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isoniazid (eye-soe-nye-a-zid)

INH, imageIsotamine, Nydrazid, imagePMS Isoniazid, Laniazid


Therapeutic: antituberculars


First-line therapy of active tuberculosis, in combination with other agents. Prevention of tuberculosis in patients exposed to active disease (alone).


Inhibits mycobacterial cell wall synthesis and interferes with metabolism. Therapeutic Effects: Bacteriostatic or bactericidal action against susceptible mycobacteria.

Adverse Reactions/Side Effects

CNS: psychosis, seizures. EENT: visual disturbances. GI: DRUG-INDUCED HEPATITIS, nausea, vomiting. Derm: rashes. Endo: gynecomastia. Hemat: blood dyscrasias. Neuro: peripheral neuropathy. Misc: fever.


Examination and Evaluation

  • Be alert for signs of drug-induced hepatitis, including anorexia, abdominal pain, severe nausea and vomiting, yellow skin or eyes, fever, sore throat, malaise, weakness, facial edema, lethargy, and unusual bleeding or bruising. Report these signs to the physician or nursing staff immediately.

  • Watch for seizures; notify physician immediately if patient develops or increases seizure activity.

  • Be alert for signs of peripheral neuropathy (numbness, tingling, decreased muscle strength). Establish baseline electroneuromyographic values at the beginning of drug treatment whenever possible, and reexamine these values periodically to document drug-induced changes in peripheral nerve function.

  • Monitor psychosis or other alterations in mental status. Notify the physician promptly if these symptoms develop (See Appendix D)

  • Monitor signs of blood dyscrasias such as leukopenia (fever, sore throat, signs of infection), thrombocytopenia (bruising, nose bleeds and bleeding gums), or unusual weakness and fatigue that might be due to anemia. Report these signs to the physician.


  • Always wash hands thoroughly and disinfect equipment (whirlpools, electrotherapeutic devices, treatment tables, and so forth) to help prevent the spread of infection. Employ universal precautions or isolation procedures as indicated for specific patients.

Patient/Client-Related Instruction

  • Instruct patient and family/caregivers to report other troublesome side effects such as severe or prolonged fever, skin rash, vision problems, breast enlargement in men, or GI problems (nausea, vomiting).


Absorption: Well absorbed following PO/IM administration.

Distribution: Widely distributed; readily crosses the blood-brain barrier. Crosses the placenta; enters breast milk in concentrations equal to plasma.

Metabolism and Excretion: 50% metabolized by the liver at rates that vary widely among individuals; 50% excreted unchanged by the kidneys.

Half-life: 1–4 hr.

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TIME/ACTION PROFILE (blood levels)

PO rapid 1–2 hr up to 24 hr
IM rapid 1–2 hr up to 24 hr


Contraindicated in: Hypersensitivity; Acute liver disease; Previous hepatitis from isoniazid.

Use Cautiously in: History of liver damage or chronic alcohol ingestion; ...

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