Table 1.

Definitions of treatment failure

Definition	Patient group	Possible mechanisms
Inadequate response	Patients who fail to reach target SU on allopurinol	Non-adherence Under dosing Partial resistance
Partial resistance	Adherent patients on “standard” allopurinol doses (≤300mg daily) who fail to achieve target SU	Impaired absorption Decreased conversion of allopurinol to oxypurinol Efficient renal excretion of oxypurinol Abnormality in XO structure and or function such that oxypurinol is rendered less effective Drug interactions