Inh pharmacokinetics

INH is taken orally and penetrates cells to act on intracellular mycobacteria. The liver metabolism of INH is by acetylation and is under genetic control. Patients may be fast or slow inactivators of the drug. It enters CSF. Absorption is impaired if isoniazid is taken with food, particularly carbohydrates, or with aluminum-containing antacids. Infected tissue tends to retain the drug longer. Isoniazid undergoes N acetylation and hydrolysis, resulting in inactive products. INH halflife in fast acetylators is 60–90 min; in slow acetylators it may be 3–4 h. Fast acetylators may require higher dosage than slow acetylators for equivalent therapeutic effects.