What captopril dose is equivalent to lisinopril 5 mg taken once daily?

Captopril Dose Equivalent to Lisinopril 5 mg

For a patient taking lisinopril 5 mg once daily, convert to captopril 25 mg three times daily (total 75 mg/day), using the established 5:1 conversion ratio.

Conversion Ratio and Dosing Equivalence

• The conversion from captopril to lisinopril follows a 5:1 daily dosage ratio, meaning 5 mg of captopril is equivalent to 1 mg of lisinopril. 1
• A prospective randomized trial demonstrated that converting from captopril to lisinopril at this 5:1 ratio maintained comparable blood pressure control in patients with mild-to-moderate hypertension. 1
• For lisinopril 5 mg once daily, the equivalent captopril dose is 25 mg three times daily (total daily dose of 75 mg captopril = 15 mg lisinopril equivalent, but starting at the 5:1 ratio from the baseline 5 mg lisinopril). 1

Guideline-Supported Dosing Regimens

Captopril Dosing

• ACC/AHA guidelines recommend starting captopril at 6.25 or 12.5 mg three times daily and gradually titrating to 50 mg three times daily for heart failure. 2
• The target maintenance dose range for captopril in hypertension is 25–50 mg three times daily. 2
• In the SAVE trial, the mean daily captopril dose was 127 mg, demonstrating that higher doses provide mortality benefit in patients with left ventricular dysfunction. 2

Lisinopril Dosing

• Lisinopril 5 mg once daily is an appropriate starting dose, particularly in elderly patients or those not on diuretics. 3
• The ATLAS trial compared low-dose lisinopril (2.5–5 mg daily) versus high-dose lisinopril (32.5–35 mg daily), with higher doses showing superior outcomes. 2
• Maintenance doses of lisinopril range from 5–20 mg daily for hypertension and heart failure. 2

Practical Conversion Algorithm

1. Calculate the equivalent daily dose: Multiply lisinopril 5 mg by 5 to get 25 mg total daily captopril dose.
2. Divide into three daily doses: Captopril requires three-times-daily dosing due to its shorter half-life, so prescribe 8.3 mg three times daily (round to practical dosing of 6.25 mg or 12.5 mg TID). 1, 4
3. Start conservatively: Begin with captopril 6.25 mg three times daily and titrate to 12.5–25 mg three times daily based on blood pressure response. 2
4. Monitor within 1–2 weeks: Check blood pressure, serum creatinine, and potassium levels after conversion. 2

Clinical Considerations

Pharmacokinetic Differences

• Lisinopril has a longer half-life and provides 24-hour blood pressure control with once-daily dosing, whereas captopril requires three-times-daily administration. 4
• A head-to-head trial showed that once-daily lisinopril was more effective than twice-daily captopril in reducing 24-hour ambulatory blood pressure, with captopril showing two blood pressure troughs during the dosing interval. 4
• In heart failure patients, lisinopril produced greater improvement in exercise duration and left ventricular ejection fraction compared to captopril, particularly in those with renal impairment or severely reduced ejection fraction (<35%). 5

Titration Strategy

• Avoid excessive diuresis before initiating ACE inhibitor therapy, and consider reducing or withholding diuretics for 24 hours before starting captopril. 2
• Increase captopril dose gradually at 5–7 day intervals, rechecking potassium and creatinine after each dose adjustment until values stabilize. 2
• The target captopril dose for optimal outcomes in heart failure is 50 mg three times daily (150 mg/day total). 2

Monitoring Requirements

• Recheck blood pressure 5–7 days after conversion to assess efficacy and detect hypotension. 2
• Monitor renal function and electrolytes within 1 week of conversion, then at 3 months, and subsequently every 6 months. 2
• Avoid potassium-sparing diuretics during the initiation phase to prevent hyperkalemia. 2
• Avoid NSAIDs and COX-2 inhibitors, which can blunt ACE inhibitor efficacy and worsen renal function. 2

Common Pitfalls to Avoid

• Do not use twice-daily captopril dosing as a substitute for three-times-daily dosing; the shorter half-life requires TID administration for consistent 24-hour blood pressure control. 4
• Do not underdose captopril; the conversion ratio of 5:1 is well-established, and using lower doses may result in inadequate blood pressure control. 1
• Do not combine captopril with other ACE inhibitors or ARBs, as dual RAAS blockade increases the risk of hyperkalemia, syncope, and acute kidney injury without added benefit. 2
• Recognize that lisinopril offers superior convenience with once-daily dosing and may provide better 24-hour blood pressure control than captopril, so conversion from lisinopril to captopril should only be done when clinically necessary (e.g., cost, availability, or specific patient factors). 1, 4