1. Clinical Overview
A triple-drug, fixed-dose combination (FDC) antihypertensive medication containing an angiotensin II receptor blocker (ARB), a dihydropyridine calcium channel blocker (CCB), and a thiazide diuretic. It is indicated for the treatment of essential hypertension in patients whose blood pressure is not adequately controlled on any two of the following antihypertensive classes: ARBs, CCBs, and thiazide diuretics. This combination provides synergistic blood pressure lowering through complementary mechanisms, often allowing for lower doses of individual components and improved adherence.
| Onset | Duration | Bioavailability |
|---|---|---|
| Olmesartan: 1-2 hours; Amlodipine: 6-12 hours; Hydrochlorothiazide: 2 hours (diuresis onset). Significant blood pressure reduction is typically observed within 1-2 weeks of initiation. | Olmesartan: >24 hours; Amlodipine: 24 hours; Hydrochlorothiazide: 6-12 hours (diuretic effect). The combination provides sustained 24-hour blood pressure control. | Olmesartan Medoxomil: ~26%; Amlodipine: 64-90%; Hydrochlorothiazide: 50-80%. |
2. Mechanism of Action
This combination exerts a multi-pronged antihypertensive effect. Olmesartan selectively blocks the binding of angiotensin II to the AT1 receptor, inhibiting its vasoconstrictive and aldosterone-secreting effects. Amlodipine inhibits the transmembrane influx of calcium ions into vascular smooth muscle and cardiac muscle, causing peripheral arterial vasodilation. Hydrochlorothiazide inhibits sodium reabsorption in the distal convoluted tubule, increasing excretion of sodium, chloride, and water, reducing plasma volume.
3. Indications & Uses
- Treatment of essential hypertension in adult patients whose blood pressure is not adequately controlled on any two of the following antihypertensive classes: angiotensin II receptor blockers, calcium channel blockers, and thiazide diuretics.
4. Dosage & Administration
Adult Dosage: One tablet (Olmesartan 40mg/Amlodipine 5mg/Hydrochlorothiazide 12.5mg) once daily. Dose may be titrated after 2-4 weeks based on response. Not for initial therapy.
Administration: Can be taken with or without food. Administer orally, preferably at the same time each day, with a glass of water. Dose should be individualized. Missed dose: Take as soon as remembered, but skip if it's almost time for the next dose. Do not double dose.
5. Side Effects
Common side effects may include:
- Dizziness
- Headache
- Peripheral edema (ankle swelling) - primarily due to amlodipine
- Fatigue
- Flushing
- Nausea
- Upper respiratory tract infection
- Hypotension (especially initial doses)
- Hyperuricemia
- Hypokalemia
- Increased blood glucose
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other Antihypertensives (e.g., ACEi, beta-blockers) | Additive hypotensive effect. Risk of severe hypotension. | Major |
| Potassium-sparing diuretics (e.g., spironolactone, amiloride) / Potassium supplements | Increased risk of hyperkalemia (olmesartan effect). | Major |
| NSAIDs (e.g., ibuprofen, diclofenac) | May reduce antihypertensive effect, increase risk of renal impairment, and antagonize diuretic effect. | Major |
| Lithium | Thiazides reduce renal clearance of lithium, increasing risk of lithium toxicity. | Major |
| CYP3A4 Inhibitors (e.g., ketoconazole, itraconazole, ritonavir, clarithromycin, grapefruit juice) | Increase amlodipine plasma concentration, risk of hypotension and edema. | Moderate |
| CYP3A4 Inducers (e.g., rifampicin, carbamazepine, phenytoin) | Decrease amlodipine plasma concentration, reducing efficacy. | Moderate |
| Corticosteroids (e.g., prednisolone) | Antagonize hypokalemic and hypotensive effects of thiazide. | Moderate |
| Antidiabetic drugs (Insulin, Sulfonylureas) | Thiazide may decrease glucose tolerance, requiring dose adjustment. | Moderate |
| Colestipol/Cholestyramine | May reduce absorption of hydrochlorothiazide. | Moderate |
| Allopurinol | Increased risk of hypersensitivity reactions when combined with thiazides. | Moderate |
| Alcohol, Barbiturates, Narcotics | Potentiation of orthostatic hypotension. | Moderate |
| Digoxin | Hypokalemia/hypomagnesemia from thiazide may predispose to digitalis toxicity. | Moderate |
7. Patient Counselling
- DO take the medication at the same time every day, with or without food.
- DO continue taking this medicine even if you feel well. Hypertension often has no symptoms.
- DO get your blood pressure checked regularly as advised by your doctor.
- DO inform all your doctors and dentists that you are taking this medicine.
- DO maintain adequate fluid intake unless advised otherwise by your doctor.
- DONT stop taking this medicine suddenly without consulting your doctor.
- DONT take over-the-counter NSAIDs (e.g., ibuprofen) for pain/fever without consulting your doctor.
- DONT use potassium supplements or salt substitutes containing potassium without medical advice.
- DONT consume grapefruit or grapefruit juice regularly.
- DONT drive or operate machinery if you experience dizziness or lightheadedness.
8. Toxicology & Storage
Overdose: Manifestations are primarily extensions of pharmacologic effects: Profound hypotension, tachycardia/bradycardia, electrolyte disturbances (hypokalemia, hyponatremia), dehydration, renal impairment, and shock. Amlodipine overdose may lead to reflex tachycardia and severe peripheral vasodilation.
Storage: Store below 30°C. Protect from light and moisture. Keep in the original blister pack or container. Keep out of reach and sight of children. Do not use after the expiry date printed on the pack.