The effects of antimuscarinic agents such as orphenadrine maybe enhanced by other drugs with antimuscarinic properties such as amantadine, some antihistamines, butyrophenones and phenothiazines, and tricyclic antidepressants. The potential hepatoxicity of paracetamol may be increased by large dose or long-term administration of the following agents because of hepatic microsomal enzyme induction: barbiturates, carbamazepine, hydantoin, isoniazid, rifampin, sulfinpyrazone.