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All drugs should be stopped and an evaluation made at the first sign of a hypersensitivity reaction. If isoniazid therapy must be reinstituted, the drug should be given only after symptoms have cleared. The drug should be restarted in very small and gradually increasing doses and should be withdrawn immediately if there is any indication of recurrent hypersensitivity reaction Use of isoniazid should be carefully monitored in the following:
- Daily users of alcohol. Daily ingestion of alcohol may be associated with a higher incidence of + isoniazid hepatitis.
- Patients with active chronic liver disease or severe renal dysfunction
- Age > 35.
- Concurrent use of any chronically administered medication
- History of previous discontinuation of isoniazid
- Existence of peripheral neuropathy or conditions predisposing to neuropathy
- Injection drug use
- Women belonging to minority groups, particularly in the postpartum period
- HIV seropositive patients.
Because there is a higher frequency of isoniazid associated hepatitis among certain patient groups including Age > 35, daily users of alcohol, chronic liver disease, injection drug use and women belonging to minority groups, particularly in the post-partum period, transaminase measurements should be obtained prior to starting and monthly during preventative therapy, or more frequently as needed. If any of the values exceed three to five times the upper limit of normal, isoniazid should be temporarily discontinued and consideration given to restarting therapy.
Carcinogenesis and Mutagenesis
Isoniazid has been shown to induce pulmonary tumors in a number of strains of mice. Isoniazid has not been shown to be carcinogenic in humans. (Note: a diagnosis of mesothelioma in a child with prenatal exposure to isoniazid and no other apparent risk factors has been reported). Isoniazid has been found to be weakly mutagenic in strains TA 100 and TA 1535 of Salmonella typhimurium (Ames assay) without metabolic activation.
Teratogenic effects: Pregnancy Category C: Isoniazid has been shown to have an embryocidal effect in rats and rabbits when given orally during pregnancy. Isoniazid was not teratogenic in reproduction studies in mice, rats and rabbits. There are no adequate and well-controlled studies in pregnant women. Isoniazid should be used as a treatment for active tuberculosis during pregnancy because the benefit justifies the potential risk to the fetus. The benefit of preventive therapy also should be weighed against a possible risk to the fetus. Preventive therapy generally should be started after delivery to prevent putting the fetus at risk of exposure; the low levels of isoniazid in breast milk do not threaten the neonate. Since isoniazid is known to cross the placental barrier, neonates of isoniazid treated mothers should be carefully observed for any evidence of adverse effects.
Nonteratogenic effects: Since isoniazid is known to cross the placental barrier, neonates of isoniazid- treated mothers should be carefully observed for any evidence of adverse effects.
The small concentrations of isoniazid in breast milk do not produce toxicity in the nursing newborn; therefore, breast feeding should not be discouraged. However, because levels of isoniazid are so low in breast milk, they can not be relied upon for prophylaxis or therapy of nursing infants.
Last reviewed on RxList: 1/11/2008
This monograph has been modified to include the generic and brand name in many instances.
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