Rifampicin, INH, ampicillin, tetracycline, neomycin, penicillin, chloramphenicol, sulphonamides, nitrofurantoin, barbiturates, phenytoin, primidone, analgesics, tranquiliser, antimigraine prep & antihistamines. Oral anticoagulants, anticonvulsants, TCAs, antihypertensives (eg guanethidine), vit, hypoglycaemic agents, hypnotic prep & theophylline.