What is Slomag (Verapamil)?
Slomag is a brand name for verapamil, a non-dihydropyridine calcium channel blocker used primarily for cardiovascular conditions including hypertension, angina, and cardiac arrhythmias. 1
Mechanism of Action
Verapamil works by inhibiting calcium influx through L-type calcium channels in arterial smooth muscle and cardiac cells, which produces several key effects 1:
- Vasodilation: Decreases systemic vascular resistance by dilating peripheral arterioles, leading to blood pressure reduction without typically causing orthostatic hypotension or reflex tachycardia 1
- Cardiac effects: Produces negative inotropic (reduced contractility), chronotropic (reduced heart rate), and dromotropic (slowed AV conduction) effects 2
- Coronary vasodilation: Dilates coronary arteries and is a potent inhibitor of coronary artery spasm 1
Primary Clinical Indications
Arrhythmias
- Supraventricular tachycardia: First-line treatment for stable, narrow-complex tachycardias when adenosine or vagal maneuvers fail, dosed at 2.5-5 mg IV over 2 minutes 3
- Atrial fibrillation/flutter rate control: 5-10 mg IV every 15-30 minutes to a total of 20-30 mg for acute control 3, 4
- Long-term rate control: 120-480 mg daily in divided doses or as sustained-release formulation 5, 4
Angina Pectoris
- Effective for vasospastic (Prinzmetal's) angina and stable angina 5, 1
- Initial dose: 120 mg daily, maintenance up to 480 mg daily 5
Hypertension
- Effective first-line treatment for mild to moderate essential hypertension 1, 6
- Particularly useful in elderly patients and those with contraindications to beta-blockers (e.g., asthma, COPD) 6
Critical Contraindications
Absolute contraindications include 5, 3:
- Second- or third-degree AV block without a pacemaker
- Severe sinus node dysfunction without a pacemaker
- Decompensated systolic heart failure or severe left ventricular dysfunction
- Cardiogenic shock or severe hypotension
- Wolff-Parkinson-White syndrome with atrial fibrillation/flutter
- Recent beta-blocker use (risk of profound bradycardia and hypotension)
- Concomitant use with dofetilide (contraindicated) 5
Common Adverse Effects
The most frequent side effects include 5, 3, 2:
- Constipation (most common)
- Hypotension
- Bradycardia
- Leg edema
- Worsening heart failure in patients with pre-existing ventricular dysfunction
- AV block
- Pulmonary edema in hypertrophic cardiomyopathy patients 5
Important Drug Interactions
Verapamil is a moderate CYP3A4 inhibitor and P-glycoprotein inhibitor, leading to significant interactions 5:
- Contraindicated: Dofetilide 5
- Requires dose adjustment: Digoxin (reduce by 30-50%), simvastatin, dabigatran, edoxaban, rivaroxaban 5
- Avoid: Grapefruit juice (increases verapamil levels) 5
- Caution with: Other AV nodal blocking agents, ivabradine 2
Formulations and Dosing
Immediate-Release
- Available as 120 mg, 180 mg, and 240 mg tablets 1
- Typically dosed 3-4 times daily for cardiovascular indications 7
Sustained-Release
- Allows once-daily dosing up to 240 mg; higher doses may require twice-daily administration 8
- Designed for sustained release in the gastrointestinal tract 1
- Tablets can be divided in half without altering sustained-release characteristics 1
Clinical Pearls
- Monitoring: Regular assessment of heart rate, blood pressure, and ECG for AV conduction abnormalities is essential during therapy 4
- Elderly patients: Consider lower initial doses due to altered pharmacokinetics 4
- Renal/hepatic impairment: Dose adjustments may be necessary 4
- Bradycardia threshold: Heart rate less than 50 beats/min is uncommon (1.4% incidence) 1