i) the absence of concise interrelations of Cmax,saquinavir with patients' body metrics (Fig. 4), making the identification of an optimum individual dose difficult; (ii) the high intraindividual variability of Cmax,saquinavir (Fig. 6) (15), decreasing the reliability at which the intended Cmax change can be maintained; and (iii) the association of high Cmax with constitutional side effects. Therefore, a saquinavir dose increase to strengthen the patient's immune system should be guided by preferably repeated plasma concentration measurements.

Unfortunately, a more practical obstacle for dose adaptation is the presently available saquinavir formulation of 500-mg coated tablets (Invirase film-coated tablets, introduced by the manufacturer as a replacement for the 200-mg capsule formulations used in the present study; Hoffmann-La Roche, Basel, Switzerland), which does not allow dose increments of <500 mg. Modifying ritonavir coadministration may provide a possibility to slightly increase the saquinavir plasma concentrations. The correlation of t1/2,saquinavir with Cmax,ritonavir indicates that altering ritonavir dosing can be expected to alter saquinavir plasma concentrations with unmodified saquinavir dosing. However, in light of the very weak correlation of Cmax,saquinavir with Cmax,ritonavir and Cmin,ritonavir (Fig. 4), this also has to be individually based on both saquinavir and ritonavir plasma concentrations. Furthermore, raising the ritonavir dose may increase the incidence of neurological or gastrointestinal side effects (5).

Despite a tendency towards a lower incidence of CD4 cell counts of <200 cells µl–1 and a higher incidence of constitutional side effects with an increasing saquinavir Cmax, CD4 cell counts of ≥200 cells µl–1 and constitutional side effects were not related statistically significantly to each other. Thus, constitutional side effects are not unavoidable when the patient's immune status is improved by raising the saquinavir dose. Therefore, lowering the saquinavir dose could be contemplated to decrease Cmax,saquinavir in patients complaining about severe constitutional side effects, such as one of the patients reported in this study, with a Cmax,saquinavir of 4,600 ng/ml, in whom these side effects were a likely cause of incompliance and antiretroviral failure. As mentioned above, the only formulation presently available, the 500-mg saquinavir formulation, limits the practicability of that approach, and decreasing the dose to 500 mg might be realistic only in cases when severely impaired liver metabolism leads to an exorbitantly high plasma saquinavir concentration (26). Once-daily dosing of saquinavir (21) or administration of a reduced dose once daily and of a standard dose at the second daily dosing occasion may also be contemplated. However, in light of the unspecific and mostly mild nature and of constitutional side effects, the possible clinical gain of a dose-adapted lower Cmax,saquinavir has to be weighed against the additional economic and logistic effects and against the nevertheless existing possibility of a lower CD4 cell count, which would more seriously compromise most patients' health by increasing the risk of infectious diseases.

Noncompartmental analysis was the simplest approach to the pharmacokinetics of saquinavir. Single-subject compartmental pharmacokinetic assessments did not provide any additional information that would be useful for personalizing saquinavir therapy and were therefore omitted from this report. Extracting therapeutically useful information from the almost nonexistent correlations of saquinavir with covariates discouraged a population approach, and such an analysis that was performed nevertheless verified these poor expectations (not shown). However, with sparse data, population pharmacokinetic modeling may be useful for assessing pharmacokinetic parameters from a few individual data points (27).

Pharmacogenetic parameters were not included in the study protocol. For the saquinavir plasma concentrations, the absence of information about the CYP3A5*1 allele, which is associated with increased saquinavir clearance and lower plasma concentrations (14), appears to be acceptable because low saquinavir concentrations were not a problem in the present study cohort. Other genetic variants such as those affecting the transmembrane transport of saquinavir into or out of infected cells or across the blood-brain barrier via P glycoprotein, MRP2, or OATP (6, 7, 13, 23, 25) may still provide a basis for saquinavir therapy personalization, especially when combined with measurements of intracellular saquinavir concentrations.

Taken together, therapeutic drug monitoring of saquinavir plasma concentrations in patients infected with protease inhibitor-susceptible HIV-1 taking 1,000 and 100 mg of saquinavir and ritonavir, respectively, is not demanded for controlling antiretroviral efficacy when compliance is not questioned. It may be contemplated to strengthen a patient's immune status or ameliorate constitutional side effects. However, in light of the only weak correlations between saquinavir concentrations and effects, the success of drug monitoring-based dose adaptations is uncertain and has to be weighed against logistic and economic efforts. Therefore, the present results advise, at least in the absence of protease inhibitor resistance mutations, reserving therapeutic drug monitoring of saquinavir for the few cases with severe therapy-jeopardizing constitutional side effects or very low CD4 cell counts with weak immune responses.


arrow
FOOTNOTES
 
* Corresponding author. Mailing address: pharmazentrum frankfurt/ZAFES, Institute of Clinical Pharmacology, Johann Wolfgang Goethe University, Theodor Stern Kai 7, 60590 Frankfurt am Main, Germany. Phone: 49-69-6301-4589. Fax: 49-69-6301-7636. E-mail: j.loetsch{at}em.uni-frankfurt.de Back

{triangledown} Published ahead of print on 18 June 2007. Back


arrow
REFERENCES
 
    1
  1. Antoniou, T., A. L. Tseng, R. P. van Heeswijk, S. E. Walker, P. Giguere, and E. J. Phillips. 2005. Steady-state pharmacokinetics and tolerability of indinavir-lopinavir/r combination therapy in antiretroviral-experienced patients. Ther. Drug Monit. 27:779-781.[CrossRef][Medline]
    2. 2
  2. Cameron, D. W., A. J. Japour, Y. Xu, A. Hsu, J. Mellors, C. Farthing, C. Cohen, D. Poretz, M. Markowitz, S. Follansbee, J. B. Angel, D. McMahon, D. Ho, V. Devanarayan, R. Rode, M. Salgo, D. J. Kempf, R. Granneman, J. M. Leonard, and E. Sun. 1999. Ritonavir and saquinavir combination therapy for the treatment of HIV infection. AIDS 13:213-224.[CrossRef][Medline]
    3. 3
  3. Casado, J. L., S. Moreno, K. Hertogs, F. Dronda, A. Antela, P. Dehertogh, M. J. Perez-Elias, and A. Moreno. 2002. Plasma drug levels, genotypic resistance, and virological response to a nelfinavir plus saquinavir-containing regimen. AIDS 16:47-52.[CrossRef][Medline]
    4. 4
  4. Dragsted, U. B., J. Gerstoft, C. Pedersen, B. Peters, A. Duran, N. Obel, A. Castagna, P. Cahn, N. Clumeck, J. N. Bruun, J. Benetucci, A. Hill, I. Cassetti, P. Vernazza, M. Youle, Z. Fox, and J. D. Lundgren. 2003. Randomized trial to evaluate indinavir/ritonavir versus saquinavir/ritonavir in human immunodeficiency virus type 1-infected patients: the MaxCmin1 Trial. J. Infect. Dis. 188:635-642.[CrossRef][Medline]
    5. 5
  5. Gatti, G., A. Di Biagio, R. Casazza, C. De Pascalis, M. Bassetti, M. Cruciani, S. Vella, and D. Bassetti. 1999. The relationship between ritonavir plasma levels and side-effects: implications for therapeutic drug monitoring. AIDS 13:2083-2089.[CrossRef][Medline]
    6. 6
  6. Honda, Y., F. Ushigome, N. Koyabu, S. Morimoto, Y. Shoyama, T. Uchiumi, M. Kuwano, H. Ohtani, and Y. Sawada. 2004. Effects of grapefruit juice and orange juice components on P-glycoprotein- and MRP2-mediated drug efflux. Br. J. Pharmacol. 143:856-864.[CrossRef][Medline]
    7. 7
  7. Janneh, O., A. Owen, B. Chandler, R. C. Hartkoorn, C. A. Hart, P. G. Bray, S. A. Ward, D. J. Back, and S. H. Khoo. 2005. Modulation of the intracellular accumulation of saquinavir in peripheral blood mononuclear cells by inhibitors of MRP1, MRP2, P-gp and BCRP. AIDS 19:2097-2102.[Medline]
    8. 8
  8. Kempf, D. J., K. C. Marsh, G. Kumar, A. D. Rodrigues, J. F. Denissen, E. McDonald, M. J. Kukulka, A. Hsu, G. R. Granneman, P. A. Baroldi, E. Sun, D. Pizzuti, J. J. Plattner, D. W. Norbeck, and J. M. Leonard. 1997. Pharmacokinetic enhancement of inhibitors of the human immunodeficiency virus protease by coadministration with ritonavir. Antimicrob. Agents Chemother. 41:654-660.[Abstract]
    9. 9
  9. Kilby, J. M., A. Hill, and N. Buss. 2002. The effect of ritonavir on saquinavir plasma concentration is independent of ritonavir dosage: combined analysis of pharmacokinetic data from 97 subjects. HIV Med. 3:97-104.[CrossRef][Medline]
    10. 10
  10. Kitchen, V. S., C. Skinner, K. Ariyoshi, E. A. Lane, I. B. Duncan, J. Burckhardt, H. U. Burger, K. Bragman, A. J. Pinching, and J. N. Weber. 1995. Safety and activity of saquinavir in HIV infection. Lancet 345:952-955.[CrossRef][Medline]
    11. 11
  11. Kurowski, M., T. Sternfeld, A. Sawyer, A. Hill, and C. Mocklinghoff. 2003. Pharmacokinetic and tolerability profile of twice-daily saquinavir hard gelatin capsules and saquinavir soft gelatin capsules boosted with ritonavir in healthy volunteers. HIV Med. 4:94-100.[CrossRef][Medline]
    12. 12
  12. Markowitz, M., M. Saag, W. G. Powderly, A. M. Hurley, A. Hsu, J. M. Valdes, D. Henry, F. Sattler, A. La Marca, J. M. Leonard, et al. 1995. A preliminary study of ritonavir, an inhibitor of HIV-1 protease, to treat HIV-1 infection. N. Engl. J. Med. 333:1534-1539.[Abstract/Free Full Text]
    13. 13
  13. Moriya, Y., T. Nakamura, M. Horinouchi, T. Sakaeda, T. Tamura, N. Aoyama, T. Shirakawa, A. Gotoh, S. Fujimoto, M. Matsuo, M. Kasuga, and K. Okumura. 2002. Effects of polymorphisms of MDR1, MRP1, and MRP2 genes on their mRNA expression levels in duodenal enterocytes of healthy Japanese subjects. Biol. Pharm. Bull. 25:1356-1359.[CrossRef][Medline]
    14. 14
  14. Mouly, S. J., C. Matheny, M. F. Paine, G. Smith, J. Lamba, V. Lamba, S. N. Pusek, E. G. Schuetz, P. W. Stewart, and P. B. Watkins. 2005. Variation in oral clearance of saquinavir is predicted by CYP3A5*1 genotype but not by enterocyte content of cytochrome P450 3A5. Clin. Pharmacol. Ther. 78:605-618.[CrossRef][Medline]
    15. 15
  15. Nettles, R., T. Kieffer, T. Parsons, J. Johnson, T. Quinn, B. Jackson, J. Cofranesco, J. Gallant, K. Carson, R. Siliciano, and C. Flexner. 2005. Frequent sampling in virologically suppressed patients taking HIV protease inhibitors of non-nucleoside reverse transcriptase inhibitors defines intra-individual pharmacokinetic variability, abstr. 642. Abstr. 12th Conf. Retrovir. Opportun. Infect. Boston, MA.
    16. 16
  16. Public Health Service Task Force. September 2006, accession date. Recommendations for use of antiretroviral drugs in pregnant HIV-1-infected women for maternal health and interventions to reduce perinatal HIV-1 transmission in the United States. National Institutes of Health, Bethesda, MD. www.aidsinfo.nih.gov.
    17. 17
  17. Pugh, R. N., I. M. Murray-Lyon, J. L. Dawson, M. C. Pietroni, and R. Williams. 1973. Transection of the oesophagus for bleeding oesophageal varices. Br. J. Surg. 60:646-649.[Medline]
    18. 18
  18. Rezk, N. L., R. D. Crutchley, R. F. Yeh, and A. D. Kashuba. 2006. Full validation of an analytical method for the HIV-protease inhibitor atazanavir in combination with 8 other antiretroviral agents and its applicability to therapeutic drug monitoring. Ther. Drug Monit. 28:517-525.[CrossRef][Medline]
    19. 19
  19. Roche Laboratories Inc. 2002. Fortovase product information. 27898325-0702. Roche Laboratories Inc., Newark, NJ.
    20. 20
  20. Schenk, M. 1996. For the first time a combination of 2 protease inhibitors investigated. Deutsch Med. Wochenschr. 121:A36. (In German.)
    21. 21
  21. Soria, A., N. Gianotti, M. Cernuschi, and A. Lazzarin. 2004. Once-daily saquinavir and ritonavir in treatment-experienced HIV-1-infected individuals. New Microbiol. 27:11-15.[Medline]
    22. 22
  22. Stürmer, M., A. Berger, and H. W. Doerr. 2003. Modifications and substitutions of the RNA extraction module in the ViroSeq HIV-1 genotyping system version 2: effects on sensitivity and complexity of the assay. J. Med. Virol. 71:475-479.[CrossRef][Medline]
    23. 23
  23. Su, Y., X. Zhang, and P. J. Sinko. 2004. Human organic anion-transporting polypeptide OATP-A (SLC21A3) acts in concert with P-glycoprotein and multidrug resistance protein 2 in the vectorial transport of saquinavir in Hep G2 cells. Mol. Pharm. 1:49-56.[CrossRef][Medline]
    24. 24
  24. Taylor, S., and A. Pereira. 2000. Penetration of HIV-1 protease inhibitors into CSF and semen. HIV Med. 1(Suppl. 2):18-22.[CrossRef][Medline]
    25. 25
  25. Woodahl, E. L., Z. Yang, T. Bui, D. D. Shen, and R. J. Ho. 2005. MDR1 G1199A polymorphism alters permeability of HIV protease inhibitors across P-glycoprotein-expressing epithelial cells. AIDS 19:1617-1625.[Medline]
    26. 26
  26. Wyles, D. L., and J. G. Gerber. 2005. Antiretroviral drug pharmacokinetics in hepatitis with hepatic dysfunction. Clin. Infect. Dis. 40:174-181.[CrossRef][Medline]
    27. 27
  27. Yukawa, E. 1999. Population-based investigations of drug relative clearance using nonlinear mixed-effect modelling from information generated during the routine clinical care of patients. J. Clin. Pharm. Ther. 24:103-113.[CrossRef][Medline]

Antimicrobial Agents and Chemotherapy, September 2007, p. 3264-3272, Vol. 51, No. 9
0066-4804/07/$08.00+0     doi:10.1128/AAC.00036-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • von Hentig, N., Lotsch, J. (2009). Cytochrome P450 3A Inhibition by Atazanavir and Ritonavir, but Not Demography or Drug Formulation, Influences Saquinavir Population Pharmacokinetics in Human Immunodeficiency Virus Type 1-Infected Adults. Antimicrob. Agents Chemother. 53: 3524-3527 [Abstract] [Full Text]  
  • Hammer, S. M., Eron, J. J. Jr, Reiss, P., Schooley, R. T., Thompson, M. A., Walmsley, S., Cahn, P., Fischl, M. A., Gatell, J. M., Hirsch, M. S., Jacobsen, D. M., Montaner, J. S. G., Richman, D. D., Yeni, P. G., Volberding, P. A. (2008). Antiretroviral Treatment of Adult HIV Infection: 2008 Recommendations of the International AIDS Society-USA Panel. JAMA 300: 555-570 [Abstract] [Full Text]  
  • von Hentig, N., Kaykhin, P., Stephan, C., Babacan, E., Sturmer, M., Staszewski, S., Lotsch, J. (2008). Decrease of Atazanavir and Lopinavir Plasma Concentrations in a Boosted Double Human Immunodeficiency Virus Protease Inhibitor Salvage Regimen. Antimicrob. Agents Chemother. 52: 2273-2275 [Abstract] [Full Text]  

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Lötsch, J.
Right arrow Articles by von Hentig, N.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Lötsch, J.
Right arrow Articles by von Hentig, N.

Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»