cause of amlodipine induced ankle edema

Cause of edema with vasodilatory drugs is multifactorial. Main reasons are arteriolar vasodilation, activation of RAS, fluid volume retention. Edema is seen in 1:10 pts on amlodipine treatment. It is primarily due to arteriolar vasodilation which causes increase in intracapillary pressure. There is an increase in fluid filtration from vascular compartment to interstitial compartment due to increased intracapillary hydrostatic pressure and /or increased permeability of post capillary venules. This occurs despite a decrease in BP with amlodipine.It is due to dilation of precapillary arterioles.

Precapillary dilation and increase in intracapillary pressure on standing is prevented normally due to myogenic reflex vasoconstriction. CCBs attenuate reflex vasoconstriction and allows increased arteriolar pressure to be transmitted to capillaries and thus cause edema.
CCBs have a direct natriuretic effect, so salt and water retention is less prononced, thus addition of diuretic does not help in reduction of amlodipine induced edema.
Generalized anasarca is rare with Amodipine therapy but very few cases are reported in the literature.