Diltiazem and Verapamil Are NOT the Same Drug
No, diltiazem and verapamil are distinct calcium channel blockers belonging to different chemical subclasses with different pharmacological properties, though they share more similarities with each other than with dihydropyridines like nifedipine. 1
Chemical Classification
- Diltiazem belongs to the benzothiazepine class of calcium channel blockers 1
- Verapamil belongs to the phenylalkylamines class 1
- These are chemically distinct compounds that bind to different receptor sites on the alpha-1 component of the calcium channel 2
Pharmacological Differences
While both drugs affect cardiac conduction and heart rate, their potency profiles differ:
- Verapamil's most potent activity is electrophysiologic, making it the strongest agent for cardiac conduction effects 3
- Diltiazem acts like a less-potent combination of verapamil and nifedipine, with intermediate effects on both cardiac conduction and vasodilation 3
- Diltiazem has the least peripheral vasodilatory effect among calcium channel blockers, while verapamil has moderate vasodilatory effects 1
Shared Clinical Properties
Both drugs do share important similarities that distinguish them from dihydropyridines:
- Both produce negative chronotropic effects (slow heart rate) 1, 4
- Both have negative dromotropic effects (slow AV conduction) and can cause AV block 1
- Both have negative inotropic effects (reduce contractility) 4
- Both are used for supraventricular tachycardia treatment, with IV formulations available 2
- Both show protective effects in non-ST elevation myocardial infarction 1
Clinical Decision-Making
Choose verapamil when:
- Maximum electrophysiologic effect is needed for arrhythmia control 3
- Treating supraventricular tachycardia requiring the most potent AV nodal blockade 2
Choose diltiazem when:
- Heart rate control is needed but less aggressive AV nodal suppression is desired 5
- Concurrent supraventricular arrhythmias or atrial fibrillation require management 5
- Patient has hypertrophic cardiomyopathy 5
Critical Contraindications (Both Drugs)
- Avoid in patients with significantly impaired left ventricular function or reduced ejection fraction 1, 6
- Avoid in patients with AV conduction abnormalities (PR >0.24 seconds, existing AV block) 1, 5
- Do not combine with beta-blockers without careful monitoring due to enhanced bradyarrhythmia and heart block risk 7, 5
- Avoid combining diltiazem with ivabradine due to severe bradycardia risk from CYP3A4 interaction 7, 5