Pharmacodynamic, pharmacokinetic and tolerability evaluation of concomitant administration of lesinurad and febuxostat in gout patients with hyperuricaemia.

OBJECTIVE: The aim of this study was to evaluate the pharmacodynamics (PDs), pharmacokinetics (PKs) and safety of lesinurad (selective uric acid reabsorption inhibitor) in combination with febuxostat (xanthine oxidase inhibitor) in patients with gout. METHODS: This study was a phase IB, multicentre, open-label, multiple-dose study of gout patients with serum uric acid (sUA) >8 mg/dl following washout of urate-lowering therapy with colchicine flare prophylaxis. Febuxostat 40 or 80 mg/day was administered on days 1-21, lesinurad 400 mg/day was added on days 8-14 and then lesinurad was increased to 600 mg/day on days 15-21. sUA, urine uric acid and PK profiles were evaluated at the end of each week. Safety was assessed by adverse events, laboratory tests and physical examinations. RESULTS: Initial treatment with febuxostat 40 or 80 mg/day monotherapy resulted in 67% and 56% of subjects, respectively, achieving a sUA level <6 mg/dl. Febuxostat 40 or 80 mg/day plus lesinurad 400 or 600 mg/day resulted in 100% of subjects achieving sUA <6 mg/dl and up to 100% achieving sUA <5 mg/dl. No clinically relevant changes in the PKs of either drug were noted. The combination was well tolerated. CONCLUSION: The clinically important targets of sUA <6 mg/dl and <5 mg/dl are achievable in 100% of patients when combining lesinurad and febuxostat.

6-Benzylamino 4-oxo-1,4-dihydro-1,8-naphthyridines and 4-oxo-1,4-dihydroquinolines as HIV integrase inhibitors.

SAR studies on the quinolone carboxylic acid class of HIV-1 integrase inhibitors focused on improving the metabolic stability and led to the discovery of 27 and 38.

Phase 2a randomized controlled trial of short-term activity, safety, and pharmacokinetics of a novel nonnucleoside reverse transcriptase inhibitor, RDEA806, in HIV-1-positive, antiretroviral-naive subjects.

RDEA806 is a novel nonnucleoside reverse transcriptase inhibitor (NNRTI) with potent in vitro activity against wild-type and NNRTI-resistant HIV-1. A phase 2a randomized, double-blind, placebo-controlled, dose-escalating study evaluated the short-term antiviral activity, safety, and pharmacokinetics (PKs) of RDEA806 monotherapy in antiretroviral-naïve, HIV-1-infected subjects. The subjects were randomized to four cohorts comprising four dosage regimens and two formulations of RDEA806 or placebo in a 3:1 ratio within each cohort. The investigators were blinded to the results for each cohort. The subjects received RDEA806 or placebo for 7 days. The primary end point was the change in the HIV RNA load from the baseline to day 9 for each of the four RDEA806 dose regimens compared to that achieved with placebo. The RDEA806 PKs and the immune response to RDEA806 were evaluated along with the safety and tolerability of each dose. Of a total of 48 enrolled subjects, 36 subjects (9 in each cohort) were randomized to RDEA806 study drug, and 12 (3 in each cohort) took placebo. A statistically significant decrease in the viral load from the baseline to day 9 was observed for all RDEA806 treatment groups (P<0.001). On day 9, the mean changes in the HIV RNA load from that at the baseline were -1.95 log10 copies/ml (400 mg twice a day), -1.39 log10 copies/ml (600 mg once a day [q.d.]), -1.62 log10 copies/ml (800 mg q.d.), and -1.70 log1) copies/ml (1,000 mg q.d.). The pharmacokinetics were linear and dose proportional. Treatment with RDEA806 was well tolerated, and there were no discontinuations due to adverse events. In conclusion, all doses of RDEA806 were safe and well tolerated and exhibited robust antiretroviral activity in this short-term monotherapy study with antiretroviral-naïve HIV-infected subjects. RDEA806 is a potent and promising novel NNRTI.

The Effects of Special Patient Population Plasma on Pharmacokinetic Quantifications Using LC-MS/MS.

BACKGROUND: Clinical development of lesinurad, a selective uric acid reabsorption inhibitor, required analysis of lesinurad in plasma from special patient populations. METHODS: EMA and FDA bioanalytical method validation guidance have recommended studying matrix effects on quantitation if samples from special patient populations are to be analyzed. In addition to lesinurad (plasma protein binding 98.2%), the matrix effects from special population plasma on the quantitation of verapamil (PPB 89.6%), allopurinol and oxypurinol (PPB negligible) were also investigated. RESULTS: The plasma from special population patients had no matrix effects on the three quantification methods with stable isotope labeled internal standard, protein precipitation extraction, and LC-MS/MS detection. The validated lesinurad plasma quantification method was successfully applied for the pharmacokinetic evaluations to support the clinical studies in renal impaired patients. CONCLUSION: Special population plasma did not affect quantitation of drugs with a wide range of plasma protein binding levels in human plasma. With the confirmation that there is no impact on quantification from the matrix, the bioanalytical method can be used to support the pharmacokinetic evaluations for clinical studies in special populations.

The Effect of Lesinurad in Combination With Allopurinol on Serum Uric Acid Levels in Patients With Gout.

The objective of the study was to evaluate the effect of lesinurad, a selective uric acid uptake inhibitor, alone and in combination with the xanthine oxidase inhibitor allopurinol, on serum uric acid and urinary urate excretion in patients with gout and hyperuricemia. A phase 1b, multicenter, open-label, multiple-dose study was carried out in patients with gout with serum uric acid ≥8 mg/dL following washout of urate-lowering therapy. Patients were treated with allopurinol 300 mg/day alone in week 1; lesinurad 400 or 600 mg/day was added in week 2, followed by lesinurad 400 or 600 mg/day alone in week 3. Serum uric acid and urine uric acid were evaluated each week. Safety was assessed throughout the study. Lesinurad 400 or 600 mg/day added to allopurinol 300 mg/day reduced serum uric acid by 60% and 72%, respectively, versus allopurinol alone (37%) or lesinurad 400 mg/day (44%) or 600 mg/day (47%) alone. A 100% response rate of serum uric acid <6 mg/dL was achieved by all combinations (serum uric acid <5 mg/dL by 50%-90%). Mean 24-hour urate excretion compared with baseline was -35% with allopurinol, +36% and +56.5% with lesinurad 400 mg/day and 600 mg/day, respectively, and -11.6% and -7.1% with the respective combination therapies. Treatments were well tolerated. In this phase 1 trial, lesinurad added to allopurinol resulted in greater serum uric acid reduction than did allopurinol or lesinurad monotherapy.

P450 phenotyping of the metabolism of selegiline to desmethylselegiline and methamphetamine.

Although there is evidence in the literature of the participation of CYP2B6 in the metabolism of selegiline, it is not clear which other CYP isoforms contribute to its metabolism. The aim of this study was to investigate the P450 isozymes (CYPs) involved in the metabolism of selegiline to desmethylselegiline (DMS) and methamphetamine (MA) using four assays: incubation of selegiline with cDNA expressed CYPs, inhibition of DMS and MA formations in human liver microsomes by CYP-selective chemical inhibitors or CYP-specific antibodies, and correlation analysis. Correlation analysis, performed in a bank of 15 individual human liver microsomes, yielded correlation coefficients for DMS and MA formation of 0.769 and 0.792, respectively, for CYP2B6 (p<0.0001) and 0.333 and 0.349, respectively, for CYP3A4 (p<0.05). These results were supported by chemical/specific antibody inhibition assays. The results of correlation analysis and chemical inhibition also indicated that CYP2A6 seems to play a small role in the metabolism of selegiline. These findings confirm that CYP2B6 plays a major role in the metabolism of selegiline and also suggest the involvement of CYP3A4 and CYP2A6.

Determination of N-acetyl retigabine in dog plasma by LC/MS/MS following off-line microElution 96-well solid phase extraction.

A high throughput off-line microElution 96-well solid phase extraction (SPE) followed by liquid chromatography with tandem mass spectrometry (LC/MS/MS) quantification for the determination of N-acetyl retigabine in dog plasma has been developed and validated. The method involves the use of microElution 96-well SPE for the simultaneous extraction of N-acetyl retigabine and rapid removal of its N-glucuronide metabolite that has shown to be problematic due to its instability using other clean-up methods. The microElution SPE technology eliminates the need for post-extraction solvent evaporation and greatly reduces sample preparation time consequently improving assay efficiency.

LC-MS/MS method for simultaneous determination of viramidine and ribavirin levels in monkey red blood cells.

A high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed for the simultaneous determinations of total viramidine (viramidine, viramidine monophosphate, viramidine diphosphate, and viramidine triphosphate) and total ribavirin (ribavirin, ribavirin monophosphate, ribavirin diphosphate, and ribavirin triphosphate) in monkey red blood cells (RBC). The method involves the addition of internal standards and perchloric acid, conversion of viramidine or ribavirin phosphorylated metabolites to viramidine or ribavirin, purification with an aminopropyl (NH(2)) solid phase extraction (SPE) cartridge, and LC-MS/MS analysis. The MS/MS is selected to monitor m/z 245-->113, 250-->113, 244-->112, and 249-->112 for ribavirin, [(13)C]ribavirin, viramidine, and [(13)C]viramidine, respectively, using positive electrospray ionization. The calibration curves are linear over a concentration range of 100-10,000 ng/mL (0.412-41.2 microM) with a lower limit of quantification (LLOQ) of 100 ng/mL for both compounds. Mean inter-assay recoveries for ribavirin are 101%, 98.9%, and 96.0%, with coefficient of variance (%CV) values between 1.95 and 4.50% for 100, 1000, and 10,000 ng/mL quality control (QC) samples, respectively. Mean inter-assay recoveries for viramidine are 96.3%, 101%, and 102%, with coefficient of variation (%CV) values between 3.61 and 7.22%, for 100, 1000, and 10,000 ng/mL QC samples, respectively. Over-curve dilution QC at 400 microg/mL (1639 microM) for both viramidine and ribavirin are used to ensure the dilution accuracy (25 X dilutions) for monkey samples. The method has been used to simultaneously determine the total concentrations of ribavirin and viramidine in monkey RBC following 5, 15, and 36 weeks dosing of viramidine or ribavirin (60 mg/kg). The concentrations of total ribavirin following ribavirin dosing are 1242 microM at week 5, 1257 microM at week 15, and 1146 microM at week 36. The concentrations of total ribavirin following viramidine dosing are 634 microM at week 5, 716 microM at week 15, and 683 microM at week 36. Only small amounts of viramidine are detected in RBC following viramidine dosing, 7.80 microM at week 5, 6.63 microM at week 15, and 10.4 microM at week 36. The results suggest that ribavirin levels in RBC were at steady state at week 5 of ribavirin or viramidine dosing. At steady state, ribavirin levels in RBC are approximately 2x after ribavirin dosing than viramidine dosing. The relatively small percentage of viramidine in RBC suggests that viramidine either poorly penetrated into RBC or was extensively converted to ribavirin following entry into RBC.

Conversion of viramidine to ribavirin in vivo by adenosine deaminase and its inhibition by 2'-deoxycoformycin.

Previously we reported that viramidine is a prodrug of ribavirin and that adenosine deaminase catalyses viramidine deamination to ribavirin in vivo. This in vivo study explores this prodrug conversion in rats and inhibition by a potent adenosine deaminase inhibitor, 2'-deoxycoformycin. We found that conversion of viramidine to ribavirin was viramidine dose-dependent in rat plasma. A single intravenous dose of 0.25 mg/kg 2'-deoxycoformycin suppressed orally administered viramidine conversion to ribavirin in plasma by 50%. The inhibition was 2'-deoxycoformycin dose-dependent and a single dose of 2 mg/kg decreased the ribavirin/viramidine area under the concentration-time curve between 0 h and 6 h ratio by 2.5-fold. These findings provide strong evidence that adenosine deaminase plays a major role in converting viramidine to ribavirin in vivo.

Sensitive and specific LC-MS/MS method for the simultaneous measurements of viramidine and ribavirin in human plasma.

Viramidine is a prodrug of ribavirin. To facilitate pharmacokinetics studies of viramidine in man, a sensitive and specific LC-MS/MS method for the simultaneous analyses of viramidine and ribavirin in human plasma was developed and validated. The method involved the addition of [13C]viramidine and [13C]ribavirin as internal standards, protein precipitation with acetonitrile, HPLC separation, and quantification by MS/MS system using positive electrospray ionization in the multiple reaction monitoring mode (MRM). The precursor-->product ion transitions were monitored at 245-->113, 250-->113, 244-->112, and 249-->112 for ribavirin, [13C]ribavirin, viramidine, and [13C]viramidine, respectively. The calibration curves for viramidine and ribavirin were linear over a concentration range of 1-1000 ng/mL. For both viramidine and ribavirin, the lower limit of quantification (LLOQ) was 1 ng/mL. For viramidine, intra- and inter-day analyses of QC samples at 1, 5, 250, and 1000 ng/mL indicated good precision (%CV between 1.0 and 7.0%) and accuracy (%bias between -4.3 and 5.2%). For ribavirin, intra- and inter-day analyses of QC samples at 1, 5, 250, and 1000 ng/mL indicated similar precision (%CV between 0.8 and 8.3%) and accuracy (%bias between -5.8 and 9.4%). Both viramidine and ribavirin were stable in human plasma stored at room temperature for at least 3 h, 4 degrees C for at least 6 h, and for at least three freeze-thaw cycles. This accurate and highly specific assay provides a useful method for evaluating the pharmacokinetics of viramidine and ribavirin in man following administration of viramidine.

In Vitro and In Vivo Interaction Studies Between Lesinurad, a Selective Urate Reabsorption Inhibitor, and Major Liver or Kidney Transporters.

BACKGROUND AND OBJECTIVES: Lesinurad is a selective uric acid reabsorption inhibitor (SURI) under investigation for the treatment of gout. This study elucidated the interaction of lesinurad with major liver and kidney transporters in vitro and evaluated the drug-drug interactions (DDIs) of lesinurad and atorvastatin, metformin, and furosemide in clinical studies. METHODS: Lesinurad interaction with membrane transporters was evaluated in validated transporter-expressing cell systems and analyzed by liquid scintillation counting. Healthy male subjects (ages 18-65 years; body mass index 18-32 kg/m(2)) received atorvastatin (40 mg; n = 28) with or without lesinurad 200 or 400 mg, or received metformin (850 mg; n = 12) or furosemide (40 mg; n = 11) with or without lesinurad 400 mg. Plasma concentrations of each concomitant drug were determined by validated liquid chromatography with tandem mass spectrometry methods. RESULTS: Lesinurad interacted in vitro with OATP1B1, OCT1, and OAT1/3 transporters. Co-administration of lesinurad 200 mg did not significantly alter plasma exposure (maximum concentration [C max] and area under the concentration-time curve [AUC]) of total atorvastatin (atorvastatin + hydroxyl-metabolites) or atorvastatin, while co-administration of lesinurad 400 mg increased the C max of total atorvastatin and atorvastatin by 17-26 %, but had no effect on AUC. Co-administration of lesinurad 400 mg had no effect on the plasma exposure of metformin. Furosemide plasma AUC was reduced by 31 % in the presence of lesinurad 400 mg, but furosemide renal clearance and diuretic activity were unchanged. CONCLUSIONS: No clinically relevant DDIs were observed between lesinurad and substrates of major liver or kidney transporters.

Lesinurad, a novel, oral compound for gout, acts to decrease serum uric acid through inhibition of urate transporters in the kidney.

BACKGROUND: Excess body burden of uric acid promotes gout. Diminished renal clearance of uric acid causes hyperuricemia in most patients with gout, and the renal urate transporter (URAT)1 is important for regulation of serum uric acid (sUA) levels. The URAT1 inhibitors probenecid and benzbromarone are used as gout therapies; however, their use is limited by drug-drug interactions and off-target toxicity, respectively. Here, we define the mechanism of action of lesinurad (Zurampic®; RDEA594), a novel URAT1 inhibitor, recently approved in the USA and Europe for treatment of chronic gout. METHODS: sUA levels, fractional excretion of uric acid (FEUA), lesinurad plasma levels, and urinary excretion of lesinurad were measured in healthy volunteers treated with lesinurad. In addition, lesinurad, probenecid, and benzbromarone were compared in vitro for effects on urate transporters and the organic anion transporters (OAT)1 and OAT3, changes in mitochondrial membrane potential, and human peroxisome proliferator-activated receptor gamma (PPARγ) activity. RESULTS: After 6 hours, a single 200-mg dose of lesinurad elevated FEUA 3.6-fold (p < 0.001) and reduced sUA levels by 33 % (p < 0.001). At concentrations achieved in the clinic, lesinurad inhibited activity of URAT1 and OAT4 in vitro, did not inhibit GLUT9, and had no effect on ABCG2. Lesinurad also showed a low risk for mitochondrial toxicity and PPARγ induction compared to benzbromarone. Unlike probenecid, lesinurad did not inhibit OAT1 or OAT3 in the clinical setting. CONCLUSION: The pharmacodynamic effects and in vitro activity of lesinurad are consistent with inhibition of URAT1 and OAT4, major apical transporters for uric acid. Lesinurad also has a favorable selectivity and safety profile, consistent with an important role in sUA-lowering therapy for patients with gout.

A Phase I Study of the Safety, Pharmacokinetics, and Pharmacodynamics of Combination Therapy with Refametinib plus Sorafenib in Patients with Advanced Cancer.

PURPOSE: To assess the safety and tolerability of the small-molecule allosteric MEK inhibitor refametinib combined with sorafenib, in patients with advanced solid malignancies. EXPERIMENTAL DESIGN: This phase I dose-escalation study included an expansion phase at the maximum tolerated dose (MTD). Patients received refametinib/sorafenib twice daily for 28 days, from a dose of refametinib 5 mg plus sorafenib 200 mg to a dose of refametinib 50 mg plus sorafenib 400 mg. Plasma levels of refametinib, refametinib metabolite M17, and sorafenib were measured for pharmacokinetic assessments. Tumors were biopsied at the MTD for analysis of MEK pathway mutations and ERK phosphorylation. RESULTS: Thirty-two patients were enrolled in the dose-escalation cohort. The MTD was refametinib 50 mg twice daily plus sorafenib 400 mg twice daily. The most common treatment-related toxicities were diarrhea and fatigue. Refametinib was readily absorbed following oral administration (plasma half-life of ∼16 hours at the MTD), and pharmacokinetic parameters displayed near-dose proportionality, with less than 2-fold accumulation after multiple dosing. Another 30 patients were enrolled in the MTD cohort; 19 had hepatocellular carcinoma. The combination was associated with significantly reduced ERK phosphorylation in 5 out of 6 patients biopsied, with the greatest reductions in those with KRAS or BRAF mutations. Disease was stabilized in approximately half of patients, and 1 patient with colorectal cancer achieved a partial response at the MTD lasting approximately 1 year. CONCLUSIONS: In this phase I study, refametinib plus sorafenib was well tolerated, with good oral absorption, near-dose proportionality, and target inhibition in a range of tumor types. Clin Cancer Res; 22(10); 2368-76. ©2015 AACR.

Pharmacokinetics of pradefovir and PMEA in healthy volunteers after oral dosing of pradefovir.

The pharmacokinetics of pradefovir and adefovir, 9-(2-phosphonylmethoxyethyl) adenine (PMEA), was evaluated in healthy male volunteers after oral dosing of pradefovir (10, 30, or 60 mg). Pradefovir was absorbed rapidly. The maximum serum concentration, the area under the concentration-time curve between 0 and 96 hours after dosing (AUC(0-96)), and the area under the plasma concentration versus time curve from time 0 to infinity (AUC(0-infinity)) of pradefovir and PMEA increased with the dose of pradefovir. The ratio of PMEA to pradefovir for AUC(0-96) and AUC(0-infinity) ranged from 1.4 to 1.8. Renal clearance of pradefovir (18-31 L/h) increased with the dose of pradefovir and was greater than glomerular filtration. The fraction of total body clearance due to renal clearance was low (0.045 to 0.083), suggesting that metabolic clearance played a significant role in the clearance of pradefovir in man. In addition, an evaluation of the food effect was conducted at the 30-mg dose. The results indicate that food intake has no effect on the extent of exposure of pradefovir and PMEA but may decrease the rate of systemic availability of PMEA.

Ascending multiple-dose pharmacokinetics of viramidine, a prodrug of ribavirin, in adult subjects with compensated hepatitis C infection.

The current study was carried out to evaluate pharmacokinetic profiles of viramidine and ribavirin in patients (n = 8 per dose group) with compensated hepatitis C infection following oral dosing of viramidine (400, 600, or 800 mg bid for 4 weeks). Pharmacokinetic parameters were determined on days 1 and 29 based on plasma, red blood cell, and urine concentrations of viramidine and ribavirin. The results indicate rapid absorption and conversion of viramidine to ribavirin after oral administration of viramidine. Viramidine and ribavirin exposure in plasma and RBCs generally increased from the 400- to 600-mg dose level of viramidine. However, no further increase in exposure was noted at the 800-mg dose. Long half-lives for viramidine (66-76 hours in plasma and 200-420 hours in red blood cells) and ribavirin (340-410 hours in plasma and 360-430 hours in red blood cells) were noted. A negligible amount of viramidine (1%-4% of dose) and a small amount of ribavirin (9%-14% of dose) were excreted in the urine. The renal clearance was low for both viramidine (5-8 L/h) and ribavirin (4-7 L/h). Significant accumulation of viramidine was noted in red blood cells (accumulation factor [R] = 5-8) but not in plasma (R = 2). Extensive accumulation of ribavirin was noted in both plasma (R = 9-17) and red blood cells (R = 77-129). Steady-state levels of ribavirin and viramidine in plasma and red blood cells were achieved by day 22. At steady state, there was extensive conversion of viramidine to ribavirin in both plasma and red blood cells. Both viramidine and ribavirin were preferentially distributed into red blood cells than plasma.

A sensitive and specific method for the determination of total ribavirin in monkey liver by high-performance liquid chromatography with tandem mass spectrometry.

A sensitive and specific method using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the analysis of total ribavirin in monkey liver is developed and validated. In this method, ribavirin and its phosphorylated metabolites are extracted with perchloric acid. The metabolites are converted to ribavirin using acid phosphatase and further purified using a NH2 solid-phase extraction (SPE) cartridge prior to LC-MS/MS analysis. [13C]Ribavirin is added with the extraction solution as an internal standard to obtain better accuracy and precision of the analysis. The MS/MS was selected to monitor 245-->113 and 250-->113 transitions using positive electrospray ionization for ribavirin and [(13)C]ribavirin. The calibration curve is linear over a concentration of 1.0-100 microg/g with a limit of quantitation (LOQ) of 1.0 microg/g. Mean inter-assay accuracy for QC at 1.0, 10 and 100 microg/g are 108, 99.7 and 99.7%, respectively. Mean inter-assay precision (CV) for QC at 1.0, 10 and 100 microg/g are 5.34, 5.24 and 4.59%, respectively. Extractability of total ribavirin from liver has been confirmed with liver obtained from monkey dosed with [14C]ribavirin. The method has been proven to be useful in the determination of total ribavirin concentration in liver from monkeys in mass balance study (10 mg/kg) and in 28 days toxicology study (300 mg/kg/day). It is also used to determine the total ribavirin concentration in human livers from hepatitis C patients received dose of 600 mg ribavirin twice daily.

Pharmacokinetics, pharmacodynamics, and safety of lesinurad, a selective uric acid reabsorption inhibitor, in healthy adult males.

Lesinurad is a selective uric acid reabsorption inhibitor under investigation for the treatment of gout. Single and multiple ascending dose studies were conducted to evaluate pharmacokinetics, pharmacodynamics, and safety of lesinurad in healthy males. Lesinurad was administered as an oral solution between 5 mg and 600 mg (single ascending dose; N=34) and as an oral solution or immediate-release capsules once daily (qday) between 100 mg and 400 mg for 10 days under fasted or fed condition (multiple ascending dose; N=32). Following single doses of lesinurad solution, absorption was rapid and exposure (maximum observed plasma concentration and area under the plasma concentration-time curve) increased in a dose-proportional manner. Following multiple qday doses, there was no apparent accumulation of lesinurad. Urinary excretion of unchanged lesinurad was generally between 30% and 40% of dose. Increases in urinary excretion of uric acid and reductions in serum uric acid correlated with dose. Following 400 mg qday dosing, serum uric acid reduction was 35% at 24 hours post-dose, supporting qday dosing. A relative bioavailability study in healthy males (N=8) indicated a nearly identical pharmacokinetic profile following dosing of tablets or capsules. Lesinurad was generally safe and well tolerated.

Pharmacokinetics and safety of viramidine, a prodrug of ribavirin, in healthy volunteers.

Ribavirin, part of the current first-line combination therapy for the treatment of chronic hepatitis C, has side effects-in particular, hemolytic anemia-that is frequently dose limiting. Based on animal studies, viramidine, a prodrug of ribavirin, is converted to ribavirin in the liver. Viramidine dosing yielded 50% higher ribavirin levels in the monkey liver but only half in plasma and red blood cells compared to ribavirin dosing. At the same dose, it also had a safer profile than ribavirin in a 28-day toxicity study in monkeys. The current study was carried out to evaluate the safety, tolerability, and pharmacokinetics of viramidine in healthy male volunteers (n = 8-18 on viramidine vs. 2 on placebo at each dose level) after oral dosing of viramidine at 200, 600, and 1200 mg. There were no serious adverse events, and most adverse events were mild. The percentages of treatment-emergent events judged to be possibly related to the study drug were 50% in the 1200-mg group, 26% in the 600-mg group, and none in the 200-mg group. Viramidine was orally absorbed and rapidly converted to ribavirin with a t(max) of 1.5 to 3.0 hours for both viramidine and ribavirin in plasma. There was dose proportionality in plasma AUC(0-168 h) and C(max) for viramidine and in plasma AUC(0-168 h) for ribavirin. Plasma AUC(0-168 h) for ribavirin was two to four times higher than plasma AUC(0-168 h) for viramidine, indicating that viramidine is extensively metabolized to ribavirin and is a prodrug of ribavirin in man. Amounts of viramidine and ribavirin excreted in the urine were small (2%-5% of dose), indicating that the main route of elimination for both viramidine and ribavirin is metabolism. Both viramidine and ribavirin were excreted into urine through the mechanism of glomerular filtration. In addition, an evaluation of the effect of a high-fat meal on the pharmacokinetics of viramidine and ribavirin after oral dosing of viramidine at 600 mg was conducted in healthy male volunteers (n = 33-34) in a crossover study design. A high-fat meal increased viramidine plasma AUC(0-168 h) by 44% and C(max) by 20%. It also increased ribavirin plasma AUC(0-168 h) by 19% and C(max) by 43%. The clinical relevance of these increases is unknown.

Viramidine, a prodrug of ribavirin, shows better liver-targeting properties and safety profiles than ribavirin in animals.

Ribavirin, part of the current first line combination therapy for the treatment of chronic hepatitis C, may cause haemolytic anaemia and poses a significant challenge to the clinical management of the disease. Viramidine, a prodrug of ribavirin, is currently under development. In-vitro partition demonstrated that viramidine had less association with RBCs than ribavirin in rat, monkey and man, and thus has less liability for haemolytic anaemia than ribavirin. In a whole body autoradiography study in rats following oral dosing (30 mg/kg) of [14C]ribavirin or [14C]viramidine to monkeys, viramidine produced 32% higher radioactivity in the liver than ribavirin, indicating a better liver-targeting properties. In portal vein-cannulated cynomolgus monkeys following single oral dosing (30 mg/kg) of [3H]viramidine or [3H]ribavirin, viramidine retained 3X higher radioactivity in the liver than ribavirin. Viramidine dosing also produced a higher viramidine to ribavirin ratio in portal plasma than in systemic plasma, indicating that the liver was the main site for the viramidine conversion to ribavirin and subsequent trapping of the drug. After multiple oral dosing (10 mg/kg) of [14C]ribavirin or [14C]viramidine to monkey, viramidine yielded three times the drug level in the liver but only half in RBCs compared to ribavirin. Viramidine and ribavirin had comparable toxicity profiles in a 28-day toxicity study in rats. In contrast, viramidine had much better safety profiles than ribavirin in a 28-day toxicity study in monkeys. In conclusion, viramidine has better liver-targeting properties and safety profiles than ribavirin in animals.

Remofovir mesylate: a prodrug of PMEA with improved liver-targeting and safety in rats and monkeys.

Adefovir dipivoxil (Hepsera), a first-line therapy for chronic hepatitis B, is an esterase-activated prodrug of PMEA. Dose-limiting nephrotoxicity necessitates suboptimal dosing at 10 mg/day. Remofovir mesylate (MB06866Q) (Hepavir B) is a CYP3A4-activated prodrug of PMEA based on the HepDirect technology that targets PMEA to the liver. In a whole body autoradiography study in rats after oral dosing (30 mg/kg) of [14C]adefovir dipivoxil or [14C]remofovir mesylate, remofovir yielded 15 times higher concentrations of radioactivity in the liver than adefovir dipivoxil, but only one-third of the concentrations in the kidney. After oral dosing (4 mg/kg) of the same radiolabelled agents in cynomolgus monkeys, remofovir mesylate yielded 60 times higher levels of total radioactivity in the liver, but only two-thirds of total radioactivity levels in the kidney. Thus, remofovir mesylate may provide better efficacy and reduced nephrotoxicity. In portal vein-cannulated rats (30 mg/kg) after a single oral dose of [14C]adefovir dipivoxil or [14C]remofovir mesylate, no PMEA was detectable in rat portal plasma early after dosing, indicating that intestinal CYP3A4 does not play a role in conversion of remofovir mesylate to PMEA. The portal/systemic extraction ratio was quite high in both models, suggesting good liver-targeting properties. Portal and systemic remofovir/PMEA ratio indicates that the liver is the site of conversion of remofovir to PMEA. 28-Day toxicity studies demonstrated renal toxicity in rats at doses of 100 mg/kg or higher with no safety concerns at 30 mg/kg and acceptable safety in monkeys at doses up to 60 mg/kg. Thus, in rats and non-human primates, remofovir mesylate has liver-targeting properties and is safer than adefovir dipivoxil.