Situation: The public health nurse makes follow-up home visits to adults enrolled in the barangay registry for hypertension and diabetes. A 60-year-old man with hypertension was started on amlodipine 6 weeks ago. Both ankles are now swollen by evening. His weight is unchanged from the last visit, his lungs are clear, and he has no shortness of breath or difficulty lying flat. What is the MOST likely mechanism of the swelling?

Ankle edema is a common side effect of amlodipine. It comes from arteriolar dilation that raises capillary pressure in the legs, not from retained salt and water, so weight is stable, the lungs are clear, and diuretics help little. The timing after starting the drug and the absence of heart failure signs point to this mechanism; the nurse reports it to the prescriber.

Mechanism of Amlodipine-Induced Ankle Edema

The swelling this patient describes is a classic example of vasodilatory edema, which is a well-recognized adverse effect of dihydropyridine calcium channel blockers such as amlodipine. The key to answering this question correctly is recognizing that the edema is not caused by fluid overload or sodium retention, but by a local hemodynamic change in the microcirculation of the dependent legs.

Pathophysiology: Arteriolar Dilation and Capillary Pressure

Amlodipine selectively blocks L-type calcium channels in vascular smooth muscle, producing arteriolar dilation. This dilation is more pronounced in the precapillary arterioles than in the postcapillary venules. The result is a rise in hydrostatic pressure inside the capillaries of the lower extremities, especially when the patient is upright. Under normal conditions, a protective reflex called postural vasoconstriction constricts these arterioles when standing, which limits the gravitational increase in capillary pressure and prevents fluid from leaking into the interstitial space. Amlodipine blunts this postural vasoconstrictor reflex, so capillary pressure rises and fluid extravasates into the subcutaneous tissue of the ankles and feet ^[1][2].

This explains why the edema is gravity-dependent—it appears by evening after the patient has been upright all day and typically improves overnight with leg elevation. It also explains why the patient’s weight is unchanged, the lungs are clear, and there is no orthopnea or dyspnea. These findings argue strongly against systemic fluid retention or heart failure.

Why the Other Options Are Incorrect

Option	Proposed Mechanism	Why It Does Not Fit This Patient
2. Fluid overload from early heart failure	Increased ventricular filling pressures lead to pulmonary congestion and systemic venous congestion	Lungs are clear; no dyspnea, orthopnea, or weight gain. Edema from heart failure is usually bilateral and accompanied by other signs such as jugular venous distension or crackles.
3. Sodium retention from a high-salt diet	Excess dietary sodium expands extracellular fluid volume	Weight is stable. Dietary sodium excess would produce generalized fluid retention, not isolated evening ankle edema without weight change.
4. Salt and water retention caused by amlodipine	Drug-induced renal sodium retention	Dihydropyridine CCBs are not primarily sodium-retaining agents. Amlodipine does not cause clinically significant renal salt and water retention; the edema is local, not systemic.

Clinical Differentiation: Vasodilatory Edema vs. Fluid Overload

Key point! The most reliable bedside clues that this is vasodilatory edema rather than heart failure or renal sodium retention are the stable body weight and clear lung fields. In true volume overload, weight increases as total body sodium and water accumulate. In amlodipine-induced edema, total body fluid is not increased—fluid is simply redistributed from the intravascular compartment into the interstitial space of the legs ^[3].

The timing is also important. The patient started amlodipine 6 weeks ago, and the edema has developed since then. The onset of dependent edema within weeks of starting a dihydropyridine CCB is consistent with the dose-dependent nature of this adverse effect ^[2][3]. The swelling is typically worse with higher doses and improves when the drug is reduced or discontinued.

Nursing Implications

Watch out! Diuretics are generally not effective for vasodilatory edema because the problem is not sodium or water excess. Giving a loop diuretic may reduce intravascular volume further without resolving the leg edema, and can cause prerenal azotemia or hypotension ^[4]. Management strategies that may help include reducing the amlodipine dose, switching to a non-dihydropyridine CCB, adding an ACE inhibitor or angiotensin receptor blocker to counteract the arteriolar dilation, or using a different antihypertensive class altogether ^[4].

The nurse’s priority is to report the new-onset ankle edema to the prescriber, document the absence of heart failure signs, and monitor for any progression to dyspnea, orthopnea, or weight gain that would suggest an alternative or additional cause. Patient education should include the expected gravity-dependent pattern, the rationale for avoiding excessive diuretic use, and the importance of not stopping amlodipine abruptly without medical guidance.