PubMed1988
Antituberculous drugs are never used alone but are often given concomitantly with drugs prescribed for other diseases. We have therefore reviewed the potential interactions of antituberculous drugs between themselves and with other drugs. Rifampicin being a potent enzyme inducer will decrease the plasma levels of a wide range of drugs. This in turn will decrease the effectiveness of these drugs if they are unmetabolized and active, or increase drug toxicity if the metabolites are toxic. Within the first category are the oral contraceptives, steroids, oral antidiabetics, oral anticoagulants and digitalis. Within the second category is thought to be isoniazid on account of its hepatotoxicity. In contrast, isoniazid (INH) is an enzyme inhibitor. Drugs with hepatic metabolism will tend to accumulate, although this seems clinically relevant only with antiepileptic drugs, diazepam, triazolam and oral anticoagulants (with high INH doses). Many other cases of drug interaction have been described, but they seem to be rare and may not be clinically relevant. INH and rifampicin do not seem to modify each other's metabolism consistently, but it may be wise to check the serum INH levels during coadministration. As said above, rifampicin does increase the hepatotoxicity of INH. INH also inhibits monoamine oxidase and will interact with other MAOI, as well as with fish, cheese or wine with high histamine or tyramine contents. The only interaction found with ethambutol is with diazepam: it increases its clearance and free fraction. Obviously, streptomycin potentiates the ototoxicity of other amino-glycosides, such as capreomycin, kanamycin or viomycin, so that combining them is strictly contra-indicated.(ABSTRACT TRUNCATED AT 250 WORDS)