Development of multidrug-resistance convertors: sense or nonsense?

This review describes the clinical relevance of the two drug transporters P -glycoprotein (Pgp) and multidrug resistance-associated protein (MRP) and t he in vitro phenomenon which is referred to as multidrug resistance (MDR). The attempts to try to block these resistance mechanisms are summarized wit h specific attention for the intentionally designed "second generation" MDR -convertors. Potential explanations of the limited clinical success rate ar e given and recommendations for the design of future studies provided.