Drug-drug interactions of antibiotics and psychotropic medication

By and large, pharmacokinetic interactions are described: macrolide antibiotics, isoniazid, ciprofloxacin and ampicillin can lead to toxic concentrations of psychotropic drugs, while rifampicin causes subtherapeutic levels. Vice versa, carbamazepine might induce subtherapeutic plasma concentrations of doxycycline. These interactions are caused by inhibition or induction of the hepatic cytochrome P450 enzyme system. Case reports suggest lithium intoxication through concomitant use of tetracycline, metronidazol and spectinomycin, which is contradicted by animal studies. Clinical symptoms depend on the therapeutic index of a given drug, e.g. toxic and subtherapeutic levels are described for clozapine but not for haloperidol. No relevant pharmacodynamic drug-drug interactions are described, although, the author emphasises psychiatric side effects of macrolide antibiotics, isoniazid, beta-lactam antibiotics and fluoroquinolones. On the whole, drug-drug interactions of antibiotics and psychotropics seem rare and usually benign, though more subtle interactions might be overlooked.