DILACOR XR
Clinical safety rating
cautionComprehensive clinical and safety monograph for DILACOR XR (DILACOR XR).
Diltiazem inhibits calcium ion influx across cardiac and vascular smooth muscle cells, resulting in dilation of coronary and systemic arteries, decreased myocardial contractility, and reduced sinoatrial and atrioventricular conduction velocity.
| Metabolism | Extensively metabolized in the liver via CYP3A4; undergoes deacetylation and N-demethylation. |
| Excretion | Renal (70% as metabolites, 3-4% as unchanged drug); biliary/fecal (25-30%) |
| Half-life | Terminal half-life: 6-12 hours (prolonged in elderly, hepatic impairment, or with CYP3A4 inhibitors) |
| Protein binding | 98-99% bound to serum albumin and alpha-1-acid glycoprotein |
| Volume of Distribution | 1.1-1.8 L/kg (high Vd indicates extensive tissue binding) |
| Bioavailability | Oral: 40-50% (first-pass metabolism; food does not affect extent) |
| Onset of Action | Oral: 30-120 minutes (extended-release formulation) |
| Duration of Action | 24 hours (once-daily dosing for sustained antihypertensive effect) |
| Molecular Weight | 414.52 |
180 to 240 mg orally once daily, administered on an empty stomach; maximum dose 480 mg once daily.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | GFR 30-60 mL/min: initiate at 120 mg once daily, titrate cautiously; GFR <30 mL/min: not recommended due to risk of accumulation. |
| Liver impairment | Child-Pugh Class A: initiate at 120 mg once daily; Child-Pugh Class B or C: avoid use. |
| Pediatric use | Safety and effectiveness in pediatric patients have not been established; no dosing recommendations. |
| Geriatric use | Start at low end of dosing range (120 mg once daily) due to increased systemic exposure and risk of hypotension; titrate slowly. |
| 1st trimester | Diltiazem (DILACOR XR) is associated with potential teratogenic effects in animal studies; human data are limited. Use only if benefit outweighs risk. |
| 2nd trimester | May cause fetal bradycardia, hypotension, or hypoglycemia; monitor fetal growth and heart rate. Use with caution. |
| 3rd trimester | Risk of uterine relaxation and potential for fetal hypoxia during labor. Avoid use near term unless essential. |
Clinical note
Comprehensive clinical and safety monograph for DILACOR XR (DILACOR XR).
| Placental transfer | Diltiazem crosses the placenta (fetal/maternal concentration ratio approximately 0.55). |
| Breastfeeding | Diltiazem is excreted into breast milk in low concentrations (estimated infant dose <1% of maternal weight-adjusted dose). No adverse effects reported in breastfeeding infants, but monitor for bradycardia or hypotension in the infant. Avoid in preterm or compromised neonates. |
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | DILACOR XR (diltiazem) is a calcium channel blocker with limited human pregnancy data. In animal studies, at doses up to 5 times the maximum recommended human dose, no teratogenic effects were observed. However, embryofetal toxicity (increased fetal loss, growth retardation) occurred at maternally toxic doses. First trimester: No adequate human studies; risk cannot be excluded. Second and third trimesters: Use only if clearly needed; may cause maternal hypotension and reduced uteroplacental blood flow, potentially leading to fetal hypoxia and growth restriction. U.S. FDA Pregnancy Category C. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and cardiac function throughout pregnancy. Watch for signs of hypotension or heart block. Fetal monitoring: assess fetal growth via ultrasound every 4-6 weeks due to potential reduced uteroplacental perfusion. Assess fetal heart rate and variability. In third trimester, consider non-stress tests or biophysical profiles. Monitor for neonatal bradycardia and hypotension after delivery. |
| Fertility Effects | No specific studies on human fertility. In animal studies, diltiazem at high doses caused reduced spermatogenesis and sperm motility in male rats, and decreased implantation in female rats. Relevance to humans is unknown. May theoretically affect uterine contractility or ovulation; no significant impact reported in clinical use. |
■ FDA Black Box Warning
None.
| Serious Effects |
Sick sinus syndrome (unless pacing)Second- or third-degree AV block (unless pacing)Left ventricular dysfunction with pulmonary congestionHypotension (systolic <90 mm Hg)Acute myocardial infarctionAtrial fibrillation/flutter with accessory bypass tract (e.g., WPW)
| Precautions | May cause hypotension, bradycardia, and heart block; avoid in patients with sick sinus syndrome or second- or third-degree AV block without a pacemaker; caution in patients with congestive heart failure; may increase risk of digitalis toxicity; abrupt withdrawal may worsen angina. |
| Food/Dietary | Avoid grapefruit and grapefruit juice as they inhibit CYP3A4 and can increase diltiazem plasma concentrations, leading to increased risk of adverse effects. Avoid high-fat meals as they may affect the absorption of the extended-release formulation. |
| Clinical Pearls | DILACOR XR is a sustained-release formulation of diltiazem, a calcium channel blocker. Do not crush or chew the capsule; swallowing whole is essential for extended-release properties. Monitor heart rate and blood pressure regularly due to risk of bradycardia and hypotension. Use with caution in patients with reduced hepatic function as diltiazem undergoes extensive first-pass metabolism. Avoid concurrent use with strong CYP3A4 inhibitors (e.g., ketoconazole) as they can increase diltiazem levels. In patients with atrial fibrillation or flutter, it may be used for rate control but contraindicated in sick sinus syndrome or second/third-degree AV block without a pacemaker. |
| Patient Advice | Swallow DILACOR XR capsules whole; do not crush, chew, or break them. · Take this medication exactly as prescribed, usually once daily. Do not stop suddenly without consulting your doctor. · Avoid grapefruit and grapefruit juice as they can increase the effects and side effects of diltiazem. · Limit alcohol intake as it may increase the risk of dizziness or fainting. · Notify your doctor if you experience slow heartbeat, shortness of breath, swelling of ankles/feet, or severe dizziness. · Keep a record of your blood pressure and pulse at home and bring it to appointments. · Do not take other medications, including over-the-counter products or herbal supplements, without consulting your healthcare provider. |
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