VASOXYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VASOXYL (VASOXYL).
Phenylephrine is a selective alpha-1 adrenergic receptor agonist, causing vasoconstriction and increased blood pressure.
| Metabolism | Primarily metabolized by monoamine oxidase (MAO) and sulfation in the liver and gut wall. |
| Excretion | Primarily renal excretion as unchanged drug and metabolites (phenylephrine is deaminated by MAO). Approximately 80-85% excreted in urine within 24 hours; negligible biliary/fecal elimination. |
| Half-life | Terminal elimination half-life is 2.5-3.0 hours; clinically relevant for dosing intervals in hypotension management. |
| Protein binding | Approximately 95% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 0.3-0.5 L/kg; indicates limited extravascular distribution consistent with a polar amine. |
| Bioavailability | Intravenous: 100%. Oral: less than 40% due to first-pass metabolism. Intramuscular: near 100% (not formally studied). |
| Onset of Action | Intravenous: within 1-2 minutes. Intramuscular: 10-15 minutes. Subcutaneous: 10-15 minutes. |
| Duration of Action | Intravenous: 15-20 minutes. Intramuscular: 30 minutes to 2 hours. Subcutaneous: 50-75 minutes; duration is dose-dependent and reflects alpha-adrenergic vasoconstriction. |
| Molecular Weight | 167.21 |
Intravenous bolus: 0.1-0.2 mg per dose; intravenous infusion: 0.1-0.2 mg/min; intramuscular or subcutaneous: 0.5-1 mg per dose.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment required; use with caution in severe renal impairment. |
| Liver impairment | No specific dose adjustment required. |
| Pediatric use | Intravenous: 0.02-0.2 mg/kg per dose; maximum 5 mg per dose. |
| Geriatric use | Initiate at lower end of dosing range due to potential increased sensitivity; monitor blood pressure closely. |
| 1st trimester | Limited human data; animal studies not available. Use only if clearly needed and potential benefit justifies risk. |
| 2nd trimester | May cause reduced uterine blood flow and fetal hypoxia. Use with caution, monitor fetal status. |
| 3rd trimester | Associated with fetal bradycardia and hypoxia. Avoid near term due to risk of uterine vasoconstriction. |
Clinical note
Comprehensive clinical and safety monograph for VASOXYL (VASOXYL).
| Placental transfer | Crosses placenta; can cause fetal bradycardia and decreased placental perfusion. |
| Breastfeeding | Excretion into breast milk is unknown. Due to short half-life and poor oral bioavailability, levels likely low. Use with caution in nursing mothers, monitor infant for adverse effects. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to phenylephrine or any componentSevere hypertensionVentricular tachycardiaPheochromocytomaUse with halothane anesthesia (risk of arrhythmias)
| Precautions | Use with caution in patients with hypertension, hyperthyroidism, bradycardia, heart block, myocardial disease, or severe atherosclerosis., May cause severe bradycardia, arrhythmias, or excessive hypertension., Avoid use with MAO inhibitors or within 14 days of discontinuation., Extravasation risk: may cause tissue necrosis; administer via central line if possible., Monitor blood pressure and heart rate continuously during infusion. |
| Food/Dietary | Avoid tyramine-rich foods (e.g., aged cheeses, cured meats, fermented products) due to risk of hypertensive crisis; maintain adequate sodium and fluid intake as directed. |
Loading safety data…
| Lactation Rating |
| L3: Limited Data - Possibly Compatible |
| Teratogenic Risk | Pregnancy Category C. Vasoxyl (methoxamine) is an alpha-1 adrenergic agonist. Animal reproduction studies have not been conducted. It is not known whether methoxamine can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Methoxamine should be given to a pregnant woman only if clearly needed. Potential risks include reduced uteroplacental blood flow due to vasoconstriction, which may lead to fetal hypoxia and bradycardia. Use only if benefit outweighs risk. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and fetal heart rate continuously during administration. Assess uterine activity and fetal well-being. Observe for signs of maternal hypertension, bradycardia, or reduced placental perfusion. |
| Fertility Effects | No data available on effects of methoxamine on human fertility. Animal studies have not been conducted. |
| Clinical Pearls | Administer via central line if possible to avoid extravasation necrosis; monitor blood pressure every 2-5 minutes during titration; correct hypovolemia before use; tachyphylaxis can occur with prolonged use; avoid abrupt discontinuation to prevent rebound hypotension. |
| Patient Advice | This medication is used to raise your blood pressure. · You will have frequent blood pressure checks. · Report any pain, redness, or swelling at the injection site immediately. · Do not stop the medication suddenly unless directed by your doctor. · You may experience headache, anxiety, or palpitations; notify your doctor if these persist. |