Direct Conversion from Enalapril 20mg BID to Lisinopril
Switch enalapril 20mg twice daily to lisinopril 20mg once daily as a direct 1:1 total daily dose conversion (40mg enalapril daily = 20-40mg lisinopril daily). Start with lisinopril 20mg once daily and titrate up to 40mg once daily if needed for blood pressure control.
Conversion Algorithm
Step 1: Calculate Total Daily Dose
- Current regimen: Enalapril 20mg BID = 40mg total daily
- Target lisinopril dose: 20-40mg once daily
Step 2: Initial Lisinopril Dosing
Start with lisinopril 20mg once daily 1. The FDA labeling recommends 10-40mg once daily as the usual dosage range for hypertension, with doses up to 80mg studied (though not providing greater effect) 1.
Step 3: Monitoring and Titration
- Check blood pressure in 1 month after conversion 2
- If blood pressure remains uncontrolled, increase to lisinopril 40mg once daily
- Both drugs are ACE inhibitors with equivalent class effects when dosed appropriately 3, 2
Key Evidence Supporting This Approach
Equivalent efficacy at matched doses: Research demonstrates that enalapril and lisinopril have comparable blood pressure lowering effects when given at equivalent total daily doses 4, 5. A study of 4,723 heart failure patients found no mortality difference between enalapril, lisinopril, and ramipril when given at equivalent doses 5.
Once-daily dosing is standard: Lisinopril's longer half-life allows for once-daily dosing 1. While enalapril 40mg daily was given as 20mg BID, lisinopril can achieve 24-hour blood pressure control with once-daily administration 4.
Important Caveats
Dosing Frequency Consideration
If blood pressure control deteriorates toward the end of the 24-hour dosing interval on once-daily lisinopril, consider splitting to twice-daily dosing (e.g., 20mg BID) 1, 6. One retrospective study showed lisinopril 20mg BID produced greater systolic blood pressure reduction (10.2 mmHg more) compared to 40mg once daily 6, though this finding conflicts with standard practice and FDA recommendations.
Renal Function Adjustment
- CrCl >30 mL/min: No dose adjustment needed 1
- CrCl 10-30 mL/min: Start with 5mg daily, titrate to maximum 40mg 1
- Hemodialysis or CrCl <10 mL/min: Start with 2.5mg daily 1
Monitoring for Adverse Effects
Watch for:
- Hypotension: Particularly after the first dose; observe for 2 hours after initial dosing 1
- Hyperkalemia: Especially with concurrent diuretics, renal impairment, or potassium supplements 2
- Acute kidney injury: Monitor creatinine, particularly in bilateral renal artery stenosis 2
- Angioedema: One study suggested increased risk with BID dosing, though this is not well-established 7
When to Avoid Direct Conversion
- Systolic BP <100 mmHg: Start with lower dose (5mg daily) 1
- Heart failure with hyponatremia (Na <130 mEq/L): Start with 2.5mg daily 1
- Concurrent diuretic use: Consider starting at 5mg daily 1
Practical Implementation
The conversion is straightforward: discontinue enalapril 20mg BID and start lisinopril 20mg once daily the next day. No washout period is needed as both are ACE inhibitors with similar mechanisms 3, 2. The patient should take lisinopril at the same time each day, preferably in the morning.
If the patient was well-controlled on enalapril 40mg daily and has normal renal function, starting at lisinopril 20mg once daily is appropriate with planned uptitration to 40mg if needed 1. This conservative approach minimizes hypotension risk while maintaining blood pressure control.