The bioavailability of two commercial preparations of allopurinol tablets

The relative bioavailability of two commercial preparations of 100 mg and 300 mg allopurinol tablets was examined in two groups of 16 healthy human subjects, one for each dosage level. Serum concentrations of allopurinol and its major metabolite, oxypurinol, were measured using a competitive protein-binding assay. After single doses of allopurinol, no significant differences between brands were revealed in the resultant serum levels of the drug or the metabolite, or in the relevant pharmacokinetic parameters. Serum oxypurinol levels were higher and more persistent than those of the parent drug. A comparison of the serum concentration profiles after 100 mg and 300 mg doses suggests that allopurinol absorption in humans may be dose dependent.