What is the onset of action of tab amlo (amlodipine)?

Onset of Action of Amlodipine

Amlodipine has a gradual onset of action with blood pressure reduction beginning within 4-8 hours after oral administration, and peak effects occurring at 6-8 hours post-dose. 1

Pharmacokinetic Profile

• Amlodipine is a dihydropyridine calcium channel blocker with distinctive pharmacokinetic characteristics that contribute to its gradual onset of action 1, 2
• The drug has an intermediate rate of absorption with peak plasma concentrations reached 6-8 hours after oral administration 1, 2
• Bioavailability is relatively high at 60-80%, allowing for predictable dosing effects 1
• The gradual onset is attributed to both the absorption rate and the physicochemical properties of the drug-receptor interaction 1

Pharmacodynamic Effects

• Following administration, amlodipine produces vasodilation by inhibiting calcium ion influx across cell membranes, with greater effects on vascular smooth muscle than cardiac muscle 3
• Blood pressure begins to decrease gradually over 4-8 hours after a single dose 1
• The antihypertensive effect slowly returns to baseline over 24-72 hours after a single dose 1
• Unlike some other antihypertensive medications, amlodipine's gradual onset does not trigger reflex tachycardia, as it doesn't activate physiological reflexes due to its slow onset 1, 4

Clinical Implications

• The gradual onset of action makes acute hypotension unlikely, which is particularly beneficial in patients with severe aortic stenosis 3
• During chronic once-daily dosing, blood pressure is decreased from baseline with minimal fluctuation over the 24-hour dosing interval 1
• The long half-life (35-50 hours) and duration of action allow for sustained antihypertensive effects beyond 24 hours 4, 2
• Blood pressure control is maintained even when a dose is missed, providing protection in cases of non-compliance 4, 5

Comparison to Other Antihypertensive Agents

• Unlike hydralazine, which has a relatively rapid onset (10-30 minutes) but unpredictable response, amlodipine provides a more gradual and predictable blood pressure reduction 6
• Compared to beta-blockers, which have varying onset times depending on the specific agent, amlodipine has a more consistent pharmacokinetic profile 6
• The calcium channel blocker's gradual onset minimizes the risk of "overshoot" hypotension that can occur with more rapidly acting agents 6

Important Considerations

• Due to its gradual onset and long half-life, amlodipine requires 1-1.5 weeks to reach steady-state plasma concentrations with once-daily administration 1, 2
• In a study evaluating the prolonged antihypertensive effect, blood pressure did not significantly increase even after 3 days of discontinuation, demonstrating the extended duration of action 5
• Dose adjustments should be made slowly, especially in patients with hepatic impairment, as the elimination half-life can be prolonged to 56 hours in these patients 3