Higher Therapeutic Plasma Oxypurinol Concentrations Might Be Required for Gouty Patients With Chronic Kidney Disease

Predicting Response or Non-response to Urate-Lowering Therapy in Patients with Gout

PURPOSE OF REVIEW

To review the extent of treatment success or failure with the xanthine oxidoreductase inhibitors allopurinol and febuxostat and indicate how the dosage of urate-lowering therapy (ULT) may be modified to increase the response in the majority of patients with gout.

RECENT FINDINGS

Gout flares are associated with serum concentrations of urate above 0.42 mmol/L (7 mg/dL). Achieving and maintaining serum urate below 0.36 mmol/L is considered an effective response to ULT. On an intention to treat basis, clinical trials indicate that allopurinol at daily doses of 100 to 300 mg decreases serum urate adequately in only about 40% of gout patients while febuxostat 80 mg daily reduces serum urate adequately in approximately 70% of gout patients. Higher doses of ULT may be required in patients receiving concomitant diuretics. The addition of a uricosuric agent to allopurinol and febuxostat therapy significantly increases the proportion of patients achieving adequate lowering of serum urate. Finally, carriers of a genetic variant of the transporter, ABCG2 (BCRP), have a decreased response to allopurinol. Careful examination of medication adherence, titration of doses, and the addition of uricosuric agents increase the percentage of patients responding to allopurinol and febuxostat.

Hypouricemic and arthritis relapse-reducing effects of compound tufuling oral-liquid in intercritical and chronic gout: A double-blind, placebo-controlled, multicenter randomized trial

TRIAL DESIGN

In the double-blind, randomized, controlled trial, we aimed to evaluate the effects of compound tufuling oral liquid (CoTOL) on serum uric acid (sUA) levels and recurrence of acute gouty arthritis in intercritical and chronic gout treatment.

METHODS

A total of 210 patients with gout were screened from 8 hospitals to observe the sUA and acute gouty arthritis recurrence rate-reducing effects of CoTOL in intercritical and chronic gout during a 12-week treatment. We treated 139 and 71 patients with CoTOL and the placebo, respectively, and evaluated their sUA levels, acute gouty arthritis recurrence rate, and adverse events at week 0, 6, and 12.

RESULTS

Twenty-five and 12 patients in the treatment and control groups, respectively, had interrupted treatments, whereas 114 and 59 cases, respectively, completed their treatments. At the end of the 12-week treatment, the average decrease in sUA was 74.26 (95% confidence interval [CI]: 56.74-91.77 μmol/L) and 28.81 μmol/L (95% CI: 4.91-52.71 μmol/L) in the treatment and control groups, respectively (P = 0.004). The average decrease rate of sUA was 12.76% (95% CI: 9.82%-15.70%) and 4.57% (95% CI: 0.42%-8.71%) in the treatment and control groups, respectively (P = 0.004), and the gouty arthritis recurrence rate of the treatment group was lower than that of the control group (from week 6 to 12, 21.93% and 50.88% in the treatment and control group, respectively, P < 0.001; from baseline to week 12, 38.5% and 63.16%, respectively, P = 0.003). Severe adverse events were not observed in either groups, and fewer leucopenia incidences were observed in the treatment group than those in the control group (3/139 vs. 7/71, respectively, P = 0.033).

CONCLUSION

CoTOL reduced sUA levels and effectively prevented acute arthritis recurrence in intercritical and chronic gout without serious adverse events.

Allopurinol for chronic gout

BACKGROUND

Allopurinol, a xanthine oxidase inhibitor, is considered one of the most effective urate-lowering drugs and is frequently used in the treatment of chronic gout.

OBJECTIVES

To assess the efficacy and safety of allopurinol compared with placebo and other urate-lowering therapies for treating chronic gout.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE on 14 January 2014. We also handsearched the 2011 to 2012 American College of Rheumatology (ACR) and European League against Rheumatism (EULAR) abstracts, trial registers and regulatory agency drug safety databases.

SELECTION CRITERIA

All randomised controlled trials (RCTs) or quasi-randomised controlled clinical trials (CCTs) that compared allopurinol with a placebo or an active therapy in adults with chronic gout.

DATA COLLECTION AND ANALYSIS

We extracted and analysed data using standard methods for Cochrane reviews. The major outcomes of interest were frequency of acute gout attacks, serum urate normalisation, pain, function, tophus regression, study participant withdrawal due to adverse events (AE) and serious adverse events (SAE). We assessed the quality of the body of evidence for these outcomes using the GRADE approach.

MAIN RESULTS

We included 11 trials (4531 participants) that compared allopurinol (various doses) with placebo (two trials); febuxostat (four trials); benzbromarone (two trials); colchicine (one trial); probenecid (one trial); continuous versus intermittent allopurinol (one trial) and different doses of allopurinol (one trial). Only one trial was at low risk of bias in all domains. We deemed allopurinol versus placebo the main comparison, and allopurinol versus febuxostat and versus benzbromarone as the most clinically relevant active comparisons and restricted reporting to these comparisons here.Moderate-quality evidence from one trial (57 participants) indicated allopurinol 300 mg daily probably does not reduce the rate of gout attacks (2/26 with allopurinol versus 3/25 with placebo; risk ratio (RR) 0.64, 95% confidence interval (CI) 0.12 to 3.52) but increases the proportion of participants achieving a target serum urate over 30 days (25/26 with allopurinol versus 0/25 with placebo, RR 49.11, 95% CI 3.15 to 765.58; number needed to treat for an additional beneficial outcome (NNTB) 1). In two studies (453 participants), there was no significant increase in withdrawals due to AE (6% with allopurinol versus 4% with placebo, RR 1.36, 95% CI 0.61 to 3.08) or SAE (2% with allopurinol versus 1% with placebo, RR 1.93, 95% CI 0.48 to 7.80). One trial reported no difference in pain reduction or tophus regression, but did not report outcome data or measures of variance sufficiently and we could not calculate the differences between groups. Neither trial reported function.Low-quality evidence from three trials (1136 participants) indicated there may be no difference in the incidence of acute gout attacks with allopurinol up to 300 mg daily versus febuxostat 80 mg daily over eight to 24 weeks (21% with allopurinol versus 23% with febuxostat, RR 0.89, 95% CI 0.71 to 1.1); however more participants may achieve target serum urate level (four trials; 2618 participants) with febuxostat 80 mg daily versus allopurinol 300 mg daily (38% with allopurinol versus 70% with febuxostat, RR 0.56, 95% CI 0.48 to 0.65, NNTB with febuxostat 4). Two trials reported no difference in tophus regression between allopurinol and febuxostat over a 28- to 52-week period; but as the trialists did not provide variance, we could not calculate the mean difference between groups. The trials did not report pain reduction or function. Moderate-quality evidence from pooled data from three trials (2555 participants) comparing allopurinol up to 300 mg daily versus febuxostat 80 mg daily indicated no difference in the number of withdrawals due to AE (7% with allopurinol versus 8% with febuxostat, RR 0.89, 95% CI 0.62 to 1.26) or SAE (4% with allopurinol versus 4% with febuxostat, RR 1.13, 95% CI 0.71 to 1.82) over a 24- to 52-week period.Low-quality evidence from one trial (65 participants) indicated there may be no difference in the incidence of acute gout attacks with allopurinol up to 600 mg daily compared with benzbromarone up to 200 mg daily over a four-month period (0/30 with allopurinol versus 1/25 with benzbromarone, RR 0.28, 95% CI 0.01 to 6.58). Based on the pooled results of two trials (102 participants), there was moderate-quality evidence of no probable difference in the proportion of participants achieving a target serum urate level with allopurinol versus benzbromarone (58% with allopurinol versus 74% with benzbromarone, RR 0.79, 95% CI 0.56 to 1.11). Low-quality evidence from two studies indicated there may be no difference in the number of participants who withdrew due to AE with allopurinol versus benzbromarone over a four- to nine-month period (6% with allopurinol versus 7% with benzbromarone, pooled RR 0.80, 95% CI 0.18 to 3.58). There were no SAEs. They did not report tophi regression, pain and function.All other comparisons were supported by small, single studies only, limiting conclusions.

AUTHORS' CONCLUSIONS

Our review found low- to moderate-quality evidence indicating similar effects on withdrawals due to AEs and SAEs and incidence of acute gout attacks when allopurinol (100 to 600 mg daily) was compared with placebo, benzbromarone (100 to 200 mg daily) or febuxostat (80 mg daily). There was moderate-quality evidence of little or no difference in the proportion of participants achieving target serum urate when allopurinol was compared with benzbromarone. However, allopurinol seemed more successful than placebo and may be less successful than febuxostat (80 mg daily) in achieving a target serum urate level (6 mg/dL or less; 0.36 mmol/L or less) based on moderate- to low-quality evidence. Single studies reported no difference in pain reduction when allopurinol (300 mg daily) was compared with placebo over 10 days, and no difference in tophus regression when allopurinol (200 to 300 mg daily) was compared with febuxostat (80 mg daily). None of the trials reported on function, health-related quality of life or participant global assessment of treatment success, where further research would be useful.

Therapeutic drug monitoring in rheumatic diseases: utile or futile?

Rapid and effective suppression of inflammation is a primary goal in the treatment of rheumatic diseases. However, the therapeutic effect of most medications may be slow to manifest, in the order of weeks or months in the case of DMARDs. Monitoring of drug concentrations allows the possibility of appropriate dose adjustment or changes in medication to achieve more rapid or better outcomes. We review the evidence for drug concentration monitoring. Despite the theoretical utility for monitoring of MTX polyglutamate concentrations in red blood cells in patients with RA, studies have not shown a clear association between concentrations and either efficacy or toxicity and routine measurement is not yet recommended. Small studies associating disease control with concentrations of anti-TNF therapies and anti-drug antibodies suggest that routine monitoring may be useful in the future. However, the data are not yet sufficient for this recommendation. With the use of allopurinol in gout, there is a putative therapeutic range for the active metabolite oxypurinol; however, adjusting the allopurinol dose to achieve a target urate concentration is likely to be most effective, and measuring oxypurinol may be best suited to assessing drug adherence. Although measuring thiopurine metabolite concentrations with AZA therapy has been shown to be useful in IBD, studies in rheumatic diseases have so far failed to confirm a useful association between concentrations and disease control or drug toxicity. Whole blood concentrations of HCQ have been associated with disease control in SLE and future studies may be able to determine a therapeutic range.

Understanding the dose-response relationship of allopurinol: predicting the optimal dosage

AIMS

The aim of the study was to identify and quantify factors that control the plasma concentrations of urate during allopurinol treatment and to predict optimal doses of allopurinol.

METHODS

Plasma concentrations of urate and creatinine (112 samples, 46 patients) before and during treatment with various doses of allopurinol (50-600 mg daily) were monitored. Non-linear and multiple linear regression equations were used to examine the relationships between allopurinol dose (D), creatinine clearance (CLcr) and plasma concentrations of urate before (UP) and during treatment with allopurinol (UT).

RESULTS

Plasma concentrations of urate achieved during allopurinol therapy were dependent on the daily dose of allopurinol and the plasma concentration of urate pre-treatment. The non-linear equation: UT = (1 - D/(ID50 + D)) × (UP - UR) + UR , fitted the data well (r(2) = 0.74, P < 0.0001). The parameters and their best fit values were: daily dose of allopurinol reducing the inhibitable plasma urate by 50% (ID50 = 226 mg, 95% CI 167, 303 mg), apparent resistant plasma urate (UR = 0.20 mmol l(-1), 95 % CI 0.14, 0.25 mmol l(-1)). Incorporation of CLcr did not significantly improve the fit (P = 0.09).

CONCLUSIONS

A high baseline plasma urate concentration requires a high dose of allopurinol to reduce plasma urate below recommended concentrations. This dose is dependent on only the pre-treatment plasma urate concentration and is not influenced by CLcr .

Uric acid as a cardiorenal risk factor - ready for prime-time?

Patients with cardiac morbidity are known to have increased risk of developing renal disease, and vice versa. Cardiorenal syndrome is a general term describing concomitant cardiac and renal dysfunction, and recently there has been renewed interest in the role of uric acid (UA) in its pathophysiology and management. There is evidence to suggest that UA-lowering drugs, such as the xanthine oxidase (XO) inhibitors allopurinol and Febuxostat, may not only retard deteriorating renal function in the context of chronic kidney disease (CKD) but also confer protective cardiovascular effects. As these diseases represent considerable health burdens, this evidence merits evaluation to determine whether or not hyperuricaemia is a cardiorenal risk factor that necessitates intervention and if existing pharmacological agents are sufficiently efficacious.

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.

Safety and efficacy of allopurinol in chronic kidney disease

OBJECTIVE

To review the evidence surrounding the use of allopurinol in chronic kidney disease (CKD) and discuss safety and efficacy considerations of such use.

DATA SOURCES

A literature search was conducted through MEDLINE (1950-July 2013), PubMed (1965-July 2013), and International Pharmaceutical Abstracts (1970-July 2013) using the search terms allopurinol and kidney or renal. In addition, reference citations from publications identified were reviewed.

STUDY SELECTION AND DATA EXTRACTION

All articles in English identified from the data sources were evaluated for inclusion.

DATA SYNTHESIS

Gout management with allopurinol in patients with CKD can be challenging because of the risk of adverse events and uncertain efficacy. Not all gout treatment guidelines provide recommendations for allopurinol use specifically in patients with CKD. Literature regarding the safety and efficacy of dosing allopurinol in CKD has shown inconsistent results and is based primarily on retrospective, case cohort or observational data. Some trials have demonstrated an increased risk of allopurinol-induced adverse reactions in patients with CKD, whereas others have not confirmed renal insufficiency as a risk factor. More CKD patients achieved a target uric acid level in studies where the allopurinol dose was titrated to effect as compared with those studies in which patients were given renally adjusted or untitrated allopurinol doses.

CONCLUSIONS

Studies evaluating allopurinol use in patients with CKD have reported inconsistent findings relative to safety and efficacy. Providers should be aware of the potential risk of allopurinol hypersensitivity syndrome as well as the need for reducing the initiation dose and gradual titration of allopurinol to safely achieve a target serum urate level in this population.

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.

Allopurinol reduces antigen-specific and polyclonal activation of human T cells

Allopurinol is the most popular commercially available xanthine oxidase inhibitor and it is widely used for treatment of symptomatic hyperuricaemia, or gout. Although, several anti-inflammatory actions of allopurinol have been demonstrated in vivo and in vitro, there have been few studies on the action of allopurinol on T cells. In the current study, we have assessed the effect of allopurinol on antigen-specific and mitogen-driven activation and cytokine production in human T cells. Allopurinol markedly decreased the frequency of IFN-γ and IL-2-producing T cells, either after polyclonal or antigen-specific stimulation with Herpes Simplex virus 1, Influenza (Flu) virus, tetanus toxoid and Trypanosoma cruzi-derived antigens. Allopurinol attenuated CD69 upregulation after CD3 and CD28 engagement and significantly reduced the levels of spontaneous and mitogen-induced intracellular reactive oxygen species in T cells. The diminished T cell activation and cytokine production in the presence of allopurinol support a direct action of allopurinol on human T cells, offering a potential pharmacological tool for the management of cell-mediated inflammatory diseases.

The epidemiology and treatment of gout

The development and expression of gout depends on three key steps: (1) chronic hyperuricemia, (2) the growth of monosodium urate (MSU) crystals, and (3) interaction between MSU crystals and the inflammatory system. Epidemiological studies have continued to improve our understanding of the environmental and genetic factors which influence chronic hyperuricemia and gout. The influence of obesity, alcohol, race, sex, age, and specific dietary components will be discussed below. The primary mechanism of hyperuricemia is insufficient renal clearance of uric acid which in turn is dependent on transport of uric acid in the proximal renal tubule. Knowledge of the transport mechanisms has improved understanding of the genetic influences on gout and is relevant to understanding of the effects of drugs which can increase or decrease renal uric acid clearance. The application of established principles of management including diagnosis through crystal identification, the gradual introduction of hypouricemic therapy with the use of prophylaxis to reduce the risk of flares, identification of a suitably low target of plasma urate, a progressive increase in therapy to achieve the target and taking steps to encourage good compliance, has the potential to improve outcomes for patients with this very common affliction. The potential role for new therapies will also be discussed.

New advances in the treatment of gout: review of pegloticase

Treatment-failure gout (TFG) affects approximately 50,000 patients or about 1% of the overall population of patients with gout in the United States of America. The severity of TFG is manifested by frequent acute attacks of disabling arthritis, chronic deforming joint disease, destructive masses of urate crystals (tophi), progressive physical disability, and poor health-related quality of life. Pegloticase (Krystexxa^®; Savient Pharmaceuticals, Inc), a novel PEGylated urate oxidase (uricase) enzyme, has been resubmitted for US Food and Drug Administration approval. In a 6-month, placebo-controlled clinical trial, 8 mg of pegloticase for every 2 weeks induced a lytic decrease of serum urate (sUr) concentrations, leading to dissolution of tophi in 40% of patients at final visit. However, 58% were nonresponders to the defined target sUr of 0.36 mmol/L (80% were nonresponders during months 3 and 6), possibly due to anti-body formation. Also, 26%–31% experienced infusion reactions (IRs) and 77% suffered from gout flares. Although long-term data are awaited, an anti-inflammatory strategy, eg, based on glucocorticosteroids, is needed to prevent pegloticase antibody formation leading to IRs and diminished or shortened efficacy, and might also prevent gout flares. According to the current clinical data, pegloticase might have an important role as a (bridging) treatment in sUr-responsive patients for tophi clearance in severe chronic refractory gout.

Management of gout: beyond allopurinol

The basic concepts of the pathogenesis and management of gout have not altered for many years. Monosodium urate monohydrate crystals drive the disease and identification of these crystals is required for certain diagnosis. In contrast, our understanding of the mediators of gouty inflammation, the appropriate target serum urate concentration during treatment, the drugs available and the best ways to use those drugs have all advanced in recent years and will be the focus of this review.

Management of hyperuricemia in gout: focus on febuxostat

Gout is the most common inflammatory arthritis in an elderly population, and can be diagnosed with absolute certainty by polarization microscopy. However, diagnosis may be challenging because atypical presentations are more common in the elderly. Management of hyperuricemia in the elderly with gout requires special consideration because of co-medication, contra-indications, and risk of adverse reactions. Urate-lowering agents include allopurinol and uricosuric agents. These also must be used sensibly in the elderly, especially when renal function impairment is present. However, if used at the lowest dose that maintains the serum urate level below 5.0 to 6.0 mg/dL (0.30 to 0.36 mmol/L), the excess urate in the body will eventually be eliminated, acute flares will no longer occur, and tophi will resolve. Febuxostat, a new xanthine oxidase inhibitor, is welcomed, as few alternatives for allopurinol are available. Its pharmacokinetics and pharmacodynamics are not significantly altered in patients with moderate renal function or hepatic impairment. Its antihyperuricemic efficacy at 80 to 120 mg/day is better than “standard dosage” allopurinol (300 mg/day). Long-term safety data and efficacy data on tophus diminishment and reduction of gout flares have recently become available. Febuxostat may provide an important option in patients unable to use allopurinol, or refractory to allopurinol.