ISOPTIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ISOPTIN (ISOPTIN).
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.
| Metabolism | Extensively metabolized in the liver via CYP3A4, CYP3A5, and CYP1A2 isoenzymes; major metabolite is norverapamil (active). |
| Excretion | Renal (70% as metabolites, 3-5% unchanged); biliary/fecal (25%) |
| Half-life | Terminal elimination half-life: 4.5-12 hours (mean 8 hours); increases with hepatic impairment or cirrhosis |
| Protein binding | 90% bound to albumin |
| Volume of Distribution | 4.5 L/kg (extensive tissue distribution, reflects high myocardial and vascular binding) |
| Bioavailability | Oral: 20-35% (extensive first-pass hepatic metabolism) |
| Onset of Action | IV: 1-5 minutes; Oral (immediate-release): 30-60 minutes; Oral (sustained-release): 1-2 hours |
| Duration of Action | IV: 10-30 minutes for antiarrhythmic effect; Oral (immediate-release): 4-6 hours; Oral (sustained-release): 12-24 hours |
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.
| Dosage form | INJECTABLE |
| Renal impairment | For CrCl <30 mL/min: Reduce dose by 50-75% of normal. For CrCl 30-50 mL/min: Start at lower end of dosing range. No specific guidelines for dialysis. |
| Liver impairment | 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%. |
| Pediatric use | 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. |
| Geriatric use | 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. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ISOPTIN (ISOPTIN).
| Breastfeeding | 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. |
| Teratogenic Risk | 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. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["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 mmHg)"]
| Precautions | ["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."] |
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| Fetal Monitoring | Monitor maternal blood pressure and heart rate regularly; fetal heart rate monitoring during third trimester; consider fetal growth ultrasound if used chronically. |
| Fertility Effects | No significant effects on fertility reported in animal studies; a single case report of reversible male infertility with verapamil, but systematic evidence lacking. |