69.Calcium channel blocker降血壓藥clevidipine含有何種結構，所以為超短效藥物？
(A)double-ester
(B)dichloro
(C)dimethyl
(D)dihydropyridine

With the exception of clevidipine, all calcium channel blockers undergo extensive first-pass metabolism in the liver and are substrates for the CYP3A4 isozyme (27,29). Additionally, several of these compounds can inhibit CYP3A4. Clevidipine was designed to have an ultra-short duration of action. Upon IV infusion, clevidipine exerts its antihypertensive actions within 2 to 4 minutes. Rapid ester hydrolysis (Fig. 23.27) inactivates the compound and allows it to be used in patients with either renal or hepatic dysfunction without any dosage adjustments (27).

──Foyes 7th P.774

Nifedipine應該是唯一具有對稱酯基，而不是double ester