Effect of furosemide on renal excretion of oxypurinol and purine bases

Females present higher dose-adjusted drug concentrations of metoprolol and allopurinol/oxypurinol than males

Females present a higher risk of adverse drug reactions. Sex-related differences in drug concentrations may contribute to these observations but they remain understudied given the underrepresentation of females in clinical trials. The aim of this study was to investigate whether anthropometric and socioeconomic factors and comorbidities could explain sex-related differences in concentrations and dosing for metoprolol and oxypurinol, the active metabolite of allopurinol. We conducted an analysis of two cross-sectional studies. Participants were self-described "White" adults taking metoprolol or allopurinol selected from the Montreal Heart Institute Hospital Cohort. A total of 1007 participants were included in the metoprolol subpopulation and 459 participants in the allopurinol subpopulation; 73% and 86% of the participants from the metoprolol and allopurinol subpopulations were males, respectively. Females presented higher age- and dose-adjusted concentrations of both metoprolol and oxypurinol (both p < 0.03). Accordingly, females presented higher unadjusted and age-adjusted concentration:dose ratio of both metoprolol and allopurinol/oxypurinol compared to males (all p < 3.0 × 10^-4 ). Sex remained an independent predictor of metoprolol concentrations (p < 0.01), but not of oxypurinol concentrations, after adjusting for other predictors. In addition to sex, age, daily dose, use of moderate to strong CYP2D6 inhibitors, weight, and CYP2D6 genotype-inferred phenotype were associated with concentrations of metoprolol (all p < 0.01). Daily dose, weight, estimated glomerular filtration rate (eGFR), and employment status were associated with oxypurinol concentrations (all p < 0.01). Females present higher dose-adjusted concentrations of metoprolol and oxypurinol than males. This suggests the need for sex-specific dosing requirements for these drugs, although this hypothesis should be validated in prospective studies.

Uric acid analogue as a possible xenobiotic marker of uric acid transporter Urat1 in rats

The inhibitor of uric acid reabsorptive transporter URAT1 in kidney is drawing attention as a drug target for hyperuricemia. However, it is difficult to evaluate efficacy of URAT1 inhibitors in vivo using laboratory animals due to species difference in uric acid metabolism. In the present study, the usefulness of exogenously administering uric acid analogues resistant to uricase was investigated for in vivo evaluation of transport activity of rUrat1 in rats. Uptake of examined four uric acid analogues by rUrat1-expressing Xenopus oocytes was significantly higher than that by water-injected oocytes. In metabolism studies, disappearance of these compounds was negligible, while uric acid was significantly decreased. When oxypurinol was administered to rats, fractional excretion (FE) was 0.4, suggesting reabsorption of oxypurinol. Moreover, FE of oxypurinol was tended to be increased, but not statistically different, by co-administration of a uricosuric agent FYU-981, while plasma concentration of oxypurinol was not affected. These results suggested that oxypurinol is a potential uric acid analogue, although it was not suitable as a probe of uric acid in in vivo study. Our findings may contribute to discovery and development of novel uricosuric agent targeting URAT1.

The pharmacokinetics of oxypurinol in people with gout

AIMS

Our aim was to identify and quantify the sources of variability in oxypurinol pharmacokinetics and explore relationships with plasma urate concentrations.

METHODS

Non-linear mixed effects modelling was applied to concentration-time data from 155 gouty patients with demographic, medical history and renal transporter genotype information.

RESULTS

A one compartment pharmacokinetic model with first order absorption best described the oxypurinol concentration-time data. Renal function and concomitant medicines (diuretics and probenecid), but not transporter genotype, significantly influenced oxypurinol pharmacokinetics and reduced the between subject variability in the apparent clearance of oxypurinol (CL/F(m)) from 65% to 29%. CL/F(m) for patients with normal, mild, moderate and severe renal impairment was 1.8, 0.6, 0.3 and 0.18 l h(-1), respectively. Model predictions showed a relationship between plasma oxypurinol and urate concentrations and failure to reach target oxypurinol concentrations using suggested allopurinol dosing guidelines.

CONCLUSIONS

In conclusion, this first established pharmacokinetic model provides a tool to achieve target oxypurinol plasma concentrations, thereby optimizing the effectiveness and safety of allopurinol therapy in gouty patients with various degrees of renal impairment.

Safety of urate-lowering therapies: managing the risks to gain the benefits

Gout is a metabolic disorder of purine metabolism and uric acid elimination. Over time, acute gout can develop into a chronic, disabling arthropathy, often associated with multiple comorbidities. Gout patients have often been undertreated, partly because of the clinician's perceived risks of a therapy outweighing its potential benefits. The approval of new therapies to treat hyperuricemia in gout has led to a new understanding of gout management and medication safety regarding new and old therapies. This review focuses on potential safety issues of currently available urate-lowering therapies and outlines strategies to minimize risks so their benefits can be reached.

Lack of effect of hydrochlorothiazide and low-dose aspirin on the renal clearance of urate and oxypurinol after a single dose of allopurinol in normal volunteers

AIMS

To determine whether low-dose aspirin and hydrochlorothiazide (HCTZ) affect the renal clearance of oxypurinol and/or urate.

METHODS

Healthy volunteers (n = 8) were treated with allopurinol (600 mg, control), and allopurinol (600 mg) co-administered with single doses of aspirin (100 mg) or HCTZ (25 mg) or a combination of the two.

RESULTS

Hydrochlorothiazide, low-dose aspirin or a combination of the two, when co-administered with allopurinol, did not significantly alter (P > 0.05) the renal clearance of oxypurinol or urate. In particular, aspirin and HCTZ, when taken together and with allopurinol, did not change (P > 0.05) oxypurinol fractional renal clearance (allopurinol alone: 0.217, 0.173-0.262; combined: 0.202, 0.155-0.250) or urate fractional renal clearance (allopurinol alone: 0.066, 0.032-0.099; combined: 0.058, 0.038-0.078).

CONCLUSIONS

A single, low-dose of aspirin or an anti-hypertensive dose of hydrochlorothiazide, when administered alone or together with allopurinol, are unlikely to alter the hypouricaemic effect of allopurinol. The effect of chronic aspirin and HCTZ dosing taken together upon the efficacy of chronic allopurinol therapy in patients with hyperuricaemia needs to be investigated.

Clinical pharmacokinetics and pharmacodynamics of allopurinol and oxypurinol

Allopurinol is the drug most widely used to lower the blood concentrations of urate and, therefore, to decrease the number of repeated attacks of gout. Allopurinol is rapidly and extensively metabolised to oxypurinol (oxipurinol), and the hypouricaemic efficacy of allopurinol is due very largely to this metabolite. The pharmacokinetic parameters of allopurinol after oral dosage include oral bioavailability of 79 +/- 20% (mean +/- SD), an elimination half-life (t((1/2))) of 1.2 +/- 0.3 hours, apparent oral clearance (CL/F) of 15.8 +/- 5.2 mL/min/kg and an apparent volume of distribution after oral administration (V(d)/F) of 1.31 +/- 0.41 L/kg. Assuming that 90 mg of oxypurinol is formed from every 100mg of allopurinol, the pharmacokinetic parameters of oxypurinol in subjects with normal renal function are a t((1/2)) of 23.3 +/- 6.0 hours, CL/F of 0.31 +/- 0.07 mL/min/kg, V(d)/F of 0.59 +/- 0.16 L/kg, and renal clearance (CL(R)) relative to creatinine clearance of 0.19 +/- 0.06. Oxypurinol is cleared almost entirely by urinary excretion and, for many years, it has been recommended that the dosage of allopurinol should be reduced in renal impairment. A reduced initial target dosage in renal impairment is still reasonable, but recent data on the toxicity of allopurinol indicate that the dosage may be increased above the present guidelines if the reduction in plasma urate concentrations is inadequate. Measurement of plasma concentrations of oxypurinol in selected patients, particularly those with renal impairment, may help to decrease the risk of toxicity and improve the hypouricaemic response. Monitoring of plasma concentrations of oxypurinol should also help to identify patients with poor adherence. Uricosuric drugs, such as probenecid, have potentially opposing effects on the hypouricaemic efficacy of allopurinol. Their uricosuric effect lowers the plasma concentrations of urate; however, they increase the CL(R) of oxypurinol, thus potentially decreasing the influence of allopurinol. The net effect is an increased degree of hypouricaemia, but the interaction is probably limited to patients with normal renal function or only moderate impairment.

Allopurinol is the most common cause of Stevens-Johnson syndrome and toxic epidermal necrolysis in Europe and Israel

BACKGROUND

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare severe cutaneous adverse reactions.

OBJECTIVES

We sought to update knowledge on the causes of SJS or TEN with a focus on the rate of allopurinol-associated cases and to identify risk factors for allopurinol-associated SJS or TEN.

METHODS

We conducted a multinational case-control study.

RESULTS

In all, 379 patients with severe cutaneous adverse reactions validated as SJS or TEN and 1505 matched hospitalized control subjects were enrolled. Allopurinol was the drug most frequently associated with SJS or TEN, with 66 exposed patients (17.4%) and 28 exposed control subjects (1.9%) (adjusted odds ratio = 18, 95% confidence interval: 11-32). Allopurinol use was greater than in a previous case-control European study. Daily doses equal to or greater than 200 mg were associated with a higher risk (adjusted odds ratio = 36, 95% confidence interval: 17-76) than lower doses (adjusted odds ratio = 3.0, 95% confidence interval: 1.1-8.4). The risk was restricted to short-term use (<or=8 weeks). The use of comedications did not increase the risk.

LIMITATIONS

Nonsystematic recording of the indications for allopurinol use was a limitation.

CONCLUSIONS

Results of this multinational study (EuroSCAR) revealed that allopurinol is the drug most commonly associated with SJS or TEN. The incidence of allopurinol-associated SJS or TEN has increased possibly because of increased use and dosages of this drug.

Correction of allopurinol dosing should be based on clearance of creatinine, but not plasma creatinine levels: another insight to allopurinol-related toxicity

BACKGROUND

Dosing of allopurinol should be corrected depending on renal function, but corrections based on either plasma creatinine (Pcr) or creatinine clearance (CrCl) have been suggested to be minimal standards of care.

METHODS

Data from a cohort database of 484 gouty patients were used to calculate estimated allopurinol doses using CrCl and estimation of the clearance of creatinine using the equation of Cockroft and Gault (CrCl-CG) if, as a hypothesis, a dosage of 300 mg/d would be prescribed in any patient with Pcr <2.0 mg/dL. Also, allopurinol-related toxicity previous to rheumatologic consultation, during previous allopurinol therapy, and the relationship between both and estimated allopurinol doses were reviewed.

RESULTS

The cutoff point of plasma creatinine <2 showed 13% sensitivity and 100% specificity to detect CrCl <50 mL/min. Correlation and agreement between CrCl and CrCl-CG were good, as was the correlation between corrected doses using CrCl and CrCl-CG. One third of patients with Pcr 1.0-1.5 mg/dL and 90% of those with Pcr 1.5-2.0 mg/dL would receive estimated doses over 400 mg/dL/d CrCl. Also, 10% and 34% would receive estimated doses over 600 mg/dL/d CrCl, respectively. Allopurinol-related toxicity previous to consultation (11%) was associated with estimated doses over 400 mg/dL/d CrCl and severe toxicity with estimated doses over 600 mg/dL/d CrCl. When patients were given doses corrected on CrCl, few side effects were observed during follow up (6.7%), and the only severe one was associated with corrected dose over 600 mg/d.

CONCLUSIONS

Dosage adjustment of allopurinol should be based on clearance of creatinine or estimation of glomerular filtration using the Cockcroft-Gault equation. Pcr is insensitive enough to detect renal function impairment so that patients may be placed at risk for overdosing side effects. Corrected doses over 600 mg/dL/d CrCl may be associated with increased risk of severe toxicity.

The influence of allopurinol on urinary purine loss after repeated sprint exercise in man

The influence of allopurinol on urinary purine loss was examined in 7 active male subjects (age 24.9 +/- 3.0 years, weight 82.8 +/- 8.3 kg, V O2peak 48.1 +/- 6.9 mL.kg(-1).min(-1)). These subjects performed, in random order, a trial with 5 days of prior ingestion of a placebo or allopurinol. Each trial consisted of eight 10-second sprints on an air-braked cycle ergometer and was separated by at least a week. A rest period of 50 seconds separated each repeated sprint. Forearm venous plasma inosine, hypoxanthine (Hx) and uric acid concentrations were measured at rest and during 120 minutes of recovery from exercise. Urinary inosine, Hx, xanthine, and uric acid excretion were also measured before and for 24 hours after exercise. During the first 120 minutes of recovery, plasma Hx concentrations, as well as the urinary Hx and xanthine excretion rates, were higher (P < .05) with allopurinol compared with the placebo trial. In contrast, plasma uric acid concentration and urinary uric acid excretion rates were lower (P < .05) with allopurinol. The total urinary excretion of purines (inosine + Hx + xanthine + uric acid) above basal levels was higher in the allopurinol trial compared with placebo. These results indicate that the total urinary purine excretion after intermittent sprint exercise was enhanced with allopurinol treatment. Furthermore, the composition of urinary purines was markedly affected by this drug.

Purine modulation of cytokine release during diuretic therapy of rheumatoid arthritis

Since free radicals are implicated in rheumatoid arthritis (RA) and since uric acid is a free radical scavenger, we examined the effects of treating RA patients with with the diuretic bumetanide to try to improve their arthritic control. Seventy patients, aged 18-75 years, were randomised to receive bumetanide 4 mg/day or placebo. Uric acid levels increased, but not that of other purines, in the blood of drug-treated patients compared with placebo-treated controls. There were no significant changes in clinical measurements of disease activity or in ESR or CRP levels. There were no over all differences in the blood levels of the cytokines, nor in the basal or stimulated production of cytokines from the blood cultures. The adenosine receptor agonist 5'N-ethylcarboxamido-adenosine (NECA) used to modify cytokine release in cultures of whole blood taken from the patients, depressed the release of tumour necrosis factor-alpha (TNFalpha), but failed to depress the release of interleukin-1b (IL-1b) or interleukin-6 (IL-6), a difference from earlier studies of healthy control subjects and, thus, a difference which may contribute to the disease activity.

Interactions between the Oocyte and Surrounding Somatic Cells in Follicular Development: Lessons from In Vitro Culture

Mammalian oogenesis occurs concomitantly with folliculogenesis in a coordinated manner in the ovaries. In vitro growth (IVG) culture systems of the oocytes have been developed as a new technology for utilizing incompetent oocytes in the ovary as a source of mature oocytes as well as for studying oogenesis, folliculogenesis, and oocyte-somatic cell interactions. The results of IVG experiments have suggested that direct association of oocytes and surrounding granulosa cells supports oocyte viability and growth through the gap junctions, which are efficient conduits for low molecular weight substances. It has been revealed that granulosa cells metabolize some molecules which are in turn transported into the oocytes. IVG systems have also provided evidence that FSH promotes the development of follicles at secondary or later stages by its stimulation of proliferation and differentiation of granulosa cells, and perhaps by its anti-apoptotic effects. In addition, interactions between granulosa cell-derived KIT ligands and oocyte KIT receptors have been suggested as initiating oocyte growth and follicular development. Furthermore, recent findings suggest there are growth factors derived from oocytes such as GDF-9 and BMP-15. With such factors, oocytes participate in follicular development by regulating the differentiation of surrounding somatic cells. These bidirectional communications between oocytes and somatic cells are important for oocyte growth and follicular development. IVG systems should provide further information regarding oogenesis and folliculogenesis in the ovary.