Diltiazem

Diltiazem is prescribed to treat:

• High blood pressure, chest pain, and certain heart rhythm disorders • Various related conditions in the cardiovascular category • Associated symptoms and complications

It is an important medication that helps manage these conditions effectively.

Diltiazem (Cardizem, Tiazac) is a non-dihydropyridine calcium channel blocker used for rate control in atrial fibrillation and atrial flutter, for angina, and for high blood pressure. Its defining property is that it acts on the heart as well as the vasculature, which is precisely what separates it from amlodipine and determines where each belongs.

Mechanism of Action

Diltiazem blocks L-type calcium channels in both vascular smooth muscle and cardiac tissue. The vascular effect produces arterial vasodilation and lowers blood pressure. The cardiac effect slows sinoatrial node firing and, more importantly, slows conduction through the atrioventricular node.

That AV nodal effect is the therapeutic point in atrial fibrillation. The atria fire chaotically at rates far above what the ventricles could sustain, and the AV node acts as a filter. Slowing its conduction reduces the proportion of impulses that reach the ventricles, controlling the ventricular rate without addressing the atrial rhythm itself — rate control rather than rhythm control.

Dihydropyridines such as amlodipine act almost exclusively on vascular smooth muscle and have negligible effect on cardiac conduction, which is why they cannot be used for rate control. Diltiazem sits between the dihydropyridines and verapamil, which has the strongest cardiac and weakest vascular effect of the three.

The negative inotropic effect — reduced contractile force — is the basis of diltiazem's main contraindication. In heart failure with reduced ejection fraction, further reducing contractility is harmful, and non-dihydropyridines are avoided. This is a common and consequential prescribing error, because rate control is often needed in exactly those patients, where a beta blocker such as metoprolol or carvedilol is the correct choice instead.

Clinical Use

For rate control in atrial fibrillation, diltiazem and beta blockers are both first-line, and the choice depends on the patient. Diltiazem is preferred in obstructive airway disease where beta blockade is unwelcome, and in patients whose blood pressure tolerates it. Beta blockers are preferred where there is coronary disease, prior infarction, or reduced ejection fraction — situations where the beta blocker itself carries additional benefit.

Combining diltiazem with a beta blocker is done cautiously and generally under specialist guidance, since both slow AV conduction and the combination can produce profound bradycardia or heart block.

For angina, diltiazem reduces myocardial oxygen demand through both rate reduction and afterload reduction, and it is particularly useful in vasospastic angina. For hypertension it is effective but is not usually the first choice unless another indication is present.

Formulations differ importantly. Immediate-release diltiazem is dosed several times daily; extended-release preparations allow once- or twice-daily dosing and are used for chronic management. The various extended-release products are not automatically interchangeable, and substitution can change the delivered profile. The heart palpitations article covers when a rhythm complaint needs evaluation, and our cardiovascular team manages rate control.

Monitoring and Follow-Up

Heart rate and blood pressure guide dosing. In atrial fibrillation, an ECG confirms both rate and rhythm, and resting heart rate is the practical target — though a rate that looks controlled at rest may still rise excessively with activity, which is worth assessing in symptomatic patients.

Diltiazem is a moderate CYP3A4 inhibitor and a P-glycoprotein inhibitor, which gives it a substantial interaction profile that is easy to underestimate. It raises levels of simvastatin and lovastatin — dose limits apply — as well as digoxin, certain immunosuppressants including tacrolimus, and some benzodiazepines. Any new medication warrants an interaction check.

Peripheral edema occurs but less than with dihydropyridines. Constipation is common, more so with verapamil. Bradycardia and AV block are the effects to watch for, particularly alongside a beta blocker or in patients with existing conduction disease. The MedlinePlus diltiazem entry covers prescribing detail, and the American Heart Association provides patient background on rate control.

Rate control and rhythm control are different strategies and patients frequently conflate them. Diltiazem does not restore normal sinus rhythm and is not intended to — the atria continue to fibrillate while the ventricular response is slowed to a tolerable rate. Many patients feel entirely well on rate control alone and need nothing more. Others remain symptomatic despite an adequately controlled rate and are candidates for rhythm control with an antiarrhythmic or ablation. Neither strategy removes the need for anticoagulation, which is decided by stroke risk rather than by rhythm, and this is the point most often misunderstood: a patient whose rate is well controlled, or whose rhythm has been restored, still has the same stroke risk and still needs the same decision about an anticoagulant such as apixaban.

Special Populations

In older adults, conduction disease is more prevalent and often undiagnosed, so bradycardia and heart block are more likely; start low and check the ECG. Hepatic impairment substantially reduces clearance and warrants dose reduction, since diltiazem is extensively metabolised by the liver; kidney impairment requires less adjustment.

Diltiazem is contraindicated in significant bradycardia, sick sinus syndrome or second- or third-degree heart block without a pacemaker, and in heart failure with reduced ejection fraction. In Wolff-Parkinson-White syndrome with atrial fibrillation it is contraindicated, because slowing AV nodal conduction can accelerate conduction down an accessory pathway and precipitate ventricular fibrillation. In pregnancy it is used when needed, though better-studied alternatives exist for hypertension. Grapefruit juice raises levels through CYP3A4 inhibition.

When to Contact Your Doctor

Report a resting heart rate persistently below 50, dizziness, fainting, or near-fainting, which suggest excessive bradycardia or heart block. Report worsening breathlessness, ankle swelling, or rapid weight gain, which may indicate heart failure — particularly important given the negative inotropic effect.

Report constipation, which is common and manageable. Report palpitations or a return of rapid, irregular heartbeat, which may mean rate control is inadequate.

Never stop diltiazem abruptly if you are taking it for angina, and always check before starting a new medication given the interaction profile.

To review your rate control, address side effects, or check whether diltiazem is the right agent for your cardiac situation, contact us or schedule a visit.