Interaction between allopurinol and pyrazinamide.

Pyrazinamide (PZA) is increasingly used with isoniazid and rifampicin, in short-course antituberculous chemotherapy in service programme conditions. Complicating arthralgias occur due to hyperuricaemia induced by the inhibition of renal tubular secretion of uric acid by pyrazinoic acid, the main PZA metabolite. Allopurinol (Al), a hypouricaemic agent, provides no substantial clinical improvement. Pharmacokinetics of PZA and its metabolites were studied in six healthy volunteers, in a cross-over design, after a single oral dose of PZA alone and, in a second trial, after the same dose together with Al. Plasma and urinary concentrations were measured by high pressure liquid chromatography with a column of cation exchange resin. Analysis of the pharmacokinetic parameters showed that Al induced marked changes in levels of PZA metabolites and accumulation of pyrazinoic acid. Despite decreasing uric acid synthesis, allopurinol increased plasma concentrations of pyrazinoic acid, which is directly responsible for the inhibition of renal urate secretion. Other drugs, which do not involve xanthine oxidase inhibition, should be used in the treatment of this side effect of chemotherapy.