Adults

Typically 1 tablet daily for adults weighing 50 kg or more, or as directed by a physician, usually part of a multi-drug regimen.

Elderly

Similar to adult dosage, with careful monitoring for renal and hepatic function, and potential dose adjustment based on tolerance and comorbidities.

Renal_impairment

Dose adjustment for Isoniazid may be necessary in severe renal impairment (CrCl <30 mL/min). Rifampicin generally does not require dose adjustment in renal impairment but caution is advised.

Onset

Rapid onset of bactericidal action, usually within hours of administration.

Excretion

Rifampicin is primarily excreted via bile into feces, with some renal excretion. Isoniazid is primarily excreted in the urine.

Half life

Rifampicin: 2-5 hours. Isoniazid: 1-4 hours (dependent on acetylator status).

Absorption

Rifampicin is well absorbed orally, but absorption is reduced when taken with food. Isoniazid is rapidly and completely absorbed after oral administration, typically not affected by food.

Metabolism

Both are primarily metabolized in the liver. Rifampicin undergoes deacetylation and induces its own metabolism. Isoniazid is metabolized primarily by N-acetylation.

Alcohol

Increases risk of hepatotoxicity.

Warfarin

Rifampicin can decrease warfarin levels, requiring increased warfarin dose. Isoniazid can increase warfarin levels, increasing bleeding risk.

Oral Contraceptives

Rifampicin significantly reduces the efficacy of oral contraceptives. Advise alternative birth control methods.

Antiretrovirals (e.g., Protease Inhibitors, NNRTIs)

Significant interactions, requiring careful monitoring and potential dose adjustments or alternative regimens.