Pyridoxine and isoniazid

Blood urate concentrations can be increased because of reduced excretion of uric acid in patients taking ethambutol (390). This is probably enhanced by combined treatment with isoniazid and pyridoxine. Special attention should be paid when tuberculostatic drug combinations include pyrazinamide. However, severe untoward clinical effects are rare, except in patients with gout or renal insufficiency (391,392). 

Therapy with ethambutol results in an increased concentration of urate in the blood in about 50% of patients, owing to decreased renal excretion of uric acid. The effect may be detectable as early as 24 hours after a single dose or as late as 90 days after treatment is started. This untoward effect is possibly enhanced by isoniazid and pyridoxine. 

This report is consistent with another much earlier report of two patients who also developed peripheral neurotoxicity when they were given vincristine after starting to take isoniazid and pyridoxine, the cumulative doses of vincristine being 11 mg and 11.2 mg, respectively, and of a case of severe neurotoxicity with an overdose of isoniazid and high-dose vincristine. ... 

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