BRETYLOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BRETYLOL (BRETYLOL).
Bretylium tosylate is an adrenergic neuron blocking agent that inhibits norepinephrine release and enhances its reuptake, resulting in postganglionic sympathetic blockade. It also has direct antiarrhythmic effects by increasing the ventricular fibrillation threshold.
| Metabolism | Bretylium is not metabolized significantly; it is excreted unchanged primarily by the kidneys. |
| Excretion | Primarily renal excretion of unchanged drug (80-90%); minor biliary/fecal elimination (10-20%) |
| Half-life | Terminal elimination half-life is 7-11 hours in normal renal function; prolonged in renal impairment (up to 30 hours) |
| Protein binding | Approximately 5-10% bound to plasma proteins (primarily albumin) |
| Volume of Distribution | 3.5-5.0 L/kg; large Vd indicates extensive tissue distribution, particularly into cardiac muscle and adrenergic neurons |
| Bioavailability | Intramuscular: ~100%; not available orally due to poor and erratic absorption |
| Onset of Action | Intravenous: 1-3 minutes; Intramuscular: 5-15 minutes |
| Duration of Action | 4-6 hours after single dose; for arrhythmia suppression, therapeutic effect may persist longer due to tissue accumulation |
Intravenous: 5-10 mg/kg over 10 minutes, then 5-10 mg/kg every 6-8 hours as needed for arrhythmias. Intramuscular: 5-10 mg/kg, may repeat every 6-8 hours.
| Dosage form | INJECTABLE |
| Renal impairment | GFR 30-90 mL/min: No adjustment. GFR <30 mL/min: Administer 50% of usual dose and extend dosing interval to every 12-24 hours. |
| Liver impairment | No specific guidelines; monitor for prolonged elimination half-life in severe hepatic impairment. |
| Pediatric use | Neonates and Infants: 2-5 mg/kg/dose IV/IM every 6-8 hours. Children: 5-10 mg/kg/dose IV/IM every 6-8 hours. |
| Geriatric use | Start with lower end of dosing range (5 mg/kg) due to reduced renal function and increased risk of hypotension. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BRETYLOL (BRETYLOL).
| Breastfeeding | Unknown if excreted in human milk; M/P ratio not available. Caution advised. |
| Teratogenic Risk | First trimester: No adequate studies; animal data suggest risk. Second and third trimesters: May cause fetal bradycardia, hypotension, hypoglycemia; avoid use. |
| Fetal Monitoring | Monitor maternal heart rate, blood pressure, ECG; fetal heart rate monitoring for bradycardia. |
■ FDA Black Box Warning
Bretylium should be used only in life-threatening arrhythmias unresponsive to other therapies, as it can cause severe hypotension due to adrenergic blockade.
| Serious Effects |
["Hypersensitivity to bretylium","Non-life-threatening arrhythmias","Severe hypotension","Concurrent use with other adrenergic-blocking agents may increase risk of hypotension"]
| Precautions | ["May cause severe hypotension, especially orthostatic hypotension","May cause initial transient hypertension due to norepinephrine release","May increase arrhythmias in digitalis toxicity","Use with caution in renal impairment","May cause nausea and vomiting"] |
| Food/Dietary | No significant food interactions. Avoid alcohol as it may worsen hypotension. |
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| Fertility Effects | No human data; animal studies show no impairment of fertility. |
| Clinical Pearls | Bretylium is a class III antiarrhythmic used for ventricular tachycardia/fibrillation. Its use is limited due to hypotension from sympathetic blockade. Monitor blood pressure closely and have vasopressors ready. It accumulates in renal failure. Initial dose may cause transient hypertension and increased arrhythmias due to norepinephrine release. |
| Patient Advice | This medication is used in hospital settings for serious heart rhythm problems. · You may experience dizziness or low blood pressure; do not get up quickly. · Report any fainting or severe lightheadedness to your nurse or doctor. · Kidney function tests will be monitored if you have kidney disease. |