Diltiazem: Advanced Calcium Channel Blockade for Cardiovascular Health
Diltiazem
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Diltiazem hydrochloride is a benzothiazepine-class calcium channel blocker (CCB) prescribed for the management of various cardiovascular conditions. It functions by inhibiting the influx of calcium ions during cardiac and vascular smooth muscle depolarization, leading to reduced myocardial contractility, slowed atrioventricular (AV) nodal conduction, and coronary and systemic arterial vasodilation. This multifaceted mechanism of action makes it a cornerstone therapy in modern cardiology for controlling heart rate, reducing blood pressure, and managing myocardial oxygen demand. Its clinical utility spans from hypertension and chronic stable angina to supraventricular tachyarrhythmias, offering a favorable efficacy and safety profile for a broad patient demographic.
Features
- Pharmaceutical class: Benzothiazepine derivative calcium channel blocker
- Available formulations: Immediate-release tablets, extended-release capsules (once-daily and twice-daily), and intravenous injection
- Standard strengths: 30 mg, 60 mg, 90 mg, 120 mg, 180 mg, 240 mg, 300 mg, 360 mg (varies by formulation and brand)
- Mechanism of Action: Inhibits transmembrane influx of calcium ions into cardiac muscle and vascular smooth muscle cells
- Bioavailability: Approximately 40% due to significant first-pass metabolism
- Protein binding: 70–80%
- Metabolism: Extensive hepatic metabolism via cytochrome P450 isoenzymes, primarily CYP3A4
- Elimination half-life: Biphasic; initial phase 1.5–3.5 hours, terminal phase 5–8 hours (extended-release formulations have prolonged absorption)
- Excretion: Primarily in urine (2–4% as unchanged drug) and feces
Benefits
- Provides effective control of hypertension by reducing peripheral vascular resistance and afterload.
- Manages chronic stable angina by decreasing myocardial oxygen demand through reduced heart rate and contractility, and by increasing coronary blood flow via vasodilation.
- Offers rapid conversion to and control of ventricular rate in atrial fibrillation and atrial flutter through selective action on the AV node.
- Exhibits a lower incidence of peripheral edema and reflex tachycardia compared to dihydropyridine CCBs like amlodipine.
- Extended-release formulations enhance adherence through once- or twice-daily dosing and provide stable 24-hour plasma concentrations for consistent therapeutic effect.
- May be used safely in combination with other antihypertensive agents, such as ACE inhibitors or diuretics, for synergistic blood pressure control.
Common use
Diltiazem is indicated for the first-line treatment of essential hypertension, either as monotherapy or in combination with other antihypertensive agents. It is a mainstay in the management of chronic stable angina pectoris, particularly in patients where beta-blockers are contraindicated or ineffective. A critical application is in the management of supraventricular tachyarrhythmias, including atrial fibrillation and atrial flutter, for controlling ventricular rate. It is also used off-label for the prevention of atrial fibrillation recurrence, treatment of unstable angina, and as part of a medical management strategy for certain cases of coronary artery spasm (Prinzmetal’s angina).
Dosage and direction
Dosage is highly individualized based on the indication, patient response, and formulation. For hypertension or angina, initial dosing with immediate-release tablets typically starts at 30 mg four times daily, titrated upward to 180–360 mg daily in divided doses. Extended-release capsules (e.g., Cardizem CD, Tiazac) allow for once-daily dosing, starting at 120–180 mg, with a maximum dose of 480 mg daily. For atrial arrhythmias, intravenous administration is used for acute control (0.25 mg/kg as a bolus, followed by an infusion of 5–15 mg/hour), followed by transition to oral therapy. Tablets and capsules should be swallowed whole, not crushed or chewed, and may be taken with or without food. Dosage adjustments are mandatory in patients with hepatic impairment or renal dysfunction.
Precautions
Close monitoring of blood pressure, heart rate, and ECG (particularly PR interval) is required, especially during initiation and titration. Use with caution in patients with congestive heart failure (CHF) with impaired ventricular function, as the negative inotropic effect may exacerbate symptoms. Hepatic enzyme levels should be monitored periodically due to extensive hepatic metabolism; dosage reduction is necessary in liver disease. May prolong AV nodal refractory periods; caution is advised in patients with sick sinus syndrome or AV block (unless a pacemaker is present). Abrupt withdrawal should be avoided, as it may precipitate angina. Patients should be advised about the potential for dizziness and to avoid driving or operating machinery until their response is known.
Contraindications
Diltiazem is contraindicated in patients with known hypersensitivity to the drug or any component of the formulation. Its use is absolutely prohibited in patients with sick sinus syndrome or second- or third-degree AV block, in the absence of a functioning ventricular pacemaker. It is contraindicated in patients with hypotension (systolic pressure < 90 mmHg) or acute myocardial infarction with pulmonary congestion documented by x-ray on admission. The intravenous formulation is contraindicated in patients with atrial fibrillation/flutter associated with an accessory bypass tract (e.g., Wolff-Parkinson-White syndrome). Concomitant use with strong CYP3A4 inhibitors that can lead to elevated diltiazem levels (e.g., itraconazole) is also contraindicated.
Possible side effect
The most common side effects are related to its vasodilatory and cardiodepressant effects. These include dizziness (3.6%), headache (3.2%), edema (3.0%), asthenia (2.6%), flushing (1.8%), and nausea (1.8%). Bradycardia and AV block (first-degree) are common cardiovascular effects. Less frequent but more serious adverse reactions include symptomatic hypotension, exacerbation of heart failure, severe bradycardia, syncope, and elevated liver enzymes (AST, ALT). Rash and erythema multiforme have been reported. Rare instances of gingival hyperplasia, as with other calcium channel blockers, can occur with prolonged use.
Drug interaction
Diltiazem is a moderate inhibitor of CYP3A4 and is itself a substrate, leading to numerous clinically significant interactions. Coadministration with beta-blockers or digoxin increases the risk of bradycardia and AV block; digoxin levels may also increase. Concurrent use with other antihypertensives (e.g., ACE inhibitors, diuretics) can potentiate hypotensive effects. Simvastatin and lovastatin levels are significantly increased, raising the risk of myopathy and rhabdomyolysis; a dose limitation is required. Cyclosporine, sirolimus, and tacrolimus levels can be increased, necessitating close monitoring. Carbamazepine, phenytoin, and rifampin (CYP3A4 inducers) can decrease diltiazem levels and efficacy. Concomitant use with ivabradine is contraindicated. Anesthetics that depress cardiac function will have additive effects.
Missed dose
If a dose of an immediate-release formulation is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should never take a double dose to make up for a missed one. For extended-release formulations taken once daily, if a dose is missed, it should be taken as soon as possible on the same day. The next dose should be taken at the regular time the following day. Consistency in administration is key to maintaining stable therapeutic plasma levels.
Overdose
Manifestations of diltiazem overdose are extensions of its pharmacological effects and can be life-threatening. Symptoms include severe hypotension, bradycardia, cardiac conduction defects (including complete heart block), heart failure, and cardiogenic shock. Non-cardiovascular symptoms may include confusion, drowsiness, slurred speech, and nausea. Treatment is primarily supportive and focused on cardiovascular stabilization. This includes vigilant hemodynamic monitoring, IV fluids for hypotension, and atropine for bradycardia. Intravenous calcium gluconate or chloride may provide temporary antagonism of calcium channel blockade. In refractory cases, vasopressors (e.g., dopamine, norepinephrine), cardiac pacing, or intravenous glucagon may be required. Due to extensive protein binding, diltiazem is not dialyzable.
Storage
Store diltiazem tablets and capsules at controlled room temperature, 20°C to 25°C (68°F to 77°F), in a tight, light-resistant container. The medication must be kept in its original container away from excess moisture, light, and heat. It should be stored out of reach of children and pets. Do not store in bathrooms or kitchen cabinets where humidity and temperature fluctuations are common. Do not use medication that is beyond its expiration date or shows signs of physical degradation.
Disclaimer
This information is for educational and professional medical reference purposes only and is not a substitute for the professional judgment of a qualified healthcare provider in diagnosing and treating patients. The content does not encompass all possible uses, directions, precautions, interactions, or adverse effects. The author and publisher are not responsible for any errors, omissions, or for any outcomes related to the use of this information. The reader is strongly advised to consult the official prescribing information and a healthcare professional for any questions about a medical condition or appropriate treatment. Never disregard professional medical advice or delay in seeking it because of something you have read here.
Reviews
“Diltiazem has been a workhorse in my cardiology practice for over two decades. Its dual action on heart rate and blood pressure makes it exceptionally useful for patients with comorbid hypertension and atrial fibrillation. The extended-release formulations have significantly improved patient adherence and provide very smooth 24-hour control with minimal peak-trough fluctuation.” – Cardiologist, 28 years of experience
“As a clinical pharmacist, I appreciate diltiazem’s predictable pharmacokinetics, though its CYP3A4 interactions require vigilant medication reconciliation. It remains a go-to agent for rate control in AFib due to its rapid IV onset and seamless transition to oral therapy. The incidence of peripheral edema is notably lower than with amlodipine, which is a significant benefit for many patients.” – Clinical Pharmacy Specialist, Cardiology
“For my chronic angina, diltiazem ER has been life-changing. I experienced some initial lightheadedness, but that subsided. My angina episodes have reduced dramatically, and I only need to remember one dose per day. It has allowed me to return to a much more active lifestyle.” – Patient, 6 years on therapy