What is Diltiazem For?
Diltiazem is a non-dihydropyridine calcium channel blocker used primarily for managing chronic stable angina, coronary artery spasm (variant angina), acute rate control in supraventricular tachycardia (SVT) including atrial fibrillation/flutter with rapid ventricular response, and hypertension. 1
Primary FDA-Approved Indications
The FDA specifically approves diltiazem for:
- Chronic stable angina
- Angina due to coronary artery spasm 1
Guideline-Supported Clinical Uses
Acute Supraventricular Tachycardia Management
Diltiazem is a first-line agent for acute SVT termination and rate control. For intravenous administration, give 0.25 mg/kg IV bolus over 2 minutes, followed by maintenance infusion at 5-10 mg/h (up to 15 mg/h) if needed 2. This applies to:
- AVNRT (AV nodal reentrant tachycardia)
- AVRT (AV reentrant tachycardia)
- Atrial fibrillation/flutter with rapid ventricular response for rate control 2, 3
The drug works by slowing AV nodal conduction, which terminates reentrant rhythms involving the AV node and controls ventricular rate in atrial arrhythmias 3.
Ongoing SVT Prevention
For chronic oral therapy, start with 120 mg daily (divided or long-acting formulation), titrating up to 360 mg daily maximum 2. This prevents recurrent SVT episodes in patients with documented arrhythmias.
Hypertension Management
Diltiazem effectively lowers blood pressure through arterial vasodilation 4, 5. Start with 120 mg daily and titrate to 360 mg daily as needed 2. It can be used as monotherapy or combined with ACE inhibitors or ARBs.
Critical caveat: Diltiazem demonstrates potent arterial vasodilator activity—approximately 1.6 times greater than sodium nitroprusside in some studies 6. This makes it highly effective but requires careful blood pressure monitoring.
Mechanism-Based Applications
Diltiazem reduces myocardial oxygen demand through three mechanisms:
- Decreased heart rate (negative chronotropic effect)
- Reduced blood pressure (afterload reduction)
- Decreased cardiac contractility (negative inotropic effect—though less pronounced than verapamil) 5, 7
This makes it particularly useful for angina management, where it both increases oxygen supply (coronary vasodilation) and decreases oxygen demand 8.
Absolute Contraindications
Do not use diltiazem in patients with 1:
- Sick sinus syndrome (without pacemaker)
- Second- or third-degree AV block (without pacemaker)
- Systolic blood pressure <90 mmHg
- Acute MI with pulmonary congestion
- Heart failure with reduced ejection fraction (HFrEF) 4
The guideline explicitly states that nondihydropyridine calcium channel blockers like diltiazem have myocardial depressant activity and demonstrate "either no clinical benefit or even worse outcomes" in HFrEF patients 4.
Critical Precautions
Use extreme caution or avoid in:
- Wolff-Parkinson-White syndrome with atrial fibrillation/flutter (can precipitate ventricular fibrillation by preferentially blocking the AV node, forcing conduction down the accessory pathway) 2
- Decompensated heart failure
- Hepatic or renal dysfunction (diltiazem is metabolized by CYP3A4) 2
- Concurrent use of other AV nodal blocking agents (beta blockers, digoxin) 2
Drug Interactions
Diltiazem is a moderate CYP3A4 inhibitor and CYP3A4 substrate 2. This creates significant interactions with:
- Statins (especially simvastatin—increased myopathy risk)
- Immunosuppressants (cyclosporine, tacrolimus—can reduce required doses by 38-103%) 9
- Anticoagulants (apixaban, rivaroxaban, dabigatran, edoxaban)
- Other antiarrhythmics (flecainide, propafenone)
Adverse Effects
Most common adverse effects include 2:
- Hypotension (especially with IV administration)
- Bradycardia
- Worsening heart failure in patients with pre-existing ventricular dysfunction
- Abnormal liver function tests (rare acute hepatic injury)
Practical tip: If hypotension is a concern with IV administration, use a slow infusion at 2.5 mg/min over up to 20 minutes rather than bolus dosing 2.
Overdose Management
In diltiazem overdose, expect bradycardia, hypotension, heart block, and cardiac failure 1. Treatment includes:
- Atropine 0.6-1.0 mg for bradycardia
- Cardiac pacing for high-degree AV block
- Intravenous calcium (1 g calcium chloride or 3 g calcium gluconate over 5 minutes, repeatable every 10-20 minutes, or continuous infusion at 2 g/hour) 1
- Vasopressors (dopamine, norepinephrine) for hypotension
- Inotropic agents (isoproterenol, dopamine, dobutamine) for cardiac failure
Note that calcium's effectiveness in reversing diltiazem toxicity has been inconsistent in reported cases 1.