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Diltiazem

Diltiazem: Generic Medication Overview

Diltiazem is a calcium-channel-blocking agent that belongs to the heart- and blood-pressure therapeutic class. It is available as a generic pill in strengths of 30 mg, 60 mg, 90 mg, and 120 mg. In Hong Kong, diltiazem is a prescription-only medication regulated by the Pharmacy and Poisons Board under the Hong Kong Department of Health. The drug is manufactured by several pharmaceutical companies and marketed globally under brand names such as Cardizem, Tiazac, and Dilacor.

How Diltiazem Works in the Body

Diltiazem belongs to the non-dihydropyridine subclass of calcium-channel blockers. It inhibits the influx of calcium ions through L-type calcium channels in the smooth muscle of blood vessels and the myocardium. By reducing intracellular calcium, diltiazem:

• Relaxes vascular smooth muscle, leading to lowered peripheral resistance and a modest reduction in blood pressure.
• Decreases myocardial contractility and heart-rate (negative inotropic and chronotropic effects), which eases the heart’s workload and helps control rapid heart rhythms.

The onset of action after oral dosing is usually observed within 30 minutes, with peak plasma concentrations reached in 2-4 hours. The drug’s therapeutic effects can last 6-12 hours, depending on the dose and formulation. Diltiazem is extensively metabolized by the liver (CYP3A4) and excreted primarily in the bile.

Conditions Treated by Diltiazem

Diltiazem is approved by major regulatory agencies (e.g., FDA, EMA) and is routinely prescribed in Hong Kong for the following indications:

• Hypertension - as monotherapy or in combination with other antihypertensives.
• Chronic stable angina - to relieve chest pain by improving coronary blood flow.
• Acute coronary syndromes (as part of a multi-drug regimen).
• Rate control in atrial fibrillation or atrial flutter - slowing ventricular response without converting rhythm.

These uses are supported by large-scale clinical trials and guideline recommendations from cardiology societies.

Evidence-Based Off-Label Uses

• Cluster headache prophylaxis - Small open-label studies have reported benefit, but robust randomized trials are lacking.
• Migraine prevention - Limited case series suggest possible efficacy; however, this indication is not approved.

Off-label use requires medical supervision and an individualized risk assessment.

Who Should Not Use Diltiazem?

Absolute Contraindications

• Known hypersensitivity to diltiazem or any excipients in the pill.
• Severe hypotension (systolic < 90 mmHg).
• Second- or third-degree atrioventricular (AV) block without a permanent pacemaker.
• Sick sinus syndrome in the absence of a pacemaker.

Relative Contraindications

• Pregnancy - Category C; use only if the potential benefit outweighs risk.
• Breast-feeding - Diltiazem passes into milk; caution advised.
• Severe hepatic impairment - Reduced clearance may increase plasma levels.
• Concurrent use of strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin) - may raise diltiazem concentrations.

Special Populations

• Elderly - Often start at lower doses (30 mg) and titrate slowly.
• Renal impairment - No dose adjustment needed for mild-to-moderate dysfunction, but monitor for accumulation in severe cases.

Safety Profile

Common Side Effects

• Headache - Usually mild, resolves with continued therapy.
• Peripheral edema - More frequent at higher doses; can be managed with leg elevation.
• Dizziness or light-headedness - Related to blood-pressure lowering; advise rising slowly from seated positions.
• Flushing - Transient sensation of warmth.

Serious Adverse Events

• Bradycardia (heart rate < 50 bpm).
• Symptomatic hypotension (e.g., fainting, shock).
• Heart block - New-onset AV block warrants immediate medical evaluation.
• Heart failure exacerbation - Rare but possible due to negative inotropic effect.

If any of these occur, seek medical attention promptly.

Drug Interactions

• Major

• Beta-blockers (e.g., metoprolol) - additive bradycardia; monitor heart rate.

• Digoxin - may increase serum digoxin levels; check levels regularly.

• CYP3A4 inhibitors (e.g., itraconazole, ritonavir) - raise diltiazem levels, increasing risk of toxicity.

• Moderate

• Statins metabolized by CYP3A4 (e.g., simvastatin) - may require dose reduction.

• Macrolide antibiotics (e.g., erythromycin) - can modestly elevate diltiazem concentrations.

Patients should provide a complete medication list, including over-the-counter drugs and herbal supplements, to their healthcare provider before starting diltiazem.

Food and Lifestyle Interactions

• Food - Can be taken with or without food; high-fat meals may slightly delay absorption.
• Alcohol - May enhance blood-pressure-lowering effects; consume in moderation.
• Driving - If dizziness occurs, avoid operating heavy machinery until symptoms resolve.

How to Take Diltiazem

• Standard dosing (adult):
• Initiate with 30 mg once daily or 30 mg twice daily for hypertension.
• For angina or rate control, start at 60 mg once daily, titrating up to 120 mg once daily based on response and tolerability.
• Maximum recommended dose: 360 mg per day (typically divided).
• Administration - Swallow whole; do not crush or chew the pill.
• Missed dose - Take it as soon as remembered unless it is near the time of the next scheduled dose; do not double-dose.
• Overdose - Symptoms may include severe hypotension, bradycardia, and cardiac arrest. Seek emergency care; treatment is supportive, with intravenous calcium gluconate as an antidote in severe cases.
• Discontinuation - Abrupt cessation is generally safe, but in patients with coronary artery disease, a gradual taper is advisable to avoid rebound angina.

Monitoring and Follow-Up

• Blood pressure and heart rate - Check within 1-2 weeks of initiation, then monthly until stable.
• Electrocardiogram (ECG) - Baseline and periodic ECGs for patients with arrhythmias or on high doses.
• Liver function tests - Periodic monitoring in patients with existing hepatic disease or those on interacting CYP3A4 inhibitors.
• Renal function - Assess creatinine clearance annually, especially in older adults.

Storage and Handling

• Store the pills at room temperature (20-25 °C), protected from excess moisture and direct sunlight.
• Keep the container tightly closed and out of reach of children.
• Do not use the medication after the expiration date printed on the package.

Medication-Specific Glossary

Calcium-Channel Blocker

A class of drugs that inhibit calcium entry into cardiac and smooth-muscle cells, leading to vasodilation and reduced cardiac contractility.

Negative Inotropy

A decrease in the force of heart muscle contraction, beneficial in conditions where the heart is over-working.

AV Block

Impairment of electrical conduction between the atria and ventricles; classified into first, second, and third degree.

CYP3A4

A liver enzyme responsible for metabolizing many drugs, including diltiazem; inhibitors can raise drug levels.

Medical Disclaimer

This article provides educational information about diltiazem and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.