What is the equivalent losartan dose for a patient currently on irbesartan 75 mg daily and how should the medication be switched and monitored?

Conversion from Irbesartan 75 mg to Losartan

Switch directly to losartan 50 mg once daily, then titrate to 100 mg daily after 2–4 weeks if blood pressure remains ≥140/90 mmHg. 1, 2

Dose Equivalence Rationale

• Irbesartan 75 mg is a sub-therapeutic dose (below the FDA-approved starting dose of 150 mg), so direct conversion requires clinical judgment rather than strict equivalence. 2
• Losartan 50 mg once daily is the standard starting dose for hypertension and represents a reasonable initial conversion point from low-dose irbesartan. 1
• Clinical trial data demonstrate that irbesartan 150–300 mg produces significantly greater blood pressure reductions than losartan 50–100 mg, indicating irbesartan is more potent milligram-per-milligram. 3, 4
• Given the patient is on only 75 mg irbesartan (half the standard starting dose), losartan 50 mg provides comparable or slightly greater AT1 receptor blockade. 5, 6

Switching Protocol

• Discontinue irbesartan and start losartan 50 mg the following day; no washout period is required because both drugs have similar pharmacokinetic profiles with once-daily dosing. 1, 2
• Losartan may be taken with or without food at any convenient time of day to promote adherence. 1
• After 2–4 weeks, if office or home blood pressure remains ≥140/90 mmHg, increase to losartan 100 mg once daily, which is the maximum recommended dose for hypertension. 1, 7

Monitoring Schedule

• Check blood pressure within 2–4 weeks after the switch to assess individual response and determine whether dose titration is needed. 8, 7
• Measure serum creatinine/eGFR and potassium within 1–2 weeks after initiating losartan, particularly if the patient has diabetes, chronic kidney disease, or is on potassium-sparing agents. 7
• Re-evaluate blood pressure every 2–4 weeks during titration, aiming for a target of <130/80 mmHg within three months of therapy initiation. 7

Target Dosing for Optimal Outcomes

• The target losartan dose for hypertension is 100 mg once daily; higher doses provide better cardiovascular outcomes than lower doses. 7, 1
• If blood pressure remains uncontrolled on losartan 100 mg daily after appropriate titration, add hydrochlorothiazide 12.5–25 mg once daily rather than exceeding the maximum losartan dose. 7, 1

Critical Safety Considerations

• Never combine losartan with ACE inhibitors or direct renin inhibitors (e.g., aliskiren), as dual RAAS blockade increases the risk of hyperkalemia, syncope, and acute kidney injury without added cardiovascular benefit. 7, 8
• Losartan is absolutely contraindicated in pregnancy; discontinue immediately if pregnancy is detected and switch to pregnancy-compatible antihypertensives such as methyldopa, labetalol, or extended-release nifedipine. 7, 8
• Monitor for hyperkalemia, especially in patients with chronic kidney disease, diabetes, or those on potassium supplements or potassium-sparing diuretics. 7, 8

Common Pitfalls to Avoid

• Do not assume 1:1 dose equivalence between irbesartan and losartan; irbesartan is more potent per milligram, so a lower losartan dose may be appropriate initially. 3, 4
• Do not delay titration to target doses; underdosing is widespread in clinical practice, with less than 25% of patients ever reaching target doses despite evidence that higher doses provide greater benefit. 7
• Do not rely solely on monotherapy dose escalation; if blood pressure remains uncontrolled on losartan 100 mg, add a thiazide diuretic or calcium-channel blocker rather than switching to another ARB. 7