Is enalapril (Angiotensin-Converting Enzyme (ACE) inhibitor) 2.5mg less potent than losartan (Angiotensin II Receptor Blocker (ARB)) 12.5mg in reducing blood pressure?

Comparison of Enalapril 2.5mg vs Losartan 12.5mg for Blood Pressure Reduction

Losartan 12.5mg is more potent than enalapril 2.5mg in reducing blood pressure based on the available evidence.

Potency Comparison

The potency of antihypertensive medications can be evaluated by examining their:

1. Recommended dosing ranges
2. Blood pressure lowering effects at specific doses
3. Clinical outcomes in comparative studies

Dosing Perspective

According to the JNC 7 guidelines and clinical trial data, the dosing ranges for these medications provide important context 1:

• Enalapril:

  • Initial dose: 2.5-5mg daily
  • Maximum dose: 10-20mg twice daily
  • Mean effective dose in clinical trials: 16.6mg daily

• Losartan:

  • Initial dose: 25-50mg daily
  • Maximum dose: 50-150mg daily
  • Mean effective dose in clinical trials: 129mg daily

The 2.5mg dose of enalapril represents the very lowest starting dose (often used in heart failure or renal impairment), while 12.5mg of losartan is half of the lowest typical starting dose of 25mg.

Relative Potency Analysis

When examining the relative potency of these specific doses:

1. Enalapril 2.5mg is at the absolute minimum of its therapeutic dosing range (approximately 15% of the mean effective dose used in clinical trials) 1.

2. Losartan 12.5mg is approximately 10% of the mean effective dose used in clinical trials, but is commonly used as part of combination therapy with hydrochlorothiazide 1.

3. The European Society of Cardiology and European Society of Hypertension guidelines note that olmesartan (another ARB) provides greater blood pressure reductions than losartan, suggesting variability in potency among ARBs 2.

Clinical Evidence

In comparative studies:

• The LIFE study demonstrated superior left ventricular mass reduction with losartan compared to atenolol, indicating its effectiveness as an antihypertensive agent 1.

• In severe hypertension, enalapril-based regimens showed slightly greater blood pressure reductions than losartan-based regimens, though both were effective 3.

• When used at their standard therapeutic doses, both medications effectively reduce blood pressure, but the 2.5mg dose of enalapril is at the very bottom of its therapeutic range 1.

Pharmacological Considerations

• Enalapril 2.5mg: As a prodrug, enalapril must be converted to enalaprilat (its active form) in the liver. Peak serum enalaprilat concentrations occur 4 hours post-dose with a prolonged terminal half-life 4.

• Losartan 12.5mg: While this is below the typical starting dose, ARBs like losartan directly block the angiotensin II receptor, which may provide more complete blockade of the renin-angiotensin system than ACE inhibitors at lower relative doses 1.

Clinical Implications

For patients requiring blood pressure reduction:

1. The 2.5mg dose of enalapril is primarily used as a starting dose in patients with heart failure or renal impairment, not as a standard antihypertensive dose 5.

2. Losartan 12.5mg, while below the standard starting dose for monotherapy, is used in fixed-dose combinations and provides measurable antihypertensive effects 1.

3. When comparing these specific doses, losartan 12.5mg would be expected to provide greater blood pressure reduction than enalapril 2.5mg due to its position within its respective therapeutic dosing range.

Conclusion

Based on the available evidence and clinical guidelines, losartan 12.5mg is more potent than enalapril 2.5mg for blood pressure reduction. The 2.5mg dose of enalapril represents the minimum starting dose (often for heart failure patients), while losartan 12.5mg, though below its standard starting dose, provides more significant antihypertensive effects at this specific dose comparison.