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.

Pharmacokinetics, pharmacodynamics, and tolerability of verinurad, a selective uric acid reabsorption inhibitor, in healthy Japanese and non-Asian male subjects.

PURPOSE: Verinurad (RDEA3170) is a selective uric acid reabsorption inhibitor in clinical development for treatment of gout and asymptomatic hyperuricemia. This study evaluated verinurad pharmacokinetics, pharmacodynamics, and tolerability in healthy Japanese and non-Asian adult male subjects. METHODS: This was a Phase I, randomized, single-blind, placebo-controlled study. Panels of 8 Japanese subjects were randomized to receive oral verinurad (2.5-15 mg) or placebo administered as a single dose in a fasted and fed state and as once-daily doses for 7 days in a fed state. Eight non-Asian subjects received verinurad 10 mg as a single dose (fasted and fed) and multiple doses in the fed state. Serial plasma/serum and urine samples were assayed for verinurad and uric acid. Safety was assessed by adverse events and laboratory data. RESULTS: Of 48 randomized subjects, 46 (Japanese, 39; non-Asian, 7) completed the study. Following single or multiple doses in Japanese subjects, maximum plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC) increased in a near dose-proportional manner. Time to Cmax (Tmax) was ~1.25-2.0 hours with fasting. A moderate-fat meal delayed Tmax (range 3.0-5.0 hours) and had a variable effect on AUC (0%-97% increase) and Cmax (0%-26% increase) across the dose groups. Following multiple verinurad 10 mg doses, Cmax and AUC were 38% and 23% higher, respectively, in Japanese vs non-Asian subjects, largely due to body weight differences. Mean reduction of serum urate following multiple verinurad 10 mg doses was 46% and 44% after 24 hours in Japanese and non-Asian subjects, respectively. Verinurad was well tolerated at all doses. CONCLUSION: Verinurad monotherapy lowered serum urate and was well tolerated in both healthy Japanese and non-Asian males, while small differences in plasma pharmacokinetics were observed. These data support further evaluation of once-daily verinurad as a treatment for gout and asymptomatic hyperuricemia.

Outcome of Treatment in Gouty Arthritis Patients: A Retrospective Study.

BACKGROUND: Effective treatment in gouty arthritis can prevent joint and renal damage. Target serum uric acid levels of < 6 mg/dl and < 5 mg/dl are recommended in gouty arthritis and those with tophi, respectively. OBJECTIVE: To evaluate: (i) whether patients achieved recommended serum uric acid target and assess influencing factors and (ii) renal function between patients who achieved and not achieved the goal. MATERIAL AND METHOD: The medical records of gouty arthritis patients treated in outpatient department at Thammasat University Hospital between January 2013 and December 2013 were reviewed. Patients were divided into adequately (ATG) and inadequately treated groups (ITG) based on the ACR uric acid criteria after six months of treatment. Factors associated with inadequate treatment were explored and post treatment renal function compared between A and ITGs. RESULTS: Of 139 patients, 46 (33%) achieved target serum uric acid concentrations. Alcoholic consumption was the significant factor influencing the outcome. 75.5% of patients were followed-up > 1 month for second evaluation of uric acid and most of them not receiving dosage up-titration even though not achieving the target. Both groups had similar alterations of renal function after treatment (p = 0.68). CONCLUSION: Most patients failed to achieve recommended uric acid targets. Alcohol consumption was identified as a key risk factorfor a suboptimal outcome. The treat-to-target approach should be underlined. Other risk factors should be explored prospectively.

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.

Potentiation of anticoagulant effect of warfarin caused by enantioselective metabolic inhibition by the uricosuric agent benzbromarone.

OBJECTIVE: To clarify the mechanism(s) for the interaction between warfarin and benzbromarone, a uricosuric agent, and to predict changes in the in vivo pharmacokinetics of (S)-warfarin from in vitro data. METHODS: Warfarin enantiomers and benzbromarone in serum, 7-hydroxywarfarin in urine, and serum unbound fractions of warfarin enantiomers were measured in patients with heart disease given warfarin with (n = 13) or without (n = 18) oral benzbromarone (50 mg/d). In vitro inhibition constants (K(i)) of benzbromarone for (S)-warfarin 7-hydroxylation were determined with use of human CYP2C9 and liver microsomes. The magnitude of changes in the formation clearance for 7-hydroxylation (CLf), the unbound oral clearance (CL(oral,u)), and the oral clearance (CL(oral)) for (S)-warfarin were predicted by equations incorporating the in vitro Ki, the theoretical maximum unbound hepatic benzbromarone concentration, and the fractions of warfarin eliminated through metabolism and of CYP2C9-mediated metabolic reaction susceptible to inhibition by benzbromarone. RESULTS: The patients given warfarin with benzbromarone required a 36% less (P < .01) warfarin dose than those given warfarin alone (2.5 versus 3.9 mg/d) to attain similar international normalized ratios (2.1 and 2.2, respectively), and the former had 65%, 53%, and 54% lower (P < .05 or P < .01) CLf, CL(oral),u, and CL(oral) for (S)-warfarin than the latter, respectively. In contrast, no significant differences were observed for (R)-warfarin kinetics between the groups. Benzbromarone was found to be a potent competitive inhibitor (Ki < 0.01 micromol/L) for (S)-warfarin 7-hydroxylation mediated by CYP2C9. The average changes in the in vivo CLf, CL(oral),u, and CL(oral)values for (S)-warfarin induced by benzbromarone were largely predictable by the proposed equations. CONCLUSION: Benzbromarone would intensify anticoagulant response of warfarin through an enantioselective inhibition of CYP2C9-mediated metabolism of pharmacologically more potent (S)-warfarin. The magnitude of changes in the in vivo warfarin kinetics may be predicted by in vitro data.

Thin-layer chromatographic analysis of some benzofuran derivatives in human plasma.

Benzofuran derivatives: amiodarone, benziodarone, benzbromarone and benzarone, extracted from plasma, were separated by TLC method on silica gel by ascending and horizontal developments, using suitable mobile phases. The substances were identified by reaction with potassium permanganate solution, either by Dragendorff (modified after Amelink) or Sonnenschein reagents (up to the amounts of 250 ng of amiodarone and benzarone and 500 ng of benziodarone and benzbromarone).

Stereoselective renal tubular secretion of a new uricosuric diuretic, 6,7-dichloro-5-(N,N-dimethylsulfamoyl)-2,3-dihydro-2-benzofurancarboxyl ic acid (S-8666), in cynomolgus monkeys.

Plasma concentration-time curves and urinary excretion of individual enantiomers of unchanged S-8666 and its N-monodemethylated metabolite, M-1, in male cynomolgus monkeys were measured after oral administration of racemic S-8666 at doses of 5, 10, and 50 mg/kg and also after intravenous injection at doses of 1, 5, and 10 mg/kg. The Tmax values for individual enantiomers of S-8666 in fasted male monkeys were 30 min after oral administration. The AUC values for S(-)-S-8666 were greater than those for R(+)-S-8666 and oral dose-AUC relationships of both enantiomers showed a linearity over the dose range used. Most of the S-8666 and a trace of M-1 were excreted in the first 24-hr urine, with no evidence of stereoselectivity from the amounts excreted. Since large portions were recovered from the urine as unchanged S-8666 after intravenous injection, most excretion occurs via the kidney. The t1/2 beta values and the Vdss for S(-)-S-8666 after intravenous injection were smaller than those for R(+)-S-8666. The CLt and the CLr values decreased with increasing intravenous doses, indicating saturation at a renal excretion process at high plasma concentrations of S-8666. The CLt and CLr values for R(+)-S-8666 were greater than those for the S(-)-enantiomer. The unbound fraction of R(+)-S-8666 in plasma was significantly greater than that of S(-)-S-8666 [21.6% for R(+), 12.0% for S(-)]. Renal clearance for the unbound fraction of S(-)-S-8666 was greater than that of R(+)-S-8666, suggesting stereoselective renal tubular secretion.

HPLC-determination of some antiinflammatory, weak analgesic and uricosuric drugs in human blood plasma and its application to pharmacokinetics.

HPLC-determination of naproxen, indomethacin, ketoprofen, fenoprofen ibuprofen, diclofenac sodium, tolfenamic acid, phenylbutazone, mofebutazone, salicylic acid, acetylsalicylic acid, phenacetin, paracetamol, sulfinpyrazone and probenecid by means of an adjustable, rapid accurate and specific method is described. Plasma samples of 0.2 ml were deproteinised and the drugs extracted simultaneously with pure acetonitrile. Aliquots of 25 mul of this primary extract were directly injected on the column. As elution solvent for drug screening was basically used 55% methanol in 50 mM phosphate buffer at pH 4.0. Optimal separation of some drugs or reasonable elution times for others were obtained by varying the methanol concentration of the elution solvent or possibly its pH. The method used for individual drug determinations is very applicable for therapeutic monitoring purposes as well as for use in pharmacokinetic investigations. As an example, the practical detection limit for naproxen in plasma was about 0.2 microgram ml-1. By concentrating the extract this could be lowered to about 0.04 microgram ml-1. The method was applied in a study of the pharmacokinetics of naproxen in a person, who ingested a single oral dose of 2.5 mg kg-1. Pronounced two-compartment kinetics were found. Vc was 0.038 1 kg-1, Vdss 0.138 1 kg-1, t 1/2 (beta) 21.3 hrs, t 1/2 (alpha) 0.99 hr and t 1/2 (ka) 0.67 hr.

Renal excretion of a slauretic-uricosuric agent (MK-196) and interaction with a urate-retaining drug, pyrazinoate, in the chimpanzee.

The excretory pattern for MK-196 is ocmpatible with that of other weak organic acids such as salicylate and probenecid. Tubular secretion of MK-196 is strongly inhibitied by probenecid and high loads of p-aminohippurate. Urinary excretion of MK-196 is increased 10-fold when the urine is alkaline. Clearances of MK-196 were not corrected for plasma protein binding of the drug which is very high (greater than 99%). Bidirectional transport processes are operative in that MK-196 is secreted by the renal tubule and passively back diffuses across the tubular epithelium by a pH-dependent process. MK-196 is able to overcome pyrazinoate-induced urate retention, whereas probenecid is not when studied by conventional clearance techniques. The uricosuric activity of MK-196 appears to be somewhat less with pyrazinoate than in its absence. When MK-196 is administered prior to pyrazinoate an attenuated uricosuric response was observed. This finding cannot be ascribed to a temporal decline in uricosuric action. Diuresis and saluresis produced by MK-196 are not influenced by pyrazinoate. The interaction of MK=196 and pyrazinoate on urate excretion is in direct contrast to results obtained with probenecid and pyrazinoate. A model has been proposed to explain this unique finding.

Gas-liquid chromatographic determination of tienilic acid (SKF 62.698) in human plasma and urine.

A gas-liquid chromatographic method is described for the determination of tienilic acid (SKF 62.698), a diuretic with uricosuric properties, in human plasma and urine. The method, which is based on the methylation of the compound, is rapid, specific and sensitive. The lowest level accurately determined is about 50 ng/ml in plasma and 1 mug/ml in urine. The first results from a human volunteer are given.