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

Objective 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. Conclusion 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.