Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ISOPTIN vs CALAN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Verapamil inhibits calcium ion influx across cardiac and vascular smooth muscle cells, blocking L-type calcium channels, leading to vasodilation and reduced myocardial contractility and conduction velocity.
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.
Treatment of hypertension,Management of angina pectoris,Control of supraventricular tachyarrhythmias (e.g., atrial fibrillation, atrial flutter, PSVT),Off-label: Cluster headache prophylaxis, prevention of migraine, bipolar disorder (manic episodes),Off-label: Hypertrophic cardiomyopathy (obstructive)
Angina pectoris (chronic stable, vasospastic, unstable),Essential hypertension,Supraventricular tachyarrhythmias (e.g., atrial fibrillation, atrial flutter, PSVT)
Initial dose: 80-120 mg orally three times daily; sustained-release: 120-240 mg orally once daily. IV: 5-10 mg slow IV push over 2 minutes, may repeat after 15-30 minutes. Maximum daily oral dose: 480 mg.
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.
Terminal elimination half-life: 4.5-12 hours (mean 8 hours); increases with hepatic impairment or cirrhosis
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.
Extensively metabolized in the liver via CYP3A4, CYP3A5, and CYP1A2 isoenzymes; major metabolite is norverapamil (active).
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 (70% as metabolites, 3-5% unchanged); biliary/fecal (25%)
Approximately 70% renal (3-4% unchanged, remainder as metabolites) and 25% biliary/fecal.
90% bound to albumin
Approximately 90% bound to plasma proteins, primarily albumin.
4.5 L/kg (extensive tissue distribution, reflects high myocardial and vascular binding)
Vd 4-5 L/kg; indicates extensive tissue distribution beyond plasma volume.
Oral: 20-35% (extensive first-pass hepatic metabolism)
Oral bioavailability is 20-35% due to extensive first-pass hepatic metabolism; IV bioavailability is 100%.
For Cr Cl <30 m L/min: Reduce dose by 50-75% of normal. For Cr Cl 30-50 m L/min: Start at lower end of dosing range. No specific guidelines for dialysis.
Cr Cl <30 m L/min: reduce dose by 50% and monitor carefully.
Child-Pugh A: No adjustment. Child-Pugh B: Reduce dose by 50% and monitor. Child-Pugh C: Use with caution, reduce dose by 70-80%.
Child-Pugh A: 50% of normal dose; Child-Pugh B: 25% of normal dose; Child-Pugh C: contraindicated or use with extreme caution.
Oral: 4-8 mg/kg/day in 3-4 divided doses; maximum 360 mg/day. IV: 0.1-0.3 mg/kg/dose (max 5 mg) over 2 minutes, repeat after 30 minutes if needed.
Oral: 4-8 mg/kg/day in 3 divided doses; IV: 0.1-0.3 mg/kg over 2 minutes, max 5 mg.
Start at lower end of dosing range (e.g., 40 mg orally three times daily); titrate slowly due to increased sensitivity and decreased clearance. Monitor for hypotension and bradycardia.
Start at lowest dose (e.g., 40 mg 3 times daily) and titrate slowly; monitor for hypotension and bradycardia.
No FDA black box warning.
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).
Heart failure: May worsen or precipitate heart failure due to negative inotropic effects.,Hypotension: Can cause symptomatic hypotension.,Conduction abnormalities: May worsen AV block, sinus node dysfunction (risk of bradycardia).,Hepatic impairment: Reduced clearance requires dose adjustment.,Concomitant beta-blockers: Additive negative inotropic and bradycardic effects.,Digoxin: Increases digoxin levels; monitor toxicity.,Neuromuscular disorders: May exacerbate myasthenia gravis or Duchenne muscular dystrophy.,Lactation: Excreted in breast milk; caution advised.
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.
Severe left ventricular dysfunction (ejection fraction <30%) or cardiogenic shock,Hypersensitivity to verapamil or any component of the formulation,Sick sinus syndrome or second/third-degree AV block (except with functioning pacemaker),Atrial flutter or fibrillation with accessory bypass tract (e.g., WPW syndrome) unless ventricular preexcitation is excluded,Concomitant use of IV beta-blockers (within a few hours),Severe hypotension (systolic <90 mm Hg)
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 verapamil levels, increasing risk of toxicity. Avoid concurrent consumption. Alcohol may exacerbate hypotension and 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.
INSUFFICIENT DATA IN HUMANS: Animal studies show no teratogenic effects at clinically relevant doses. First trimester: case reports not indicating major malformations but risk cannot be excluded. Second/third trimester: may cause fetal bradycardia, hypotension, and intrauterine growth restriction due to placental hypoperfusion; avoid use near term due to risk of uterine atony.
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.
Verapamil (ISOPTIN) is excreted into human breast milk with a milk-to-plasma ratio of approximately 0.6. Limited data suggest low infant doses (estimated 0.1-1% of maternal weight-adjusted dose); caution advised, especially in preterm or ill infants.
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.
Pharmacokinetic changes in pregnancy (increased volume of distribution, enhanced clearance) may require dose titration; no specific recommended dose adjustment, but clinical efficacy and toxicity should guide dosing; consider starting at lower doses and titrating to effect.
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.
IV verapamil (Isoptin) can cause hypotension and bradycardia; have calcium gluconate at bedside to reverse. Avoid in patients with pre-existing heart block or systolic heart failure. Use ECG monitoring during IV administration. In atrial fibrillation, may convert to sinus rhythm but risk of ventricular preexcitation with WPW syndrome.
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.
Do not stop taking suddenly; may cause chest pain or irregular heartbeat.,Avoid grapefruit and grapefruit juice while taking this medication.,Do not drink alcohol; may increase dizziness and drops in blood pressure.,Take with food or milk if stomach upset occurs.,Report slow or irregular heartbeat, shortness of breath, or swelling of ankles.
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 ISOPTIN vs CALAN, answered by our medical review team.
ISOPTIN is a Calcium Channel Blocker that works by Verapamil inhibits calcium ion influx across cardiac and vascular smooth muscle cells, blocking L-type calcium channels, leading to vasodilation and reduced myocardial contractility and conduction velocity.. 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 ISOPTIN 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 ISOPTIN is: Initial dose: 80-120 mg orally three times daily; sustained-release: 120-240 mg orally once daily. IV: 5-10 mg slow IV push over 2 minutes, may repeat after 15-30 minutes. Maximum daily oral dose: 480 mg.. 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 ISOPTIN 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. ISOPTIN is classified as Category C. INSUFFICIENT DATA IN HUMANS: Animal studies show no teratogenic effects at clinically relevant doses. First trimester: case reports not indicating major malformations but risk cann. 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.