Impaired response or insufficient dosage? Examining the potential causes of "inadequate response" to allopurinol in the treatment of gout

A Genome-Wide Association Study of Oxypurinol Concentrations in Patients Treated with Allopurinol

Cohort studies have identified several genetic determinants that could predict the clinical response to allopurinol. However, they have not been commonly used for genome-wide investigations to identify genetic determinants on allopurinol metabolism and concentrations. We conducted a genome-wide association study of a prior cross-sectional investigation of patients from the Montreal Heart Institute Biobank undergoing allopurinol therapy. Four endpoints were investigated, namely plasma concentrations of oxypurinol, the active metabolite of allopurinol, allopurinol, and allopurinol-riboside, as well as allopurinol daily dosing. A total of 439 participants (mean age 69.4 years; 86.4% male) taking allopurinol (mean daily dose 194.5 mg) and who had quantifiable oxypurinol concentrations were included in the genome-wide analyses. Participants presented with multiple comorbidities and received concomitant cardiovascular medications. No association achieved the predefined genome-wide threshold values for any of the endpoints (all p > 5 × 10-8). Our results are consistent with prior findings regarding the difficulty in identifying genetic determinants of drug concentrations or pharmacokinetics of allopurinol and its metabolites, as well as allopurinol daily dosing. Given the size of this genome-wide study, collaborative investigations involving larger and diverse cohorts may be required to further identify pharmacogenomic determinants of allopurinol and measure their clinical relevance to personalize allopurinol therapy.

Clinical characteristics of adolescent-onset gout in Chinese: A hospital-based cross-sectional study

OBJECTIVE

Adolescent-onset gout has a greater impact on the lives and health of patients than adult-onset gout. However, there is a relative lack of clinical information on adolescent-onset gout. Hence, we analyzed a Chinese cohort.

METHODS

We studied clinical features of 9,003 Chinese patients. Gout onset age of 12 - 19 years is defined as adolescent-onset group (AG), 20 - 40 years as early-onset group (EG), and 41 - 64 years as late-onset group (LG). Multivariable regression analysis evaluated factors associated with recurrent flares, serum urate (SU) levels, and underexcretion type in AG.

RESULTS

Compared with EG and LG, the AG had higher SU levels [AG: 9.5 (2.2) mg/dL, EG: 8.6 (2.1) mg/dL, LG: 7.73 (2.0) mg/dL, P < 0.001], higher percentage of positive family history of gout (AG: 41.8 %, EG: 29.6 %, LG: 24.6 %, P < 0.001), underexcretion type (AG: 62.4 %, EG: 62.5 %, LG: 58.8 %, P = 0.04), recurrent flares (AG: 78.1 %, EG: 70.3 %, LG: 68.9 %, P = 0.01). Urate-lowering therapy (ULT) initiated [OR 6.58 (95 % CI 1.35 - 32.00)] and hypercholesterolemia [OR 4.16 (95 % CI 1.28 - 13.53)] were associated with recurrent flares. eGFR was identified to be a significant variable of increasing SU levels [beta -0.24 (95 % CI -0.04 to -0.01)]. Hypertriglyceridemia [OR 0.35 (95 % CI 0.17 - 0.71)] was related to underexcretion type.

CONCLUSION

Adolescent-onset gout patients had clinically distinctive features with higher SU levels, BMI, positive gout family history, underexcretion type and recurrent flares. These specific populations were less likely to achieve ULT target, requiring more clinical attention.

Population pharmacokinetic modelling of febuxostat in healthy subjects and people with gout

AIMS

To investigate and characterise the pharmacokinetics of febuxostat and the effect of the covariates of renal function and body size descriptors on the pharmacokinetics of the drug.

METHODS

Blood samples (n = 239) were collected using sparse and rich sampling strategies from healthy (n = 9) and gouty (n = 29) subjects. Febuxostat plasma concentrations were measured by a validated high-performance liquid chromatography method. Population pharmacokinetic analysis was performed using NONMEM. A common variability on bioavailability (FVAR) approach was used to test the effect of fed status on absorption parameters. Covariates were modelled using a power model.

RESULTS

The time course of the plasma concentrations of febuxostat is best described by a two-compartment model. In the final model, the population mean for apparent clearance (CL/F), apparent central volume of distribution (Vc/F), apparent peripheral volume of distribution (Vp/F), absorption rate constant (ka) and apparent intercompartmental clearance (Q/F) were 6.91 l h^-1 , 32.8 l, 19.4 l, 3.6 h^-1 and 1.25 l h^-1 , respectively. The population parmater variability (coefficient of variation) for CL/F, Vc/F and Vp/F were 13.6, 22 and 19.5%, respectively. Food reduced the relative biovailability and ka by 67% and 87%, respectively. Renal function, as assessed by creatinine clearance, was a significant covariate for CL/F while body mass index was a significant covariate for Vc/F.

CONCLUSIONS

Renal function and body mass index were significant covariates. Further work is warranted to investigate the clinical relevance of these results, notably as renal impairment and obesity are common occurrences in people with gout.

Allopurinol blocks aortic aneurysm in a mouse model of Marfan syndrome via reducing aortic oxidative stress

BACKGROUND

Increasing evidence indicates that redox stress participates in MFS aortopathy, though its mechanistic contribution is little known. We reported elevated reactive oxygen species (ROS) formation and NADPH oxidase NOX4 upregulation in MFS patients and mouse aortae. Here we address the contribution of xanthine oxidoreductase (XOR), which catabolizes purines into uric acid and ROS in MFS aortopathy.

METHODS AND RESULTS

In aortic samples from MFS patients, XOR protein expression, revealed by immunohistochemistry, increased in both the tunicae intima and media of the dilated zone. In MFS mice (Fbn1^C1041G/+), aortic XOR mRNA transcripts and enzymatic activity of the oxidase form (XO) were augmented in the aorta of 3-month-old mice but not in older animals. The administration of the XOR inhibitor allopurinol (ALO) halted the progression of aortic root aneurysm in MFS mice. ALO administrated before the onset of the aneurysm prevented its subsequent development. ALO also inhibited MFS-associated endothelial dysfunction as well as elastic fiber fragmentation, nuclear translocation of pNRF2 and increased 3'-nitrotyrosine levels, and collagen maturation remodeling, all occurring in the tunica media. ALO reduced the MFS-associated large aortic production of H₂O₂, and NOX4 and MMP2 transcriptional overexpression.

CONCLUSIONS

Allopurinol interferes in aortic aneurysm progression acting as a potent antioxidant. This study strengthens the concept that redox stress is an important determinant of aortic aneurysm formation and progression in MFS and warrants the evaluation of ALO therapy in MFS patients.

Comparative Effectiveness of Allopurinol and Febuxostat in Gout Management

BACKGROUND

The relative efficacy and safety of allopurinol and febuxostat when used according to current guidelines for the treatment of hyperuricemia are unknown. This double-blind noninferiority trial examined these issues.

METHODS

Participants with gout and hyperuricemia (with at least 33% having stage 3 chronic kidney disease) were randomly assigned to allopurinol or febuxostat in this 72-week trial, with doses titrated to target serum urate. The trial had three phases: titration (weeks 0 to 24), maintenance (weeks 25 to 48), and observation (weeks 49 to 72). Allopurinol and febuxostat were initiated at daily doses of 100 and 40 mg, with maximum titration to 800 and 120 mg, respectively. Antiinflammatory prophylaxis was given during phases 1 and 2. The primary end point was the proportion of patients experiencing one or more flares during phase 3, with a prespecified noninferiority margin of less than 8 percentage points between allopurinol and febuxostat. Secondary end points included efficacy in patients with chronic kidney disease, proportion achieving target serum urate levels, and serious adverse events.

RESULTS

This study included 940 participants; 20.1% withdrew, with similar proportions in treatment arms. During phase 3, 36.5% of allopurinol-treated participants had one flare or more compared with 43.5% of febuxostat-treated participants (P<0.001 for noninferiority). Overall, 80% of participants achieved mean target urates during phase 2 with no differences by treatment. There were no treatment differences (including cardiovascular events) in serious adverse events.

CONCLUSIONS

Allopurinol and febuxostat achieved serum urate goals in patients with gout; allopurinol was noninferior to febuxostat in controlling flares. Similar outcomes were noted in participants with stage 3 chronic kidney disease. (Funded by the Cooperative Studies Program of the Department of Veterans Affairs Office of Research and Development; ClinicalTrials.gov identifier, NCT02579096.).

Why do patients with gout not take allopurinol?

Objective

The objectives of this study were to examine the reasons patients give for non-adherence to allopurinol and examine differences in intentional non-adherence for patients with and without serum urate at treatment target.

Methods

Sixty-nine men with gout attending rheumatology clinics, all prescribed allopurinol for at least six months, completed the Intentional Non-Adherence Scale (INAS). Differences in the types of intentional non-adherence were analysed between those with and without a serum urate (SU) at treatment target (<0.36mmol/L, 6mg/dL).

Results

Among most frequently endorsed reasons for not taking their urate lowering medication was because participants wanted to lead a normal life (23%) or think of themselves as a healthy person again (20%). Patients also reported not taking allopurinol as way of testing if they really needed it (22%). Participants with SU above target endorsed significantly more INAS items as reasons for not taking their medicine, had higher medicine-related concerns and were more likely to give testing treatment as a reason for non-adherence. Participants who were younger, single and non-NZ European also endorsed more reasons for not taking their allopurinol.

Conclusion

Major reasons behind the decision not to take allopurinol relate to wanting to lead a normal life and the strategy of testing treatment to see if patients could reduce the dose without getting symptoms. The results provide some potentially modifiable targets for adherence interventions and also some indications to clinicians about how urate-lowering treatment may be purposely framed for patients in order to improve adherence.

Achievement of the target serum urate level among patients with gout treated with allopurinol or febuxostat in an arthritis clinic in the Philippines

OBJECTIVE

Gout is an important cause of disability among Filipinos, despite measures for effective management. This study aims to determine attainment of target serum uric acid level (SUA ≤ 6 mg/dl) among patients with gout given urate-lowering therapy (ULT) over 6-12 months.

METHODS

This is a single-center, prospective cohort study conducted in one adult Arthritis Clinic at the University of the Philippines-Philippine General Hospital which included 138 patients with gout (1977 ACR criteria), SUA ≥ 6 mg/dl prior to ULT, initiated on ULT (allopurinol or febuxostat), with six months minimum follow-up and with SUA determination post-treatment.

RESULTS

37.7% (52/138) and 36.2% (50/138), achieved target SUA at 6 and 12 months. The factors associated with achieving target SUA in 6 months are BMI > 25 kg/m² [OR 6.98, 95% confidence interval (CI) 1.44-33.88, p value = .016], allopurinol dose ≥ 300 mg (OR 15.76, 95% CI 2.24-111.06, p value = .006), and baseline SUA (OR 0.52, 95% CI 0.33-0.82, p value = .005). The factors associated with achieving target SUA in 12 months are employment (OR 5.51, 95% CI 1.00-30.33, p value = .050), baseline SUA (OR 0.45, 95% CI 0.28-0.74, p value = .002), and age at onset of gout (OR 1.08, 95% CI 1.01-1.15, p value = .026).

CONCLUSION

Target SUA level was not achieved at 6 and 12 months of ULT in most of this cohort. This mirrors the deficient control of gout and should urge health professionals to fully study and address the problem.

Refractory gout - does it exist?

Refractory gout (RG) has been increasingly recognized to be a major problem in clinical care. Patients diagnosed with RG have been assumed to be non-adherent, or under-dosed, to the greater part. In a minority, pathophysiological mechanisms have been discussed. During the last two decades, however, none of the studies differentiated non-adherence from impaired response to drug treatment. A definition of adherence has been proposed in the case of allopurinol treatment (oxipurinol in serum, >20 µmol/l), which would seem to confirm a dose of about 50 mg/d being taken by the patients. Guidelines for treating gout published by national or international rheumatology societies do provide very little, if any, information on how to evaluate patients with RG. Coinciding with the development of the xanthine oxidase inhibitor, febuxostat, a moderate increase in the number of publications on RG was observed, with a sharp rise following after its approval for clinical use. It was demonstrated recently that intensive training and supervision of patients with gout resulted in very low numbers of patients not reaching treatment targets. It should be remembered that allopurinol, is an ideal instrument for differentiating non-adherence from true impaired response. We conclude that, apart from very rare patients, needing confirmation of such a diagnosis by metabolic ward studies, RG does not exist, and with close to hundred percent, treatment failure is due to patient and physician behavior.

An update on the genetics of hyperuricaemia and gout

A central aspect of the pathogenesis of gout is elevated urate concentrations, which lead to the formation of monosodium urate crystals. The clinical features of gout result from an individual's immune response to these deposited crystals. Genome-wide association studies (GWAS) have confirmed the importance of urate excretion in the control of serum urate levels and the risk of gout and have identified the kidneys, the gut and the liver as sites of urate regulation. The genetic contribution to the progression from hyperuricaemia to gout remains relatively poorly understood, although genes encoding proteins that are involved in the NLRP3 (NOD-, LRR- and pyrin domain-containing 3) inflammasome pathway play a part. Genome-wide and targeted sequencing is beginning to identify uncommon population-specific variants that are associated with urate levels and gout. Mendelian randomization studies using urate-associated genetic variants as unconfounded surrogates for lifelong urate exposure have not supported claims that urate is causal for metabolic conditions that are comorbidities of hyperuricaemia and gout. Genetic studies have also identified genetic variants that predict responsiveness to therapies (for example, urate-lowering drugs) for treatment of hyperuricaemia. Future research should focus on large GWAS (that include asymptomatic hyperuricaemic individuals) and on increasing the use of whole-genome sequencing data to identify uncommon genetic variants with increased penetrance that might provide opportunities for clinical translation.

The Role of a “Treat-to-Target” Approach in the Long-Term Renal Outcomes of Patients with Gout

Background: Although gout is accompanied by the substantial burden of kidney disease, there are limited data to assess renal function as a therapeutic target. This study evaluated the importance of implementing a “treat-to-target” approach in relation to renal outcomes. Methods: Patients with gout who underwent continuous urate-lowering therapy (ULT) for at least 12 months were included. The effect of ULT on renal function was investigated by means of a sequential comparison of the estimated glomerular filtration rate (eGFR). Results: Improvement in renal function was only demonstrated in subjects in whom the serum urate target of <6 mg/dL was achieved (76.40 ± 18.81 mL/min/1.73 m2 vs. 80.30 ± 20.41 mL/min/1.73 m2, p < 0.001). A significant difference in the mean change in eGFR with respect to serum urate target achievement was shown in individuals with chronic kidney disease stage 3 (−0.35 ± 3.87 mL/min/1.73 m2 vs. 5.33 ± 11.64 mL/min/1.73 m2, p = 0.019). Multivariable analysis predicted that patients ≥65 years old had a decreased likelihood of improvement (OR 0.31, 95% CI 0.13–0.75, p = 0.009). Conclusions: The “treat-to-target” approach in the long-term management of gout is associated with better renal outcomes, with a greater impact on those with impaired renal function.

Genome-Wide Association and Functional Studies Reveal Novel Pharmacological Mechanisms for Allopurinol

Allopurinol, which lowers uric acid (UA) concentration, is increasingly being recognized for its benefits in cardiovascular and renal disease. However, response to allopurinol is variable. We gathered samples from 4,446 multiethnic subjects for a genome-wide association study of allopurinol response. Consistent with previous studies, we observed that the Q141K variant in ABCG2 (rs2231142), which encodes the efflux pump breast cancer resistance protein (BCRP), associated with worse response to allopurinol. However, for the first time this association reached genome-wide level significance (P = 8.06 × 10^-11 ). Additionally, we identified a novel association with a variant in GREM2 (rs1934341, P = 3.22 × 10^-6 ). In vitro studies identified oxypurinol, the active metabolite of allopurinol, as an inhibitor of the UA transporter GLUT9, suggesting that oxypurinol may modulate UA reabsorption. These results provide strong evidence for a role of BCRP Q141K in allopurinol response, and suggest that allopurinol may have additional hypouricemic effects beyond xanthine oxidase inhibition.

Moving the Needle: Improving the Care of the Gout Patient

Gout is a the most common inflammatory arthritis in the United States. It is a significant cause of morbidity, disability, lost work days, and high healthcare utilization due to intermittent attacks, chronic inflammation, and joint damage. Despite our understanding of the prelude and pathophysiology of gout, hyperuricemia, it is still poorly misunderstood by patients and poorly managed by healthcare providers. Several parallel treatment paradigms have been developed by professional societies around the world based on the understanding of how hyperuricemia occurs, gout epidemiology, expert opinion, and clinical trials data in order to lower uric acid and eventually eliminate the patient's crystal burden. This review focuses on both the treatment of acute attacks, and more importantly, the long-term management of gout and the lowering of serum uric acid levels to a goal of < 6 mg/dl (0.360 mmol/l) or treating to target. Treating to a target serum uric acid goal is an opportunity to decrease morbidity and improve the quality of care of every gout patient.

Adherence and Outcomes with Urate-Lowering Therapy: A Site-Randomized Trial

PURPOSE

The purpose of this study was to test a pharmacist-led intervention to improve gout treatment adherence and outcomes.

METHODS

We conducted a site-randomized trial (n=1463 patients) comparing a 1-year, pharmacist-led intervention to usual care in patients with gout initiating allopurinol. The intervention was delivered primarily through automated telephone technology. Co-primary outcomes were the proportion of patients adherent (proportion of days covered ≥0.8) and achieving a serum urate <6.0 mg/dl at 1 year. Outcomes were reassessed at year 2.

RESULTS

Patients who underwent intervention were more likely than patients of usual care to be adherent (50% vs 37%; odds ratio [OR] 1.68; 95% confidence interval [CI] 1.30, 2.17) and reach serum urate goal (30% vs 15%; OR 2.37; 95% CI 1.83, 3.05). In the second year (1 year after the intervention ended), differences were attenuated, remaining significant for urate goal but not for adherence. The intervention was associated with a 6%-16% lower gout flare rate during year 2, but the differences did not reach statistical significance.

CONCLUSIONS

A pharmacist-led intervention incorporating automated telephone technology improved adherence and serum urate goal in patients with gout initiating allopurinol. Although this light-touch, low-tech intervention was efficacious, additional efforts are needed to enhance patient engagement in gout management and ultimately to improve outcomes.

Impact of Non-Adherence and Flare Resolution on the Cost-Effectiveness of Treatments for Gout: Application of a Linked Pharmacometric/Pharmacoeconomic Model

BACKGROUND

Dual urate-lowering therapy (ULT) with lesinurad in combination with either allopurinol or febuxostat is an option for patients with gout unsuccessfully treated on either monotherapy. Treatment failure is often a result of poor medication adherence. Imperfect adherence in clinical trials may lead to biased estimates of treatment effect and confound the results of cost-effectiveness analyses.

OBJECTIVES

To estimate the impact of varying medication adherence on the cost effectiveness of lesinurad dual therapy and estimate the value-based price of lesinurad at which the incremental cost-effectiveness ratio is equal to £20,000 per quality-adjusted life-year (QALY).

METHODS

Treatment effect was simulated using published pharmacokinetic-pharmacodynamic models and scenarios representing adherence in clinical trials, routine practice, and perfect use. The subsequent cost and health impacts, over the lifetime of a patient cohort, were estimated using a bespoke pharmacoeconomic model.

RESULTS

The base-case incremental cost-effectiveness ratios comparing lesinurad dual ULT with monotherapy ranged from £39,184 to £78,350/QALY gained using allopurinol and £31,901 to £124,212/QALY gained using febuxostat, depending on the assumed medication adherence. Results assuming perfect medication adherence imply a per-quarter value-based price of lesinurad of £45.14 when used in dual ULT compared with allopurinol alone and £57.75 compared with febuxostat alone, falling to £25.41 and £3.49, respectively, in simulations of worsening medication adherence.

CONCLUSIONS

The estimated value-based prices of lesinurad only exceeded that which has been proposed in the United Kingdom when assuming both perfect drug adherence and the eradication of gout flares in sustained treatment responders.

Impact of diuretics on the urate lowering therapy in patients with gout: analysis of an inception cohort

Background

Diuretics have been associated with impaired response and refractoriness in gout, but whether this effect is still present with new urate-lowering drugs (ULD) and treat-to-target strategies is unknown. The aim of the present study was to assess the impact of the diuretics on the response to ULD in patients with gout. 

Methods

This was a retrospective analysis of an inception cohort. Participants were classified according to the type of ULD prescribed. We analysed the maximal dose of ULD (primary outcome variable), serum urate (SU) reduction, and the achievement of different SU targets (6 mg/dL, 5 mg/dL, and 4 mg/dL), according to the type of ULD prescribed and use of diuretics (loop and/or thiazide). We adjusted for confounders using multiple linear regression analysis.

Results

We included 245 patients: 208 treated with allopurinol (66 on diuretics, 31.7%), 35 with febuxostat (19 on diuretics, 57.6%), and 2 with benzbromarone. Significantly fewer participants in the allopurinol plus diuretics subgroup achieved SU levels of less than 5 mg/dL, but we found no other significant differences in SU targets associated with diuretics. Regarding the maximum ULD dose, a simple linear regression suggested an inverse relationship with diuretics (beta = − 0.125, p = 0.073), but this did not hold in the multivariable analysis (beta = − 0.47, p = 0.833). There was no association with febuxostat (beta = − 0.116, p = 0.514).

Conclusion

Diuretics do not appear to have a significant impact on managing gout.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1559-2) contains supplementary material, which is available to authorized users.

Impact of non-adherence on the safety and efficacy of uric acid-lowering therapies in the treatment of gout

AIMS

Dual-urate-lowering therapy (ULT) with xanthine oxidase inhibitor and uricosuric medications is a treatment option for severe gout. Uricosuric agents can cause hyperuricosuria, a risk factor for nephrolithiasis and acute uric acid nephropathy. The aims of the present study were to simulate the relationship between suboptimal drug adherence and efficacy, and to quantify the risk of hyperuricosuria in gout patients receiving mono- and dual-ULTs.

METHODS

The impact of poor medication adherence was studied using two-compartment pharmacokinetic (PK) models based on published evidence, and a semi-mechanistic four-compartment pharmacodynamic (PD) model. The PKPD model was used to simulate mono and dual-ULT in gout patients with either under-excretion (lowered clearance) or overproduction of uric acid, with suboptimal adherence modelled as either a single drug holiday of increasing duration or doses taken at random.

RESULTS

Simulation results showed a surge in urinary uric acid occurring when dosing is restarted following missed doses. For under-excreters taking a 20-day drug holiday, the addition of 200 mg (or 400 mg) lesinurad to 80 mg febuxostat increased the percentage of patients experiencing hyperuricosuria from 0% to 1.4% (or 3.1%). In overproducers, restarting ULTs following drug holidays of more than 5 days leads to over 60% of patients experiencing hyperuricosuria.

CONCLUSIONS

Suboptimal medication adherence may compromise the safety and efficacy of mono- and dual-ULTs, especially in patients with gout resulting from an overproduction of uric acid. Clinicians and pharmacists should consider counselling patients with respect to the risks associated with partial adherence, and offer interventions to improve adherence or tailor treatments, where appropriate.

Effectiveness of an electronic patient-centred self-management tool for gout sufferers: a cluster randomised controlled trial protocol

INTRODUCTION

Gout is increasing despite effective therapies to lower serum urate concentrations to 0.36 mmol/L or less, which, if sustained, significantly reduces acute attacks of gout. Adherence to urate-lowering therapy (ULT) is poor, with rates of less than 50% 1 year after initiation of ULT. Attempts to increase adherence in gout patients have been disappointing. We aim to evaluate the effectiveness of use of a personal, self-management, 'smartphone' application (app) to achieve target serum urate concentrations in people with gout. We hypothesise that personalised feedback of serum urate concentrations will improve adherence to ULT.

METHODS AND ANALYSIS

Setting and designPrimary care. A prospective, cluster randomised (by general practitioner (GP) practices), controlled trial.

PARTICIPANTS

GP practices will be randomised to either intervention or control clusters with their patients allocated to the same cluster.

INTERVENTION

The intervention group will have access to the Healthy.me app tailored for the self-management of gout. The control group patients will have access to the same app modified to remove all functions except the Gout Attack Diary.

PRIMARY AND SECONDARY OUTCOMES

The proportion of patients whose serum urate concentrations are less than or equal to 0.36 mmol/L after 6 months. Secondary outcomes will be proportions of patients achieving target urate concentrations at 12 months, ULT adherence rates, serum urate concentrations at 6 and 12 months, rates of attacks of gout, quality of life estimations and process and economic evaluations. The study is designed to detect a ≥30% improvement in the intervention group above the expected 50% achievement of target serum urate at 6 months in the control group: power 0.80, significance level 0.05, assumed 'dropout' rate 20%.

ETHICS AND DISSEMINATION

This study has been approved by the University of New South Wales Human Research Ethics Committee. Study findings will be disseminated in international conferences and peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ACTRN12616000455460.

Pegloticase in gout treatment - safety issues, latest evidence and clinical considerations

Gout is a common rheumatic condition, with increasing prevalence in recent decades. The mainstay of treatment for gout is oral urate-lowering therapy (ULT), typically with xanthine oxidase inhibitors (XOIs). Unfortunately, a proportion of patients have persistent gout that is refractory to ULT. Pegloticase, a recombinant pegylated uricase, has been approved by the US Food and Drug Administration for the treatment of refractory gout. However, concern has been raised regarding the risk of infusion reactions, which are now understood to be largely due to the development of antipegloticase antibodies. Discontinuation of pegloticase upon failure to lower serum urate has been shown to markedly reduce infusion reaction risk, but deprives patients of what, in many cases, is a last-resort treatment. In this manuscript, we review the rationale, mechanism of action, efficacy and safety of pegloticase. Additionally, we focus on potential strategies to reduce pegloticase immunogenicity and potentially make this important agent available to a wider group of patients requiring treatment.

Impact of comorbidities on gout and hyperuricaemia: an update on prevalence and treatment options

Gout, the most prevalent inflammatory arthritis worldwide, is associated with cardiovascular and renal diseases, and is an independent predictor of premature death. The frequencies of obesity, chronic kidney disease (CKD), hypertension, type 2 diabetes, dyslipidaemias, cardiac diseases (including coronary heart disease, heart failure and atrial fibrillation), stroke and peripheral arterial disease have been repeatedly shown to be increased in gout. Therefore, the screening and care of these comorbidities as well as of cardiovascular risk factors are of outmost importance in patients with gout. Comorbidities, especially CKD, and drugs prescribed for their treatment, also impact gout management. Numerous epidemiological studies have shown the association of asymptomatic hyperuricaemia with the above-mentioned diseases and cardiovascular risk factors. Animal studies have also produced a mechanistic approach to the vascular toxicity of soluble urate. However, causality remains uncertain because confounders, reverse causality or common etiological factors might explain the epidemiological results. Additionally, these uncertainties remain unsolved despite recent studies using Mendelian randomisation or therapeutic approaches. Thus, large randomised placebo-controlled trials are still needed to assess the benefits of treating asymptomatic hyperuricaemia.

ABCG2 polymorphisms in gout: insights into disease susceptibility and treatment approaches

As a result of the association of a common polymorphism (rs2231142, Q141K) in the ATP-binding cassette G2 (ABCG2) transporter with serum urate concentration in a genome-wide association study, it was revealed that ABCG2 is an important uric acid transporter. This review discusses the relevance of ABCG2 polymorphisms in gout, possible etiological mechanisms, and treatment approaches. The 141K ABCG2 urate-increasing variant causes instability in the nucleotide-binding domain, leading to decreased surface expression and function. Trafficking of the protein to the cell membrane is altered, and instead, there is an increased ubiquitin-mediated proteasomal degradation of the variant protein as well as sequestration into aggresomes. In humans, this leads to decreased uric acid excretion through both the kidney and the gut with the potential for a subsequent compensatory increase in renal urinary excretion. Not only does the 141K polymorphism in ABCG2 lead to hyperuricemia through renal overload and renal underexcretion, but emerging evidence indicates that it also increases the risk of acute gout in the presence of hyperuricemia, early onset of gout, tophi formation, and a poor response to allopurinol. In addition, there is some evidence that ABCG2 dysfunction may promote renal dysfunction in chronic kidney disease patients, increase systemic inflammatory responses, and decrease cellular autophagic responses to stress. These results suggest multiple benefits in restoring ABCG2 function. It has been shown that decreased ABCG2 141K surface expression and function can be restored with colchicine and other small molecule correctors. However, caution should be exercised in any application of these approaches given the role of surface ABCG2 in drug resistance.

Genomic sequencing of uric acid metabolizing and clearing genes in relationship to xanthine oxidase inhibitor dose

It remains unclear why the dose of xanthine oxidase inhibitors (XOI) allopurinol or febuxostat varies among patients though they reach similar serum uric acid (SUA) goal. We pursued genomic sequencing of XOI metabolism and clearance genes to identify single-nucleotide polymorphisms (SNPs) relate to differences in XOI dose. Subjects with a diagnosis of Gout based on the 1977 American College of Rheumatology Classification Criteria for the disorder, who were on stable doses of a XOI, and who were at their goal SUA level, were enrolled. The primary outcome was relationship between SNPs in any of these genes to XOI dose. The secondary outcome was relationship between SNPs and change in pre- and post-treatment SUA. We enrolled 100 subjects. The average patient age was 68.6 ± 10.6 years old. Over 80% were men and 77% were Caucasian. One SNP was associated with a higher XOI dose: rs75995567 (p = 0.031). Two SNPs were associated with 300 mg daily of allopurinol: rs11678615 (p = 0.022) and rs3731722 on Aldehyde Oxidase (AO) (His1297Arg) (p = 0.001). Two SNPs were associated with a lower dose of allopurinol: rs1884725 (p = 0.033) and rs34650714 (p = 0.006). For the secondary outcome, rs13415401 was the only SNP related to a smaller mean SUA change. Ten SNPs were identified with a larger change in SUA. Though multiple SNPs were identified in the primary and secondary outcomes of this study, rs3731722 is known to alter catalytic function for some aldehyde oxidase substrates.

Pilot study of a multidisciplinary gout patient education and monitoring program

OBJECTIVE

Gout patient self-management knowledge and adherence to treatment regimens are poor. Our objective was to assess the feasibility and acceptability of a multidisciplinary team-based pilot program for the education and monitoring of gout patients.

METHODS

Subjects completed a gout self-management knowledge exam, along with gout flare history and compliance questionnaires, at enrollment and at 6 and 12 months. Each exam was followed by a nursing educational intervention via a structured gout curriculum. Structured monthly follow-up calls from pharmacists emphasized adherence to management programs. Primary outcomes were subject and provider program evaluation questionnaires at 6 and 12 months, program retention rate and success in reaching patients via monthly calls.

RESULTS

Overall, 40/45 subjects remained in the study at 12 months. At 12 months, on a scale of 1 (most) to 5 (least), ratings of 3 or better were given by 84.6% of subjects evaluating the usefulness of the overall program in understanding and managing their gout, 81.0% of subjects evaluating the helpfulness of the nursing education program, and 50.0% of subjects evaluating the helpfulness of the calls from the pharmacists. Knowledge exam questions that were most frequently answered incorrectly on repeat testing concerned bridge therapy, the possibility of being flare-free, and the genetic component of gout.

CONCLUSIONS

Our multidisciplinary program of gout patient education and monitoring demonstrates feasibility and acceptability. We identified variability in patient preference for components of the program and persistent patient knowledge gaps.

Treatment of hyperuricemia in gout: current therapeutic options, latest developments and clinical implications

Despite being the most common type of inflammatory arthritis, gout is often poorly managed. Except for febuxostat and pegloticase, research in new therapeutic agents for the management of hyperuricemia in gout remained insufficient for several decades. With emerging evidence of possible roles of hyperuricemia in cardiometabolic comorbidities, as well as more convincing evidence regarding poor outcomes (e.g. disability, recurrent hospital admissions) in patients with uncontrolled gout, several agents are current under development. Increasing knowledge regarding renal urate transporters has resulted in the development of new generation uricosurics such as lesinurad and arhalofenate. This review aims at discussing current therapeutic strategies for gout, as well as their limitations and the possible role of emerging agents in the chronic management of hyperuricemia in gout. Drugs in phases I and II of development will be discussed, along with new agents and therapeutic classes, such as purine nucleoside phosphorylase inhibitors and dual-action drugs. These new developments are encouraging, and will hopefully contribute to a more adequate management of hyperuricemia in gout.

Knowledge, illness perceptions and stated clinical practice behaviour in management of gout: a mixed methods study in general practice

The objective of the present study is to explore knowledge, illness perceptions and stated practice behaviour in relation to gout in primary care. This is a mixed methods study among 32 general practitioners (GPs). The quantitative assessment included the Gout Knowledge Questionnaire (GKQ; range 0–10; better) and Brief Illness Perceptions Questionnaire (BIPQ; nine items, range 0–10; stronger). Structured individual interviews obtained further qualitative insight into knowledge and perceptions, in the context of daily practice. Among 32 GPs, 18 (56.3 %) were male, mean age 44.4 years (SD 9.6) and mean working experience 17.1 years (SD 9.7). Median score [interquartile ranges (IQR)] on the GKQ was 7.8 [6.7–8.9] and 9.0 [8.0–10.0], when presented as open or multiple-choice questions, respectively. The BIPQ (median; [IQR]) revealed that gout was seen as a chronic disease (8.0; [7.0–9.0]), affecting life and emotions moderately (6.5; [5.0–7.0]), having many severe symptoms (8.0; [7.0–9.0]) and in which treatment could be very helpful (8.0; [7.0–9.0]). Further interviews revealed large variation in specific aspects of knowledge and about gaps concerning indications for uric acid-lowering therapy (UALT), duration of UALT, target serum uric acid (sUA) level or duration of prophylactic treatment. Finally, patients’ adherence was not checked systematically. Specific knowledge gaps and discrepancies between perceptions and stated practice behaviour were identified, which might hamper effective management of this well-treatable disease. Improving evidence on the rationale and effectiveness of treatment targets and adherence interventions, tailoring guidelines to general practice and intensification of implementation of guidelines in primary health care seem to be needed.

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.

Pharmacogenetic considerations in the treatment of gout

Gout is one of the most common forms of arthritis and the prevalence is increasing. Management comprises rapid and effective control of the inflammation in acute gout and sustained urate lowering in the long term. Improving the outcomes for cheaper old drugs and for the increasing number of new, more expensive agents is an important clinical goal. The role of pharmacogenetics in predicting response and adverse events to gout therapies is of considerable interest. Currently, prospective screening is employed to detect HLA-B*5801 carriage and glucose-6-phosphate dehydrogenase deficiency, to minimize occurrence of allopurinol hypersensitivity and pegloticase-related hemolytic anemia. In the future it is likely that other genetic markers of drug response will make the transition to clinical practice to further improve the efficacy and safety of gout therapies. In this review, we will examine the potential clinical relevance of specific genetic variants in the management of gout.