Efflux transport systems for drugs at the blood-brain barrier and blood-cerebrospinal fluid barrier (Part 1).

Penetration through the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB) is necessary if a drug is to achieve the required concentration for a desired pharmacological effect. Efflux transport systems at the BBB and BCSFB provide a protective barrier function by removing drugs from the brain or cerebrospinal fluid and transferring them to the systemic circulation, respectively; several transporters at the BBB and BCSFB have been identified. Efflux transport should be taken into consideration during drug development to improve brain penetration and to avoid drug-drug interactions involving these transporters and subsequent side effects.