Table II. Examples of drug-drug interactions involving drug transporters. MDR, multidrug resistance; CNS, centra! nervous system; OCT, organic cation transporter; OATP, organic anion transporting peptide; OAT, organic ion transporter.

Drug - substrate	Inhibitor / inducer	Interaction	Effect
Loperamide	Quinidine	MDR1 inhibition	Increased CMS penetration of loperamide37
Digoxin	Paroxetine	MDR1 inhibition	Increased CNS penetration of digoxin75
Cyclosporins	St John's wort	MDR1 induction	Decreased plasma level of cyclosporine91
Desipramine	Ritonavir	OCT1 inhibition	Decreased hepatic uptake with poorer access to CYP3A492
Fexofenadine	Fruit juices	OATP inhibition	Decreased oral bioavailability93
Penicillin	Probenecid	OAT inhibition	Prolonged penicillin half-life by reduced renal clearance81