Randomised clinical trial: arbaclofen placarbil in gastro-oesophageal reflux disease--insights into study design for transient lower sphincter relaxation inhibitors.

BACKGROUND: Arbaclofen placarbil is a pro-drug of the gamma-aminobutyric acid-B agonist R-baclofen that has been shown to reduce reflux episodes in patients with gastro-oesophageal reflux disease (GERD). AIM: To evaluate the efficacy and safety of arbaclofen placarbil vs. placebo as adjunctive therapy in subjects with troublesome GERD symptoms despite therapy with once-daily doses of a proton pump inhibitor (PPI) and to identify the characteristics of patients who were responders. METHODS: Patients (n = 460) with symptomatic GERD experiencing troublesome symptoms on once-daily PPI therapy were enrolled in this phase II, randomised, multicentre, double-blind, placebo-controlled, dose-ranging study. Patients were randomised to receive placebo or arbaclofen placarbil (20 or 40 mg once daily, 20 or 30 mg twice daily) with their current PPI for 6 weeks. Patients recorded heartburn and other GERD symptoms in a daily diary and rated severity of each event. The primary endpoint was percent change from baseline in heartburn events per week. RESULTS: In the primary analysis, there was no significant difference between arbaclofen placarbil and placebo. Post hoc analyses removing mild and very mild heartburn events resulted in greater percent reductions for all arbaclofen placarbil doses with nominal P values <0.05 for each dose compared with placebo. There was a dose-related increase for the most common adverse events. CONCLUSIONS: Arbaclofen placarbil was not superior to placebo in the primary analysis. Post hoc analyses suggest that subjects with more clinically relevant moderate or severe symptoms are more likely to respond to arbaclofen placarbil (clinicaltrials.gov NCT00978016).

A phase I, single-dose study of the disposition of 14C-radiolabeled gabapentin enacarbil in healthy male volunteers.

UNLABELLED: Gabapentin enacarbil (GEn) is a prodrug of gabapentin that is effective in restless legs syndrome (RLS) and has dose-proportional gabapentin exposure. OBJECTIVE: This Phase I, open-label, non-randomized, single-center study of 14C-GEn in healthy male volunteers (XenoPort, Inc. protocol: XP065) characterized the mass balance, absorption, metabolism, and elimination pathways of GEn after oral administration of 14C-GEn. METHODS: Subjects received GEn 600 mg as two gelatin capsules containing 300 mg immediate release GEn solution each with approximately 50 µCi of 14C-GEn. Pharmacokinetic assessments included total radioactivity excreted in urine (Aeu(0-t)) and feces (Aef(0-t)), mean maximum concentration (Cmax), 14C-GEn-derived radioactivity in plasma and whole blood, and gabapentin area under the concentration-time curve extrapolated to infinity (AUC0-inf). Tolerability was assessed using adverse events (AEs), vital signs, clinical laboratory tests, and ECGs. Six male subjects aged 24 - 46 years were recruited to the study. RESULTS: Mean total recovery of 14C-GEn-derived radioactivity was 99.3% (94.1% in urine and 5.2% in feces). Mean Cmax and AUC for GEn-derived total radioactivity were similar in whole blood and plasma; the blood to plasma ratio for 14C-GEn-derived total radioactivity was 0.91. 14C-gabapentin was the only radioactive species present in blood. More than 85% of the radioactive dose was recovered in urine within 24 h of dosing. Eight treatment-emergent AEs were reported by 3 subjects; all were mild in intensity. There were no clinically relevant changes in vital signs, laboratory values, or ECGs. CONCLUSIONS: GEn was extensively absorbed and rapidly eliminated from plasma and whole blood.

The effect of food with varying fat content on the clinical pharmacokinetics of gabapentin after oral administration of gabapentin enacarbil.

UNLABELLED: Gabapentin enacarbil, an actively transported prodrug of gabapentin, provides sustained and dose-proportional exposure to gabapentin. OBJECTIVE: To evaluate the effect of food of varying fat content on the pharmacokinetics and tolerability of gabapentin enacarbil. METHODS, MATERIALS AND SUBJECTS: A randomized, open-label, crossover study of 1,200 mg gabapentin enacarbil was conducted in 12 healthy adults, under four conditions: fasted, or following low-fat (200 - 300 kcal total, approximately 6% from fat), moderate-fat (500 - 600 kcal total, approximately 30% from fat) or high-fat meals (1,000 kcal total, approximately 50% from fat), separated by a washout period of >or= 5 days. RESULTS: Ten subjects completed treatment under all four conditions. Data from all subjects were used for pharmacokinetic and safety analyses unless stated otherwise. Mean (standard deviation) bioavailability (based on urinary recovery) of gabapentin from gabapentin enacarbil was 42.0 (6.1)% (fasted), 64.3 (13.2)% (low-fat meal), 64.9 (16.9)% (moderate-fat meal), and 76.1 (14.4)% (high-fat meal). Gabapentin exposures (AUC(inf)) in fed conditions were 23% (low-fat meal), 31% (moderate-fat meal), and 40% (high-fat meal) greater than the exposure under fasted condition. Fed conditions did not significantly delay median t(max), but a trend for delayed gabapentin enacarbil absorption was seen in t(max) ranges following moderate- and high-fat meals compared with the fasted state or low-fat meal. The most commonly reported treatment-emergent adverse events (TEAEs) were dizziness (4 subjects), balance disorder (4 subjects) and somnolence (3 subjects). All TEAEs were rated as mild in intensity. CONCLUSION: Administration of gabapentin enacarbil with food enhanced gabapentin exposure compared with fasted conditions, regardless of the fat or caloric content, and gabapentin enacarbil was generally well tolerated.

Antiviral efficacy and pharmacokinetics of oral adefovir dipivoxil in chronically woodchuck hepatitis virus-infected woodchucks.

The antiviral efficacy of orally administered adefovir dipivoxil was evaluated in an 18-week study (12 weeks of treatment and 6 weeks of recovery) conducted with woodchucks chronically infected with woodchuck hepatitis virus (WHV). Adefovir dipivoxil is a prodrug of adefovir designed to enhance its oral bioavailability. Following administration of 15 mg of adefovir dipivoxil per kg of body weight in four WHV-infected animals, the mean maximum concentration of adefovir in serum was 0.462 microg/ml, with an elimination half-life of 10.2 h, and the oral bioavailability of adefovir was estimated to be 22.9% (+/-11.2%). To study antiviral efficacy, the animals were divided into three groups. There were six animals each in a high-dose group (15 mg/kg/day) and a low-dose group (5 mg/kg/day). A vehicle control group consisted of five animals because WHV DNA was detectable only by PCR at the time of the study in one of the original six animals. Efficacy was evaluated by determining the levels of WHV DNA in serum. The geometric mean WHV DNA level for the high-dose group diminished by >40-fold (>1.6 log(10)) after 2 weeks of treatment and >300-fold (>2.5 log(10)) at 12 weeks. There was a >10-fold reduction in five of six low-dose animals by 2 weeks, but levels were unchanged in one animal. By 12 weeks of treatment there was a >45-fold (>1.6 log(10)) reduction of WHV DNA levels, and serum WHV DNA levels were below the limit of quantification in three of six animals. Viral DNA levels returned to pretreatment levels during the 6-week recovery period. There were no clinically significant changes in body weight, hematology, or serum chemistry values, including bicarbonate or lactate, in any of the treated animals. No histologic evidence of liver injury was apparent in the biopsies. Under the conditions of this study, adefovir dipivoxil was an effective antihepadnaviral agent.

Metabolism of the influenza neuraminidase inhibitor prodrug oseltamivir in the rat.

The metabolism of [2-acetyl-(14)C]oseltamivir (GS4104, Ro 64-0796), the prodrug of the novel influenza neuraminidase inhibitor GS4071 (Ro 64-0802), was examined in rats after oral dosing. Intact oseltamivir was observed only in lung and urine, accounting for 37 and 15% of the total radioactivity in these samples, respectively. GS4071 was the major metabolite in plasma, tissues, and urine, and accounted for 32 to 56% of the radioactivity present in these samples. The second most abundant peak in these samples (13-24% of radioactivity) was a novel metabolite (M3). This metabolite was purified from urine of rats dosed orally with oseltamivir and was identified by liquid chromatography-mass spectrometry and NMR as the (R)-omega-carboxylic acid metabolite of oseltamivir. The omega-carboxylic acid metabolite of oseltamivir could not be produced in vitro. However, omega-hydroxylated products of oseltamivir were produced by rat liver microsomes. Both the (R)- and (S)-omega-hydroxylated products were observed, but formation of the (R)-isomer predominated. These data indicated that in the rat, oseltamivir was primarily metabolized to the active influenza neuraminidase inhibitor GS4071 and, to a lesser extent, to an (R)-omega-carboxylic acid metabolite.

Single-dose pharmacokinetics and safety of the oral antiviral compound adefovir dipivoxil in children infected with human immunodeficiency virus type 1. The Pediatrics AIDS Clinical Trials Group.

The acyclic phosphonate analog adefovir is a potent inhibitor of retroviruses, including human immunodeficiency virus (HIV) type 1, and, unlike some antiviral nucleosides, does not require the initial phosphorylation step for its activity. Two oral dosages of the adefovir prodrug adefovir dipivoxil were evaluated in a phase I study with children with HIV infection. A total of 14 patients were stratified into age groups ranging from 6 months to 18 years of age. Eight patients received 1.5 mg of adefovir dipivoxil per kg of body weight, and six patients received 3.0 mg of adefovir dipivoxil per kg. Serum samples were obtained at intervals during the 8 h postdosing and were analyzed for adefovir concentrations. Patients were monitored for adverse effects. All samples collected resulted in quantifiable levels of adefovir (lower limit of quantitation, 25 ng/ml) from each patient. The areas under the concentration-versus-time curves (AUCs) were similar (P = 0.85) for the 1.5- and 3.0-mg/kg doses, while the apparent oral clearance (CL/F) was significantly higher (P = 0.05) for the 3-mg/kg dose. Pharmacokinetic parameters differed by patient age. In comparing those children older and younger than the median age of 5.1 years, AUC (P = 0.03), maximum concentration of drug in serum (P = 0.004), and the concentration at 8 h postdosing (P = 0.02) were significantly lower for the younger children. There were no significant differences for apparent volume of distribution and CL/F normalized to body surface area, but there was a suggestive difference in half-life (P = 0.07) among the subjects in the older and younger age groups. No significant adverse events were encountered. These data provide the basis for a multidose phase II study of adefovir dipivoxil in HIV-infected infants and children.

Aryl ester prodrugs of cyclic HPMPC. I: Physicochemical characterization and in vitro biological stability.

PURPOSE: The chemical, enzymatic, and biological stabilities and physical properties of a series of salicylate and aryl ester prodrugs of the antiviral agent, cyclic HPMPC, were evaluated to support the selection of a lead compound for clinical development. METHODS: Chemical stabilities of the prodrugs in buffered solutions at 37 degrees C were determined. Stability was also studied in the presence of porcine liver carboxyesterases (PLCE) at pH 7.4 and 25 degrees C. Tissue stabilities were examined in both human and dog intestinal homogenates, plasmas and liver homogenates. Prodrug and product concentrations were determined by reverse phase HPLC. RESULTS: Chemical degradation of the prodrugs resulted in the formation of both cyclic HPMPC and the corresponding HPMPC monoester. Chemical stability was dependent on the orientation of the exo-cyclic ligand; the equatorial isomers were 5.4- to 9.4-fold more reactive than the axial isomers. In the presence of PLCE, the salicylate prodrugs cleaved exclusively to give cyclic HPMPC and not the HPMPC monoester. In plasma, but not intestinal or liver homogenates, the salicylate esters of cyclic HPMPC cleaved readily with a rate dependent on the chain length of the alkyl ester substituent. CONCLUSIONS: The carboxylate function on the salicylate prodrugs of cyclic HPMPC provides an additional handle to chemically modify the lipophilicity, solubility and the biological reactivity of the prodrug. In tissue and enzymatic studies, the major degradation product is cyclic HPMPC. The salicylate ester prodrugs are attractive drug candidates for further in vivo evaluation.

Clinical pharmacokinetics of the antiviral nucleotide analogues cidofovir and adefovir.

Cidofovir and adefovir are members of a new class of antiviral compounds. They are acyclic phosphonate analogues of deoxynucleoside monophosphates. Both compounds undergo intracellular activation to form diphosphates that are potent inhibitors of viral DNA polymerases. Cidofovir has broad spectrum antiviral activity against herpesviruses, papillomaviruses and poxviruses, whereas adefovir has potent activity against retroviruses and certain DNA viruses, including herpesviruses and hepadnaviruses. Intravenous cidofovir is approved for treatment of cytomegalovirus retinitis in patients with AIDS. Cidofovir and adefovir are dianionic at physiological pH and have low oral bioavailability in animals and humans. After intravenous administration to HIV-infected patients, the pharmacokinetics of both drugs are independent of dose and are consistent with preclinical data. Systemic exposure is proportional to the intravenous dose and both drugs are cleared by the kidney and excreted extensively as unchanged drug in the urine. Intracellular activation of a small fraction (< 10%) of the dose by cellular kinases leads to prolonged antiviral effects that are not easily predicted from conventional pharmacokinetic studies. The observed rate of elimination of cidofovir and adefovir from serum may not reflect the true duration of action of these drugs, since the antiviral effect is dependent on concentrations of the active phosphorylated metabolites that are present within cells. For both drugs, > 90% of an intravenous dose is recovered unchanged in the urine over 24 hours. Metabolism does not contribute significantly to the total clearance of either drug. Concomitant oral probenecid decreases both the renal clearance of cidofovir and the incidence of nephrotoxicity, presumably by blocking its active tubular secretion. This is the basis of the clinical use of concomitant probenecid as a nephroprotectant during cidofovir therapy. Subcutaneous administration produces exposure equivalent to that following intravenous administration. Drug interaction studies with cidofovir are ongoing, but there is no evidence of an interaction between zidovudine and either cidofovir or adefovir. Clearance of cidofovir in patients with renal impairment showed a linear relationship to creatinine clearance. The low oral bioavailability of adefovir has led to the development of an oral prodrug, adefovir dipivoxil, currently in development for the treatment of HIV and hepatitis B infections.

Pharmacokinetics of cidofovir in renal insufficiency and in continuous ambulatory peritoneal dialysis or high-flux hemodialysis.

BACKGROUND: Cidofovir is an antiviral agent used for the treatment of cytomegalovirus infection in patients with acquired immunodeficiency syndrome. Because cidofovir is primarily eliminated by the kidneys and because its main adverse effect is nephrotoxicity, an understanding of the pharmacokinetic disposition of cidofovir in patients with renal insufficiency is necessary. METHODS: Twenty-four subjects were enrolled into this study and were divided into 6 groups depending on their degree of renal dysfunction, including subjects receiving maintenance continuous ambulatory peritoneal dialysis and high-flux hemodialysis. The creatinine clearance (CLCR) for subjects not receiving dialysis ranged from 12 to 164 mL/min. Each subject received a single 0.5 mg/kg intravenous dose of cidofovir over 1 hour. Subjects not receiving dialysis were given intravenous hydration with 1 L normal saline solution and concomitant oral probenecid. Serial serum and urine samples were collected to determine pharmacokinetic parameters with use of noncompartmental methods. RESULTS: Mean +/- SD cidofovir clearance (CL) in control subjects (normal renal function; n = 5) was 1.7 +/- 0.1 mL/min/kg, which decreased with declining renal function as indicated by the regression equation: CL (mL/min/kg) = 0.94 x CLCR (mL/min/kg) + 0.064 (r2 = 0.91). Mean volume of distribution at steady state did not change significantly in subjects with kidney disease and cidofovir serum elimination half-life was significantly increased in subjects with severe renal impairment. Cidofovir was not significantly cleared during continuous ambulatory peritoneal dialysis, but high-flux hemodialysis resulted in the removal of 52% +/- 11% of the dose administered. CONCLUSION: The significant (P < .001) correlation observed between CLCR and CL in subjects with varying degrees of renal insufficiency indicates that aggressive dosage reduction of cidofovir would be necessary in subjects with kidney disease to ensure comparable drug exposure based on serum levels.

Clinical pharmacokinetics of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine in human immunodeficiency virus-infected patients.

The pharmacokinetics and bioavailability of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosi ne (cyclic HPMPC) were examined at four doses in 22 patients with human immunodeficiency virus infection. Two groups of six patients received a single dose of cyclic HPMPC at 1.5 or 3.0 mg/kg of body weight by each of the oral and intravenous routes in a random order with a 2-week washout period between administrations. Additional patients received single intravenous doses of cyclic HPMPC at 5.0 mg/kg (n = 6) or 7.5 mg/kg (n = 4). Serial serum and urine samples were collected at intervals over 24 h after dosing. The concentrations of cyclic HPMPC and cidofovir in serum and urine samples were determined by validated reverse-phase ion-pairing high-performance liquid chromatography methods with derivatization and fluorescence detection. After intravenous administration of cyclic HPMPC, concentrations of cyclic HPMPC declined in a biexponential manner, with a mean +/- standard deviation half-life of 1.09 +/- 0.12 h (n = 22). The pharmacokinetics of cyclic HPMPC were independent of dose over the dose range of 1.5 to 7.5 mg/kg. The total clearance of cyclic HPMPC from serum and the volume of distribution of intravenous cyclic HPMPC were 198 +/- 39.6 ml/h/kg and 338 +/- 65.1 ml/kg, respectively (n = 22). The renal clearance of cyclic HPMPC (132 +/- 27.3 ml/h/kg; n = 22) exceeded the creatinine clearance (86.2 +/- 16.3 ml/h/kg), indicating active tubular secretion. The cyclic HPMPC excreted in urine in 24 h accounted for 71.3% +/- 16.0% of the administered dose. Cidofovir was formed from cyclic HPMPC in vivo with a time to the maximum concentration in serum of 1.64 +/- 0.23 h (n = 22). Cidofovir levels declined in an apparent monoexponential manner, with a mean terminal half-life of 3.98 +/- 1.26 h (n = 22). The cidofovir excreted in urine in 24 h accounted for 9.40% +/- 2.33% of the administered cyclic HPMPC dose. Exposure to cidofovir after intravenous administration of cyclic HPMPC was dose proportional and was 14.9% of that from an equivalent dose of cidofovir. The present study suggests that intravenous cyclic HPMPC also has a lower potential for nephrotoxicity in humans compared to that of intravenous cidofovir. The oral bioavailabilities of cyclic HPMPC were 1.76% +/- 1.48% and 3.10% +/- 1.16% with the administration of doses of 1.5 and 3.0 mg/kg, respectively (n = 6 per dose). The maximum concentrations of cyclic HPMPC in serum were 0.036 +/- 0.021 and 0.082 +/- 0.038 microgram/ml after the oral administration of doses of 1.5 and 3.0 mg/kg, respectively. Cidofovir reached quantifiable levels in the serum of only one patient for each of the 1.5- and 3.0-mg/kg oral cyclic HPMPC doses.

High-performance liquid chromatographic determination of GS4071, a potent inhibitor of influenza neuraminidase, in plasma by precolumn fluorescence derivatization with naphthalenedialdehyde.

GS4071 is a potent inhibitor of influenza neuraminidase. A precolumn fluorescence derivatization HPLC method is described for the analysis of GS4071 in rat plasma. Plasma samples were subjected to solid-phase extraction on C18 extraction columns. After extraction, GS4071 was derivatized with naphthalenedialdehyde in the presence of potassium cyanide to produce highly fluorescent cyano[f]benzoisoindole derivatives. Derivatized samples were stable for >24 h at 4 degrees C. The samples were analyzed by an isocratic HPLC method using fluorescence detection at 420 nm excitation and 470 nm emission wavelength. The method was validated and applied to the analysis of plasma samples from pre-clinical pharmacokinetic studies in rats. The limit of detection for GS4071 was 20 ng/ml. For five replicate samples at 50, 400, and 1000 ng/ml, the within-day precision values were 16.9, 9.4 and 4.5%, respectively, and the between-day precision values were 16.9, 7.9, and 2.1%, respectively. The method was linear from 25 to 1600 ng/ml and the total recovery was >68% over this concentration range.

Isolation and identification of a metabolite of cidofovir from rat kidney.

Cidofovir is an acyclic nucleotide analog with potent and broad-spectrum antiviral activity against adenoviruses and herpesviruses including cytomegalovirus (CMV). Cidofovir undergoes intracellular phosphorylation by host enzymes to cidofovir phosphate and cidofovir diphosphate (the active form). An unidentified metabolite has been observed previously in rat tissues and in urine of rabbits, rats and monkeys dosed with cidofovir. In the present study, this metabolite was isolated from rat kidney following an intravenous dose of 100 mg kg-1 cidofovir. The metabolite (metabolite I) was separated from cidofovir and impurities using extraction on anion-exchange resin followed by preparative normal and reversed-phase high-performance liquid chromatography (HPLC). The isolated metabolite I was subjected to proton, 13C and phosphorus nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization mass spectroscopy, and confirmed to be cidofovir-phosphocholine. The uptake of cidofovir by rat kidney was saturated at an intravenous dose of 100 mg kg-1, probably as a result of saturation of the renal tubular secretion pathway. However, the relative abundance of cidofovir phosphocholine was not affected by dose.

Effect of oral probenecid coadministration on the chronic toxicity and pharmacokinetics of intravenous cidofovir in cynomolgus monkeys.

In animals and humans, intravenous administration of the antiviral nucleotide analogue cidofovir results in a dose-limiting nephrotoxicity characterized by damage to the proximal tubular epithelial cells. Probenecid, a competitive inhibitor of organic anion transport in the proximal tubular epithelial cells, was evaluated for its effect on the chronic toxicity and pharmacokinetics of cidofovir. Cynomolgus monkeys (5/sex/group) received cidofovir for 52 consecutive weeks as a once weekly intravenous bolus injection at 0 (saline), 0.1, 0.5, or 2.5 mg/kg/dose alone or at 2.5 mg/kg/dose in combination with probenecid (30 mg/kg/dose via oral gavage 1 h prior to cidofovir administration). Cidofovir-associated histopathological changes were seen only in the kidneys, testes, and epididymides. Nephrotoxicity (mild to moderate cortical tubular epithelial cell karyomegaly, tubular dilation, basement membrane thickening) was present only in monkeys receiving 2.5 mg/kg/dose cidofovir without probenecid. The incidence and severity of testicular (hypo- and aspermatogenesis) and epididymal (severe oligo- and aspermia) changes were increased in monkeys administered cidofovir at 2.5 mg/kg/dose, either alone or in combination with oral probenecid. Renal drug clearance was decreased between Weeks 1 and 52 in the 2.5 mg/kg/dose groups and resulted in an increased systemic exposure to cidofovir (as measured by AUC) that was significantly greater in monkeys administered cidofovir alone (312% increase in males, 98% in females) than in those coadministered probenecid (32% increase in males, 3% in females). These results demonstrate that oral probenecid coadministration protects against the morphological evidence of nephrotoxicity and the accompanying decrease in renal clearance in monkeys receiving chronic intravenous cidofovir treatment.

Safety, pharmacokinetics, and antiretroviral activity of intravenous 9-[2-(R)-(Phosphonomethoxy)propyl]adenine, a novel anti-human immunodeficiency virus (HIV) therapy, in HIV-infected adults.

9-[2-(R)-(Phosphonomethoxy)propyl]adenine (PMPA) is a nucleotide analogue with potent antiretroviral activity in vitro and in simian models. A randomized, double-blind, placebo-controlled, dose-escalation clinical trial of intravenous PMPA monotherapy was conducted in 20 human immunodeficiency virus (HIV)-infected adults with CD4 cell counts of >/=200 cells/mm3 and plasma HIV RNA levels of >/=10,000 copies/ml. Two dose levels were evaluated (1 and 3 mg/kg of body weight/day). Ten subjects were enrolled at each dose level (eight randomized to receive PMPA and two randomized to receive placebo). On day 1, a single dose of PMPA or placebo was administered by intravenous infusion. Beginning on study day 8, PMPA or placebo was administered once daily for an additional 7 consecutive days. All subjects tolerated dosing without significant adverse events. Mean peak serum PMPA concentrations were 2.7 +/- 0.9 and 9.1 +/- 2.1 microgram/ml in the 1- and 3-mg/kg cohorts, respectively. Serum concentrations declined in a biexponential fashion, with a terminal half-life of 4 to 8 h. At 3 mg/kg/day, a single infusion of PMPA resulted in a 0.4 log10 median decline in plasma HIV RNA by study day 8. Following 7 consecutive days of study drug administration thereafter, the median changes in plasma HIV RNA from baseline were -1.1, -0.6, and 0.1 log10 in the 3-mg/kg/day, 1-mg/kg/day, and placebo dose groups, respectively. Following the final dose in the 3-mg/kg/day cohort, the reduction in HIV RNA was sustained for 7 days before returning toward baseline. Further studies evaluating an oral prodrug of PMPA are under way.

Administration of 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) for prevention of perinatal simian immunodeficiency virus infection in rhesus macaques.

Simian immunodeficiency virus (SIV) infection of newborn macaques is a useful animal model to explore novel strategies to reduce perinatal human immunodeficiency virus (HIV) infection. The availability of two easily distinguishable virus isolates, SIVmac251 and the simian/human immunodeficiency virus chimera SHIV-SF33, allows tracing the source of infection following inoculation with both viruses by different routes. In the present study, we evaluated the efficacy of pre- and postinoculation treatment regimens with 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) to protect newborn macaques against simultaneous oral SIVmac251 and intravenous SHIV-SF33 inoculation. Untreated newborns became persistently infected following virus inoculation. When three pregnant macaques were given a single subcutaneous dose of PMPA 2 hr before cesarean section, their newborns became SIV-infected following SIV and SHIV inoculation shortly after birth. In contrast, when four newborn macaques were inoculated simultaneously with SIV and SHIV, and started immediately on PMPA treatment for 2 weeks, only one animal became persistently SIV-infected; the remaining three PMPA-treated newborns, however, had some evidence of an initial transient virus infection but were seronegative and healthy at 8 months of age. Our data demonstrate that PMPA treatment can reduce perinatal SIV infection and suggest that similar strategies may also be effective against HIV.

Intravitreal and plasma cidofovir concentrations after intravitreal and intravenous administration in AIDS patients with cytomegalovirus retinitis.

This study was undertaken to evaluate the intravitreal and plasma concentrations of cidofovir (HPMPC) after intravitreal and intravenous administration in AIDS patients with cytomegalovirus retinitis. Cohort series; undiluted vitreous and blood were collected from 9 patients at the time of pars plana vitrectomy. Vitreous samples from 9 eyes of 9 patients and plasma samples from 4 patients were assayed with high-performance liquid chromatography to determine cidofovir levels. The only eye that had a detectable vitreous concentration (673.7 ng/ml) was injected with 20 microg 24 hours prior to the surgery. The remaining samples including plasma were below the detection point of the assay (100 ng/ml) and were injected between 5 and 40 days prior to sampling. The intravitreal concentration of cidofovir in humans is consistent with pharmacokinetics data in laboratory animals, and suggests that the long duration of antiviral effect (1-3 months) in clinical trials is due to a prolonged intracellular half-life in retinal tissue.

Identification of GS 4104 as an orally bioavailable prodrug of the influenza virus neuraminidase inhibitor GS 4071.

GS 4071 is a potent carbocyclic transition-state analog inhibitor of influenza virus neuraminidase with activity against both influenza A and B viruses in vitro. GS 4116, the guanidino analog of GS 4071, is a 10-fold more potent inhibitor of influenza virus replication in tissue culture than GS 4071. In this study we determined the oral bioavailabilities of GS 4071, GS 4116, and their respective ethyl ester prodrugs in rats. Both parent compounds and the prodrug of the guanidino analog exhibited poor oral bioavailability (2 to 4%) and low peak concentrations in plasma (Cmaxs; Cmax <0.06 microg/ml). In contrast, GS 4104, the ethyl ester prodrug of GS 4071, exhibited good oral bioavailability (35%) as GS 4071 and high Cmaxs of GS 4071 (Cmax = 0.47 microg/ml) which are 150 times the concentration necessary to inhibit influenza virus neuraminidase activity by 90%. The bioavailability of GS 4104 as GS 4071 was also determined in mice (30%), ferrets (11%), and dogs (73%). The plasma of all four species exhibited high, sustained concentrations of GS 4071 such that at 12 h postdosing the concentrations of GS 4071 in plasma exceeded those necessary to inhibit influenza virus neuraminidase activity by 90%. These results demonstrate that GS 4104 is an orally bioavailable prodrug of GS 4071 in animals and that it has the potential to be an oral agent for the prevention and treatment of influenza A and B virus infections in humans.

Pharmacokinetics and bioavailability of the anti-human immunodeficiency virus nucleotide analog 9-[(R)-2-(phosphonomethoxy)propyl]adenine (PMPA) in dogs.

The pharmacokinetics, bioavailability, and metabolism of the anti-human immunodeficiency virus nucleotide analog 9[(R)-2-(phosphonomethoxy)propyl]adenine (PMPA) were determined in beagle dogs following intravenous, intraperitoneal, and oral administration. Fasted male beagle dogs (n = 5) were pretreated with pentagastrin and received PMPA (10 mg/kg of body weight) by the intravenous and oral routes with a washout period of 1 week between doses. A further group of male dogs received PMPA as a single dose via the intravenous (1 mg/kg; n = 5) and the intraperitoneal (10 mg/kg; n = 3) routes, with 1-week washout period between doses. The concentrations of PMPA in plasma and urine were determined over 48 h postdosing by fluorescence derivatization and high-performance liquid chromatography (HPLC). The potential for metabolism or biliary excretion of PMPA was evaluated in a dog with a chronic indwelling bile cannula. Urine, feces, and bile were collected at intervals over 48 h following the intravenous administration of [14C]PMPA (10 mg/kg; 55 microCi/kg). The concentrations of PMPA in plasma after intravenous injection were best described by an open two-compartment model with a terminal half-life of approximately 10 h. PMPA was excreted unchanged in urine (70%); recovery in feces (0.42%) or bile (0.26%) was negligible. The plasma clearance of PMPA (0.28+/-0.05 liter/h/kg) was substantially greater than the glomerular filtration rate in this species, suggesting active tubular secretion of PMPA. No metabolites of [14C]PMPA were observed in urine, feces, or bile on the basis of HPLC with radioactive flow detection. The remainder of the dose was probably excreted unchanged in urine beyond 48 h postdosing. The mean+/-standard deviation observed bioavailabilities of PMPA following oral and intraperitoneal administration at 10 mg/kg were 17.1%+/-1.88% and 73.5%+/-10.5%, respectively.

Penetration of GS4071, a novel influenza neuraminidase inhibitor, into rat bronchoalveolar lining fluid following oral administration of the prodrug GS4104.

GS4071 is a novel potent inhibitor of influenza neuraminidase (Ki < 1 nM) with low (< 5%) oral bioavailability in animals. An ethyl ester prodrug of GS4071, GS4104, has exhibited good oral bioavailability in rat, mouse, and dog models and is currently being developed for the treatment of influenza A and B virus infections. Since influenza virus replicates primarily in the surface epithelial cells of the respiratory tract, the ability of the prodrug to deliver GS4071 to the bronchoalveolar lining fluid (BALF) following an oral dose of GS4104 should be an important indicator of its potential efficacy. In the present study, we determined the concentration-time profiles of GS4071 in the BALF and plasma of rats following oral administration of GS4104. The BALF was sampled by bronchoalveolar lavage with endogenous urea as a dilution marker. The concentration of GS4071 in BALF reached a peak at 2 h (1 h after the plasma peak) and declined at a slower rate than plasma levels, suggesting slow clearance of drug from the lung acini. The ratios of the area-under-the-curve (AUC) values of GS4071 in BALF to those in plasma were 1.05 for AUC from 0 to 6 h (AUC(0-6)) and 1.51 for AUC(0-infinity), indicating significant penetration of the parent drug into the lower respiratory tracts of rats following oral administration of the prodrug. No unchanged GS4104 was detected in BALF.

Anti-human immunodeficiency virus (HIV) activity, safety, and pharmacokinetics of adefovir dipivoxil (9-[2-(bis-pivaloyloxymethyl)-phosphonylmethoxyethyl]adenine) in HIV-infected patients.

A randomized, double-blind, placebo-controlled, dose-escalation study of adefovir dipivoxil, an oral prodrug of adefovir, was conducted in 36 human immunodeficiency virus (HIV)-infected subjects to evaluate its anti-HIV activity, safety, and pharmacokinetics. Subjects received placebo or one of three dosages of adefovir dipivoxil daily for 14 days. Median decreases in serum p24 antigen of 31% (P = .02), 25% (P = .31), and 30% (P = .01) occurred in each drug-treated group, respectively, compared with an increase of 17% in the placebo group. Median decreases in serum HIV RNA of 0.4-0.6 log10 copies/mL occurred in the drug-treated groups (P = .03), compared with no change in the placebo group. Gastrointestinal complaints and reversible liver transaminase elevations were the most frequently noted adverse events. Decreases in serum free carnitine occurred in each drug-treated group during treatment. After 14 days of dosing, adefovir dipivoxil demonstrated anti-HIV activity and was best tolerated at the lowest dosage studied, 125 mg daily.