Post-hoc analysis of pegloticase pivotal trials in chronic refractory gout: relationship between fluctuations in plasma urate levels and acute flares.

OBJECTIVES: To determine factors associated with gout flares in subjects treated with pegloticase. METHODS: Gout flares from two randomised controlled trials comparing pegloticase (8 mg every 2 weeks [q2] or monthly [q4]) versus placebo were analysed. Responders had persistent urate lowering (<6mg/dL) whereas, non-responders had transient urate lowering during the 6-month RCTs. Gout flares (self-reported) were defined as acute joint pain and swelling requiring treatment. Gout flare prophylaxis (colchicine, 0.6 mg once or twice daily, or a non-steroidal anti-inflammatory drug) was initiated 1 week before the first infusion and continued throughout the study. Plasma urate at the time of flare and the change in urate preceding a flare were analysed. RESULTS: Mean flare rates increased with pegloticase versus placebo during the first 3 months followed by marked reductions during months 4-6. The increase in flares with pegloticase during the first 3 months was most evident (p=0.0006) and the decrease during the second 3 months was least marked (p=0.0006) in subjects receiving monthly pegloticase. Fluctuation in urate levels was highest in monthly responders (p=0.002) and was associated with flare occurrence. Multivariate linear regression analysis indicated the only variables significantly associated with flares were treatment group and absolute change in plasma urate before flares. CONCLUSIONS: Pegloticase treatment increased flares during the first 3 months of treatment in all groups when plasma urate was significantly lowered and was followed by a decline in months 4-6 in patients maintaining a low plasma urate. Flares associated with pegloticase treatment were associated with decreases and fluctuations in plasma urate levels.