Relationship of the Calcitonin Gene-Related Peptide Monoclonal Antibody Galcanezumab Pharmacokinetics and Capsaicin-Induced Dermal Blood Flow in Healthy Subjects.

Galcanezumab, a humanized monoclonal antibody targeting calcitonin gene-related peptide, was recently approved for migraine prophylaxis. The pharmacokinetic/pharmacodynamic (PK/PD) relationship between galcanezumab concentration and inhibition of capsaicin-induced dermal blood flow (CIDBF) was evaluated using first-in-human data following 6 single subcutaneous doses (1 to 600 mg) or multiple (4) 150-mg doses every 2 weeks in 7 cohorts (7 actively treated subjects and 2 placebo-treated healthy subjects). Galcanezumab pharmacokinetics were best described by a 1-compartment model with delayed first-order absorption/linear elimination. Apparent estimates (between-subject variability) of clearance, volume of distribution, absorption rate constant, and lag time were 0.0106 L/h (27%CV), 11.2 L (21%CV), 0.0192 h-1 (89%CV), and 0.202 hours, respectively. Estimated elimination half-life was about 30 days. An effect compartment link model described the concentration-effect relationship; estimated maximum inhibitory effect was 70.5%, and 50% maximum inhibitory effect concentration (IC50 ) was 1060 ng/mL. Galcanezumab showed dose- and concentration-dependent potent and durable inhibition of CIDBF. Simulated effect compartment concentrations were maintained above IC50 after 12 weeks of dosing. Near-maximal CIDBF inhibition occurred with 150 mg biweekly for 12 weeks lasting ≥24 weeks or with ≥30 mg every 2 weeks or 195 mg every 13 weeks. Quantitative modeling of galcanezumab PK/PD supported dose selection for the phase 2 proof-of-concept study.

Applications of Bayesian statistical methodology to clinical trial design: A case study of a phase 2 trial with an interim futility assessment in patients with knee osteoarthritis.

Development of new pharmacological treatments for osteoarthritis that address unmet medical needs in a competitive market place is challenging. Bayesian approaches to trial design offer advantages in defining treatment benefits by addressing clinically relevant magnitude of effects relative to comparators and in optimizing efficiency in analysis. Such advantages are illustrated by a motivating case study, a proof of concept, and dose finding study in patients with osteoarthritis. Patients with osteoarthritis were randomized to receive placebo, celecoxib, or 1 of 4 doses of galcanezumab. Primary outcome measure was change from baseline WOMAC pain after 8 weeks of treatment. Literature review of clinical trials with targeted comparator therapies quantified treatment effects versus placebo. Two success criteria were defined: one to address superiority to placebo with adequate precision and another to ensure a clinically relevant treatment effect. Trial simulations used a Bayesian dose response and longitudinal model. An interim analysis for futility was incorporated. Simulations indicated the study had ≥85% power to detect a 14-mm improvement and ≤1% risk for a placebo-like drug to pass. The addition of the second success criterion substantially reduced the risk of an inadequate, weakly efficacious drug proceeding to future development. The study was terminated at the interim analysis due to inadequate analgesic efficacy. A Bayesian approach using probabilistic statements enables clear understanding of success criteria, leading to informed decisions for study conduct. Incorporating an interim analysis can effectively reduce sample size, save resources, and minimize exposure of patients to an inadequate treatment.

Evaluation of the Safety, Pharmacokinetics, Pharmacodynamics, and Efficacy After Single and Multiple Dosings of LY3016859 in Healthy Subjects and Patients With Diabetic Nephropathy.

Two phase 1 studies (TGAA and TGAB) evaluated the safety, pharmacokinetics, pharmacodynamics, and efficacy of LY3016859 (LY), a monoclonal antibody that binds epiregulin and transforming growth factor α (TGF-α), administered intravenously or subcutaneously. In TGAA, 56 healthy subjects received a single dose of LY (0.1-750 mg intravenously, 50 mg subcutaneously) or placebo. In TGAB part A, 15 patients with diabetic nephropathy (DN) received 2 doses of LY (10-750 mg intravenously) or placebo, and in TGAB part B, 45 patients with DN received 5 doses of LY (50-750 mg intravenously) or placebo. Pharmacokinetics, pharmacodynamics, anti-LY antibodies, and change in proteinuria and albuminuria were evaluated. Single and multiple doses of LY administered 3 weeks apart were well tolerated. Pharmacokinetics were nonlinear in healthy subjects and patients with DN, indicating target-mediated drug disposition. Epiregulin level increased in both studies, and TGF-α levels increased in the TGAB study, consistent with target engagement; however, LY treatment did not significantly reduce proteinuria or albuminuria in patients with DN. There was no obvious effect of LY on the disease-related biomarkers monocyte chemoattractant protein-1, synaptopodin, or transferrin. Although LY administration resulted in a high frequency of anti-LY antibodies, pharmacokinetics, target engagement, and efficacy were not impacted.

Distinct mobilization of leukocytes and hematopoietic stem cells by CXCR4 peptide antagonist LY2510924 and monoclonal antibody LY2624587.

Stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 play a critical role in mobilization and redistribution of immune cells and hematopoietic stem cells (HSCs). We evaluated effects of two CXCR4-targeting agents, peptide antagonist LY2510924 and monoclonal antibody LY2624587, on mobilizing HSCs and white blood cells (WBCs) in humans, monkeys, and mice. Biochemical analysis showed LY2510924 peptide blocked SDF-1/CXCR4 binding in all three species; LY2624587 antibody blocked binding in human and monkey, with minimal activity in mouse. Cellular analysis showed LY2624587 antibody, but not LY2510924 peptide, down-regulated cell surface CXCR4 and induced hematological tumor cell death; both agents have been shown to inhibit SDF-1/CXCR4 interaction and downstream signaling. In animal models, LY2510924 peptide induced robust, prolonged, dose- and time-dependent WBC and HSC increases in mice and monkeys, whereas LY2624587 antibody induced only moderate, transient increases in monkeys. In clinical trials, similar pharmacodynamic effects were observed in patients with advanced cancer: LY2510924 peptide induced sustained WBC and HSC increases, while LY2624587 antibody induced only minimal, transient WBC changes. These distinct pharmacodynamic effects in two different classes of CXCR4 inhibitors are clinically important and should be carefully considered when designing combination studies with immune checkpoint inhibitors or other agents for cancer therapy.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the CGRP Binding Monoclonal Antibody LY2951742 (Galcanezumab) in Healthy Volunteers.

Background: Calcitonin gene-related peptide (CGRP) is pivotal in the pathophysiology of migraine headaches and represents a promising target for migraine treatment. The humanized monoclonal antibody galcanezumab (LY2951742) binds to CGRP and may be effective in migraine prophylaxis. Objectives: The primary objective was to evaluate the safety and tolerability of single and multiple doses of galcanezumab in humans. Secondary objectives included assessing the pharmacokinetics and evaluating target engagement. Methods: A double-blind, randomized, placebo-controlled study (NCT 01337596) with single escalating and multiple subcutaneous (SC) doses of galcanezumab was performed in healthy male volunteers. Single doses of 1, 5, 25, 75, 200, and 600 mg of galcanezumab (n = 7/dose) or placebo (n = 2/dose) were injected SC in six consecutive cohorts of nine subjects each. One cohort of nine subjects received multiple (4) 150 mg doses of galcanezumab or placebo every other week. Target engagement was evaluated by measuring inhibition of capsaicin-induced increase in dermal blood flow (DBF). Findings: Sixty-three subjects were randomized and included in the safety analyses. Galcanezumab was well tolerated in single doses (1-600 mg SC) and consecutive doses (150 mg SC). There was no dose-dependent difference in type or frequency of treatment-emergent adverse events, and no clinically meaningful difference when compared with placebo. Pharmacokinetics were linear. Galcanezumab induced a robust, dose-dependent, and durable inhibition of capsaicin-induced increase in DBF, supporting the continued clinical development of galcanezumab for prophylaxis in migraine patients.

LY3045697: Results from two randomized clinical trials of a novel inhibitor of aldosterone synthase.

INTRODUCTION: LY3045697 is a potent and selective aldosterone synthase (CYP11B2) inhibitor that was developed as a safer alternative to mineralocorticoid receptor antagonists. Effects of LY3045697 on aldosterone and cortisol synthesis, as well as potassium ion homeostasis, were evaluated in two clinical studies in healthy subjects. MATERIALS AND METHODS: Two incomplete, placebo-controlled crossover-design clinical studies examined safety, pharmacodynamics, and pharmacokinetics under single and repeated dose conditions in healthy subjects. Pharmacodynamics was assessed following oral potassium challenge and intravenous adrenocorticotropic hormone procedures with spironolactone 25 mg/d as an active comparator. RESULTS: A total of 51 subjects participated in the two studies, which included 38 males and 13 females (of non-childbearing potential), from 18-65 years old. LY3045697 caused rapid dose and concentration-dependent unstimulated plasma aldosterone concentration reduction seen as early as 4 h after the first dose at dose levels as low as 1 mg, and reaching near complete suppression at high doses. The potency (IC50) decreased significantly upon multiple dosing. After eight days of dosing, post-adrenocorticotropic hormone challenge plasma aldosterone concentration increase was dose-dependently blunted by LY3045697 with high potency with a dose as low as 0.1 mg resulting in substantial effect, and with an overall IC50 of 0.38 ng/ml. Minor reductions in cortisol were observed only at the top dose of 300 mg. LY3045697 is generally safe and tolerated, and exhibits linear pharmacokinetics. CONCLUSIONS: LY3045697 is a potent and highly selective aldosterone synthase inhibitor with selectivity for CYP11B2, offering a substantial potential advantage over previous aldosterone synthase inhibitors evaluated in the clinic.

A Phase 1 Study of LY2874455, an Oral Selective pan-FGFR Inhibitor, in Patients with Advanced Cancer.

BACKGROUND: We report here a phase 1 study of LY2874455, a potent oral selective pan-fibroblast growth factor receptor (FGFR) inhibitor. OBJECTIVE: The primary objective was to determine the recommended phase 2 dosing (RP2D). Secondary objectives included determining toxicity, antitumor activity, pharmacokinetics (PK), and pharmacodynamic (PD) properties of LY2874455. PATIENTS AND METHODS: This study comprised two parts: (a) dose escalation with 3 + 3 cohorts in patients with solid tumors and (b) dose-expansion cohorts in patients with gastric cancer (GC) and non-small cell lung cancer (NSCLC). Part A: 36 patients in 11 dose cohorts ranging from 2 to 24 mg twice daily (BID). RP2D was 16 mg BID. Part B: GC cohort, 29 patients, NSCLC cohort, 27 patients, all treated at the RP2D. RESULTS: LY2874455 was slowly absorbed and generally showed linear PK. The effective half-life was ∼12 h. PD properties of LY2874455 occurred at doses ≥10 mg by increases in serum phosphorus. Phosphate binders were administered to control serum phosphorus. LY2874455 was generally well tolerated; most toxicities were grade 1 or 2; most frequent were hyperphosphatemia, diarrhea, and stomatitis. EFFICACY: part A: 24 patients evaluable: 1 patient in the 14-mg BID cohort with GC had a partial response (PR); 14 patients had stable disease (SD); part B: NSCLC cohort: 11 of 12 evaluable patients had SD; GC cohort: 15 patients evaluable: 1 patient with PR; 12 patients with SD. CONCLUSIONS: LY2874455 has an RP2D of 16 mg BID and demonstrated good tolerability and activity in solid-organ cancer patients. The role of FGFR inhibition on tumor growth in patients requires further study. (NCT01212107).

Prognostic and predictive value of circulating tumor cells and CXCR4 expression as biomarkers for a CXCR4 peptide antagonist in combination with carboplatin-etoposide in small cell lung cancer: exploratory analysis of a phase II study.

Background Circulating tumor cells (CTCs) and chemokine (C-X-C motif) receptor 4 (CXCR4) expression in CTCs and tumor tissue were evaluated as prognostic or predictive markers of CXCR4 peptide antagonist LY2510924 plus carboplatin-etoposide (CE) versus CE in extensive-stage disease small cell lung cancer (ED-SCLC). Methods This exploratory analysis of a phase II study evaluated CXCR4 expression in baseline tumor tissue and peripheral blood CTCs and in post-treatment CTCs. Optimum cutoff values were determined for CTC counts and CXCR4 expression in tumors and CTCs as predictors of survival outcome. Kaplan-Meier estimates and hazard ratios were used to determine biomarker prognostic and predictive values. Results There was weak positive correlation at baseline between CXCR4 expression in tumor tissue and CTCs. Optimum cutoff values were H-score ≥ 210 for CXCR4+ tumor, ≥7% CTCs with CXCR4 expression (CXCR4+ CTCs), and ≥6 CTCs/7.5 mL blood. Baseline H-score for CXCR4+ tumor was not prognostic of progression-free survival (PFS) or overall survival (OS). Baseline CXCR4+ CTCs ≥7% was prognostic of shorter PFS. CTCs ≥6 at baseline and cycle 2, day 1 were prognostic of shorter PFS and OS. None of the biomarkers at their respective optimum cutoffs was predictive of treatment response of LY2510924 plus CE versus CE. Conclusions In patients with ED-SCLC, baseline CXCR4 expression in tumor tissue was not prognostic of survival or predictive of LY2510924 treatment response. Baseline CXCR4+ CTCs ≥7% was prognostic of shorter PFS. CTC count ≥6 at baseline and after 1 cycle of treatment were prognostic of shorter PFS and OS.

Occupancy of Nociceptin/Orphanin FQ Peptide Receptors by the Antagonist LY2940094 in Rats and Healthy Human Subjects.

Therapeutic benefits from nociceptin opioid peptide receptor (NOP) antagonism were proposed for obesity, eating disorders, and depression. LY2940094 ([2-[4-[(2-chloro-4,4-difluoro-spiro[5H-thieno[2,3-c]pyran-7,4'-piperidine]-1'-yl)methyl]-3-methyl-pyrazol-1-yl]-3-pyridyl]methanol) is a novel, orally bioavailable, potent, and selective NOP antagonist. We studied NOP receptor occupancy (RO) after single oral LY2940094 doses in rat hypothalamus and human brain by use of liquid chromatography with tandem mass spectrometry (LC-MS/MS) (LSN2810397) and positron emission tomography (PET) ([(11)C]NOP-1A) tracers, respectively. A bolus plus constant infusion tracer protocol with PET was employed in humans at 2.5 and 26.5 hours after administration of the LY2940094 dose. The RO was calculated from the change in regional distributional volume (VT) corrected for nondisplaceable volume using Lasson plots. The RO followed a simple Emax relationship to plasma LY2940094 concentration, reaching near complete occupancy in both species. For rat hypothalamus, the plasma concentration at half-maximum RO (EC50) was 5.8 ng/ml. In humans, LY2940094 was well tolerated and safe over the 4-40 mg dose range, and it peaked in plasma at 2 to 6 hours after a 1- to 2-hour lag, with approximate dose-proportional exposure. After 4-40 mg doses, NOP RO was similar across the prefrontal cortex, occipital cortex, putamen, and thalamus, with EC50 of 2.94 to 3.46 ng/ml, less than 2-fold lower than in rats. Over 4-40 mg doses, LY2940094 mean plasma levels at peak and 24 hours were 7.93-102 and 1.17-14.1 ng/ml, corresponding to the cross-region average NOP RO of 73%-97% and 28%-82%, respectively. The rat EC50 translates well to humans. LY2940094 readily penetrates the human brain, and a once-daily oral dose of 40 mg achieves sustainably high (>80%) NOP RO levels suitable for testing clinical efficacy.

Discovery of 6-(4-{[5-Cyclopropyl-3-(2,6-dichlorophenyl)isoxazol-4-yl]methoxy}piperidin-1-yl)-1-methyl-1H-indole-3-carboxylic Acid: A Novel FXR Agonist for the Treatment of Dyslipidemia.

The farnesoid X receptor (FXR) is a member of the "metabolic" subfamily of nuclear receptors. Several FXR agonists have been reported in the literature to have profound effects on plasma lipids in animal models. To discover novel and effective therapies for dyslipidemia and atherosclerosis, we have developed a series of potent FXR agonists that robustly lower plasma LDL and vLDL in LDLr-/- mice. To this end the novel piperidinylisoxazole system LY2562175 was discovered. This molecule is a potent and selective FXR agonist in vitro and has robust lipid modulating properties, lowering LDL and triglycerides while raising HDL in preclinical species. The preclinical ADME properties of LY2562175 were consistent with enabling once daily dosing in humans, and it was ultimately advanced to the clinic for evaluation in humans. The synthesis and biological profile of this molecule is discussed.

A decade of innovation in pharmaceutical R&D: the Chorus model.

Chorus is a small, operationally independent clinical development organization within Eli Lilly and Company that specializes in drug development from candidate selection to clinical proof of concept. The mission of Chorus is to achieve proof of concept rapidly and at a low cost while positioning successful projects for 'pharma-quality' late-stage development. Chorus uses a small internal staff of experienced drug developers and a network of external vendors to design and implement chemistry, manufacturing and control processes, preclinical toxicology and biology, and Phase I/II clinical trials. In the decade since it was established, Chorus has demonstrated substantial productivity improvements in both time and cost compared to traditional pharmaceutical research and development. Here, we describe its development philosophy, organizational structure, operational model and results to date.

Population pharmacokinetic modeling of LY2189102 after multiple intravenous and subcutaneous administrations.

Interleukin-1 beta (IL-1ß) is an inflammatory mediator which may contribute to the pathophysiology of rheumatoid arthritis (RA) and type 2 diabetes mellitus (T2DM). Population pharmacokinetics (PK) of LY2189102, a high affinity anti-IL-1ß humanized monoclonal immunoglobulin G4 evaluated for efficacy in RA and T2DM, were characterized using data from 79 T2DM subjects (Study H9C-MC-BBDK) who received 13 weekly subcutaneous (SC) doses of LY2189102 (0.6, 18, and 180 mg) and 96 RA subjects (Study H9C-MC-BBDE) who received five weekly intravenous (IV) doses (0.02-2.5 mg/kg). Frequency of anti-drug antibody (ADA) development appears dose-dependent and is different between studies (36.7% in Study H9C-MC-BBDK vs. 2.1% in Study H9C-MC-BBDE), likely due to several factors, including differences in patient population and background medications, administration routes, and assays. A two-compartment model with dose-dependent bioavailability best characterizes LY2189102 PK following IV and SC administration. Typical elimination and distribution clearances, central and peripheral volumes of distribution are 0.222 L/day, 0.518 L/day, 3.08 L, and 1.94 L, resulting in a terminal half-life of 16.8 days. Elimination clearance increased linearly, yet modestly, with baseline creatinine clearance and appears 37.6% higher in subjects who developed ADA. Bioavailability (0.432-0.721) and absorption half-life (94.3-157 h) after SC administration are smaller with larger doses. Overall, LY2189102 PK is consistent with other therapeutic humanized monoclonal antibodies and is likely to support convenient SC dosing.

A phase I trial of LY2510924, a CXCR4 peptide antagonist, in patients with advanced cancer.

PURPOSE: Overexpression of C-X-C motif receptor 4 (CXCR4) is implicated in tumor progression. LY2510924 is a peptide antagonist, which blocks stromal cell-derived factor-1 (SDF1) from CXCR4 binding. EXPERIMENTAL DESIGN: This phase I study included two parts: a 3+3 dose escalation (part A) and dose confirmation (part B). LY2510924 was administered as a daily subcutaneous injection on a 28-day cycle. The primary objective was to determine the recommended phase II dose. Secondary objectives included safety, pharmacokinetics, efficacy, and pharmacodynamic response, including mobilization of CD34(+) hematopoietic stem cells into the peripheral blood. RESULTS: Forty-five patients were enrolled, 25 in part A and 20 in part B. Patients were administered increasing doses of LY2510924: 1.0, 2.5, 5.0, 10, 20, and 30 mg/day for part A and 2.5 or 20 mg/day for part B. Two patients (30-mg/day cohort) experienced dose-limiting toxicities of grade 3 increased neutrophil count. The maximum tolerated dose (MTD) was 20 mg/day. The most common drug-related treatment-emergent adverse events were fatigue (9%), injection-site reaction (9%), injection site pruritus (7%), and nausea (7%). The best response was stable disease for nine patients (20%). At the end of cycle 1, mean peak LY2510924 plasma concentration and the 24-hour area under the plasma concentration versus time curve increased slightly more than dose proportionally. LY2510924 dose dependently increased CD34(+) cell counts in peripheral blood up to 18-fold. CONCLUSIONS: LY2510924 demonstrated CD34(+) cell mobilization at doses ≥2.5 mg/day with a tolerable safety profile up to an MTD of 20 mg/day.

Double-blind, randomized study evaluating the glycemic and anti-inflammatory effects of subcutaneous LY2189102, a neutralizing IL-1ß antibody, in patients with type 2 diabetes.

OBJECTIVE: Inflammation is associated with pancreatic ß-cell apoptosis and reduced insulin sensitivity. Literature suggests that interleukin (IL)-1ß may contribute to the pathogenesis of type 2 diabetes mellitus (T2DM). This study aimed to determine the efficacy, safety, and tolerability of LY2189102, a neutralizing IL-1ß antibody, in T2DM patients. RESEARCH DESIGN AND METHODS: Phase II, randomized, double-blind, parallel, placebo-controlled study of subcutaneous LY2189102 (0.6, 18, and 180 mg) administered weekly for 12 weeks in T2DM patients on diet and exercise, with or without approved antidiabetic medications. RESULTS: LY2189102 reduced HbA1c at 12 weeks (adjusted mean differences versus placebo: -0.27, -0.38 and -0.25% for 0.6, 18 and 180 mg doses, respectively), and fasting glucose at multiple time points compared with placebo. LY2189102 also reduced postprandial glycemia, and inflammatory biomarkers, including hs-CRP and IL-6. LY2189102 was generally well tolerated. CONCLUSIONS: Weekly subcutaneous LY2189102 for 12 weeks was well tolerated, modestly reduced HbA1c and fasting glucose, and demonstrated significant anti-inflammatory effects in T2DM patients. Neutralizing IL-1ß holds promise as a convenient adjuvant treatment for T2DM.

Evaluation of a mathematical model of diabetes progression against observations in the Diabetes Prevention Program.

The seminal publication of the Diabetes Prevention Program (DPP) results in 2002 has provided insight into the impact of major therapies on the development of diabetes over a time span of a few years. In the present work, the publicly available DPP data set is used to calibrate and evaluate a recently developed mechanistic mathematical model for the long-term development of diabetes to assess the model's ability to predict the natural history of disease progression and the effectiveness of preventive interventions. A general population is generated from which virtual subject samples corresponding to the DPP enrollment criteria are selected. The model is able to reproduce with good fidelity the observed time courses of both diabetes incidence and average glycemia, under realistic hypotheses on evolution of disease and efficacy of the studied therapies, for all treatment arms. Model-based simulations of the long-term evolution of the disease are consistent with the transient benefits observed with conventional therapies and with promising effects of radical improvement of insulin sensitivity (as by metabolic surgery) or of ß-cell protection. The mechanistic diabetes progression model provides a credible tool by which long-term implications of antidiabetic interventions can be evaluated.

Mathematical models of diabetes progression.

Few attempts have been made to model mathematically the progression of type 2 diabetes. A realistic representation of the long-term physiological adaptation to developing insulin resistance is necessary for effectively designing clinical trials and evaluating diabetes prevention or disease modification therapies. Writing a good model for diabetes progression is difficult because the long time span of the disease makes experimental verification of modeling hypotheses extremely awkward. In this context, it is of primary importance that the assumptions underlying the model equations properly reflect established physiology and that the mathematical formulation of the model give rise only to physically plausible behavior of the solutions. In the present work, a model of the pancreatic islet compensation is formulated, its physiological assumptions are presented, some fundamental qualitative characteristics of its solutions are established, the numerical values assigned to its parameters are extensively discussed (also with reference to available cross-sectional epidemiologic data), and its performance over the span of a lifetime is simulated under various conditions, including worsening insulin resistance and primary replication defects. The differences with respect to two previously proposed models of diabetes progression are highlighted, and therefore, the model is proposed as a realistic, robust description of the evolution of the compensation of the glucose-insulin system in healthy and diabetic individuals. Model simulations can be run from the authors' web page.

Clinical pharmacokinetics of alamifovir and its metabolites.

Alamifovir, a purine nucleotide analogue prodrug, and its hydrolyzed derivatives have shown preclinical efficacy activity against wild-type and lamivudine-resistant hepatitis B virus. Two studies were conducted to examine the single- and multiple-dose alamifovir pharmacokinetics after oral administration in healthy males. In study 1, subjects were given single doses (0.2 to 80 mg), with a subset receiving 20 mg in a fed state. Study 2 subjects were dosed with 2.5 to 15 mg twice daily for 15 days. Plasma samples were collected over 72 h in study 1 and over 24 h on days 1 and 15 in study 2. Concentrations of alamifovir and its major metabolites were determined using liquid chromatography/tandem mass spectrometry methods. The data were analyzed using a noncompartmental technique. Although alamifovir was rapidly absorbed, there was limited systemic exposure due to its rapid hydrolysis and formation of at least three metabolites, suggesting that alamifovir acts as a prodrug. The major metabolites detected were 602074 and 602076, with 602075 detectable only in higher-dose groups. Maximum 602074 plasma concentration was achieved at approximately 0.5 h (T(max)) and declined with a 1- to 2-h terminal half-life (t(1/2)). Maximum concentrations of 602076 (C(max)) averaged 10% of the 602074 C(max) and reached T(max) in 2.5 h with a 4-h t(1/2). Food appeared to decrease the extent of absorption of the compound. Multiple dosing resulted in minimal accumulation, and the concentrations following multiple doses could be predicted using the single-dose data. Alamifovir was well tolerated and the pharmacokinetics were characterized in these studies.