[Pharmacokinetic problems in clinical practice: role of drug transporters]

Drug disposition is controlled by drug metabolism and drug transport. In the last decade numerous drug transporters have been identified and characterized in the context of drug uptake, efflux and interactions. This article reviews major advancements in this field. Efflux pumps like the multidrug resistance protein 1 (MDR1, ABCB1) are expressed in the intestine where they secrete drugs back into the intestinal lumen. Inhibitors of ABCB1 can increase the bioavailability of such drugs due to an increased absorption. Inducers of metabolism (rifampicin, carbamazepine, St. John's Wort) also induce the expression of drug transporters like ABCB1. Subsequently, an increased intestinal secretion in addition to an increased metabolism can diminish plasma levels of drugs, for example ciclosporin. The relevance of uptake transporters is increasingly recognized. SLCO1B1 is a hepatic uptake transporter involved in the absorption of statins. Inhibition of SLCO1B1 as well as common genetic variants can lead to increased bioavailability and to adverse reactions, ultimately culminating in rhabdomyolysis.