Isoniazid (Laniazid) Systemic Anti-infectives Antituberculosal agents Treatment and prevention of Tuberculosis (a chronic Lung Infection) Use in combination with other drugs. (Adults) 5 mg/kg/day; max 300 mg/day. (Infants and children) 10 to 20 mg/kg/day; max 300 mg/day, take on empty stomach. Category C Leg pain, nausea, hepatitis, hypersensitivity reactions. Pregnancy Risk Categories defined: A: Studies in pregnant women failed to show a risk to the fetus in the first trimester - with no evidence of risk in the later trimesters. B: Animals studies indicate no adverse effect to the fetus, but there are no adequate, clinical studies in pregnant women. C: Animal studies have shown an adverse effect on the fetus, but there are no adequate, clinical studies in humans. Despite potential risks, the drug may be useful in pregnant women. D: There is evidence of risk to the human fetus, but the potential benefits of use in pregnant women may be acceptable, despite potential risks. X: Studies in animals or humans show fetal abnormalities, or adverse reaction reports indicate evidence of fetal risk. Warning: the risks involved clearly outweigh any potential benefit from using the drug in pregnant women, regardless of trimester. NR: Not rated (i.e., no information available at this time as to the potential risks or benefits).