Quinidine sulfate dihydrate is a diastereomer of quinine and a Na+ channel blocker. It is also a class I antiarrhythmic drug. It is a substrate (0.05 μM in Caco-2 cells) of P-glycoprotein and can also act as an inhibitor at higher concentrations (~2 μM in Caco-2 cells). Quinidine is also an inhibitor of the cytochrome P450 enzymes 2D6/3A4, and can lead to increased blood levels of lidocaine, Beta blockers, opioids, and some anti-depressants. MW: 782.9. Purity ≥97% by HPLC