Differential pharmacological regulation of drug efflux and pharmacoresistant schizophrenia.

Pharmacoresistant schizophrenia is a significant impediment to the successful management of the disease. The expression and function of P-glycoprotein (P-gp) has recently been implicated in this phenomenon. P-gp is a multidrug efflux transporter that prevents drug substrates from crossing the blood-brain barrier (BBB). Although the direct interaction between individual antipsychotic agents and P-gp has been demonstrated, the effect of antipsychotic drug combinations used in disease management on P-gp transport function remains to be elucidated. This could have important clinical implications in some individuals as dosage adjustments based on plasma drug concentration changes may not always be appropriate if drug-drug interactions and the resulting changes in drug concentration in the brain are not considered. This paper introduces the potential impact that combination antipsychotic therapy may have on P-gp function at the BBB and discusses the consequences of this in the prevention and circumvention of unfavourable therapeutic response in schizophrenic disorders.