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Isoniazid (INH)

- Indications for Use:
    - for active TB, and the prevention of TB;

- Dosage:
    - IM and IV routes rareley used;
    - adult:
         - 3-5mg/kg/24hr PO qd (up to 300mg/day) for 9 months as combination therapy;
         - prophylaxis: 300mg/kg/24hr PO for 12 months;
    - peds:
         - active TB: 10-20 mg/kg/24hr PO (or IM) upto max dose of 300 mg/24hr for 9 months as combination therapy;
         - prophylaxis: 10 mg/kg/24hr PO for 12 months;

- Cautions:
    - drug induced hepatitis;
           - increased hepatotoxicity may occur w/ concomitant use of rifampin, phenytoin, ETOH, and is more common w/ previous infectious hepatitis;
           - contraindicated with acute liver dz or w/ h/o INH associatted liver damage;
           - in persons younger than 35 years of age, routine monitoring of adverse effects of Isoniazid should consist of monthly symptom review;
           - for persons 35 and older, in addition to monthly symptom reviews, hepatic enzymes should be measured prior to starting INH and periodically through out treatment;
    - peripheral neuropathy:
           - may be caused be interference with metabolism of pyridoxine;
           - alcoholics and diabetics are at higher risk;
           - to prevent peripheral neuropathy can give pyridoxine 50-100mg/day;
    - opthalomologic exam (before and during therapy) is recomended;
    - may cause hallucinations:
    - will increase levels of carbamazepine & phenytoin (look for incr Nystagmus, N, V, ataxia;
    - will incr effects of benzodiazepines;
    - INH will incr effects of oral anticoagulants;
    - may cause hemolysis in pt w/ G6PD deficiency;

- Misc:
    - note: Ratio of CSF to Blood Level (%): NormalMeninges / Inflammed Meninges:  20-90;
    - Dosing Regimens for Patients with Renal Insufficiency: (Dose for 70kgAdult{gm/dosing interval in hours})

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