Rifampin, ampicillin, penicillin V, tetracyclines, neomycin, chloramphenicol, sulfonamides, nitrofurantoin, barbiturates, phenylbutazone, meprobamate, phenacetin, pyrazolone-containing analgesics, chlorpromazine, dihydroergotamine, chlordiazepoxide; antihypertensives, anticonvulsants, oral anticoagulants, hypoglycemic agents; theophyllines, phenothiazines, corticosteroids, β-adrenergic antagonists, TCAs, caffeine, cyclosporin. Increased sedative effect w/ diazepam & chlordiazepoxide.