Are diltiazem and verapamil the same?

Are Diltiazem and Verapamil the Same?

No, diltiazem and verapamil are not the same drug, but they are both nondihydropyridine calcium channel blockers with similar mechanisms of action and clinical effects, though they differ in chemical structure, specific pharmacological properties, and side effect profiles. 1

Chemical Classification and Structure

• Diltiazem is a benzothiazepine, while verapamil is a phenylalkylamine—these are distinct chemical classes despite both being nondihydropyridine calcium channel blockers 1, 2
• Both drugs inhibit calcium influx through L-type calcium channels in cardiac myocytes and vascular smooth muscle, but their different chemical structures result in slightly different binding characteristics 1, 3, 4
• Research demonstrates that both drugs preferentially block inactivated calcium channels in a state-dependent fashion, with inactivated channels having higher affinity for these agents than rested or open channels 5

Shared Pharmacological Properties

Both diltiazem and verapamil have similar effects on the cardiovascular system that distinguish them from dihydropyridine calcium channel blockers:

• Negative chronotropic effects: Both decrease heart rate by slowing sinus node discharge 1
• Negative inotropic effects: Both reduce myocardial contractility, which can be problematic in patients with left ventricular dysfunction 1
• AV nodal conduction slowing: Both slow atrioventricular nodal conduction, making them useful for supraventricular arrhythmias 1
• Metabolism: Both are metabolized by cytochrome P450 3A4 and should not be combined with ivabradine due to severe bradycardia risk 1

Key Differences Between the Two Drugs

Side Effect Profiles

• Verapamil causes constipation (especially in elderly patients) due to decreased intestinal motility—this is a distinctive side effect not typically seen with diltiazem 1
• Verapamil may cause more serious adverse effects and has been associated with higher discontinuation rates in clinical trials compared to diltiazem 6
• Both can cause hypotension, bradycardia, and peripheral edema, but the constipation issue is specific to verapamil 1

Dosing and Administration

• Verapamil IV dosing: 2.5-5 mg IV bolus over 2 minutes (over 3 minutes in older patients), can repeat 5-10 mg every 15-30 minutes to total 20-30 mg 1
• Diltiazem IV dosing: 0.25 mg/kg (15-20 mg) IV over 2 minutes, can give additional 0.35 mg/kg (20-25 mg) in 15 minutes if needed, with maintenance infusion at 5-15 mg/hour 1
• For chronic oral therapy in angina, typical doses are verapamil 240-480 mg/day and diltiazem 180-360 mg/day 6, 7, 8

Drug Interactions

• Verapamil is a moderate CYP3A4 inhibitor and also inhibits P-glycoprotein, leading to more extensive drug interaction potential 1
• Diltiazem is also a moderate to weak CYP3A4 inhibitor but has slightly different interaction profiles with statins and other medications 1
• Both significantly increase exposure to simvastatin and lovastatin (3.6-5 fold increases), but diltiazem may have slightly less pronounced effects 1

Clinical Equivalence in Specific Conditions

Angina Pectoris

• Both drugs show essentially equivalent efficacy in treating stable exertional angina, with similar reductions in angina frequency and improvements in exercise tolerance 6, 7, 8
• In hypertrophic cardiomyopathy, diltiazem and verapamil demonstrate comparable effects on symptoms, exercise capacity, and echocardiographic parameters 6
• Both reduce myocardial oxygen demand through reductions in afterload, heart rate, and contractility 1

Supraventricular Arrhythmias

• Both are effective for acute conversion of PSVT and rate control in atrial fibrillation/flutter when adenosine fails or for longer-lasting control 1
• The choice between them is often based on availability, familiarity, and side effect considerations rather than efficacy differences 1

Critical Contraindications (Identical for Both)

Both diltiazem and verapamil are absolutely contraindicated in:

• Decompensated systolic heart failure or left ventricular dysfunction due to negative inotropic effects that can precipitate hemodynamic collapse 1, 9
• Pre-excited atrial fibrillation (WPW syndrome with AF/flutter) as they can precipitate ventricular fibrillation 1, 9
• AV block greater than first degree or significant sinus node dysfunction without a pacemaker 1
• Hypotension or cardiogenic shock 1

Clinical Decision-Making

When choosing between diltiazem and verapamil:

• Prefer diltiazem in elderly patients or those prone to constipation, as verapamil's effect on intestinal motility can be problematic 1, 6
• Either agent is appropriate for rate control in supraventricular arrhythmias or treatment of angina in patients without contraindications 1
• Consider diltiazem if concerned about tolerability, as it may have fewer serious side effects requiring discontinuation 6
• In heart failure with preserved ejection fraction, both remain contraindicated if there is any systolic dysfunction component 9
• For drug interaction concerns, review specific CYP3A4 and P-glycoprotein interactions, particularly with statins, as verapamil may have more extensive interactions 1