From the FDA Drug Label
Within the physiologic pH range, amlodipine is an ionized compound (pKa=8. 6), and its kinetic interaction with the calcium channel receptor is characterized by a gradual rate of association and dissociation with the receptor binding site, resulting in a gradual onset of effect. Because of the gradual onset of action, acute hypotension is unlikely.
The onset of action for amlodipine is gradual.
- The exact time to onset is not specified in the label.
- Gradual onset is mentioned in relation to the kinetic interaction with the calcium channel receptor and the likelihood of acute hypotension 1, 1, 1.
From the Research
Amlodipine typically begins to work within 6-12 hours after taking the first dose, but its full therapeutic effect is not achieved until after 7-10 days of consistent use. This calcium channel blocker has a gradual onset of action compared to other antihypertensives, which contributes to its lower incidence of reflex tachycardia 2. Patients should be advised that blood pressure reduction will be progressive over the first week of treatment, and the maximum effect may take up to 2 weeks to manifest.
The slow onset is due to amlodipine's pharmacokinetic properties, including its high bioavailability and long half-life of 35-50 hours, which allows for once-daily dosing 2. This gradual onset is actually beneficial as it reduces the risk of hypotension that can occur with rapidly-acting antihypertensives. Patients should continue taking amlodipine regularly even if they don't notice immediate effects, and blood pressure monitoring should be performed after 1-2 weeks to assess the response to therapy.
Some key points to consider when prescribing amlodipine include:
- Its ability to sustain anti-hypertensive effect for more than 24 hours following a single dose 2
- Its ability to control blood pressure in patients with a systolic/diastolic BP of 130/80 mm Hg or higher, diabetes, or chronic kidney disease without worsening glycemic or kidney function 2
- Its cost-effectiveness and potential to be cost-saving when compared with usual care 2
- Common side effects such as edema, palpitations, dizziness, and flushing, which are more common with the higher dose of 10 mg 2