Reduction of isoniazid bioavailability in normal men by concomitant intake of food.

The influence of food intake on the bioavailability of isoniazid (INH) has been examined in nine healthy male volunteers. INH was administered as a single oral dose, both in fasting state and together with a standardized breakfast. Numerous venous blood samples were obtained 5 min-6 hours after the INH ingestion, and the concentrations of unmetabolized INH in serum were assessed by spectrophotometry. The observations indicate that both the peak concentration and the total amount of INH absorbed are greatly reduced when the drug is ingested together with food. Hence it is recommended that, in the treatment of tuberculosis with INH, the drug should be given on an empty stomach. The data may also have some bearing on the use of INH for assessing acetylation rates and estimating dosages of hydralazine and related drugs.