Lisa K. Stamp

Using allopurinol above the dose based on creatinine clearance is effective and safe in patients with chronic gout, including those with renal impairment.

OBJECTIVE To determine the efficacy and safety of increasing the allopurinol dose above the proposed creatinine clearance-based dose in patients with gout. METHODS Patients with gout who had been receiving a stable dose of allopurinol for ≥ 1 month were recruited. The dose of allopurinol was increased to obtain the target serum urate level of <0.36 mmoles/liter (<6 mg/dl). Patients were seen monthly until the serum urate concentration was <0.36 mmoles/liter for 3 consecutive months and then were seen every 3 months for at least 12 months. Data were analyzed using the dosage of allopurinol (mg/day) greater than the recommended dosage, as defined by the Hande criteria. RESULTS Ninety patients were enrolled. The mean age of the patients was 58.7 years (range 27-83 years), 87.9% were male, and 81.9% were of European ancestry. Forty-five patients had a serum urate concentration of ≥ 0.36 mmoles/liter, and the dose of allopurinol was increased in these patients. Rashes developed in 3 patients, and either allopurinol was discontinued or dose escalation was ceased in these patients. Seven patients were lost to followup or developed intervening medical problems that precluded dose escalation. In 31 (88.8%) of 35 patients who completed the study, the serum urate level was <0.36 mmoles/liter at 12 months. Two of the 5 patients who had a serum urate level ≥ 0.36 mmoles/liter had undetectable levels of plasma oxypurinol, indicating noncompliance with allopurinol treatment. A significant reduction in the serum urate concentration was observed for all allopurinol doses above the recommended dose. Eighteen of 45 patients were receiving furosemide; those receiving furosemide were just as likely as those not receiving furosemide to achieve a serum urate concentration of <0.36 mmoles/liter (72% versus 88.5%; P = 0.24). Patients receiving furosemide required a higher dose of allopurinol to achieve the target serum urate concentration. No serious adverse events were observed. CONCLUSION Increasing the dose of allopurinol above the proposed creatinine clearance-based dose led to a significant reduction in the serum urate concentration. Approximately 89% of patients achieved a serum urate concentration of <0.36 mmoles/liter. In this cohort, toxicity was not increased in patients receiving higher doses of allopurinol, including those with renal impairment.

Starting dose is a risk factor for allopurinol hypersensitivity syndrome: A proposed safe starting dose of allopurinol

OBJECTIVE Allopurinol is the most commonly used urate-lowering therapy in gout. Allopurinol hypersensitivity syndrome (AHS) is a rare but potentially fatal adverse event. Dosing guidelines based on creatinine clearance have been proposed based on the recognition that dosages of ≥300 mg/day may be associated with AHS, particularly in patients with renal impairment. However, the relationship between the allopurinol starting dose and AHS is unknown. This study was undertaken to determine the relationship between allopurinol dosing and AHS. METHODS A retrospective case-control study of patients with gout who developed AHS between January 1998 and September 2010 was undertaken. For each case, 3 controls with gout who were receiving allopurinol but did not develop AHS were identified. Controls were matched with cases for sex, diuretic use at the time of initiating allopurinol, age (±10 years), and estimated glomerular filtration rate (estimated GFR). Starting dose and dose at the time of the reaction in cases were compared between cases and controls. RESULTS Fifty-four AHS cases and 157 controls were identified. There was an increase in the risk of AHS as the starting dose of allopurinol corrected for the estimated GFR increased. For the highest quintile of starting dose per estimated GFR, the odds ratio was 23.2 (P < 0.01). Receiver operating characteristic analysis indicated that 91% of AHS cases and 36% of controls received a starting dose of allopurinol of ≥1.5 mg per unit of estimated GFR (mg/ml/minute). CONCLUSION Our findings indicate that starting allopurinol at a dose of 1.5 mg per unit of estimated GFR may be associated with a reduced risk of AHS. In patients who tolerate allopurinol, the dose can be gradually increased to achieve the target serum urate level.

Pharmacokinetics of Oral Methotrexate in Patients With Rheumatoid Arthritis

OBJECTIVE There is evidence supporting a therapeutic range for methotrexate polyglutamate (MTXGlu) concentrations in the treatment of rheumatoid arthritis (RA). Knowledge of the pharmacokinetics of MTXGlu1-5 is required for optimal timing of blood sampling. The aim of this study was to determine the time to steady state and the half-life of accumulation of red blood cell (RBC) MTXGlu1-5 in patients with RA commencing oral MTX, and the time for RBC MTXGlu1-5 to become undetectable and the half-life of elimination of RBC MTXGlu1-5 in patients ceasing treatment with oral MTX. METHODS Ten patients beginning treatment and 10 patients stopping treatment with low-dose oral MTX were recruited. Blood samples were initially collected weekly, with gradual extension to monthly collection over the study period. RBC MTXGlu1-5 concentrations were assayed by high-performance liquid chromatography. Results were analyzed using a first-order exponential method. RESULTS The median times to reach steady state in RBCs (defined as 90% of the maximum concentration) were 6.2, 10.6, 41.2, 149, and 139.8 weeks, respectively, for MTXGlu1, MTXGlu2, MTXGlu3, MTXGlu4, and MTXGlu5. The median half-life of accumulation for RBC MTXGlu1-5 ranged from 1.9 weeks to 45.2 weeks. The median times for MTXGlus to become undetectable in RBCs were 4.5, 5.5, 10, 6, and 4 weeks, respectively, for MTXGlu1, MTXGlu2, MTXGlu3, MTXGlu4, and MTXGlu5. The median half-life of elimination for RBC MTXGlu1-5 ranged from 1.2 weeks to 4.3 weeks. CONCLUSION There is wide interpatient variability of RBC MTXGlu1-5 accumulation and elimination in adults with RA. These data also suggest that after a dose change, >6 months are required for RBC MTXGlu1-5 to reach steady state. Such delays in achieving steady state suggest that more rapid dose escalation or subcutaneous administration from the outset should be considered.

Allopurinol Dosing in Renal Impairment: Walking the Tightrope Between Adequate Urate Lowering and Adverse Events

Allopurinol is the mainstay of urate‐lowering therapy for patients with gout and impaired renal function. Although rare, a life‐threatening hypersensitivity syndrome may occur with this drug. The risk of this allopurinol hypersensitivity syndrome (AHS) is increased in renal impairment. The recognition that AHS may be because of delayed‐type hypersensitivity to oxypurinol, the main metabolite of allopurinol, and that oxypurinol concentrations are frequently elevated in patients with renal impairment prescribed standard doses of allopurinol has led to the widespread adoption of allopurinol‐dosing guidelines. These guidelines advocate allopurinol dose reduction according to creatinine clearance in patients with renal impairment. However, recent studies have challenged the role of these guidelines, suggesting that AHS may occur even at low doses of allopurinol, and that these guidelines lead to under‐treatment of hyperuricemia, a key therapeutic target in gout. Based on current data, we advocate gradual introduction of allopurinol according to current treatment guidelines, with close monitoring of serum uric acid concentrations. In patients with severe disease and persistent hyperuricemia, allopurinol dose escalation above those recommended by the guidelines should be considered, with careful evaluation of the benefits and risks of therapy. Further work is needed to clarify the safety and efficacy of allopurinol dose escalation, particularly in patients with renal impairment.

Role of the urate transporter SLC2A9 gene in susceptibility to gout in New Zealand Māori, Pacific Island, and Caucasian case-control sample sets.

OBJECTIVE To examine the role of genetic variation in the renal urate transporter SLC2A9 in gout in New Zealand sample sets of Māori, Pacific Island, and Caucasian ancestry and to determine if the Māori and Pacific Island samples could be useful for fine-mapping. METHODS Patients (n= 56 Māori, 69 Pacific Island, and 131 Caucasian) were recruited from rheumatology outpatient clinics and satisfied the American College of Rheumatology criteria for gout. The control samples comprised 125 Māori subjects, 41 Pacific Island subjects, and 568 Caucasian subjects without arthritis. SLC2A9 single-nucleotide polymorphisms rs16890979 (V253I), rs5028843, rs11942223, and rs12510549 were genotyped (possible etiologic variants in Caucasians). RESULTS Association of the major allele of rs16890979, rs11942223, and rs5028843 with gout was observed in all sample sets (P = 3.7 x 10(-7), 1.6 x 10(-6), and 7.6 x 10(-5) for rs11942223 in the Māori, Pacific Island, and Caucasian samples, respectively). One 4-marker haplotype (1/1/2/1; more prevalent in the Māori and Pacific Island control samples) was not observed in a single gout case. CONCLUSION Our data confirm a role of SLC2A9 in gout susceptibility in a New Zealand Caucasian sample set, with the effect on risk (odds ratio >2.0) greater than previous estimates. We also demonstrate association of SLC2A9 with gout in samples of Māori and Pacific Island ancestry and a consistent pattern of haplotype association. The presence of both alleles of rs16890979 on susceptibility and protective haplotypes in the Māori and Pacific Island sample is evidence against a role for this nonsynonymous variant as the sole etiologic agent. More extensive linkage disequilibrium in Māori and Pacific Island samples suggests that Caucasian samples may be more useful for fine-mapping.

A strong role for the ABCG2 gene in susceptibility to gout in New Zealand Pacific Island and Caucasian, but not Māori, case and control sample sets

Genetic variation in ABCG2 (rs2231142, Q141K), encoding a uric acid transporter, is associated with gout in diverse populations. The aim of this study was to examine a role for ABCG2 in gout susceptibility in New Zealand Māori, Pacific Island and Caucasian samples. Patients (n = 185, 173 and 214, for Māori, Pacific Island and Caucasian, respectively) satisfied the American College of Rheumatology gout classification criteria. The comparison samples comprised 284, 129 and 562 individuals, respectively, without gout. rs2231142 was genotyped and stratification accounted for using genomic control markers. Association of the minor allele of rs2231142 with gout was observed in the Pacific Island samples (OR = 2.80, P(STRAT) < 0.001 after accounting for effects of population structure), but not in the Māori samples (OR = 1.08, P(STRAT)= 0.70), with heterogeneity in association evident between the Māori and Pacific Island datasets (P(HET) = 0.001). A similar dichotomy in association was observed when samples were stratified into Western (Tonga, Samoa, Niue, Tokelau) versus Eastern Polynesian (Māori, Cook Island) origin (OR = 2.59, P(STRAT) < 0.001; OR = 1.12, P(STRAT)= 0.48, respectively; P(HET) = 0.005). Association with gout was observed in the Caucasian samples (OR = 2.20, P = 3.2 × 10(-8)). Unlike SLC2A9, which is a strong risk factor for gout in both Māori and Pacific Island people, ABCG2 rs2231142 has a strong effect only in people of Western Polynesian ancestry. Our results emphasize the need to account for sub-population differences when undertaking biomedical genetic research in a group defined by a geographical region and shared ancestry but characterized by migratory events that create bottlenecks and altered genetic structure in the founder populations.

Interleukin-17: the missing link between T-cell accumulation and effector cell actions in rheumatoid arthritis?

The prominence of T cells and monocyte/macrophages in rheumatoid synovium suggests T cells may localize and amplify the effector functions of monocyte/macrophages in rheumatoid disease. However, while T cells are abundant in rheumatoid joints, classic T‐cell derived cytokines are scarce, especially when compared to the levels of monokines IL‐1β and TNF‐α. For this reason, it has been speculated that monocyte/macrophages may act independently of T cells in rheumatoid disease and that the role of T cells may be more or less irrelevant to core disease mechanisms. The question of T‐cell influence requires re‐evaluation in light of the characterization of IL‐17, a T‐cell derived cytokine that is abundant in rheumatoid synovium and synovial fluid. IL‐17 has a number of pro‐inflammatory effects, both directly and through amplification of the effects of IL‐1β and TNF‐α. IL‐17 is able to induce expression of pro‐inflammatory cytokines and stimulate release of eicosanoids by monocytes and synoviocytes. Furthermore, IL‐17 has been implicated in the pathogenesis of inflammatory bone and joint damage through induction of matrix metalloproteinases and osteoclasts, as well as inhibition of proteoglycan synthesis. In animal models of arthritis, intra‐articular injection of IL‐17 results in joint inflammation and damage. The recognition of IL‐17 as a pro‐inflammatory T cell derived cytokine, and its abundance within rheumatoid joints, provides the strongest candidate mechanism to date through which T cells can capture and localize macrophage effector functions in rheumatoid arthritis. As such, IL‐17 warrants consideration for its potential as a therapeutic target in rheumatoid arthritis.

Determinants of red blood cell methotrexate polyglutamate concentrations in rheumatoid arthritis patients receiving long-term methotrexate treatment.

OBJECTIVE Methotrexate (MTX) is the most commonly used disease-modifying antirheumatic drug (DMARD) in the management of rheumatoid arthritis (RA). MTX is transported into cells, where additional glutamate moieties are added and it is retained as MTX polyglutamates (MTXGlu [referred to as a group as MTXGlun]). There is large interpatient variability in MTXGlun concentrations. This study was undertaken to determine nongenetic factors that influence red blood cell (RBC) MTXGlun concentrations in patients receiving long-term stable low-dose oral MTX. METHODS One hundred ninety-two patients receiving long-term oral MTX for the treatment of RA were recruited. Trough MTXGlun concentrations were measured by high-performance liquid chromatography. Univariate analysis was performed to determine variables influencing MTXGlun concentrations. Backward stepwise multivariate regression analysis was done to determine variables that affect individual MTXGlun concentrations; variables with P values of <0.1 in the univariate analysis for any MTXGlun were included. RESULTS Univariate analysis revealed that increased age, lower estimated glomerular filtration rate (GFR), higher MTX dosage, longer duration of MTX treatment, and use of prednisone were associated with significantly higher MTXGlun concentrations. Smokers had significantly lower concentrations of MTXGlu3, MTXGlu3-5, and MTXGlu1-5. Sex, rheumatoid factor and anti-cyclic citrullinated peptide status, RBC folate level, and body mass index had no significant effect on MTXGlun levels. Concomitant use of other DMARDs was associated with lower MTXGlu2 levels, and treatment with nonsteroidal antiinflammatory drugs was associated with lower MTXGlu3 and MTXGlu1-5 concentrations. Multivariate regression analysis revealed that age, MTX dosage, and estimated GFR were the major determinants of MTXGlun concentrations. CONCLUSION Large interpatient variability in MTXGlun concentrations can be explained, at least in part, by a combination of factors, particularly age, MTX dosage, and renal function. There are complex interactions between smoking, RBC folate levels, and concentrations of MTXGlun.

Methotrexate polyglutamate concentrations are not associated with disease control in rheumatoid arthritis patients receiving long-term methotrexate therapy†

OBJECTIVE There are limited data suggesting that methotrexate polyglutamate (MTXGlu) concentrations can guide MTX dosing in patients with rheumatoid arthritis (RA). The aim of this study was to define a therapeutic range of red blood cell (RBC) MTXGlu(n) concentrations (where n refers to the number of glutamate groups), including threshold values for efficacy and adverse effects in patients receiving long-term oral MTX treatment. METHODS A cross-sectional study of 192 patients receiving oral MTX was undertaken. Disease activity was assessed by the swollen and tender joint counts, the C-reactive protein level, and the Disease Activity Score in 28 joints (DAS28). High disease activity was defined as a DAS28 of >3.2. A standardized questionnaire regarding common MTX adverse effects was completed. RESULTS The MTX dosage was significantly higher in patients in whom the swollen joint count and DAS28 were higher. The MTXGlu(4), MTXGlu(5), MTXGlu(3-5), and MTXGlu(1-5) concentrations were significantly higher in patients with high disease activity. After correction for age, the estimated glomerular filtration rate, and the MTX dosage, the association remained significant for MTXGlu(5). RBC folate concentrations were significantly higher in the group with high disease activity. There was no association between any MTXGlu(n) concentration and adverse effects. CONCLUSION In contrast to other studies, the results of the present study did not show a relationship between the MTXGlu(n) concentration and reduced disease activity in patients with RA who were receiving long-term MTX therapy. However, disease activity was influenced by the RBC folate level, which may be a more important factor than MTXGlu(n) concentrations for disease control. In accordance with the findings of previous studies, we were unable to show a relationship between MTXGlu(n) concentrations and adverse effects. Prospective studies will be important to determine whether there is a role for measuring MTXGlu(n) concentrations in patients receiving long-term treatment with MTX.

Urate crystal deposition in asymptomatic hyperuricaemia and symptomatic gout: a dual energy CT study

Background The aim of this study was to compare the frequency and volume of dual energy CT (DECT) urate deposits in people with asymptomatic hyperuricaemia and symptomatic gout. Methods We analysed DECT scans of the feet from asymptomatic individuals with serum urate ≥540 µmol/L (n=25) and those with crystal proven gout without clinically apparent tophi (n=33). Results DECT urate deposits were observed in 6/25 (24%) participants with asymptomatic hyperuricaemia, 11/14 (79%) with early gout (predefined as disease duration ≤3 years) and 16/19 (84%) with late gout (p<0.001). DECT urate deposition was observed in both joints and tendons in the asymptomatic hyperuricaemia group, but significantly less frequently than in those with gout (p≤0.001 for both joint and tendon sites). The volume of urate deposition was also significantly lower in those with asymptomatic hyperuricaemia, compared with the early and the late gout groups (p<0.01 for both comparisons). Similar urate volumes were observed in the early and late gout groups. Conclusions Although subclinical urate deposition can occur in people with asymptomatic hyperuricaemia, these deposits occur more frequently and at higher volumes in those with symptomatic gout. These data suggest that a threshold of urate crystal volume may be required before symptomatic disease occurs.