An association study of ABCG2 rs2231142 on the concentrations of allopurinol and its metabolites.

ABCG2 is a gene that codes for the human breast cancer resistance protein (BCRP). It is established that rs2231142 G>T, a single nucleotide polymorphism of the ABCG2 gene, is associated with gout and poor response to allopurinol, a uric acid-lowering agent used to treat this condition. It has also been suggested that oxypurinol, the primary active metabolite of allopurinol, is a substrate of the BCRP. We thus hypothesized that carrying the rs2231142 variant would be associated with decreased oxypurinol concentrations, which would explain the lower reduction in uric acid. We performed a cross-sectional study to investigate the association between the ABCG2 rs2231142 variant and oxypurinol, allopurinol, and allopurinol riboside concentrations in 459 participants from the Montreal Heart Institute Hospital Cohort. Age, sex, weight, use of diuretics, and estimated glomerular filtration rate were all significantly associated with oxypurinol plasma concentration. No association was found between rs2231142 and oxypurinol, allopurinol and allopurinol riboside plasma concentrations. Rs2231142 was not significantly associated with daily allopurinol dose in the overall population, but an association was observed in men, with T carriers receiving higher doses. Our results do not support a major role of ABCG2 in the pharmacokinetics of allopurinol or its metabolites. The underlying mechanism of the association between rs2231142 and allopurinol efficacy requires further investigation.

Relationships Between Allopurinol Dose, Oxypurinol Concentration and Urate-Lowering Response-In Search of a Minimum Effective Oxypurinol Concentration.

The aims of this study were to determine factors that predict serum urate (SU) lowering response to allopurinol and the conversion of allopurinol to oxypurinol, and to determine a minimum therapeutic oxypurinol concentration. Data from 129 participants in a 24-month open, randomized, controlled, parallel-group, comparative clinical trial were analyzed. Allopurinol dose, SU, and plasma oxypurinol concentrations were available at multiple time points. The slope for the association between allopurinol dose and SU was calculated as a measure of sensitivity to allopurinol. The slope for the association between allopurinol dose and oxypurinol was calculated as a measure of allopurinol metabolism. Receiver operating characteristic (ROC) curves were used to identify a minimum oxypurinol concentration predictive of SU < 6 mg/dL. There was a wide range of SU concentrations for each allopurinol dose. The relationship between sensitivity to allopurinol and allopurinol metabolism for each 100 mg allopurinol dose increase varied between individuals. Body mass index (P = 0.023), creatinine clearance (CrCL; P = 0.037), ABCG2 Q141K (P = 0.019), and SU (P = 0.004) were associated with sensitivity to allopurinol. The minimum oxypurinol concentration for achieving the urate target was found to be about 104 µmol/L, but predictive accuracy was poor (ROC curve area under the curve (AUC) 0.65). The minimum therapeutic oxypurinol concentration was found to increase with decreasing renal function. Although there is a positive relationship between change in oxypurinol and change in SU concentration, a minimum therapeutic oxypurinol is dependent on CrCL and cannot reliably predict SU target. Other variables, including ABCG2 Q141K genotype, impact on sensitivity to allopurinol (ACTRN12611000845932).

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.

Ultra-performance hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry for simultaneous determination of allopurinol, oxypurinol and lesinurad in rat plasma: Application to pharmacokinetic study in rats.

A fixed dose combination of lesinurad and allopurinol has been recently approved by USFDA and EMA for treatment of gout-associated hyperuricemia in patients who have not achieved target serum uric acid levels with allopurinol alone. In this study, an ultra-performance hydrophilic interaction liquid chromatography (UPHILIC) coupled with tandem mass spectrometry method was developed and validated for simultaneous determination of allopurinol, oxypurinol and lesinurad in rat plasma. Liquid liquid extraction using ethyl acetate as extracting agent was used for samples extraction procedure. Acquity UPLC HILIC column (100 mm x 2.1, 1.7µm) was used for separation of allopurinol, oxypurinol, lesinurad and internal standard (5-Florouracil). The mobile phase consisting of acetonitrile, water and formic acid (95:5:0.1, v/v/v), were eluted at 0.3 mL/min flow rate having total chromatographic run time of 3 min per sample. The analytes were detected on Acquity triple quadrupole mass spectrometer equipped with a Z-Spray electrospray ionization (ESI). The ESI source was operated in negative mode and multiple reaction monitoring was used for ion transition for all compounds. The precursor to product ion transition of m/z 134.94 > 64.07 for allopurinol, 150.89 > 41.91 for oxypurinol, 401.90 > 176.79 for lesinurad and 128.85 >41.92 for internal standard were used for identification and quantification. The calibration curves for all analytes were found to be linear with weighing factor of 1/x2 using regression analysis. The developed assay was successfully applied in an oral pharmacokinetic study of allopurinol, oxypurinol and lesinurad in rats.

Individualising the dose of allopurinol in patients with gout.

AIMS: The aims of the study were to: 1) determine if a plasma oxypurinol concentration-response relationship or an allopurinol dose-response relationship best predicts the dose requirements of allopurinol in the treatment of gout; and 2) to construct a nomogram for calculating the optimum maintenance dose of allopurinol to achieve target serum urate (SU) concentrations. METHODS: A nonlinear regression analysis was used to examine the plasma oxypurinol concentration- and allopurinol dose-response relationships with serum urate. In 81 patients (205 samples), creatinine clearance (CLCR ), concomitant diuretic use and SU concentrations before (UP ) and during (UT ) treatment were monitored across a range of allopurinol doses (D, 50-700 mg daily). Plasma concentrations of oxypurinol (C) were measured in 47 patients (98 samples). Models (n = 47 patients) and predictions from each relationship were compared using F-tests, r2 values and paired t-tests. The best model was used to construct a nomogram. RESULTS: The final plasma oxypurinol concentration-response relationship (UT = UP - C*(UP - UR )/(ID50 + C), r2  = 0.64) and allopurinol dose-response relationship (UT = UP - D* (UP - UR )/(ID50 + D), r2  = 0.60) did not include CLCR or diuretic use as covariates. There was no difference (P = 0.87) between the predicted SU concentrations derived from the oxypurinol concentration- and allopurinol dose-response relationships. The nomogram constructed using the allopurinol dose-response relationship for all recruited patients (n = 81 patients) required pretreatment SU as the predictor of allopurinol maintenance dose. CONCLUSIONS: Plasma oxypurinol concentrations, CLCR and diuretic status are not required to predict the maintenance dose of allopurinol. Using the nomogram, the maintenance dose of allopurinol estimated to reach target concentrations can be predicted from UP .

ABCG2 loss-of-function polymorphism predicts poor response to allopurinol in patients with gout.

Many patients fail to achieve the recommended serum urate (SU) target (<6 mgdl-1) with allopurinol. The aim of our study was to examine the association of ABCG2 with SU target in response to standard doses of allopurinol using a cohort with confirmed adherence. Good response was defined as SU<6 mgdl-1 on allopurinol ⩽300 mgd-1 and poor response as SU⩾6 mgdl-1 despite allopurinol >300 mgd-1. Adherence was confirmed by oxypurinol concentrations. ABCG2 genotyping was performed using pre-designed single nucleotide polymorphism (SNP) TaqMan assays. Of 264 patients, 120 were good responders, 68 were poor responders and 76 were either non-adherent or could not be classified. The minor allele of ABCG2 SNP rs2231142 conferred a significantly increased risk of poor response to allopurinol (odds ratio=2.71 (1.70-4.48), P=6.0 × 10-5). This association remained significant after adjustment for age, sex, body mass index, ethnicity, estimated glomerular filtration rate, diuretic use and SU off urate-lowering therapy. ABCG2 rs2231142 predicts poor response to allopurinol, as defined by SU⩾6 mgdl-1 despite allopurinol >300 mgd-1.

A population pharmacokinetic model to predict oxypurinol exposure in patients on haemodialysis.

PURPOSE: The aims of this study were to characterise the population pharmacokinetics of oxypurinol in patients receiving haemodialysis and to compare oxypurinol exposure in dialysis and non-dialysis patients. METHODS: Oxypurinol plasma concentrations from 6 gout people receiving haemodialysis and 19 people with gout not receiving dialysis were used to develop a population pharmacokinetic model in NONMEM. Deterministic simulations were used to predict the steady-state area under the oxypurinol plasma concentration time curve over 1 week (AUC7days). RESULTS: The pharmacokinetics of oxypurinol were best described by a one-compartment model with a separate parameter for dialytic clearance. Allopurinol 100 mg daily produced an AUC7days of 279 µmol/L h in dialysis patients, a value 50-75 % lower than the AUC7days predicted for patients with normal renal function taking 200 to 400 mg daily (427-855 µmol/L h). Dosing pre-dialysis resulted in about a 25-35 % reduction in exposure compared to post-dialysis. CONCLUSIONS: Oxypurinol is efficiently removed by dialysis. The population dialytic and total (non-dialytic) clearance of oxypurinol were found to be 8.23 and 1.23 L/h, standardised to a fat-free mass of 70 kg and creatinine clearance of 6 L/h, respectively. Our results suggest that if the combination of low-dose allopurinol and haemodialysis does not result in sustained urate lowering below treatment targets (serum urate ≤0.36 mmol/L), then allopurinol doses may be increased to optimise oxypurinol exposure.

Allopurinol hypersensitivity: investigating the cause and minimizing the risk.

Allopurinol is the most commonly prescribed urate-lowering therapy for the management of gout. Serious adverse reactions associated with allopurinol, while rare, are feared owing to the high mortality. Such reactions can manifest as a rash combined with eosinophilia, leukocytosis, fever, hepatitis and progressive kidney failure. Risk factors for allopurinol-related severe adverse reactions include the recent introduction of allopurinol, the presence of the HLA-B(*)58:01 allele, and factors that influence the drug concentration. The interactions between allopurinol, its metabolite, oxypurinol, and T cells have been studied, and evidence exists that the presence of the HLA-B(*)58:01 allele and a high concentration of oxypurinol function synergistically to increase the number of potentially immunogenic-peptide-oxypurinol-HLA-B(*)58:01 complexes on the cell surface, thereby increasing the risk of T-cell sensitization and a subsequent adverse reaction. This Review will discuss the above issues and place this in the clinical context of reducing the risk of serious adverse reactions.

Predicting allopurinol response in patients with gout.

AIMS: The primary aim of this research was to predict the allopurinol maintenance doses required to achieve the target plasma urate of ≤0.36 mmol l(-1) . METHODS: A population analysis was conducted in nonmem using oxypurinol and urate plasma concentrations from 133 gout patients. Maintenance dose predictions to achieve the recommended plasma urate target were generated. RESULTS: The urate response was best described by a direct effects model. Renal function, diuretic use and body size were found to be significant covariates. Dose requirements increased approximately 2-fold over a 3-fold range of total body weight and were 1.25-2 fold higher in those taking diuretics. Renal function had only a modest impact on dose requirements. CONCLUSIONS: Contrary to current guidelines, the model predicted that allopurinol dose requirements were determined primarily by differences in body size and diuretic use. A revised guide to the likely allopurinol doses to achieve the target plasma urate concentration is proposed.

Insights into the poor prognosis of allopurinol-induced severe cutaneous adverse reactions: the impact of renal insufficiency, high plasma levels of oxypurinol and granulysin.

OBJECTIVE: Allopurinol, an antihyperuricaemic agent, is one of the common causes of life-threatening severe cutaneous adverse reactions (SCAR), including drug rash with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrosis (TEN). The prognostic factors for allopurinol-related SCAR remain unclear. This study aimed to investigate the relationship of dosing, renal function, plasma levels of oxypurinol and granulysin (a cytotoxic protein of SJS/TEN), the disease severity and mortality in allopurinol-SCAR. METHODS: We prospectively enrolled 48 patients with allopurinol-SCAR (26 SJS/TEN and 22 DRESS) and 138 allopurinol-tolerant controls from 2007 to 2012. The human leucocyte antigen (HLA)-B*58:01 status, plasma concentrations of oxypurinol and granulysin were determined. RESULTS: In this cohort, HLA-B*58:01 was strongly associated with allopurinol-SCAR (p<0.001, OR (95% CI) 109 (25 to 481)); however, the initial/maintenance dosages showed no relationship with the disease. Poor renal function was significantly associated with the delayed clearance of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001, OR (95% CI) 8.0 (3.9 to 17)). Sustained high levels of oxypurinol after allopurinol withdrawal correlated with the poor prognosis of allopurinol-SCAR. In particular, the increased plasma levels of oxypurinol and granulysin linked to the high mortality of allopurinol-SJS/TEN (p<0.01), and strongly associated with prolonged cutaneous reactions in allopurinol-DRESS (p<0.05). CONCLUSIONS: Impaired renal function and increased plasma levels of oxypurinol and granulysin correlated with the poor prognosis of allopurinol-SCAR. Allopurinol prescription is suggested to be avoided in subjects with renal insufficiency and HLA-B*58:01 carriers. An early intervention to increase the clearance of plasma oxypurinol may improve the prognosis of allopurinol-SCAR.

Maternal allopurinol administration during suspected fetal hypoxia: a novel neuroprotective intervention? A multicentre randomised placebo controlled trial.

OBJECTIVE: To determine whether maternal allopurinol treatment during suspected fetal hypoxia would reduce the release of biomarkers associated with neonatal brain damage. DESIGN: A randomised double-blind placebo controlled multicentre trial. PATIENTS: We studied women in labour at term with clinical indices of fetal hypoxia, prompting immediate delivery. SETTING: Delivery rooms of 11 Dutch hospitals. INTERVENTION: When immediate delivery was foreseen based on suspected fetal hypoxia, women were allocated to receive allopurinol 500 mg intravenous (ALLO) or placebo intravenous (CONT). MAIN OUTCOME MEASURES: Primary endpoint was the difference in cord S100ß, a tissue-specific biomarker for brain damage. RESULTS: 222 women were randomised to receive allopurinol (ALLO, n=111) or placebo (CONT, n=111). Cord S100ß was not significantly different between the two groups: 44.5 pg/mL (IQR 20.2-71.4) in the ALLO group versus 54.9 pg/mL (IQR 26.8-94.7) in the CONT group (difference in median -7.69 (95% CI -24.9 to 9.52)). Post hoc subgroup analysis showed a potential treatment effect of allopurinol on the proportion of infants with a cord S100ß value above the 75th percentile in girls (ALLO n=5 (12%) vs CONT n=10 (31%); risk ratio (RR) 0.37 (95% CI 0.14 to 0.99)) but not in boys (ALLO n=18 (32%) vs CONT n=15 (25%); RR 1.4 (95% CI 0.84 to 2.3)). Also, cord neuroketal levels were significantly lower in girls treated with allopurinol as compared with placebo treated girls: 18.0 pg/mL (95% CI 12.1 to 26.9) in the ALLO group versus 32.2 pg/mL (95% CI 22.7 to 45.7) in the CONT group (geometric mean difference -16.4 (95% CI -24.6 to -1.64)). CONCLUSIONS: Maternal treatment with allopurinol during fetal hypoxia did not significantly lower neuronal damage markers in cord blood. Post hoc analysis revealed a potential beneficial treatment effect in girls. TRIAL REGISTRATION NUMBER: NCT00189007, Dutch Trial Register NTR1383.

Determination of allopurinol and oxypurinol in human plasma and urine by liquid chromatography-tandem mass spectrometry.

Allopurinol is used widely for the treatment of gout, but its pharmacokinetics is complex and some patients show hypersensitivity, necessitating careful monitoring and improved detection methods. In this study, a sensitive and reliable liquid chromatography-tandem mass spectrometry method was developed to determine the concentrations of allopurinol and its active metabolite oxypurinol in human plasma and urine using 2,6-dichloropurine as the internal standard (IS). Analytes and the IS were extracted from 0.5ml aliquots of plasma or urine using ethyl acetate and separated on an Agilent Eclipse Plus C18 column using methanol and ammonium formate-formic acid buffer containing 5mM ammonium formate and 0.1% formic acid (95:5, v/v) as the mobile phase (A) for allopurinol or methanol plus 5mM ammonium formate aqueous solution (95:5, v/v) as the mobile phase (B) for oxypurinol. Allopurinol was detected in positive ion mode and the analysis time was about 7min. The calibration curve was linear from 0.05 to 5µg/mL allopurinol in plasma and 0.5-30µg/mL in urine. The lower limit of quantification (LLOQ) was 0.05µg/mL in plasma and 0.5µg/mL in urine. The intra- and inter-day precision and relative errors of quality control (QC) samples were ≤11.1% for plasma and ≤ 8.7% for urine. Oxypurinol was detected in negative mode with an analysis time of about 4min. The calibration curve was linear from 0.05 to 5µg/mL in plasma (LLOQ, 0.05µg/mL) and from 1 to 50µg/mL in urine (LLOQ, 1µg/mL). The intra- and inter-day precision and relative errors were ≤7.0% for plasma and ≤9.6% for urine. This method was then successfully applied to investigate the pharmacokinetics of allopurinol and oxypurinol in humans.

An audit of a therapeutic drug monitoring service for allopurinol therapy.

BACKGROUND: Oxypurinol, the active metabolite of allopurinol, is the major determinant of the hypouricemic effect of allopurinol. Monitoring oxypurinol concentrations is undertaken to determine adherence to therapy, to investigate reasons for continuing attacks of acute gout and/or insufficiently low plasma urate concentrations despite allopurinol treatment, and to assess the risk of allopurinol hypersensitivity, an adverse effect that has been putatively associated with elevated plasma oxypurinol concentrations. METHODS: An audit of request forms requesting plasma oxypurinol concentration measurements received by the pathology service (SydPath) at St Vincent's Hospital, Darlinghurst, Sydney was undertaken for the 7-year period January 2005-December 2011. Patient demographics, biochemical data, including plasma creatinine and uric acid concentrations, comorbidities, and concomitant medications were recorded. RESULTS: There were 412 requests for determination of an oxypurinol concentration. On 48% of occasions, the time of allopurinol dosing was recorded, while just 79 (19%) blood samples were collected 6-9 hours postdosing, the time window used to establish the therapeutic range for oxypurinol. For these optimally interpretable concentrations, 32 (8%) were within the putative therapeutic range (5-15 mg/L), while 5 (1%) were below and 41 (10%) above this range. The daily dose of allopurinol was documented on only one-third of the request forms. Individually, plasma urate and creatinine concentrations were requested concomitantly with plasma oxypurinol concentrations in 66% and 58% of the cases, respectively; while plasma oxypurinol, urate, and creatinine concentrations were requested concomitantly in 49% of the cases. CONCLUSIONS: Requesting clinicians and blood specimen collectors often fail to provide relevant information (dose, times of last dose, and blood sample collection) to allow the most useful interpretation of oxypurinol concentrations. Concomitant plasma urate and creatinine concentrations should be requested to allow more complete interpretation of the data.

The population pharmacokinetics of allopurinol and oxypurinol in patients with gout.

PURPOSE: The aims of this study were to develop a population pharmacokinetic model for allopurinol and oxypurinol and to explore the influence of patient characteristics on allopurinol and oxypurinol pharmacokinetics. METHODS: Data from 92 patients with gout and 12 healthy volunteers were available for analysis. A parent-metabolite model with a two-compartment model for allopurinol and a one-compartment model for oxypurinol was fitted to the data using non-linear mixed effects modelling. RESULTS: Renal function, fat-free mass (FFM) and diuretic use were found to predict differences in the pharmacokinetics of oxypurinol. The population estimates for allopurinol clearance, inter-compartmental clearance, central and peripheral volume were 50, 142 L/h/70 kg FFM, 11.4, 91 L/70 kg FFM, respectively, with a between-subject variability of 33 % (coefficient of variance, CV) for allopurinol clearance. Oxypurinol clearance and volume of distribution were estimated to be 0.78 L/h per 6 L/h creatinine clearance/70 kg FFM and 41 L/70 kg FFM in the final model, with a between-subject variability of 28 and 15 % (CV), respectively. CONCLUSIONS: The pharmacokinetic model provides a means of predicting the allopurinol dose required to achieve target oxypurinol plasma concentrations for patients with different magnitudes of renal function, different body mass and with or without concomitant diuretic use. The model provides a basis for the rational dosing of allopurinol in clinical practice.

Furosemide increases plasma oxypurinol without lowering serum urate--a complex drug interaction: implications for clinical practice.

OBJECTIVE: To determine the effects of furosemide on serum urate (SU), plasma oxypurinol and urinary urate. METHODS: Twenty-three cases with gout receiving furosemide and allopurinol were recruited. Twenty-three controls with gout receiving allopurinol but no diuretics were matched on age, gender, estimated glomerular filtration rate and allopurinol dose. SU, plasma oxypurinol and urinary urate were assessed on a single occasion. The effects of a single dose of furosemide 40 mg were examined in a separate group of 10 patients receiving allopurinol but not diuretic. RESULTS: Cases had significantly higher SU and plasma oxypurinol compared with controls despite receiving similar doses of allopurinol. There was no difference in urinary urate excretion. There was a significant increase in area under the curve (AUC)(0-24) for oxypurinol after administration of furosemide 40 mg. CONCLUSION: The interaction between allopurinol and furosemide results in increased SU and plasma oxypurinol. The exact mechanisms remain unclear but complex interactions that result in attenuation of the hypouricaemic effects of oxypurinol are likely. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry, www.anzctr.org.au, 12609000529246.

Improving the use of allopurinol in chronic gout: monitoring oxypurinol levels to guide therapy.

Urate-lowering therapy (ULT), adjusted to achieve and maintain a serum uric acid (SUA) of <6 mg/dl, remains the standard of care for the chronic management of gout. New urate-lowering medications are important options; however, these agents should be reserved for patients who do not tolerate or cannot achieve SUA <6 mg/dl on allopurinol. The result of oxypurinol monitoring to guide allopurinol therapy suggests that allopurinol should still be considered first-line ULT for gout.