Diltiazem
Cardizem Retard · Cardizem Unotard · Coramil
The intermediate form among calcium channel blockers: slows the AV node like verapamil but with less negative inotropy and more vasodilation, and causes less constipation. The cardiac oral formulations were withdrawn from the Swedish market in 2025 — only a rectal ointment remains registered — so oral and intravenous diltiazem require a named-patient licence. Verapamil or a beta-blocker is therefore the practical first choice for rate control in this setting.
Contraindicated in heart failure with reduced ejection fraction, AV block II–III without a pacemaker, sick sinus syndrome, and atrial fibrillation with pre-excitation (WPW) — AV nodal blockade can cause accelerated conduction over the accessory pathway and ventricular fibrillation. Combination with a beta-blocker, particularly intravenously, can cause severe bradycardia and asystole.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Acute rate control in atrial fibrillation | 0,25 mg/kg iv over 2 minutes, may be repeated with 0,35 mg/kg after 15 minutes | only with narrow QRS without pre-excitation and preserved EF |
| Continued rate control | Infusion 5–15 mg/hour iv, titrated against ventricular rate | iv formulation not marketed in Sweden, requires licence |
| Rate control, oral maintenance | 180–360 mg daily as a sustained-release formulation | titrate to resting heart rate |
| Angina pectoris, including vasospastic | 180–360 mg daily as a sustained-release formulation | the best-documented indication for diltiazem |
| Hypertension | 180–360 mg daily as a sustained-release formulation | rarely first-line choice |
No established dose adjustment — only a few per cent is excreted unchanged renally. Monitor heart rate and blood pressure in severe renal failure. Not removed by haemodialysis.
Reduce dose and titrate slowly — high first-pass metabolism means exposure increases markedly in cirrhosis.
Insufficient documentation in children. Rate control in children is managed by a paediatric cardiologist using other agents.
Do not use diltiazem for rate control in a patient with reduced left ventricular function — the negative inotropy can trigger decompensation, and a beta-blocker or digoxin is the right choice. Also do not give diltiazem in broad-complex tachycardia of uncertain origin: in pre-excited atrial fibrillation, AV nodal blockade can induce ventricular fibrillation.
Pharmacokinetics
- BIOAVAIL.
- approximately 40 % (first-pass)
- t½
- 3–6 h
- PROTEIN BINDING
- approximately 80 %
- METABOLISM
- CYP3A4, deacetylation
- ACTIVE METABOLITE
- Desacetyldiltiazem
- EXCRETION
- Biliary and renal, 2–4 % unchanged
- INHIBITS
- CYP3A4 and P-gp (moderate)
- ONSET
- 3 minutes iv · 4–6 h to Cmax for sustained release