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Cardizem

What is Cardizem?

Cardizem is a prescription medication marketed under the brand name Cardizem that contains the active ingredient diltiazem. Diltiazem belongs to the calcium-channel blocker class of drugs and is used to manage conditions affecting the heart and blood vessels. In Hong Kong, Cardizem is regulated by the Department of Health and is available only with a medical prescription. The medication is supplied as a pill in the following strengths: 30 mg, 60 mg, 90 mg, 120 mg, and 180 mg.

How Cardizem Works in the Body

Diltiazem reduces the influx of calcium ions through L-type calcium channels located primarily in cardiac muscle and vascular smooth muscle. By limiting calcium entry, the drug produces two complementary effects:

• Vasodilation - Relaxation of arterial smooth muscle lowers peripheral resistance, which helps reduce blood pressure.
• Negative cardiac inotropy and chronotropy - Decreased calcium availability diminishes the force of heart muscle contraction and slows the heart rate, which is useful in controlling certain rhythm disorders.

These actions begin within 30-60 minutes after oral administration, reach peak plasma concentrations typically within 1-3 hours, and the therapeutic effect can last up to 12 hours for immediate-release formulations. Diltiazem is extensively metabolized by the liver (primarily CYP3A4) and excreted through both renal and biliary pathways.

Conditions Treated by Cardizem

Cardizem is approved by major regulatory agencies-including the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA)-for the following indications, which are also recognized by Hong Kong health authorities:

• Hypertension (high blood pressure) - Helps lower systolic and diastolic pressures when used alone or in combination with other antihypertensives.
• Chronic stable angina - Reduces the frequency of chest pain episodes by improving coronary blood flow.
• Certain supraventricular tachyarrhythmias - Particularly atrial flutter and atrial fibrillation, where rate control is needed.

Typical patient populations include adults with diagnosed hypertension, individuals experiencing exertional chest discomfort due to coronary artery disease, and patients with documented supraventricular arrhythmias. Cardizem is not indicated for acute myocardial infarction or severe heart failure without specialist supervision.

Evidence-Based Off-Label Uses

Research literature and clinical guidelines have explored additional applications of diltiazem beyond its approved labels. Where sufficient evidence exists, these uses are highlighted, but they remain off-label and should be pursued only under specialist guidance.

• Rate control in atrial fibrillation (AF) or atrial flutter - Several randomized controlled trials demonstrate that diltiazem effectively slows ventricular response in AF, offering an alternative to beta-blockers. Because this indication is not formally approved by the Hong Kong Department of Health, clinicians must weigh benefits against potential contraindications.
• Prevention of postoperative atrial fibrillation - Prophylactic use of diltiazem in cardiac surgery patients has shown reductions in new-onset AF in observational studies. This practice is considered investigational in Hong Kong.

Disclaimer: Off-label use requires medical supervision and individualized risk assessment. Patients should discuss potential benefits and risks with a qualified healthcare provider.

Who Should Not Use Cardizem?

Absolute Contraindications

• Known hypersensitivity to diltiazem or any excipients in the pill formulation.
• Severe uncontrolled heart failure (ejection fraction < 30 %) or cardiogenic shock.
• Second- or third-degree atrioventricular (AV) block without a permanent pacemaker.
• Sick sinus syndrome in the absence of pacing support.
• Acute myocardial infarction with ongoing ischemia.

Relative Contraindications

• Moderate hepatic impairment (Child-Pugh B) - dose adjustments may be necessary.
• Renal impairment (creatinine clearance < 30 mL/min) - careful monitoring recommended.
• Pregnancy (especially the third trimester) and lactation - diltiazem crosses the placenta and appears in breast milk; risk-benefit assessment is essential.
• Elderly patients - heightened sensitivity to hypotension and bradycardia may require lower starting doses.

Special Populations

• Pregnancy/Lactation: Category C (animal studies show risk; no well-controlled human studies). Use only if potential benefit justifies the risk.
• Geriatric: Initiate at the lowest available dose (30 mg) and titrate slowly.
• Pediatric: Cardizem is not approved for patients under 18 years for most indications; dosing data are limited.

Safety Profile: Side Effects and Interactions

Common Side Effects

• Headache - often mild and transient.
• Peripheral edema - swelling of ankles or feet, particularly at higher doses.
• Flushing - warm sensation, usually self-limited.
• Dizziness - related to blood-pressure lowering; advise caution when standing.
• Nausea - generally mild; can be mitigated by taking the pill with food.

Serious Adverse Events

• Severe bradycardia - heart rate < 50 bpm may require medical attention.
• Hypotension - systolic pressure < 90 mmHg can lead to syncope.
• Heart block - new onset AV block may necessitate immediate discontinuation.
• Liver enzyme elevation - monitor hepatic function if prolonged therapy is anticipated.

Drug Interactions

• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin, grapefruit juice) - increase diltiazem plasma levels, raising risk of bradycardia and hypotension.
• CYP3A4 inducers (e.g., rifampin, carbamazepine) - reduce efficacy by lowering concentrations.
• Beta-blockers - additive effects on heart rate and contractility; co-administration should be closely supervised.
• Digoxin - may raise digoxin levels, increasing the potential for toxicity.
• Antihypertensives (e.g., ACE inhibitors, ARBs) - can amplify blood-pressure lowering; monitor for orthostatic symptoms.

Food and Lifestyle Interactions

• Grapefruit products - potentiate diltiazem exposure; avoid regular consumption.
• Alcohol - may enhance vasodilatory effects, leading to dizziness.
• Driving or operating machinery - caution is advised until individual response is known, especially after dose initiation.
• Exercise - moderate activity is permissible, but high-intensity workouts may precipitate dizziness in the early treatment phase.

If specific interaction data for Cardizem are limited, patients should always inform their healthcare provider of all concomitant medications, supplements, and herbal products.

How to Take Cardizem

Standard Dosing

• Hypertension or angina (immediate-release tablets): Start with 30 mg taken three times daily. Dose may be increased in 30 mg increments to a maximum of 180 mg per day based on blood-pressure response.
• Extended-release formulations (if prescribed): Typical starting dose is 120 mg once daily, with possible titration up to 180 mg daily.
• Rate control for atrial fibrillation (off-label): Initiate with 30 mg once daily; increase cautiously while monitoring heart rate and ECG.

All dosages referenced correspond to the 30 mg, 60 mg, 90 mg, 120 mg, and 180 mg strengths available in Hong Kong.

Special Populations

• Renal impairment: No dose adjustment is required for mild to moderate dysfunction, but monitor for accumulation in severe cases.
• Hepatic impairment: Reduce initial dose by 50 % (e.g., start with 30 mg) and titrate slowly.
• Elderly: Begin with the lowest dose (30 mg) and increase only if tolerated.

Administration Tips

• Swallow the pill whole with a full glass of water. Do not crush or chew extended-release tablets.
• The medication may be taken with or without food; however, taking it with meals can lessen gastrointestinal upset.
• Store pills at room temperature, away from excess moisture and direct sunlight.

Missed Dose

• If a dose is forgotten and the scheduled time is still ≥ 4 hours away, take the missed pill. If it is within 4 hours of the next dose, skip the missed pill and continue with the regular schedule. Do not double the dose.

Overdose

• Symptoms may include profound hypotension, severe bradycardia, and heart block. Immediate medical attention is required. Treatment focuses on supportive measures, intravenous fluids, and, if necessary, atropine for bradycardia.

Discontinuation

• Cardizem can be stopped abruptly for hypertension, but gradual tapering is recommended when used for chronic angina or arrhythmia control to avoid rebound tachycardia or hypertension.

Monitoring and Follow-Up

• Blood pressure: Check weekly after initiation, then monthly once stable.
• Heart rate and ECG: Baseline ECG before starting, followed by periodic monitoring especially when dose changes.
• Liver function tests: Baseline and at 3-month intervals for long-term therapy.
• Renal function: Assess serum creatinine annually or sooner if comorbid kidney disease exists.
• Patient education: Encourage reporting of dizziness, palpitations, or swelling promptly.

Storage and Handling

• Keep the medication in its original container, tightly closed.
• Store at 15-30 °C (59-86 °F), protected from moisture and direct light.
• Do not use the medication after the expiration date printed on the package.
• Dispose of unused tablets according to local pharmacy or hazardous waste guidelines; keep out of reach of children.

Medication-Specific Glossary

Calcium-Channel Blocker

A class of drugs that inhibit calcium ion entry into cardiac and vascular smooth muscle cells, producing vasodilation and reduced cardiac contractility.

QTc Prolongation

Extension of the corrected QT interval on an ECG, which can increase the risk of ventricular arrhythmias. Diltiazem has a modest effect on QTc.

Therapeutic Window

The dosage range that provides effective treatment without unacceptable side effects. For diltiazem, this window is relatively wide but requires individualized titration.

Medical Disclaimer

This article provides educational information about Cardizem 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.