ABSTRACT
This study evaluated the pulmonary disposition of eravacycline in 20 healthy adult volunteers receiving 1.0 mg of eravacycline/kg intravenously every 12 h for a total of seven doses over 4 days. Plasma samples were collected at 0, 1, 2, 4, 6, and 12 h on day 4, with each subject randomized to undergo a single bronchoalveolar lavage (BAL) at 2, 4, 6, or 12 h. Drug concentrations in plasma, BAL fluid, and alveolar macrophages (AM) were determined by liquid chromatography-tandem mass spectrometry, and the urea correction method was used to calculate epithelial lining fluid (ELF) concentrations. Pharmacokinetic parameters were estimated by noncompartmental methods. Penetration for ELF and AM was calculated by using a ratio of the area under the concentration time curve (AUC0–12) for each respective parameter against free drug AUC (fAUC0–12) in plasma. The total AUC0–12 in plasma was 4.56 ± 0.94 μg·h/ml with a mean fAUC0–12 of 0.77 ± 0.14 μg·h/ml. The eravacycline concentrations in ELF and AM at 2, 4, 6, and 12 h were means ± the standard deviations (μg/ml) of 0.70 ± 0.30, 0.57 ± 0.20, 0.34 ± 0.16, and 0.25 ± 0.13 with a penetration ratio of 6.44 and 8.25 ± 4.55, 5.15 ± 1.25, 1.77 ± 0.64, and 1.42 ± 1.45 with a penetration ratio of 51.63, respectively. The eravacycline concentrations in the ELF and AM achieved greater levels than plasma by 6- and 50-fold, respectively, supporting further study of eravacycline for patients with respiratory infections.
INTRODUCTION
The world today is facing an emerging crisis of bacterial resistance in both community- and hospital-acquired pathogens. Extensive use of antibiotics, along with increased industrialization and international transit have all contributed to the rise in antimicrobial resistance, morbidity, and mortality (1–8). According to ATS/IDSA guidelines, the second most common nosocomial infection in the United States is hospital-acquired pneumonia representing 25% of all intensive care unit infections, an excess cost of $40,000 per patient, and an average increase in hospital stay of 7 to 9 days (8).
Eravacycline (TP-434) is a novel fluorocycline antibiotic being developed as an intravenous (i.v.) and oral medication for the treatment of serious infections caused by antibiotic-resistant bacteria (9). In vitro microbiological studies of eravacycline have demonstrated potent, broad-spectrum Gram-positive and Gram-negative antibacterial effect exhibiting activity against S. aureus isolates expressing methicillin resistance, as well as Enterobacteriaceae isolates expressing resistance genes from multiple classes of extended-spectrum β-lactamase (ESBLs) (9). When tested against clinical isolates of A. baumannii, eravacycline displayed 2-fold greater susceptibility than tigecycline (9), whereas additional testing on Gram-positive isolates of Enterococcus displayed no difference in potency with or without the presence of vancomycin resistance (9). The results from a prospective, randomized, double-blind, phase II study evaluating the safety and efficacy of eravacycline dosed once or twice daily versus ertapenem given once daily in complicated intra-abdominal infections (cIAI) demonstrated >92% clinical cure rates at the test of cure visit, with 100% cure rates in the twice-daily dosing group with infections caused by ESBL-producing, levofloxacin- and ertapenem-resistant organisms (10).
Although preclinical and clinical data offer insight into the use of eravacycline to treat bacterial infections, overall success is dependent upon optimizing drug exposures at the site of infection. We sought here to explore the intrapulmonary penetration of eravacycline in healthy adult subjects.
MATERIALS AND METHODS
Study design.This was a prospective, open-label, randomized pharmacokinetic and safety study that occurred at the Clinical Research Center and Same-Day Surgi-Center at Hartford Hospital, Hartford, CT. The study protocol was approved by the Hartford Hospital Institutional Review Board, and all subjects provided written informed consent prior to participation.
Participants.Twenty healthy adult subjects were invited to participate in the present study. Key inclusion criteria included healthy male or nonpregnant, nonlactating healthy female subjects aged 18 to 65 years, body mass index (BMI) inclusive of 18 to 33 kg/m2 or, if outside the range, considered not clinically significant, and the willingness to use adequate methods of contraception. Key exclusion criteria included previous administration of eravacycline, previous participation in a clinical research study within the previous 3 months, serious adverse reaction or serious hypersensitivity to tetracyclines, midazolam, lidocaine, or similar compounds, those who have smoked within the last 6 months, a history of regular alcohol consumption exceeding 21 U per week in males and 14 U per week in females, a positive test for drugs of abuse, any clinically significant abnormal biochemistry, hematology, coagulation, or urinalysis test results, a positive viral status for hepatitis B or C virus or human immunodeficiency virus at screening, a history of any drug or alcohol abuse in the past 2 years, a history of chronic respiratory disorders, anatomy not conducive for bronchoscopy, donation or loss of blood exceeding 400 ml in the previous 3 months, the use of any prescribed or over-the-counter drug or herbal remedies (with the exception of anti-inflammatory, anti-hypertensive, or hormone replacement medications), or a failure to satisfy the investigator of fitness to participate for any other reason.
Each subject participated in the study for ∼8 weeks, which included a 30-day screening, a 6-day dosing and observation period, and a 20-day follow-up period. At screening, a detailed medical and surgical history was taken, and a physical examination and clinical laboratory testing were performed. Prior to the dosing, subjects underwent clinical laboratory testing again to confirm that no changes from the screening visit had occurred.
Study medication.Eravacycline as 52.5-mg vials were supplied by Tetraphase Pharmaceuticals (Watertown, MA) and stored frozen at between −15 and −25°C protected from light during storage until administration. Eravacycline vials were reconstituted to a 5-mg/ml concentration with 10 ml of sterile water for injection. Subjects received eravacycline dosed at 1.0 mg/kg, with a total drug amount capped at 100 mg. Eravacycline was further diluted into empty Viaflex bags (Hospira, Inc., Lake Forest, IL) using 0.45% NaCl for final infusion at a concentration no greater than 0.2 mg/ml. Final infusion volumes were determined by subject weight (in kg) × 5, not to exceed 500 ml. Subjects weighing >100 kg received a maximum of 100 mg of eravacycline in 500 ml of 0.45% NaCl to limit the volume of drug infused to 500 ml. The final product for infusion has been determined to be stable for up to 8 h following reconstitution.
Dosing and plasma sampling.Subjects received seven i.v. doses of 1.0 mg of eravacycline/kg every 12 h as a 1-h infusion to achieve steady state. Subjects were required to eat standardized meals 1 h prior to administration of the study medication. Blood samples were collected around the seventh dose from a peripheral i.v. catheter at 0 h (predose, within 30 min of infusion) and 1, 2, 4, 6, and 12 h after the start of study drug administration for plasma eravacycline concentration analysis. Blood samples were collected into a 10-ml BD Vacutainer tube (Becton Dickinson, Franklin Lakes, NJ) containing the anticoagulant sodium heparin. In addition, blood samples for urea analysis were collected in simultaneous conjunction with the subjects' randomized bronchoalveolar lavage (BAL) time point. All blood samples were centrifuged at 3,000 × g for 10 min at 4°C, and separate plasma samples were stored at −80°C until further analysis.
Protein binding assessment.Protein binding was assessed using data generated by Singh et al. (11). In brief, protein binding was assessed over a concentration range of 0.1 to 100 μg/ml, and the relationship between the total drug concentration and protein binding was nonlinear. Utilizing the free fraction of eravacycline to the total concentration of eravacycline in plasma, a power function was created to calculate the bound concentration of eravacycline, and we subtracted the bound portion of drug from the total amount to determine the free concentration of eravacycline in plasma.
Bronchoscopy and BAL.A single bronchoscopy with BAL was performed by a pulmonologist at one of four prespecified time points: 2, 4, 6, or 12 h after the start of infusion (five subjects per group) of the seventh dose. Prior to the bronchoscopy, subjects were required to fast for 6 h, and then they received premedication with the following agents ∼30 min prior to the bronchoscopy: 4% lidocaine aerosolized via jet nebulizer and atomizer in the nares and oropharynx, 2% lidocaine jelly topically applied in the nasal passageway, and (if needed) 1 mg of i.v. midazolam. A fiber optic bronchoscope (Olympus BF-Q180; Olympus America, Inc., Center Valley, PA) was inserted via the nasal route into the medial segment of the right middle lobe. Four separate 50-ml aliquots of 0.9% sodium chloride were instilled into the right middle lobe at precisely the scheduled time of the BAL, with each lavage sample immediately aspirated into an associated lukens trap. The volume of the first aspirate was discarded to prevent contamination from large cell types or premedications. Samples from aliquots 2, 3, and 4 were individually measured and then pooled and recorded. Two 4-ml aliquots of the pooled aspirate were placed immediately on ice and sent to the clinical laboratory for analysis of the cell count with differential. The remainder of the pooled lavage samples were placed on ice and transported back to the Clinical Research Center for centrifugation at 400 × g at 4°C for 10 min to separate the alveolar macrophages (AM; cell pellet) and epithelial lining fluid (ELF; supernatant). After centrifugation, the cell pellet was resuspended (using 5% of the total volume from the pooled lavage aspirates) with 0.9% sodium chloride. From the supernatant, 1.5 ml was pipetted into two cryovials (USA Scientific, Ocala, FL) for determination of the urea concentration, and 10 ml was collected into 15-ml conical tubes for drug assay. After processing, all samples were immediately placed in a −80°C freezer until further analysis.
Analytical eravacycline concentration determination.Plasma, BAL fluid supernatant, and BAL fluid cell pellet samples were assayed by Medpace Bioanalytical Laboratories (Cincinnati, OH) for eravacycline concentrations by using an API 5500 liquid chromatography-tandem mass spectrometry system (Applied Biosystems, Carlsbad, CA). The samples were chromatographed on a Kinetix 2.6μ PFP column (100 by 2.1 mm; Phenomenex, Torrance, CA). The mobile phases were 0.15% trifluoroacetic acid (TFA) in water (mobile phase A) and 0.15% TFA in 60/40 isopropanol-methanol (mobile phase B) run with a gradient from 20% B to 90% B in 5 min. The standard curve ranges for eravacycline in plasma, BAL fluid, and alveolar macrophages were 5 to 500 ng/ml. Plasma samples were extracted using a solid-phase extraction, dried under a stream of nitrogen gas, and then reconstituted in 10/90 methanol-water with 0.1%TFA. The r2 value for linearity in plasma samples was ≥0.9991. BAL fluid and cell pellet samples were acidified with 0.1% TFA and had an r2 value for linearity of ≥0.9981. Quality control samples were prepared and analyzed at 15, 85, and 375 ng/ml for plasma, BAL samples, and alveolar macrophages. In plasma, the coefficient of variation (CV) of eravacycline concentration determination was ≤3.7%, with an overall bias from −1.3 to 1.7%. The overall CV in BAL fluid and alveolar macrophages were ≤7.5%, with an overall bias from −5.3 to −0.3%. For subjects whose eravacycline concentrations were below the lower limit of quantification (BLQ; 5 ng/ml) but still had an identifiable peak on the chromatogram, one-half of the lower limit of quantification was used to calculate the concentration of drug.
Urea concentration determination.The urea concentrations of BAL fluid and plasma were analyzed by colorimetric enzymatic assay (Teco Diagnostics, Anaheim, CA) via spectrophotometer detection method (Cary 50 Series; Varian, Walnut Creek, CA) by the Center for Anti-Infective Research and Development (Hartford, CT). The assay was linear with an r2 of ≥0.9995 for both BAL fluid and serum urea concentrations over the range of 0.1 to 2.0 mg/dl. Quality control samples of 0.15 and 1.5 mg/dl had intra- and interday variability %CV values of 3.30 and 1.25% and 5.3 and 2.3%, respectively.
Calculation of drug concentrations in ELF and AM.Determination of the ELF volume and drug concentrations has been previously discussed (12, 13). The calculations of volume and antibiotic concentrations recovered from the BAL fluid are characterized by the following equations. First, VELF = VBAL × ureaBAL/ureaplasma, where VELF represents the ELF volume calculated from the BAL sample, VBAL is the volume of the BAL fluid collected, and ureaBAL and ureaplasma are the concentrations of urea in BAL fluid and plasma, respectively.
In the equation drugELF = drugBAL × VBAL/VELF, the drugELF characterizes the calculated concentration of eravacycline in ELF fluid, and drugBAL represents the eravacycline concentrations found in BAL fluid. Characterizations of eravacycline concentrations in alveolar macrophages are determined by the results of the BAL cell count and differential (both samples A and B), specifically the white blood cell (WBC) counts, the percent histiocytes, and the percent monocytes. The %AM is derived from the sum of histiocytes and monocytes. By taking the average WBC counts and multiplying that value by 1,000, the mean number of WBCs per ml is determined. The mean number of AM per ml is then calculated by the following equation: mean AM count = (%AMA + %AMB)/2 × the mean WBC count, where %AMA is the %AM from sample A, and %AMB is the %AM from sample B. Based on this, we are able to calculate the mean AM in BAL fluid as follows: mean AM in BAL = mean AM count × VBAL.
To determine the total amount of eravacycline in the cell pellet, the following equation is used: Amtpellet = drugpellet × Vpellet, where drugpellet is the concentration of eravacycline within the reconstituted cell pellet, and Vpellet is the volume used to reconstitute the cell pellet. Based on this, the amount of eravacycline in the AM could be calculated using the following equation: drugAM = Amtpellet/(mean AM in BAL × VAM), where VAM is the mean cell volume of an alveolar macrophage (2.42 μl/106 cells).
Pharmacokinetic analysis.Determination of plasma pharmacokinetics of eravacycline in study subjects were estimated using noncompartmental analysis (WinNonlin 5.3; Pharsight Corp., Mountain View, CA). Estimated pharmacokinetic parameters included the area under the concentration-time curve of the dosing interval (AUC0–12) calculated using the linear/log trapezoidal rule, the fAUC0–12 calculated by correcting concentrations for free drug and then using the linear/log trapezoidal rule, the volume of distribution at steady state (Vss), and clearance (CL). In a phase I multiple ascending dose study, the calculated half-life of eravacycline ranged from 30 to 60 h (14). Further, a previous population pharmacokinetic model has described the half-life of eravacycline to be ∼48 h (15). Since the half-life of this compound exceeds the 12-h sampling period used in this current study this pharmacokinetic parameter was not determined. Observed parameters included the maximum concentration achieved (Cmax) and the minimum concentration achieved (Cmin). Calculations of the ELF and AM AUC0–12 were performed using the trapezoidal rule and were based on the mean concentrations per time point. Penetrations were calculated using the mean ratio of the ELF or AM compartment AUC0–12 to the plasma fAUC0–12.
Safety assessment.The tolerability and safety of eravacycline was determined by recording adverse events that occurred during the study. Study subjects underwent a thorough exit evaluation consisting of a physical examination and clinical laboratory testing prior to exiting the Clinical Research Center and a follow-up visit 14 days later consisting of a final physical examination and clinical laboratory testing.
Statistics.The sample size was based on n = 5 samples per time point to a total of n = 20 participants. This was based on clinical rationale and previous bronchopulmonary assessments which have historically used n = 5 participants at each time point (12, 16, 17). To measure the statistical significance between plasma drug concentrations, a paired t test was used to compare the predose plasma concentrations to the 12-h-postinfusion concentrations. Analysis of variance was used to evaluate the statistical significance of ELF and AM characteristics between BAL groups.
RESULTS
Participants.Twenty subjects were enrolled and completed the study. The study population consisted of healthy adults ranging in age from 19 to 47 years (mean age, 31 ± 7 years). Of the 20 subjects, 13 were male. Fifteen were Caucasian, four were African-American, and one was considered mixed, with 6 of the 20 subjects identifying their ethnicity as Hispanic. The means ± the standard deviations (SD) for weight and BMI were 80 ± 15 kg and 27 ± 5 kg/m2, respectively. There were three subjects whose BMIs were outside the specified range and judged not to be clinically significant, with BMIs of 33.3, 33.8, and 35.3 kg/m2. The mean ± the SD dose administered was 79.4 ± 13.9 mg (range, 49.4 to 100 mg). One subject received the maximum allowed dose of 100 mg.
Plasma pharmacokinetics and protein binding.The plasma pharmacokinetics of eravacycline are listed in Table 1. All plasma samples were above the lower limit of quantitation. There was no statistical difference between eravacycline concentrations taken immediately prior to and at 12 h after the seventh dose, indicating steady-state concentrations were achieved (P = 0.830). Protein binding ranged from 79.3 to 87.1% bound with a mean ± SD of 82.5% ± 1.7%. This resulted in a steady-state plasma fAUC0–12 of 0.77 ± 0.14 μg·h/ml. Mean concentrations of total and free drug are represented in Table 2, with free drug represented in Fig. 1.
Individual and mean pharmacokinetic parameter estimates after eravacycline treatmenta
Mean plasma eravacycline concentrations taken predose and at 1, 2, 4, 6, and 12 h after the start of infusion
Eravacycline concentrations achieved in plasma, ELF, and AM (plasma and ELF [n = 5 at 2, 4, 6, and 12 h], AM [n = 5 at 2 and 4 h, n = 3 at 6 h, and n = 4 at 12 h]).
Pulmonary pharmacokinetics.Bronchoscopy exams were initiated 5 ± 3 min prior to scheduled BAL time, with an elapsed BAL lavage sample collection time of 4 ± 1 min. Each subject had duplicate aliquots of BAL fluid sent to the clinical laboratory for the cell count and differential. Three subjects had WBC clumping and AM cell counts reported to be ≤70% (range, 18 to 70%). Since these values were well below the 80% typically observed for AM and in the context of noted cell clumping, these three subjects were excluded from subsequent AM concentration analysis. The mean ELF and AM characteristics are shown in Table 3, and concentrations in the ELF and AM for mean data and individual concentrations are represented in Fig. 1 and 2, respectively. There were no statistical differences among cell counts, %AM values, volumes of BAL fluid, and volumes of ELF at each of the four BAL time points (P > 0.134). Of note, there were three subjects from the 12-h BAL group and two subjects from the 6-h BAL group whose eravacycline concentrations in BAL fluid were BLQ (5 ng/ml). In addition, there was one subject in the 12-h BAL group whose eravacycline concentration in AM was BLQ. For subjects whose eravacycline concentrations were found to be BLQ, all subjects had an identifiable peak on the chromatogram, therefore one-half of the BLQ was used to calculate their concentrations in the matrix of interest. The calculated AUC0–12 values for ELF and AM were 4.93 and 39.53 μg·h/ml, respectively. Assuming eravacycline concentrations in the ELF and AM are free drug concentrations, comparison of the ELF and AM AUC0–12 to the fAUC0–12 in plasma showed penetration ratios of 6.44 and 51.63 for each respective matrix.
BAL, ELF, and AM characteristics and eravacycline ELF and AM concentrations per BAL time point
Individual eravacycline concentrations in the ELF and AM at each BAL time point (ELF [n = 5 at 2, 4, 6, and 12 h], AM [n = 5 at 2 and 4 h, n = 3 at 6 h, and n = 4 at 12 h]).
Safety and tolerability.Eravacycline was tolerated by all of the study subjects, with no serious adverse events and no discontinuations due to adverse events. There were a total of 78 adverse drug events from 19 of 20 participants, 64 (82.1%) of which were determined to be related to study medication. All adverse events were mild (55/78 [70.5%]) or moderate (23/78 [29.5%]) in nature. Nausea was experienced in 18 of 20 (90%) subjects, infusion-related irritation in 13 of 20 (65%) subjects, vomiting in 7 of 20 (35%) subjects, and headache in 6 of 20 (30%) of subjects. During the study, there were a total of 11 concomitant medications recorded. All subjects received lidocaine as a pre-anesthetic prior to bronchoscopy and BAL during the study. Furthermore, 30% of the subjects received ondansetron for the control of nausea during the study. Midazolam was used in 3 of 20 (15%) subjects for sedation prior to bronchoscopy. Ibuprofen was administered to 3 of 20 (15%) subjects for headache relief. Other medications recorded during the follow-up period included acetaminophen and diphenhydramine, hydrocortisone cream, ciprofloxacin, and probiotics.
DISCUSSION
This study was performed to evaluate the pulmonary disposition of eravacycline, a novel, broad-spectrum fluorocycline antibiotic derived from the class of tetracyclines being developed for potential first-line empirical treatment of serious infections, including acute bacterial pneumonias. While society continues to advance modern medicine, nosocomial pneumonia still represents the second most common hospital-acquired infection in the United States (8). Given the spectrum of activity and relative potency of eravacycline against increasingly common multidrug-resistant bacteria, there is a potential for use in this currently unmet medical need (9).
Eravacycline was tolerated by all subjects. Ninety percent of the subjects experienced nausea with seven also reported vomiting. Although this is higher than has been previously reported for eravacycline studies (14), this level is very similar to Conte's study of intrapulmonary tigecycline penetration, wherein 28 of 32 healthy volunteers experienced nausea and 7 reported emesis (18). In a phase II cIAI trial, eravacycline at 1.0 mg/kg i.v. every 12 h was well tolerated, with 16 of 56 patients experiencing a treatment-related adverse event, of which 6 (10.7%) reported nausea (10). Comparative published rates for tigecycline in pooled phase III cIAI data were 24.4% nausea and 19.2% emesis (19).
Plasma pharmacokinetic data were slightly lower in the present study compared to data observed in a previous multiple-ascending-dose study (14). We saw a relative decrease in Cmax and AUC values for eravacycline in the plasma by roughly 30%. This is not thought to be erroneous but instead related to subtle differences in the two study populations; specifically, a volume of distribution that was ca. 35% greater was seen in our subject mix. In our study, participants with BMIs up to 35.3 were included. The three participants with BMIs ≥ 33.0 were similar to the group's average with respect to plasma eravacycline concentrations, clearance, and volume of distribution. Further, the present study represents the average weight and BMI of the U.S. population quite well (20). Population pharmacokinetic studies have been conducted and suggest neither body weight nor BMI correlated with eravacycline pharmacokinetic concentrations (15). Concentrations achieved in the ELF and AM are useful in postulating the effect of antimicrobials in respiratory infections, specifically pneumonia. Although not considered the exact site of infection, the ELF and AM are useful models for adjacent areas which may be harboring infection in the lung (13, 21). Antimicrobials that infiltrate the ELF are associated with the treatment of extracellular pathogens, such as S. aureus, S. pneumoniae, and E. coli, whereas agents that accumulate in the AM are often used to treat intracellular organisms such as Salmonella and Legionella species.
While the pharmacodynamic driver of efficacy has yet to be determined for eravacycline in lung infection, the results of our study indicate penetration into the lungs, gleaning insight into this compound's possible utility in respiratory infections. The intrapulmonary eravacycline concentrations were significantly higher than the free plasma concentrations. Over the 12-h dosing interval, the Cmax and AUC0–12 were 0.70 ± 0.30 μg/ml and 4.93 μg·h/ml for ELF and 8.25 ± 4.55 μg/ml and 39.53 μg·h/ml for AM, respectively. Although there is no clear mechanism defined to explain why eravacycline concentrates in the ELF and AM, the penetration of antibiotics into the lung is believed to be due to multiple known and unknown mechanisms dependent on molecular weight, liposolubility, and energy dependence. These mechanisms include passive diffusion, permeation, active transport, and bulk flow (22).
Examining a similarly available antimicrobial agent provides a comparative basis for evaluating the potential use of eravacycline. Tigecycline is the first commercially available glycylcycline, a derivative from tetracyclines that shares a similar spectrum of activity and side effect profile to that of eravacycline. Conte et al. examined the steady-state total plasma levels and intrapulmonary pharmacokinetics of tigecycline in 30 human subjects using clinical doses (18). Subject characteristics were similar with respect to weight; however, BMI is likely to be higher in our population since the inclusion criteria were less stringent. Over the dosing interval, the Cmax, AUC0–12, and penetration ratio were 0.37 ± 0.36 μg/ml, 2.28 μg·h/ml, and 1.32 for ELF and 15.2 ± 7.6 μg/ml, 134 μg·h/ml, and 77.46 for AM, respectively. The results of the present study were further confirmed by Rubino et al., who determined the median ELF penetration ratio of tigecycline to be 1.15 (interquartile range, 0.823 to 2.45) (23). When comparing the bronchopulmonary distribution of eravacycline to these available data for tigecycline, eravacycline appears to have twice the Cmax and AUC0–12 in ELF. When considering the AM profile, the Cmax of eravacycline is ca. 50% and the AUC0–12 is 25% of the values determined for tigecycline. The recommended treatment duration of tigecycline for community-acquired pneumonia is 7 to 10 days and, given the relative similarities, a similar treatment duration would be expected for eravacycline in the setting of pneumonia.
As with all studies, there should be some discussion on possible limitations. Foremost, ELF and AM pharmacokinetic characterizations were based on composite data instead of individual concentration-time profiles because of the infeasible nature of accomplishing this. Moreover, the study population consisted of healthy adult volunteers; future studies should assess a population more indicative of the intended use (i.e., patients of all ages with pulmonary infections). Furthermore, four of the study subjects had eravacycline concentrations in BAL fluid that were BLQ, and since there were detectable peaks present on the chromatogram, concentrations of one-half the BLQ were used. If these samples were removed from the analysis, the mean concentration at the time points affected would increase since subjects with one-half the BLQ being used had lower ELF concentrations than others in the group. In the calculation of AM drug concentrations, monocytes and histiocytes were the only cells used in calculating concentrations, leading to the possibility of recovered drug from other cell lineages or the lack of contribution from other cells. Of the few methods available to correlate drug concentrations between plasma and ELF, the urea method was used, which inherently assumes urea will cross membranes freely; thus, urea concentrations in each compartment are automatically presumed to be in equilibrium. In our study, the lavage fluid dwell times on average did not exceed 1 min, but it has been shown with lavage fluid dwell times of >1 min that the ELF volume is overestimated (24, 25). It is also important to note that protein binding in the intrapulmonary compartment is assumed to be inconsequential, and thus there is no assumed difference between total and free drug concentrations in the intrapulmonary compartments (13). Therefore, all calculations compared total drug in the ELF and AM to free drug in plasma. The degree to which eravacycline had penetrated into the ELF and AM may be a conservative estimate considering that the sampling scheme chosen here does not characterize the initial distribution phase in ELF and AM.
In conclusion, eravacycline was tolerated by all study subjects, with no discontinuations and only mild to moderate adverse events reported. Previous experience with eravacycline has shown that nausea and vomiting are more prevalent in healthy subjects than in patient populations. Intrapulmonary penetrations into the ELF and AM of the lungs were approximately 6- and 50-fold greater than in plasma. These data demonstrate the bronchopulmonary disposition of eravacycline and support further studies to delineate its role in the management of respiratory infections.
ACKNOWLEDGMENTS
This study was supported with funds provided by Tetraphase Pharmaceuticals, Watertown, MA, and has been funded in whole or in part with federal funds from the Biomedical Advanced Research and Development Authority, Office of the Assistant Secretary for Preparedness and Response, Office of the Secretary, Department of Health and Human Services, under contract HHSO100201200002C.
We appreciated the assistance of Lee Steere for his efforts involving venous access and drug administration, Mary Anne Banevicius for her efforts in urea analysis, and Patrick Horn for his efforts with safety analysis. We also express gratitude toward the entire staff of the Center for Anti-Infective Research and Development for their efforts in accomplishing this study.
D.P.N. has received research grants and is a consultant for Tetraphase Pharmaceuticals, Inc. S.R. is an employee of Tetraphase Pharmaceuticals, Inc.
FOOTNOTES
- Received 20 September 2013.
- Returned for modification 26 October 2013.
- Accepted 18 January 2014.
- Accepted manuscript posted online 27 January 2014.
- Copyright © 2014, American Society for Microbiology. All Rights Reserved.
