The most appropriate next step in management is to switch amlodipine to lisinopril. Based on the normal physical examination findings and laboratory test results, this patient most likely has drug-induced edema caused by the calcium channel blocker amlodipine. Peripheral edema is a common side effect of calcium channel blockers, occurring in up to 25% of patients who take these medications. The risk of developing edema appears to be both dose and treatment duration dependent, with high doses and long treatment times associated with an increased incidence. Drug-induced edema typically resolves after withdrawal of the offending drug. Therefore, the first step in the management of this patient is to discontinue amlodipine and switch to an alternative antihypertensive agent, such as lisinopril.

Compression stockings may help to reduce this patient's edema; however, compression stockings may not be needed if his edema is due to his medication and an acceptable agent could be substituted for amlodipine in his antihypertensive therapy. Additionally, compliance with wearing compression stockings is often low due to the difficulty that patients experience in donning and removing the stockings.

Lower extremity venous duplex ultrasonography may be used in evaluating for the presence of venous thrombosis; however, this patient's clinical presentation and lack of calf tenderness are not consistent with a deep venous thrombosis. Therefore, venous duplex ultrasonography is not necessary or cost effective in this patient.

Diuretics are often used to treat generalized edema caused by cirrhosis or heart failure, as these conditions are associated with total body volume overload. However, the mechanism of lower extremity edema in this patient is associated with the vasodilatory properties of the medication and not volume overload. Therefore, diuretics are only minimally helpful in treating edema caused by calcium channel blockers. Additionally, diuretics may lead to electrolyte abnormalities and kidney dysfunction.