What is the onset of action and duration of Enalaprilat (Angiotensin-Converting Enzyme inhibitor) IV in a patient with impaired renal function?

Enalaprilat IV: Onset of Action and Duration

Enalaprilat IV has an onset of action within 15 minutes, with maximum effect occurring at 1-4 hours, and a duration of action of approximately 6 hours in most patients, though this duration is dose-related. 1

Pharmacokinetic Profile in Normal Renal Function

• Onset begins within 15 minutes of IV administration, with blood pressure reduction typically evident by this time 1
• Peak effect occurs between 1-4 hours after administration, representing maximal blood pressure reduction 1
• Duration of hemodynamic effects is approximately 6 hours for recommended doses, though this is dose-dependent and may vary 1
• The serum concentration profile is polyexponential with a prolonged terminal phase (>30 hours) representing a small fraction bound to ACE, but the effective half-life for accumulation is approximately 11 hours 1, 2

Modified Pharmacokinetics in Renal Impairment

In patients with impaired renal function (GFR ≤30 mL/min), the pharmacokinetics are significantly altered:

• Peak and trough enalaprilat levels increase substantially when creatinine clearance falls below 30 mL/min 1
• Time to peak concentration is prolonged in renal insufficiency 1
• Time to steady-state may be delayed compared to patients with normal renal function 1
• The effective half-life is prolonged at this level of renal impairment, necessitating dosage adjustment 1
• More than 90% of enalaprilat is excreted unchanged in urine within 24 hours in normal renal function, making renal impairment particularly impactful 1

Clinical Implications for Dosing

For patients with renal impairment, dose reduction is mandatory:

• The FDA label specifies that dosage adjustments are required when GFR ≤30 mL/min to prevent drug accumulation 1
• Research supports that 0.625 mg is an appropriate initial dose for hypertensive crisis, as higher doses (1.25 mg, 2.5 mg, 5 mg) do not improve response rates or magnitude of blood pressure reduction 3
• In patients with severe renal insufficiency, higher serum concentrations and delayed urinary excretion occur, increasing risk of prolonged hypotension 2

Practical Monitoring Considerations

• Blood pressure should be monitored frequently after administration, particularly in volume-depleted patients who are at risk for symptomatic hypotension 1
• The onset within 15 minutes allows for relatively rapid assessment of initial response 1, 4
• Enalaprilat is dialyzable at 62 mL/min, which may be relevant for management of excessive hypotension in dialysis patients 1

Important Caveats

• Abrupt withdrawal has not been associated with rapid blood pressure rebound, providing some safety margin 1
• Symptomatic postural hypotension is infrequent but should be anticipated in volume-depleted patients 1
• In renal impairment, the prolonged effective half-life means effects may persist longer than the typical 6-hour duration, requiring extended monitoring 1
• Baseline renal function assessment is essential before administration, particularly checking serum creatinine and calculating GFR 5