Pregnancy: Although safe use of isoniazid during pregnancy has not been definitely established, isoniazid has been used to treat clinical tuberculosis in pregnant women. Isoniazid is considered part of the treatment of choice for tuberculosis occurring during pregnancy, as the risk to the mother and fetus of untreated tuberculosis is far greater than treatment of the disease. Prophylactic therapy is best postponed until after delivery, unless the woman is positive for HIV infection and has evidence of tuberculosis infection.
Lactation: No adverse effects have been reported, but there is a potential risk of peripheral neuritis or hepatic damage. Breast-fed infants should be carefully observed for evidence of adverse effects.