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. |
| Molecular Weight | 317.32 |
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 | Limited human data; animal studies show no teratogenicity at clinical doses. Use only if clearly needed. |
| 2nd trimester | May cause maternal hypertension and decreased uterine blood flow; use cautiously and monitor. |
| 3rd trimester | May cause fetal hypoxia due to vasoconstriction; avoid for prolonged use or near term. |
Clinical note
Comprehensive clinical and safety monograph for METARAMINOL BITARTRATE (METARAMINOL BITARTRATE).
| Placental transfer | Crosses placenta; extent is dose-dependent. May cause fetal bradycardia and hypertension. |
| Breastfeeding | Excreted into breast milk in small amounts; unlikely to affect infant due to poor oral bioavailability. Monitor for hypertension in infant. |
| Lactation Rating |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to metaraminol or bisulfitesSevere hypertensionPheochromocytomaNarrow-angle glaucomaConcurrent use with MAOIs or within 14 days of MAOI therapyTachyarrhythmias or ventricular fibrillation
| 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. |
| Food/Dietary | No known food interactions. Maintain adequate hydration unless contraindicated. |
Loading safety data…
| L2 (Safely Compatible) |
| 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. |
| 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. |
| Clinical Pearls |
| Metaraminol is a direct-acting alpha-1 agonist with some beta-1 activity; used for acute hypotension not due to hypovolemia. Administer via IV infusion with careful BP monitoring; avoid extravasation (risk of necrosis). Tachyphylaxis may occur with prolonged use. Contraindicated in pheochromocytoma and MAOI use. |
| Patient Advice | This medication is given to raise your blood pressure and requires continuous monitoring. · Report any pain, redness, or swelling at the injection site immediately. · You may experience headache, anxiety, or palpitations; inform your nurse if these occur. · Avoid sudden position changes to prevent dizziness. |