Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CARDIZEM SR vs CALAN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Diltiazem inhibits calcium ion influx across cardiac and vascular smooth muscle cell membranes during depolarization, leading to negative inotropic, chronotropic, and dromotropic effects, and vasodilation.
Verapamil inhibits calcium ion influx through voltage-gated L-type calcium channels in cardiac and vascular smooth muscle, leading to decreased myocardial contractility, slowed AV conduction, and vasodilation.
Hypertension,Angina pectoris due to coronary artery spasm (Prinzmetal's variant angina),Chronic stable angina (classic effort-associated angina)
Angina pectoris (chronic stable, vasospastic, unstable),Essential hypertension,Supraventricular tachyarrhythmias (e.g., atrial fibrillation, atrial flutter, PSVT)
Oral: Initial dose 60-120 mg twice daily; titrate to maximum 360 mg/day divided into two doses.
Initial: 80-120 mg orally 3 times daily; maintenance: 240-480 mg/day in 3-4 divided doses. IV: 5-10 mg over 2 minutes, may repeat after 15-30 minutes.
3.0-4.5 hours for diltiazem; metabolites (e.g., desacetyldiltiazem) up to 10 hours. Clinical context: dosing interval adjustment in hepatic impairment.
Terminal elimination half-life is 3-7 hours for immediate-release; can be prolonged to 12-16 hours with sustained-release due to slow absorption; increased in hepatic impairment.
Primarily hepatic via CYP3A4; undergoes extensive first-pass metabolism.
Extensively metabolized in the liver via CYP3A4, CYP1A2, and CYP2C8 isoenzymes; undergoes N-dealkylation and O-demethylation; first-pass metabolism results in low bioavailability (20-35%).
Renal: 2-4% unchanged; hepatic metabolism: ~60-70% (including active metabolites); fecal: ~30-40%.
Approximately 70% renal (3-4% unchanged, remainder as metabolites) and 25% biliary/fecal.
Approximately 70-80%, primarily to albumin and alpha-1-acid glycoprotein.
Approximately 90% bound to plasma proteins, primarily albumin.
3.1-5.1 L/kg; large Vd indicates extensive tissue distribution (e.g., myocardium, vascular smooth muscle).
Vd 4-5 L/kg; indicates extensive tissue distribution beyond plasma volume.
Oral (sustained-release): approximately 40-50% due to first-pass metabolism; variable among formulations.
Oral bioavailability is 20-35% due to extensive first-pass hepatic metabolism; IV bioavailability is 100%.
For GFR < 10 m L/min: Use with caution and reduce dose by 25-50%; consider extended dosing interval.
Cr Cl <30 m L/min: reduce dose by 50% and monitor carefully.
Child-Pugh Class B: Reduce dose by 50%; Child-Pugh Class C: Use not recommended.
Child-Pugh A: 50% of normal dose; Child-Pugh B: 25% of normal dose; Child-Pugh C: contraindicated or use with extreme caution.
Safety and efficacy not established; no specific weight-based dosing guidelines available.
Oral: 4-8 mg/kg/day in 3 divided doses; IV: 0.1-0.3 mg/kg over 2 minutes, max 5 mg.
Initial dose 60 mg twice daily; titrate slowly due to increased risk of bradycardia and hypotension.
Start at lowest dose (e.g., 40 mg 3 times daily) and titrate slowly; monitor for hypotension and bradycardia.
None.
Contains verapamil hydrochloride. Risk of serious adverse effects including hypotension, bradycardia, AV block, and cardiac arrest. Must not be administered to patients with severe left ventricular dysfunction, cardiogenic shock, or sick sinus syndrome (unless paced).
Cardiac conduction abnormalities: bradycardia, AV block, sick sinus syndrome,Heart failure: use with caution in patients with compromised ventricular function,Hypotension,Hepatic impairment,Concomitant use with beta-blockers may increase risk of bradycardia and AV block,Abrupt discontinuation may exacerbate angina
May cause hypotension, bradycardia, AV block, and exacerbation of heart failure. Avoid in patients with pre-existing conduction abnormalities. Use caution with beta-blockers, digoxin, and CYP3A4 inhibitors. Abrupt withdrawal may exacerbate angina. May increase lithium and carbamazepine levels.
Sick sinus syndrome (except in patients with a functioning artificial ventricular pacemaker),Second- or third-degree AV block (except in patients with a functioning artificial ventricular pacemaker),Hypotension (systolic blood pressure < 90 mm Hg),Acute myocardial infarction with pulmonary congestion,Known hypersensitivity to diltiazem
Severe left ventricular dysfunction, cardiogenic shock, sick sinus syndrome (without pacemaker), second- or third-degree AV block (without pacemaker), atrial flutter/fibrillation with accessory bypass tract (e.g., WPW syndrome), concurrent use of IV beta-blockers.
Grapefruit and grapefruit juice increase diltiazem levels by inhibiting CYP3A4 metabolism; avoid concurrent use. No other significant food restrictions. Alcohol may enhance hypotensive effects and increase risk of dizziness.
Avoid grapefruit and grapefruit juice as they inhibit CYP3A4 metabolism, increasing verapamil levels and risk of toxicity. Limit alcohol intake as it may enhance hypotensive effects. High-fat meals may delay absorption but not extent; take consistently with regard to meals.
FDA Pregnancy Category C. No adequate studies in pregnant women. In animal studies, diltiazem has been shown to cause embryofetal toxicity (skeletal abnormalities, reduced fetal weight) at doses 5-10 times the maximum recommended human dose. Risk to fetus cannot be ruled out; use only if potential benefit justifies potential risk.
First trimester: No increased risk of major malformations observed in human studies; animal studies show fetal toxicity at high doses. Second and third trimesters: May cause fetal bradycardia, hypotension, and impaired placental perfusion; avoid use for pregnancy-induced hypertension due to risk of fetal hypoxia.
Diltiazem is excreted into human breast milk at low concentrations. Estimated infant dose is <1% of maternal weight-adjusted dose. M/P ratio not established. Although risk to nursing infant is likely low, caution is advised. Monitor infant for bradycardia, hypotension, and feeding difficulties.
Verapamil (CALAN) is excreted into breast milk; M/P ratio approximately 0.6. The relative infant dose is low (estimated <5% of maternal weight-adjusted dose). No adverse effects reported in breastfed infants. Caution in preterm infants or those with renal impairment.
No specific dose adjustment guidelines for pregnancy; however, pharmacokinetic changes in pregnancy (increased volume of distribution, altered hepatic metabolism) may require dose titration based on clinical response and tolerability. Start at lowest effective dose and monitor closely.
Pregnancy may increase clearance of verapamil; monitoring of therapeutic effect advised. Dose may need adjustment based on clinical response. Avoid use in pregnancy-induced hypertension.
Cardizem SR is a sustained-release calcium channel blocker indicated for hypertension and angina. Onset: 2-3 hours, duration: 12-24 hours. Avoid concurrent use with beta-blockers due to risk of bradycardia and heart block. Contraindicated in sick sinus syndrome (unless pacemaker), second- or third-degree AV block, hypotension (SBP <90 mm Hg), and acute MI with pulmonary congestion. Monitor liver function and renal function; dose adjustment needed in hepatic impairment. Use caution in patients with decreased left ventricular function (ejection fraction <40%). Do not crush or chew capsules; swallow whole.
Calan (verapamil) is a class IV antiarrhythmic and calcium channel blocker. Use caution in patients with hepatic impairment due to reduced clearance; dose adjustment may be needed. Avoid in patients with pre-existing bradycardia, second- or third-degree AV block, or sick sinus syndrome unless a pacemaker is present. May increase digoxin levels; monitor digoxin concentrations. Use with caution in patients with hypertrophic cardiomyopathy. For IV administration, have calcium gluconate available to reverse hypotension or bradycardia. Not recommended for use in acute myocardial infarction or cardiogenic shock.
Take this medication exactly as prescribed, with or without food, at the same time each day.,Swallow the capsule whole; do not crush, chew, or open it.,Avoid grapefruit and grapefruit juice while on this medication; they can increase the drug's effect and risk of side effects.,Do not stop taking this medication suddenly; abrupt discontinuation may worsen chest pain or increase blood pressure.,Contact your healthcare provider if you experience slow heartbeat, fainting, dizziness, shortness of breath, or swelling of the legs/ankles.,Limit alcohol consumption as it may increase the risk of side effects such as dizziness or fainting.,Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding.,Keep all appointments to check your blood pressure and heart rhythm.
Take exactly as prescribed; do not skip doses or stop abruptly without consulting your doctor.,Avoid grapefruit juice as it can increase verapamil levels and risk of side effects.,If you miss a dose, take it as soon as you remember unless it is almost time for the next dose; do not double the dose.,Avoid alcohol as it may worsen side effects like dizziness or low blood pressure.,Report symptoms of bradycardia (slow heart rate), palpitations, shortness of breath, or swelling of ankles/feet.,This medication may cause dizziness; avoid driving or operating machinery until you know how it affects you.,Do not consume grapefruit or its juice during treatment.,Keep a regular medication schedule and do not change brands without doctor approval.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about CARDIZEM SR vs CALAN, answered by our medical review team.
CARDIZEM SR is a Calcium Channel Blocker that works by Diltiazem inhibits calcium ion influx across cardiac and vascular smooth muscle cell membranes during depolarization, leading to negative inotropic, chronotropic, and dromotropic effects, and vasodilation.. CALAN is a Calcium Channel Blocker that works by Verapamil inhibits calcium ion influx through voltage-gated L-type calcium channels in cardiac and vascular smooth muscle, leading to decreased myocardial contractility, slowed AV conduction, and vasodilation.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CARDIZEM SR and CALAN depend on the specific clinical indication. These are both Calcium Channel Blocker agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of CARDIZEM SR is: Oral: Initial dose 60-120 mg twice daily; titrate to maximum 360 mg/day divided into two doses.. The standard adult dose of CALAN is: Initial: 80-120 mg orally 3 times daily; maintenance: 240-480 mg/day in 3-4 divided doses. IV: 5-10 mg over 2 minutes, may repeat after 15-30 minutes.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between CARDIZEM SR and CALAN in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. CARDIZEM SR is classified as Category C. FDA Pregnancy Category C. No adequate studies in pregnant women. In animal studies, diltiazem has been shown to cause embryofetal toxicity (skeletal abnormalities, reduced fetal we. CALAN is classified as Category C. First trimester: No increased risk of major malformations observed in human studies; animal studies show fetal toxicity at high doses. Second and third trimesters: May cause fetal . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.