Drug Information: Verapamil
Verapamil is a phenylalkylamine calcium channel blocker used to treat hypertension, angina, and certain types of arrhythmia, including atrial fibrillation. It works by blocking the influx of calcium ions into cardiac and vascular smooth muscle cells, leading to vasodilation and reduced heart rate and contractility. This makes it effective in managing conditions characterized by excessive heart rate or high blood pressure. It’s available in both immediate-release and extended-release formulations.
Category
Antiarrhythmic
Mechanism of Action
Verapamil exerts its therapeutic effects by acting as a calcium channel blocker, specifically targeting L-type calcium channels. These channels are predominantly found in cardiac muscle and vascular smooth muscle cells. By blocking these channels, Verapamil reduces the influx of calcium ions into these cells.
In cardiac muscle, decreased calcium influx leads to reduced myocardial contractility (negative inotropy) and a slowing of sinoatrial (SA) and atrioventricular (AV) nodal conduction (negative chronotropy and dromotropy, respectively). This slowing of AV nodal conduction is particularly important in treating supraventricular tachycardias, as the AV node is a critical part of the re-entrant circuit in many of these arrhythmias.
In vascular smooth muscle, reduced calcium influx leads to vasodilation, decreasing peripheral vascular resistance and lowering blood pressure. The vasodilation is more pronounced in arterial than venous smooth muscle.
The overall effect of Verapamil is a reduction in heart rate, blood pressure, and myocardial contractility, making it useful in treating various cardiovascular conditions. The relative selectivity for myocardial calcium channels compared to vascular smooth muscle calcium channels is less pronounced than in some other calcium channel blockers, so it’s crucial to consider its potential for causing bradycardia and hypotension.
Clinical Uses
Verapamil is widely used in the management of several cardiovascular conditions:
* **Atrial Fibrillation and Flutter:** Verapamil is frequently used to control the ventricular rate in patients with atrial fibrillation or atrial flutter. By slowing AV nodal conduction, it reduces the number of atrial impulses that are conducted to the ventricles, thus lowering the heart rate.
* **Supraventricular Tachycardia (SVT):** Verapamil is effective in terminating or preventing re-entrant SVT, particularly AV nodal re-entrant tachycardia (AVNRT). Its effect on AV nodal conduction interrupts the re-entrant circuit.
* **Hypertension:** As a calcium channel blocker, Verapamil causes vasodilation, reducing peripheral vascular resistance and lowering blood pressure. It can be used as monotherapy or in combination with other antihypertensive agents.
* **Angina Pectoris:** Verapamil is used to treat both stable and unstable angina. It reduces myocardial oxygen demand by reducing heart rate, contractility, and afterload (blood pressure). It can also help prevent vasospastic angina (Prinzmetal’s angina) by preventing coronary artery spasm.
* **Migraine Prophylaxis:** While not a primary treatment, Verapamil is sometimes used off-label for migraine prevention in patients who have not responded to other therapies.
* **Cluster Headaches:** Verapamil is considered a first-line treatment for chronic cluster headaches.
Dosage
**Adults:**
* **Hypertension:** Typical initial dose is 80 mg orally three times daily. Extended-release formulations are available, with typical starting doses ranging from 120-240 mg once daily.
* **Angina:** 80-120 mg orally three times daily.
* **Atrial Fibrillation/SVT:** Intravenous (IV) bolus of 2.5-5 mg over 2 minutes, may repeat with 5-10 mg every 15-30 minutes, up to a total dose of 20 mg. Oral maintenance doses are similar to those used for hypertension and angina.
**Pediatrics:** (Use with caution, expert consultation recommended)
* **SVT:** IV dose of 0.1-0.3 mg/kg over 2 minutes (maximum single dose of 5 mg in infants and 10 mg in children). May repeat once after 15 minutes. Oral maintenance is not commonly used in children.
**Important Considerations:** Dosage must be individualized based on the patient’s condition, response to therapy, and other medications. The elderly may require lower doses. Renal or hepatic impairment may also necessitate dosage adjustments. Always consult the prescribing information and a healthcare professional for accurate dosing information.
Indications
* Hypertension
* Angina Pectoris (stable, unstable, and vasospastic)
* Supraventricular Tachycardia (SVT)
* Atrial Fibrillation (rate control)
* Atrial Flutter (rate control)
* Migraine Prophylaxis (off-label)
* Cluster Headaches
Contraindications
* Hypersensitivity to Verapamil
* Severe Hypotension (systolic blood pressure < 90 mmHg)
* Cardiogenic Shock
* Severe Left Ventricular Dysfunction
* Sick Sinus Syndrome (unless a functioning pacemaker is present)
* Second- or Third-Degree AV Block (unless a functioning pacemaker is present)
* Wolff-Parkinson-White (WPW) Syndrome with Atrial Fibrillation/Flutter (risk of paradoxical increase in ventricular rate)
* Concomitant use of intravenous beta-blockers
* Severe Congestive Heart Failure
FAQ
**Q: What is Verapamil used for?**
A: Verapamil is used to treat high blood pressure, angina (chest pain), and certain heart rhythm disorders like atrial fibrillation and supraventricular tachycardia.
**Q: How does Verapamil work?**
A: Verapamil works by blocking calcium channels in the heart and blood vessels. This reduces the heart’s workload, widens blood vessels, and slows down the heart rate.
**Q: What are the common side effects of Verapamil?**
A: Common side effects include constipation, dizziness, headache, low blood pressure, and swelling of the ankles and feet.
**Q: Can I take Verapamil if I have low blood pressure?**
A: No, Verapamil is contraindicated in patients with severe hypotension.
**Q: What medications should I avoid while taking Verapamil?**
A: Avoid taking Verapamil with beta-blockers (especially intravenously), digoxin, certain antiarrhythmics, and grapefruit juice, as these can interact and cause adverse effects. Always inform your doctor of all medications you are taking.
**Q: How should I take Verapamil?**
A: Take Verapamil exactly as prescribed by your doctor. Do not crush or chew extended-release tablets.
**Q: What should I do if I miss a dose of Verapamil?**
A: If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not double the dose to catch up.
**Q: Is Verapamil safe during pregnancy?**
A: Verapamil should be used during pregnancy only if clearly needed and after careful consideration of the risks and benefits. Consult your doctor.
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