METARAMINOL BITARTRATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for METARAMINOL BITARTRATE (METARAMINOL BITARTRATE).
Indirect-acting sympathomimetic amine that increases blood pressure primarily through release of norepinephrine from postganglionic adrenergic nerve terminals, with some direct alpha-1 adrenergic receptor agonism.
| Metabolism | Hepatic metabolism via monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). |
| Excretion | Primarily renal (85-90% unchanged) via tubular secretion; minimal biliary/fecal (<5%). |
| Half-life | 2-4 hours; may be prolonged in renal impairment (up to 8 hours). |
| Protein binding | Low, approximately <5% binding to albumin. |
| Volume of Distribution | 0.3-0.5 L/kg; indicates distribution primarily in extracellular fluid. |
| Bioavailability | IM: ~90%; SubQ: ~70-80%. Not administered orally due to extensive first-pass metabolism and poor absorption. |
| Onset of Action | IV: 1-2 minutes; IM: 10-15 minutes; SubQ: 15-20 minutes. |
| Duration of Action | IV: 20-60 minutes; IM: 20-90 minutes; SubQ: 20-60 minutes. Duration is dose-dependent and shorter with rapid IV administration. |
Adult: 0.5–5 mg intravenously (IV) or intramuscularly (IM) as a single dose, repeated every 10–15 minutes as needed; or 5–10 mg IM as initial dose; or continuous IV infusion: 15–100 mg in 500 mL of 5% dextrose or normal saline, titrated to blood pressure response.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment guidelines for renal impairment. Use with caution in severe renal impairment due to potential accumulation and prolonged effect. Monitor blood pressure closely. |
| Liver impairment | No specific dose adjustment guidelines for hepatic impairment. Use with caution in severe hepatic impairment due to altered pharmacokinetics. Monitor blood pressure closely. |
| Pediatric use | Children: 0.01–0.2 mg/kg/dose IV or IM, repeated every 10–15 minutes as needed; or continuous IV infusion: 0.4–5 mcg/kg/min, titrated to desired effect. Maximum single dose: 5 mg. |
| Geriatric use | Elderly patients may be more sensitive to pressor effects. Start at lower end of dosing range (0.5–1 mg IV or IM) and titrate cautiously. Monitor for hypertension, bradycardia, and volume overload. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for METARAMINOL BITARTRATE (METARAMINOL BITARTRATE).
| Breastfeeding | No data on excretion into human milk; M/P ratio unknown. Due to short half-life and intravenous use, exposure likely low. Caution advised; consider benefits of breastfeeding vs. potential risk. |
| Teratogenic Risk | Metaraminol is a vasopressor used in acute hypotensive states, not a chronic therapy. No adequate and well-controlled studies in pregnant women. Animal reproduction studies are lacking. Potential fetal risks include decreased uteroplacental blood flow and fetal hypoxia due to maternal vasoconstriction. Use only if clearly needed and benefit outweighs risk. First trimester: limited data; second and third trimesters: risk of fetal hypoxia if maternal blood pressure is excessively elevated or uterine perfusion compromised. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to metaraminol or any component; hypertension; use with MAO inhibitors or within 14 days of MAOI therapy; pheochromocytoma; concurrent use with cyclopropane or halogenated hydrocarbon anesthetics due to risk of ventricular arrhythmias.
| Precautions | May cause severe hypertension, bradycardia, extravasation leading to tissue necrosis, and tachyphylaxis with prolonged use. Monitor blood pressure closely. Avoid abrupt discontinuation. Use with caution in patients with hypertension, hyperthyroidism, diabetes, or peripheral vascular disease. |
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| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and cardiac output continuously during administration. Assess fetal heart rate if feasible, especially if used near term, as vasoconstriction may affect placental perfusion. Monitor for signs of maternal hypertension, arrhythmias, or extravasation. |
| Fertility Effects | No data on effect on fertility in humans. Animal studies not available. Single or occasional use is unlikely to impact fertility. |