How should I transition a patient on lisinopril 30 mg daily (angiotensin‑converting enzyme inhibitor) to losartan (angiotensin‑II receptor blocker), including the appropriate losartan dose, wash‑out interval, and necessary monitoring of blood pressure, renal function, and electrolytes?

Transitioning from Lisinopril 30 mg to Losartan

Switch directly from lisinopril 30 mg to losartan 100 mg once daily without a washout period, then monitor blood pressure, renal function, and potassium within 1–2 weeks.

Equivalent Dosing and Rationale

• Lisinopril 30 mg daily corresponds to losartan 100 mg once daily based on target dosing for heart failure and hypertension; both represent high therapeutic doses within their respective classes. 1, 2
• The target dose of losartan for optimal cardiovascular outcomes is 100 mg once daily for hypertension and heart failure with reduced ejection fraction, with evidence showing that higher doses (100–150 mg) provide superior benefits compared to 50 mg. 1, 3
• Lisinopril 30 mg exceeds the standard target of 20–35 mg for heart failure, indicating your patient requires robust renin‑angiotensin system blockade; losartan 100 mg delivers comparable AT₁ receptor antagonism. 2

Switching Protocol: No Washout Required

• Discontinue lisinopril and start losartan 100 mg the following day—no washout interval is necessary because both agents block the same pathway and the risk of rebound hypertension or clinical deterioration outweighs any theoretical concern about overlapping effects. 1
• ACE inhibitors and ARBs should never be combined because dual renin‑angiotensin system blockade increases hyperkalemia, syncope, and acute kidney injury by 2–3‑fold without added cardiovascular benefit. 1, 4
• Losartan reaches peak plasma concentration 1–2 hours after administration, and its active metabolite E‑3174 (which is 10–40 times more potent) has a half‑life of 6–9 hours, providing effective 24‑hour AT₁ receptor blockade at the 100 mg dose. 5, 3

Monitoring Requirements

Timing of Laboratory Checks

• Measure serum creatinine, eGFR, and potassium within 1–2 weeks after the switch to detect early renal or electrolyte changes. 1
• Recheck these parameters again at 3 months, then every 6 months during maintenance therapy. 1

Expected and Acceptable Changes

• A modest, transient rise in serum creatinine of 0.1–0.3 mg/dL is common and reflects hemodynamic adjustment (reduced efferent arteriolar tone) rather than tubular injury; do not discontinue losartan unless creatinine increases by ≥100% or exceeds 4 mg/dL. 1, 4
• An increase in creatinine up to 50% above baseline or to 3 mg/dL is acceptable; beyond this threshold, seek specialist advice. 1

Blood Pressure Monitoring

• Assess office blood pressure every 2–4 weeks after the switch, aiming for a target of <130/80 mmHg in most adults. 1
• In elderly or frail patients, measure blood pressure in both seated and standing positions (at 1 minute and 3 minutes after standing) to detect orthostatic hypotension. 1
• Asymptomatic hypotension does not require dose reduction; if symptomatic hypotension occurs, consider reducing diuretic dose before lowering losartan. 1

Potassium Surveillance

• Hyperkalemia risk is highest in patients with chronic kidney disease, diabetes, or those receiving potassium‑sparing diuretics or supplements; monitor potassium closely in these populations. 1
• If potassium rises to >5.0 mmol/L, avoid potassium supplements and "low‑salt" substitutes with high potassium content, and consider adding or increasing loop diuretics. 1

Dosing Considerations and Titration

• Losartan 100 mg once daily is the maximum recommended dose for hypertension; it can be administered as a single daily dose or split into 50 mg twice daily if more consistent 24‑hour coverage is needed. 1, 5
• For heart failure with reduced ejection fraction, the target dose is 100–150 mg daily; the HEAAL trial demonstrated that 150 mg was superior to 50 mg, with a 10% relative risk reduction in death or heart failure hospitalization. 1
• Do not underdose—less than 25% of patients in clinical practice are titrated to target doses, which compromises efficacy; aim for at least 50% of the target dose (50 mg daily) as the minimum effective threshold. 1

Combination Therapy if Blood Pressure Remains Uncontrolled

• If blood pressure remains ≥140/90 mmHg on losartan 100 mg after 4–8 weeks, add hydrochlorothiazide 12.5–25 mg once daily rather than exceeding the maximum losartan dose. 1
• For grade 2 hypertension (≥160/100 mmHg), consider initiating two agents from the outset (e.g., losartan plus a thiazide diuretic or a dihydropyridine calcium‑channel blocker). 1
• If triple therapy is required, add a dihydropyridine calcium‑channel blocker (e.g., amlodipine 5–10 mg) to the ARB‑diuretic combination. 1

Critical Safety Precautions

• Absolute contraindications to losartan include pregnancy (all trimesters), history of ARB‑induced angioedema, and severe bilateral renal‑artery stenosis. 1
• Avoid NSAIDs unless essential, as they attenuate losartan's antihypertensive effect and worsen renal function. 6, 1
• Discontinue losartan immediately if angioedema occurs; although less common than with ACE inhibitors, ARB‑induced angioedema is a serious adverse event. 1
• Patients with mild‑to‑moderate hepatic impairment should start at 25 mg once daily because plasma concentrations are approximately five‑fold higher than in healthy individuals. 1

Common Pitfalls to Avoid

• Do not restart at a lower dose (e.g., 50 mg) when the patient was stable on a high‑dose ACE inhibitor; this leads to underdosing and suboptimal outcomes. 1, 3
• Do not delay the switch by inserting an unnecessary washout period; continuous renin‑angiotensin system blockade is essential for patients with hypertension or heart failure. 1
• Do not stop losartan prematurely for mild hyperkalemia; implement potassium‑lowering strategies (discontinue supplements, add loop diuretics) before discontinuing the medication. 1
• Do not combine losartan with an ACE inhibitor or direct renin inhibitor (aliskiren); this is contraindicated and increases adverse events without improving outcomes. 1, 4