Neuropsychiatric Effects of Antimicrobial Agents

Antimicrobial drugs used in clinical practice are selected on the basis of their selective toxicity against bacterial cells. However, all exhibit multiple offsite interactions with eukaryotic cell structures, resulting in adverse reactions during antimicrobial pharmacotherapy. A multitude of these side effects involve the nervous system as antimicrobials at clinically relevant concentrations seem to interact with many of the same molecules usually implicated in the action of psychotropic drugs. The importance of such events cannot be overstated, as the misdiagnosis of an adverse drug reaction as a symptom of a primary psychiatric or neurological disorder entails great suffering for the patient affected as well as significant costs for the healthcare system. The neuropsychiatric effects of antimicrobial drugs are extensively documented in the literature. A number of antimicrobial drugs have the potential to exert CNS effects and many are associated with stimulant, psychotomimetic and epileptogenic properties, mediated by GABA antagonism (beta-lactams, quinolones and clarithromycin), NMDA agonism (d-cycloserine, aminoglycosides, and perhaps quinolones), MAO inhibition (linezolid, metronidazole and isoniazid weakly) as well as more exotic mechanisms, as in the case of trimethoprim, isoniazid, ethambutol, rifampicin and the tetracyclines. While those effects are generally undesirable, they may also under certain circumstances be beneficial, and further research is warranted in that direction.