Pharmacologic Class: Mycolic acid inhibitor
Actions and uses: Isoniazid is a first-line drug for the treatment of M. tuberculosis because decades of experience have shown it to have a superior safety profile and to be the most effective, single drug for the infection. The drug acts by inhibiting the synthesis of mycolic acids, which are essential components of mycobacterial cell walls. It is bacteriocidal for actively growing organisms but bacteriostatic for dormant mycobacteria. It is selective for M. tuberculosis. Isoniazid may be used alone for chemoprophylaxis, or in combination with other antituberculosis drugs for treating active disease. Approximately 10% of patients will develop resistance to isoniazid during long-term therapy.
Administration alerts: Give on an empty stomach, 1 hour after or 2 hours before meals. For IM administration, administer deep IM, and rotate sites. The drug is pregnancy category C.
Adverse effects: The most common adverse effects of isoniazid are numbness of the hands and feet, rash, and fever. Neurotoxicity is a concern during therapy, and patients may exhibit paresthesia of the feet and hands, convulsions, optic neuritis, dizziness, coma, memory loss, and various psychoses.
Warning: Although rare, hepatotoxicity is a serious and sometimes fatal adverse effect; thus, the patient should be monitored carefully for jaundice, fatigue, elevated hepatic enzymes, or loss of appetite. Liver enzyme tests are usually performed monthly during therapy to identify early hepatotoxicity. Hepatotoxicity usually appears in the first 1 to 3 months of therapy but may occur at any time during treatment. Older adults and those with daily alcohol consumption are at greater risk of developing hepatotoxicity.
Contraindications: Isoniazid is contraindicated in patients with hypersensitivity to the drug and in patients with severe hepatic impairment.
Interactions: Drug–Drug: Aluminum-containing antacids should not be administered concurrently because they can decrease the absorption of isoniazid. When disulfiram is taken with INH, lack of coordination or psychotic reactions may result. Drinking alcohol with INH increases the risk of hepatotoxicity. Isoniazid may increase serum levels of phenytoin and carbamazepine.
Treatment of Overdose: Isoniazid overdose may be fatal. Treatment is mostly symptomatic. Pyridoxine (vitamin B6) may be infused in a dose equal to that of the isoniazid overdose to prevent seizures and to correct metabolic acidosis. The dose may be repeated several times until the patient regains consciousness
RELATED;
1. DRUG USE IN RELATION TO PREGNANCY
2. TUBERCULOSIS
3. ETHAMBUTOR
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