epirubicin + quinidine

Epirubicin + quinidine is an investigational combination of two small molecule drugs, epirubicin and quinidine, studied primarily in the context of advanced breast cancer. Epirubicin is an anthracycline antineoplastic agent that intercalates DNA and inhibits topoisomerase II, leading to cytotoxicity in rapidly dividing cells. Quinidine is a class Ia antiarrhythmic agent that blocks sodium channels and also acts as a P-glycoprotein inhibitor; it was investigated for its potential to reverse multidrug resistance (MDR) by inhibiting drug efflux pumps such as P-glycoprotein (MDR1), thereby increasing intracellular concentrations of chemotherapeutic agents like epirubicin. Clinical studies have shown that while this combination achieves plasma levels of quinidine sufficient to modulate MDR in vitro, it does not significantly alter the toxicity profile or efficacy outcomes compared with epirubicin alone in patients with advanced breast cancer[1][2].