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Previous Article | Next Article 
Antimicrobial Agents and Chemotherapy, October 2000, p. 2816-2823, Vol. 44, No. 10
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Safety, Tolerability, and Pharmacokinetics of
Single Oral Doses of BCH-10652 in Healthy Adult Males
Patrick F.
Smith,1,2,*
Alan
Forrest,1,2
Charles H.
Ballow,2
David E.
Martin,3 and
Louise
Proulx4
The State University of New York at Buffalo
School of Pharmacy1 and The Clinical
Pharmacokinetics Laboratory, Millard Fillmore
Hospital,2 Buffalo, New York;
PharmaResearch Corporation, Morrisville, North
Carolina3; and BioChem Pharma Inc.,
Laval, Canada4
Received 31 January 2000/Returned for modification 14 May
2000/Accepted 22 July 2000
 |
ABSTRACT |
Racemic dOTC (BCH-10652) is a novel nucleoside reverse
transcriptase inhibitor consisting of two enantiomers of
2'-deoxy-3'-oxa-4'-thiocytidine, (
)dOTC and (+)dOTC, that have both
shown activity against human immunodeficiency virus type 1. The
objectives of this study were to characterize the safety, tolerability,
and stereospecific pharmacokinetics of single oral doses of racemic
dOTC in healthy, nonsmoking adult male volunteers. Subjects received
single oral doses of 100, 200, 400, 800, and 1,600 mg of racemic dOTC
in a placebo-controlled, dose-rising, incomplete crossover study
design, and the pharmacokinetics of both (+)dOTC and ()dOTC were
determined. At least six subjects were studied at each dose level, with
each subject studied in three of five periods, receiving two different
doses of racemic dOTC and one placebo dose. Plasma and urine drug
concentrations were measured for 24 to 48 h after each dose.
Pharmacokinetic models were fitted to the plasma concentrations of
(+)dOTC and ()dOTC using maximum likelihood and maximum a posteriori
Bayesian procedures. Statistical hypothesis testing was by
nonparametric analysis of variance (where possible) and, when tests
with dose as a covariate were performed, by linear mixed-effects
modeling. The mean terminal elimination half-lives for (+)dOTC and
()dOTC were 15.3 h (coefficient of variation [CV], 28%) and 11.3 h
(CV, 43%), respectively (P < 0.05). The mean CV for
total oral clearance (liter/h/65 kg) was 17.5 (25%) for (+)dOTC and
21.5 (24%) for ()dOTC; for oral steady-state volume of distribution
(liter/65 kg), values were 61.8 (24%) for (+)dOTC and 34.1 (33%) for
()dOTC (P < 0.05). The mean CV for renal clearance
(liter/h/65 kg) of (+)dOTC was 10.4 (19%) and for ()dOTC was 13.6 (20%) (P < 0.05). There was no significant effect of
dose size on the pharmacokinetics of racemic dOTC. All doses were well
tolerated, and no serious adverse events or laboratory abnormalities
were observed.
| |
INTRODUCTION |
Progress in the fight against human
immunodeficiency virus (HIV) infection has proceeded at a rapid pace in
recent years, with the number of AIDS-related deaths between 1994 and
1998 decreasing from 33 to 5 per 100 person years (2). A
better understanding of the epidemiology, pathogenesis, and virology of
HIV and AIDS has led to the introduction of treatment and prevention
strategies that have effectively altered the natural course of this
disease. It is now understood that an effective treatment regimen
requires multiple drugs in combination, which often leads to complex,
inconvenient, and sometimes intolerable or serious medication-related
side effects. Clearly, new agents that are more effective, less toxic,
and more convenient are necessary to further improve the medical care
of HIV-infected patients.
Racemic dOTC (BCH-10652) is a novel reverse transcriptase inhibitor of
the 4'-thio heterosubstituted class of nucleoside analogues and is a
racemic mixture of the enantiomers of 2'-deoxy-3'-oxa-4'-thiocytidine. Both enantiomers, ()dOTC and (+)dOTC, exhibit equipotent activities against HIV type 1 (HIV-1), with mean 50% inhibitory concentrations against wild-type clinical isolates reported as 1.76 µM and against clinical isolates resistant to 3TC and AZT as approximately 2.5 µM
(6). The purpose of this first-time study with humans was to
investigate the safety, tolerability, and pharmacokinetics of single
oral doses of racemic dOTC in healthy adult male volunteers.
| |
MATERIALS AND METHODS |
The study protocol was approved by the Millard Fillmore Health
Systems Institutional Review Board (Buffalo, N.Y.), and written informed consent was obtained for each subject prior to study participation. Racemic dOTC and identical-appearing placebo was supplied by BioChem Pharma Inc. (Laval, Quebec, Canada).
Study population.
The study participants were healthy,
non-HIV-infected adult male volunteers. Subjects were nonsmokers
between 18 and 50 years of age who had a total body weight of 
50
kg and were within 10% of ideal body weight. Exclusion criteria
included any clinically relevant abnormality identified during the
screening physical or laboratory examination; a history of significant
cardiac, renal, hepatic, neurologic, or hematologic abnormality; a
history of alcohol or drug abuse within 6 months of the study;
treatment with an investigational drug within 30 days prior to the
first study session; use of prescription or nonprescription drugs
within 1 week prior to or during the study; or donation of 1 U of blood within 60 days prior to the first dose of study medication.
Study design.
This was a randomized, single-dose,
single-blind, placebo-controlled, dose-ranging, three-period incomplete
crossover study. In five study periods, racemic dOTC was administered
orally in capsules at doses of 100, 200, 400, 800, and 1,600 mg, in
order from lowest to highest dose. At each dose level, six subjects received active drug, and three subjects received placebo. Each individual subject received two of the five doses of racemic dOTC and
one dose of placebo throughout the entire study. Escalation to the next
dose in the sequence was allowed only after safety and tolerability of
the current dose level was demonstrated in at least three subjects.
Prior to each study period, subjects were admitted to the Clinical
Research Center and were maintained in the fasting state, except for
water, for at least 10 h before dosing. Subjects remained in the
fasting state for at least 5 h after dosing. All doses were
administered with 240 ml of tepid water. Blood samples for ()dOTC and
(+)dOTC serum concentration measurements were drawn prior to dosing
(time zero) and at 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 16, 20, and 24 h after dosing. Midway through the study, the plasma
sampling strategy was extended to include samples at 36 and 48 h
after dosing, and the 6- and 10-h samples were removed. All blood
samples were immediately separated at 4°C by centrifugation and
stored at approximately 20°C until analyzed. Urine samples were
collected during the intervals of 0 to 4, 4 to 8, 8 to 12, 12 to 16, 16 to 20, and 20 to 24 h after dosing. The exact start and stop times
of each urine collection period and the total volume were recorded; a
50-ml aliquot of urine from each interval was processed and stored for assay.
For drug assay, ()dOTC and (+)dOTC were extracted from human plasma
using a solid-phase extraction cartridge. Plasma drug concentrations of
each enantiomer were measured by reverse-phase high-pressure liquid
chromatography with UV detection, using 2',3'-dideoxycytidine as an
internal standard. The internal standard, ()dOTC, and (+)dOTC had
column retention times of approximately 15, 20, and 21.5 min, respectively. For assay accuracy, ()dOTC had a coefficient of variation (CV) range of 2.4 to 4.5% for interassay and 1.0 to 4.2%
for intraassay variability. For (+)dOTC, the CV range was between 2.4 and 3.9% for interassay and between 1.3 and 2.7% for intraassay
variability. The lower limit of quantitation for both enantiomers was
3.0 ng/ml, and no interference from endogenous human plasma components
was identified. The assay was linear over the range of 3.0 to 1,000 ng/ml for both enantiomers. Concentrations above 1,000 ng/ml were
diluted to obtain a concentration within the linear portion of the
calibration curve and were reanalyzed. Quantitation was performed using
the peak height ratio method, and samples were assayed in random order.
Safety and tolerability.
All subjects underwent an
initial-screening physical examination within 30 days prior to
receiving the first dose of study medication. This examination included
a complete medical history, physical examination, and 12-lead
electrocardiogram (ECG). Continuous dual-lead ECG monitoring was
performed for 1 h. Blood and urine specimens were obtained for
standard clinical laboratory tests.
Prior to dosing, another physical examination was performed, including
supine vital signs, 12-lead ECG, and collection of blood and urine
specimens for clinical laboratory studies. Dual-lead ECG monitoring was
performed beginning 1 h prior to dosing and continuing until
12 h postdose. A resting 12-lead ECG was also obtained at 2, 4, 8, 12, and 24 h postdose. Supine heart rate and blood pressure were
obtained prior to dosing and at 0.5, 1, 2, 3, 4, 6, 8, 12, and 24 h after dosing. Assessment of adverse events was done at the same time
as vital sign assessment by direct questioning, spontaneous reporting,
and direct nursing observation. All subjects underwent a poststudy
physical examination, including a 12-lead ECG and safety laboratory
tests, approximately 7 days following the last dose of study medication.
Pharmacokinetic analyses.
Pharmacokinetic parameters were
determined by fitting candidate pharmacokinetic models to the data of
each subject individually, initially using the maximum likelihood
procedure available in Adapt II, release 4 (4, 5). The
maximum likelihood results were then used to compute maximum a
posteriori Bayesian priors. To achieve the most reliable parameter
estimates, the Bayesian priors also included an additional 12 subjects
from another single-dose study in a similar population of healthy adult
male volunteers (9). Following computation of the Bayesian
priors, the data for each individual subject were reanalyzed using the
maximum a posteriori fitting procedure, with the priors updated one
additional time before the final parameter estimates were obtained
(11). Model discrimination was accomplished using the rule
of parsimony (7) and Akaike's information criterion
(1). Weighting was by the fitted inverse of the residual
(observation) variance; standard deviation was assumed to be linear
with drug concentration. In all analyses, both enantiomers were
comodeled for each individual subject. The maximum observed
concentration (Cmax) and time of maximum
observed concentration (Tmax) were determined by
graphical inspection. Renal clearance (CLR) was computed as
the total amount of each enantiomer excreted in urine over 24 h
divided by the plasma area under the concentration-time curve for
24 h (AUC0-24). The standard linear trapezoidal rule
was used to calculate AUC. Fractional renal clearance for each
enantiomer was calculated as F × CLR/CLT,
where F is oral bioavailability and CLT is total clearance.
Volumes, clearances, and AUC and Cmax values
were normalized for body size (65 kg); Cmax and
AUC values were also normalized to dose (800 mg).
Statistical comparisons of pharmacokinetic parameters.
Related-groups analyses were accomplished using the Wilcoxon
signed-rank procedure. Linear mixed effects modeling, as implemented in
SAS 6.12 for Windows (8), was used for summary statistics and to test the association between dose (as a categorical independent variable) and pharmacokinetic parameter values. Because dOTC is largely
cleared as unchanged drug in the urine, creatinine clearance (CCR) was considered as a covariate. Pharmacokinetic
parameters tested included total oral clearances, renal clearances,
steady-state apparent volumes of distribution
(VSS), half-lives, Cmax,
and Tmax.
| |
RESULTS |
Demographics.
Table 1 is a
summary of the characteristics of the 16 male volunteers who were
studied in at least one drug-containing study period. The normalized
creatinine clearance (CCR in ml/min/65 kg) was estimated by
the method of Cockcroft and Gault (3), based on serum
creatinine, age, weight, and gender. One subject voluntarily withdrew
after receiving one 800-mg dose, and another withdrew after
participating in one placebo period. Both of these subjects withdrew
for reasons unrelated to the study, and both completed the end-of-study
evaluations and were normal. The six subjects who were studied in the
1,600-mg group, compared to those who received 200 mg, tended to be
smaller (P = 0.035), younger (P = 0.062), and to have a higher normalized CCR
(P = 0.098). There were no other statistically
significant demographic differences between groups.
Safety and tolerability.
All oral doses were well tolerated by
the subjects, and no serious adverse events were reported during the
study. A total of 11 adverse events were reported by eight subjects,
the most common being headache, upper respiratory tract infection, and irritation and redness at the intravenous catheter site, each being
reported twice. None of these events were considered to be related to
the study drug, and all were resolved prior to completion of the study.
There were no clinically significant changes in ECGs or laboratory
values, and all vital signs remained within normal limits. No
abnormalities were reported following the end-of-study physical examinations.
Pharmacokinetics.
Log-linear plots of individual
concentration-time profiles showed that there was no clear, terminal,
log-linear phase for a study of 24 h duration, with the apparent
half-lives based on the last three observations being systematically
shorter than half-lives based on the last two observations. Therefore,
the sampling strategy was altered for the 800- and 1,600-mg study periods; the 6- and 10-h samples were omitted, and samples at 36 and
48 h were added.
The final pharmacokinetic model was a linear, two-compartment model,
with absorption occurring during one to three first-order input phases,
each following a fitted lag time (Fig.
1). Another study using intravenous dOTC
determined that a three-compartment model was superior, by Akaiki's
Information Criterion, to a two-compartment model (9).
However, when dOTC is administered orally, absorption proceeds
simultaneously with distribution, masking the ability to distinguish
between the distributional compartments. Therefore, a two-compartment
model is utilized for oral dOTC. Details of the three-compartment
pharmacokinetic model have been reported previously (9).
All subjects were fitted assuming that absorption characteristics for
the two enantiomers were similar. The percent of total dose absorbed
(D%) in phases I and III were fitted parameters, enabling direct
computation of the phase II D%, as the total sum of D%'s was
required to equal 100%. The fit of the model to the data was
excellent: for (+)dOTC, the median r2 was 0.998, with a range of 0.993 to 1.00; for ()dOTC, the median r2 was 0.998, with a range of 0.992 to 1.00. The
mean plasma concentration versus time curves for ()dOTC and (+)dOTC
are presented in Fig. 2. The final
pharmacokinetic parameters for each enantiomer are summarized in Tables
2 and 3;
absorption characteristics are summarized in Table
4.
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|
FIG. 2.
Mean ()dOTC (A) and (+)dOTC (B) concentration versus
time plots for all subjects following oral doses of racemic dOTC.
|
|
Comparing enantiomers, median modeled values of oral clearance for
(+)dOTC were 19.5% lower than those for ()dOTC (P < 0.001), the oral total steady-state distribution volumes were
100% larger (P < 0.001), and the terminal plasma
half-life was 55.2% longer (P < 0.001). The
intersubject variability in total oral clearance (CLT/F),
for the two-compartment model, was quite small [the CV for (+)dOTC was
17.4% and for ()dOTC was 18.7%]. The median and mean values of
Cmax (normalized for body size) were larger for (+)dOTC than for ()dOTC (P = 0.002). There was no
significant difference in Tmax (P > 0.6) between enantiomers.
When CLR values were compared between enantiomers, (+)dOTC
was 23.5% lower than ()dOTC (P < 0.05), which is
consistent with the difference found in total oral clearances. The
intersubject variability of CLR was also low, with a CV
less than or equal to 20% for both enantiomers. The median CV fraction
of total clearance that was renal for ()dOTC and (+)dOTC was 0.66 (23.9%) and 0.62 (22.8%), respectively. Because CLT/F is
conditioned on F and CLR is not, the fractional renal
clearance (F × CLR/CLT) should be adjusted for absolute bioavailability, which was determined to be
approximately 80% for both ()dOTC and (+)dOTC in a separate study
(9). When bioavailability is considered, it suggests that 80 to 90% of bioavailable dOTC is eliminated unchanged in the urine.
Lastly, because the values of renal clearance for ()dOTC and (+)dOTC
are much larger than normal values of the glomerular filtration rate,
it appears that both enantiomers undergo active secretion into the urine.
AUC0-24 for both enantiomers was observed to increase
linearly with increasing doses across all subjects. A significant difference by dose was found between oral clearances of both ()dOTC (P = 0.023) and (+)dOTC (P = 0.023)
between the 100- and 1,600-mg doses. Upon further inspection, it became
clear that the difference in the 1,600-mg group was due to a single
subject outlier. This subject's oral clearance of both isomers in the
1,600-mg dose [40.6 and 33.7 liter/h/65 kg for ()dOTC and (+)dOTC,
respectively] was significantly higher than that of the other subjects
at the same dose level and was also significantly higher than the same subject's oral clearance when administered 800 mg [25.2 and 20.0 liter/h/65 kg for ()dOTC and (+)dOTC, respectively]. This subject's renal clearances in the two study periods were not different, indicating strongly that the observed difference was due to a decreased
oral absorption during the 1,600-mg study period. When this subject was
removed from the analysis, there was no significant difference in oral
clearance. Figures 3 and
4 depict the lack of effect of dose on
total oral and renal clearances, with a dashed line identifying the
single subject outlier in oral clearance. No other tested
pharmacokinetic parameters differed significantly by dose (P > 0.05 for all comparisons).
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FIG. 3.
Comparison of total oral clearances and dose across all
subjects for ()dOTC and (+)dOTC. Lines connect study periods for each
individual subject; the dashed line indicates the individual subject
outlier in oral clearance.
|
|
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|
FIG. 4.
Comparison of renal clearances and dose across all
subjects for ()dOTC and (+)dOTC. Lines connect study periods for each
individual subject; the dashed line indicates the individual subject
outlier in oral clearance.
|
|
| |
DISCUSSION |
The results of the present study found racemic dOTC to be
safe and well tolerated following single oral doses between 100 and
1,600 mg. Plasma pharmacokinetics of oral (+)dOTC and ()dOTC are well
described by a linear, two-compartment model (in addition to the
absorption site) with elimination from the central compartment. The
data showed multiple peaks and other changes in slope after oral
administration. This behavior was well described by two or three
"absorption phases," in which a portion of the dose is released and
absorbed, with each phase having a separate lag time and absorption rate constant.
The pharmacokinetics of dOTC showed small intersubject variability.
When (+)dOTC was compared to ()dOTC, median CLT/F was 19.5% lower, terminal half-life was 55.2% longer, and Vss/F was 100%
larger for (+)dOTC. There was no significant effect of dose size on the
pharmacokinetics of dOTC. The relatively long half-lives would support
dosing intervals of 12 to 24 h. However, as with all nucleoside
reverse transcriptase inhibitors, a long plasma half-life may not
equate to a long duration of drug action, as intracellular triphosphate
concentrations are the active moiety. Early clinical efficacy data from
short-term monotherapy studies have found racemic dOTC to have
significant anti-HIV-1 activity when administered either once or twice
daily (R. Wood, B. Trope, R. Van Leeuwen, D. E. Martin, and L. Proulx, Abstr. 39th Intersci. Conf. Antimicrob. Agents Chemother.,
abstr. 503, 1999), and efficacy was not related to plasma trough
concentrations (10).
An interim analysis found a longer half-life than expected, making it
necessary to alter the sampling strategy midway through the study. The
duration of sampling was therefore extended from 24 to 48 h for
the 800- and 1,600-mg doses. This change allowed an improved
characterization of the terminal elimination phase, which may not have
been adequately described with only 24 h of serum sampling. The
change also provides an excellent example of the utility of having
real-time access to interim study results to allow modification of
sampling strategies early in phase I investigations.
The primary route of dOTC elimination is renal (80 to 90% of
bioavailable drug is eliminated unchanged in the urine) and must include active secretion of both enantiomers. This large degree of
renal elimination may require a dose adjustment in patients suffering
from renal impairment. This dependence on renal clearance also makes
drug interactions involving hepatic enzymes less likely; however,
interactions with renally secreted drugs may be present and should be
investigated in future studies.
Due to the limited number of agents currently available to treat HIV
disease, more effective medications are needed as alternatives to both
empiric and salvage therapy. Agents with long half-lives that can be
dosed infrequently and thereby improve adherence are also desirable.
Racemic dOTC is a mixture of two enantiomers that has shown activity
against HIV-1 strains of virus resistant to other reverse transcriptase
inhibitors and has a beneficial pharmacokinetic profile. Future
clinical trials will be needed to establish the safety, tolerability,
and efficacy of chronic administration in the treatment of HIV infection.
| |
ACKNOWLEDGMENTS |
This work was supported in part by a grant from BioChem Pharma Inc.
We thank John Adams for his insightful comments regarding the content
of the manuscript.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Roswell Park
Cancer Institute, Elm and Carlton Streets, Buffalo, N.Y. 14263. Phone: (716) 845-3281. E-mail: Pfsmith{at}acsu.buffalo.edu.
| |
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Antimicrobial Agents and Chemotherapy, October 2000, p. 2816-2823, Vol. 44, No. 10
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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Abstract
Introduction
