Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
TIAZAC 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, a benzothiazepine calcium channel blocker, inhibits calcium ion influx across cardiac and vascular smooth muscle cell membranes, resulting in coronary vasodilation, peripheral vasodilation, decreased myocardial contractility, and decreased AV nodal 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.
Hypertension,Chronic stable angina pectoris,Atrial fibrillation or atrial flutter (rate control),Paroxysmal supraventricular tachycardia (PSVT)
Angina pectoris (chronic stable, vasospastic, unstable),Essential hypertension,Supraventricular tachyarrhythmias (e.g., atrial fibrillation, atrial flutter, PSVT)
Oral: 120-360 mg once daily; maximum 540 mg daily.
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 is 5-7 hours for immediate-release; for TIAZAC (extended-release), effective half-life is approximately 6-9 hours due to prolonged absorption
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.
Hepatic via CYP3A4 isoenzyme; extensive first-pass metabolism; metabolites include N-desmethyl diltiazem (active) and others.
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, 60% as inactive metabolites); Fecal (30%); Biliary (minor)
Approximately 70% renal (3-4% unchanged, remainder as metabolites) and 25% biliary/fecal.
70-80% bound to plasma proteins (albumin)
Approximately 90% bound to plasma proteins, primarily albumin.
Approximately 1.7 L/kg; suggests extensive tissue distribution
Vd 4-5 L/kg; indicates extensive tissue distribution beyond plasma volume.
Approximately 40% for oral immediate-release; extended-release formulation has comparable bioavailability with reduced peak-to-trough fluctuations
Oral bioavailability is 20-35% due to extensive first-pass hepatic metabolism; IV bioavailability is 100%.
No specific adjustment required; use with caution in severe renal impairment (Cr Cl <30 m L/min).
Cr Cl <30 m L/min: reduce dose by 50% and monitor carefully.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce total dose by 50%; Child-Pugh Class C: reduce total dose by 60-70%.
Child-Pugh A: 50% of normal dose; Child-Pugh B: 25% of normal dose; Child-Pugh C: contraindicated or use with extreme caution.
Not established; use in children <18 years is not recommended.
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 (120 mg daily); titrate slowly due to increased sensitivity and potential for 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).
Bradycardia and heart block (risk increased with beta-blockers or digoxin),Heart failure with reduced ejection fraction (may worsen in acute MI or pulmonary congestion),Hypotension,Increased risk of gastrointestinal bleeding in elderly,Hepatic impairment (dose adjustment may be required),Abrupt withdrawal may exacerbate angina or cause rebound hypertension,Concurrent use with CYP3A4 inhibitors (e.g., clarithromycin, itraconazole) increases diltiazem levels
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 (unless paced),Second- or third-degree AV block (unless paced),Hypotension (systolic < 90 mm Hg),Cardiogenic shock,Atrial fibrillation/flutter with accessory bypass tract (e.g., Wolff-Parkinson-White syndrome, Lown-Ganong-Levine syndrome),Acute myocardial infarction with pulmonary congestion,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.
Avoid grapefruit juice and grapefruit products due to CYP3A4 inhibition, which can increase diltiazem levels. Limit sodium intake as part of hypertension management. No significant interaction with other foods.
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.
TIAZAC (diltiazem) is classified as FDA Pregnancy Category C. First trimester: Limited human data; animal studies have shown embryotoxic and teratogenic effects at high doses. Second and third trimesters: No well-controlled studies; risk of fetal bradycardia, hypotension, and hypocalcemia due to calcium channel blockade. Use only if benefit outweighs 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. The milk-to-plasma ratio is approximately 0.4 to 0.8. Relative infant dose is estimated to be <1% of maternal weight-adjusted dose; considered compatible with breastfeeding. Monitor infant for potential adverse effects such as bradycardia, hypotension, or sedation.
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.
Pregnancy may alter the pharmacokinetics of diltiazem due to increased plasma volume, renal clearance, and hepatic metabolism. Dose adjustments may be necessary; titrate to clinical effect. No specific dosing guidelines; use the lowest effective dose and monitor blood pressure and heart rate 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.
TIAZAC (diltiazem extended-release) is a nondihydropyridine calcium channel blocker used for hypertension and stable angina. Avoid use in patients with sick sinus syndrome or second/third-degree AV block without a pacemaker. It is a substrate of CYP3A4; monitor for interactions with strong inhibitors (e.g., ketoconazole) or inducers (e.g., rifampin). In hepatic impairment, start at lowest dose. Use with beta-blockers increases risk of bradycardia and heart failure. May cause gingival hyperplasia; stress good oral hygiene.
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 TIAZAC exactly as prescribed, usually once daily. Swallow the capsule whole; do not crush, chew, or open.,Do not stop taking this medication abruptly, as it may worsen chest pain or blood pressure.,Avoid drinking grapefruit juice or eating grapefruit while on this drug, as it can increase side effects.,Common side effects include dizziness, headache, swelling in the ankles/feet, and constipation. Contact your doctor if you experience very slow heartbeat, fainting, or shortness of breath.,Inform your doctor about all other medications, especially beta-blockers, digoxin, or other blood pressure drugs.
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 TIAZAC vs CALAN, answered by our medical review team.
TIAZAC is a Calcium Channel Blocker that works by Diltiazem, a benzothiazepine calcium channel blocker, inhibits calcium ion influx across cardiac and vascular smooth muscle cell membranes, resulting in coronary vasodilation, peripheral vasodilation, decreased myocardial contractility, and decreased AV nodal 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 TIAZAC 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 TIAZAC is: Oral: 120-360 mg once daily; maximum 540 mg daily.. 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 TIAZAC 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. TIAZAC is classified as Category C. TIAZAC (diltiazem) is classified as FDA Pregnancy Category C. First trimester: Limited human data; animal studies have shown embryotoxic and teratogenic effects at high doses. Seco. 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.