What is the onset of action of captopril (angiotensin-converting enzyme inhibitor) in a patient with hypertensive urgency?

Onset of Action of Captopril in Hypertensive Urgency

Captopril begins to lower blood pressure within 30 minutes of oral administration, with maximal effects occurring at 60-90 minutes after dosing. 1, 2

Pharmacokinetic Profile

• Captopril is rapidly absorbed after oral administration, reaching peak blood levels at approximately one hour 1
• The presence of food reduces absorption by 30-40%, so captopril should be given one hour before meals 1
• Approximately 75% of the oral dose is absorbed on average 1
• The apparent elimination half-life of unchanged captopril is less than 2 hours 1

Clinical Onset in Hypertensive Urgency

• In a randomized study of 65 patients with hypertensive urgencies, captopril 25 mg produced an average blood pressure reduction of 79.4 mmHg systolic and 33 mmHg diastolic within 60 minutes 2
• Within 30 minutes of oral administration of 25 mg captopril in hypertensive emergencies, blood pressure decreased from 239/134 to 204/118 mmHg 3
• The antihypertensive effect was maintained for at least 6 hours after medication 2

Dosing Considerations for Hypertensive Urgency

• For hypertensive urgency (BP >180/120 mmHg WITHOUT acute target organ damage), captopril can be started at low doses of 12.5-25 mg orally due to risk of sudden BP drops in volume-depleted patients 4
• The 2017 ACC/AHA guidelines note that ACE inhibitors have a relatively slow onset of action (15 minutes) and unpredictability of BP response, making them less ideal for hypertensive emergencies but acceptable for urgencies 5
• Captopril is contraindicated in pregnancy and should not be used in acute MI or bilateral renal artery stenosis 5

Mechanism and Duration of Effect

• Blood pressure reductions are usually maximal 60-90 minutes after oral administration of an individual dose 1
• The duration of effect is dose-related, and the antihypertensive effects persist longer than demonstrable inhibition of circulating ACE 1
• In patients with IV captopril infusion for accelerated hypertension, blood pressure rose within 15 minutes of stopping the infusion, demonstrating the short effective half-life 6

Important Clinical Caveats

• Patients with hypertensive urgency should be managed with oral medications and outpatient follow-up within 2-4 weeks—NOT with IV medications or hospital admission 4, 7
• Captopril and other ACE inhibitors should be used at low initial doses because patients with severe hypertension can be very sensitive to these agents 5
• Avoid rapid BP lowering in hypertensive urgency, as this may cause cerebral, renal, or coronary ischemia in patients with chronic hypertension who have altered autoregulation 5, 4
• In patients with renal impairment, retention of captopril occurs and dosing adjustments are necessary 1