INDICATIONS & DOSAGE
Actively growing tubercle bacilli
Adults: 5 mg/kg P.O. or LM. daily in a single dose, up to 300 mg/day, continued for 6 months to 2 years.
Infants and children: 10 to 20 mg/kg P.O. or LM. daily in a singlc dose, up to 300 mg/day, continued long enough to prevent relapse. CoadministratIOn of at Icast one other antrtubcrculotic IS recommended.
Prevention of tubercle bacilli in those exposed to tuberculosis or those with positive skin test whose chest X -rays and bacteriologic studies are consistent with nonprogressive tuberculosis-
Adults: 300 mg P.O. daily in a single dose, continued for 6 months to1 year.
Infants and children: 10 mg/kg PO. daily in a single dose, up to 300 mg/day, continued for 1year.
CNS: peripheral neuropathy, seizures, toxic enccphalopathy, memory impairment, toxic psychosis.
EENT: optic neuritis and atrophy.
GI: nausea, vomiting, epigastric distress.
Hematologic: agranulocytosis, hemolytic anemia, aplastic anemia, eosll1ophilia, thrombocytopenia, sideroblastic anemia.
Hepatic: hepatitis, jaundicc, elevated serum transaminase levels, bilirubinemia.
Metabolic: hyperglycemia, metabolic acidosis, hypocalcemia, hypophosphatemia.
Skin: irritation at LM. injection site.
Other: rheumatic and lupuslike syndromes, hypersensitivity reactions, pyridoxine deficiency.
Drug-drug. Aluminum-containing antodds and laxatives: may decrease the rate and amount of isoniazid absorbed. lsoni azid is given at least I hour before antacid or laxative.
Benzodiazepines: isoniazid may inhibit the metabolic clearance of benzodiazepincs that undergo oxidative metabolism (diazcpam, triazolam), possibly increasing the activity of the benzodiazepine. Monitor closely.
Carbamazepine, halothane: increased risk of isoniazid hepatotoxicity. Use together cautiously.
Carbamazepine, phenytoin: increased plasma lcvels of these anticonvulsants. Monitor closely.
Cycloserine, meperidine. may increase CNS adverse reactions and hypotension (meperidine only). Safcty precautions should be instituted.
Disulfiram: may cause neurologic symptoms, including changes in behavior and coordination. Avoid concomitant use. b!llurane: in rapid acetylators of isoniazid, high output renal failure may occur becausc of nephrotoxic levels of inorganIC fluoride. Renal function must be monitored.
Ketoconazole: serum concentrations of ketoconazole may be decreased. The patient should be monitored for lack of efficacy.
Oral anticoagulants: anticoagulant activity may be enhanced. Monitor patient closely.
Drug-food. Foods containing tyramine: may cause hypertensivc crisis. Avoid such foods or eat in small quantities.
Drug-lifestyle. Alcohol use: may be associated with increased incidence of isoniazid related hepatitis. Avoid con comitant use.
EFFECTS ON DIAGNOSTIC TESTS
Isoniazid altcrs results of urine glucose tests that use cupric sulfate method (Benedict’s reagent or Diastix)
Contraindicated in patients with acute hepatic disease or isoniazid associated liver damage
• Use cautiously in patients with chronic nonisoniazid-associated liver disease, seizure disorders (especially in those taking phenytoin), severe renal impairment, and chronic alcoholism and in elderly patients.
• Isoniazid must be given with other antituberculotics to prevent the development of resistant organisms.
• Keep in mind that isoniazid pharmacokinetics may vary among patients because drug is metabolized in the liver by genetically controlled acetylation. Fast acety lators metabolize the drug up to five times as fast as slow acetylators. About 50% of blacks and whites are slow acetylators; over 80% of Chinese, Japanese, and Inuits are fast acetylators.
• Peripheral neuropathy is more common in patients who are slow acety lators or who are malnourished, alcoholic, or diabetic.
• Hepatic function must be monitored closely for changes. Elevated liver function study results occur in about 15% of patients; most abnormalities are mild and transient, but some may persist through out treatment.
• Pyridoxine may be given to prevent peripheral neuropathy, especially in mal nourished patients.
• Take drug exactly as prescribed; don’t discontinue it without health care provider’s approval.
• Take drug with food if Gl irritation occurs.
• Notify hcalth care provider immediately if signs and symptoms of liver impairment (anorexia, fatigue, malaise, jaundice, dark urine) occur
• Avoid alcoholic beverages while taking drug. Also, avoid certain foods (fish, such as skipjack and tuna, and tyramine containing products, such as aged cheese, beer, and chocolate) because drug has some MAO inhibitor activity.
• Complete the full course of drug treatment, which may take months or years.
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About the Author
Tablets: 100 mg, 300 mg
Oral solution: 50 mg/5 ml
Injection: 100 mg/ml
Unknown. Appears to inhibit cell-wall biosynthcsis by interfering with lipid and DNA synthesis (bactericidal).