DILTZAC
Clinical safety rating
cautionComprehensive clinical and safety monograph for DILTZAC (DILTZAC).
Diltiazem is a calcium channel blocker that inhibits calcium ion influx across cardiac and vascular smooth muscle cells, resulting in dilation of coronary and systemic arteries and decreased myocardial contractility and conduction velocity.
| Metabolism | Hepatic via CYP3A4; undergoes extensive first-pass metabolism |
| Excretion | Renal: 60-70% as metabolites, 2-4% unchanged; Biliary/Fecal: 20-30% as metabolites. |
| Half-life | Terminal elimination half-life: 3.5-5.0 hours (healthy adults). Prolonged in elderly (6-8 hours) and in hepatic impairment (10-12 hours). |
| Protein binding | 80-85% bound to plasma proteins (albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | 5-6 L/kg (suggests extensive tissue distribution). |
| Bioavailability | Oral immediate-release: 40-60% (due to extensive first-pass hepatic metabolism). Extended-release: 30-40%. Intravenous: 100%. |
| Onset of Action | Oral: 30-60 minutes (immediate-release), 2-4 hours (extended-release). Intravenous: 3-5 minutes. |
| Duration of Action | Oral immediate-release: 4-6 hours. Oral extended-release: 12-24 hours (depending on formulation: CD, SR, XR). Intravenous: 1-3 hours (hemodynamic effects). |
| Molecular Weight | 414.52 |
Oral: 30-120 mg 3-4 times daily; maximum 480 mg/day. IV: 0.25 mg/kg over 2 min, then 0.35 mg/kg after 15 min if needed; continuous infusion 5-15 mg/hour.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | No adjustment required for GFR >30 mL/min. For GFR 10-30 mL/min, reduce dose by 25%. For GFR <10 mL/min, reduce dose by 50%. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50%. Child-Pugh C: reduce dose by 75%. |
| Pediatric use | Oral: 1-3 mg/kg/day divided 3-4 times; maximum 3 mg/kg/day. IV: 0.25 mg/kg over 2 min; may repeat 0.35 mg/kg after 15 min; infusion 5-15 mcg/kg/min. |
| Geriatric use | Start at lowest dose (30 mg 3-4 times daily) due to increased bioavailability and reduced clearance; titrate slowly. IV dose: 0.2 mg/kg over 2 min. |
| 1st trimester | Limited human data; animal studies show teratogenic effects at high doses. Use only if benefit outweighs risk. |
| 2nd trimester | May cause fetal bradycardia and hypotension; monitor fetal heart rate. Use with caution. |
| 3rd trimester | Risk of uterine relaxation and potential for postpartum hemorrhage; avoid near term. |
Clinical note
Comprehensive clinical and safety monograph for DILTZAC (DILTZAC).
| Placental transfer | Crosses placenta; fetal serum concentrations are 10-20% of maternal levels. |
| Breastfeeding | Diltiazem is excreted into breast milk in low concentrations. Monitor infant for bradycardia and hypotension. American Academy of Pediatrics considers it compatible with breastfeeding. |
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | First trimester: No definitive evidence of teratogenicity in animal studies; human data limited. Second and third trimesters: Chronic use may cause fetal bradycardia, hypoxia, and growth restriction due to maternal hypotension and reduced placental perfusion. |
| Fetal Monitoring | Monitor maternal heart rate, blood pressure, and ECG; fetal monitoring for heart rate decelerations and growth ultrasound in chronic use. |
| Fertility Effects | No known significant impact on fertility in humans; animal studies show no impairment at therapeutic doses. |
■ FDA Black Box Warning
None.
| Serious Effects |
Sick sinus syndromeSecond- or third-degree AV block (except with functioning pacemaker)Severe hypotension (systolic <90 mmHg)Acute myocardial infarction with pulmonary congestionHypersensitivity to diltiazem
| Precautions | May cause heart block, bradycardia, exacerbation of heart failure, hypotension, and hepatotoxicity. Monitor liver function, ECG, and blood pressure. Avoid abrupt discontinuation; taper gradually. |
| Food/Dietary | Avoid grapefruit and grapefruit juice; they may increase diltiazem levels and risk of side effects. Alcohol may enhance blood pressure-lowering effects and cause dizziness. A high-fat meal may increase absorption, but this is not clinically significant. |
| Clinical Pearls | Diltzac is a calcium channel blocker (diltiazem) used for hypertension, angina, and atrial fibrillation. Avoid in patients with sick sinus syndrome (without pacemaker), second/third-degree AV block, or severe hypotension. Use with caution in hepatic impairment and renal failure. Monitor heart rate and ECG for bradycardia. Adjust dose with CYP3A4 inhibitors (e.g., grapefruit) or inducers. Advise gradual withdrawal to avoid rebound hypertension. |
| Patient Advice | Take exactly as prescribed; do not stop abruptly or change dose without consulting your doctor. · Avoid grapefruit and grapefruit juice while taking Diltzac. · Do not drive or operate heavy machinery if you experience dizziness or lightheadedness. · Monitor for signs of heart failure (swelling of ankles, feet, or sudden weight gain) and report immediately. · Your doctor may need to do regular blood tests to check liver function and monitor your heart rate and blood pressure. |
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