Mephentermine

# Mephentermine ## Overview - **Classification**: Sympathomimetic amine, Vasopressor - **Mechanism**: Primarily causes indirect release of norepinephrine from adrenergic nerve endings, leading to increased heart rate, cardiac contractility, and peripheral vasoconstriction. Also has some direct alpha and beta adrenergic receptor stimulating effects. ## Primary Indications 1. **Hypotension** - Treatment of acute hypotensive states (e.g., due to spinal anesthesia, shock, surgical procedures). 2. **Adjunct in Shock** - Used as an adjunct in the treatment of shock to restore blood pressure. ## Adult Dosing ### Standard Dosing **Acute Hypotension (e.g., due to spinal anesthesia, shock)** - **Dose**: **15-30 mg** - **Frequency**: Slow IV injection; may repeat with **10-20 mg** doses as needed. - **Route**: Intravenous (IV) slowly, or Intramuscular (IM) - **Duration**: As needed to maintain blood pressure. - **Maximum**: Cumulative dose should be monitored based on patient response. **Maintenance of Blood Pressure (Continuous Infusion)** - **Dose**: **0.1-0.5 mg/min** (e.g., **600 mg** in **500 mL** D5W or NS = **1.2 mg/mL**) - **Frequency**: Continuous infusion, titrated to effect - **Route**: Intravenous (IV) - **Special considerations**: Often initiated with a bolus dose before starting infusion. ### Dose Adjustments - **Renal Impairment**: Use with caution. Mephentermine is excreted renally; lower doses or extended intervals may be needed. - **Hepatic Impairment**: Use with caution. Mephentermine is metabolized in the liver; consider reduced doses in severe impairment. - **Elderly Patients**: Start with lower doses and titrate slowly due to increased sensitivity to pressor effects and potential comorbidities. ## Pediatric Dosing **Note**: Mephentermine use in pediatrics is not well-established and generally not first-line. Use with extreme caution and under expert supervision. Dosing data is limited. ### Neonates (0-28 days) - **Use in neonates is generally not recommended** due to lack of safety and efficacy data. ### Infants (1-12 months) - **Dose**: Limited data. Some sources suggest **0.4 mg/kg** IV as a single bolus. - **Frequency**: Single dose, if used. - **Maximum**: **15 mg** per single dose. - **Special Notes**: Reserve for critical, refractory hypotension under strict monitoring. ### Children (1-12 years) - **Dose**: Limited data. Some sources suggest **0.4 mg/kg** IV as a single bolus. - **Frequency**: Single dose, if used. - **Maximum**: **15 mg** per single dose. - **Special Notes**: Continuous infusion: **0.005-0.01 mg/kg/min** IV, titrated to effect. Closely monitor HR and BP. ### Adolescents (13-18 years) - **Dose**: Approach adult dosing, starting at the lower end of the adult range. - **Frequency**: As per adult recommendations, titrated to effect. - **Maximum**: Adult maximum dose, with careful monitoring. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to mephentermine or related amines. - **Absolute**: Severe hypertension, pheochromocytoma. - **Absolute**: Within 14 days of Monoamine Oxidase Inhibitor (MAOI) use. - **Absolute**: Severe cerebral arteriosclerosis. - **Absolute**: Cardiac decompensation, thyrotoxicosis. ### Common Adverse Effects - **Common (1-10%)**: Tachycardia, palpitations, anxiety, nervousness, dizziness, headache. - **Common (1-10%)**: Nausea, vomiting, restlessness, tremor. - **Serious but Rare**: Arrhythmias (ventricular), severe hypertension, cerebral hemorrhage, myocardial ischemia. ### Key Drug Interactions - **MAOIs**: Risk of severe, potentially fatal hypertensive crisis. **Contraindicated**. - **Tricyclic Antidepressants (TCAs)**: Potentiation of pressor effect; monitor BP closely. - **Halogenated Anesthetics (e.g., Halothane)**: Increased risk of cardiac arrhythmias. - **Digitalis**: Increased risk of cardiac arrhythmias. - **Oxytocics (e.g., Ergot alkaloids)**: Exaggerated pressor effects, risk of stroke or hemorrhage. ## Monitoring & Follow-up - **Before Treatment**: Assess baseline blood pressure, heart rate, and cardiac status. - **During Treatment**: Continuous monitoring of blood pressure, heart rate, and ECG. - **During Treatment**: Monitor urine output and fluid status. - **Clinical Signs**: Watch for signs of excessive vasoconstriction, arrhythmias, or hypertension. ## Clinical Pearls - 💡 **Tip 1**: Mephentermine has a rapid onset of action (1-2 minutes IV). - 💡 **Tip 2**: Often preferred for hypotension in obstetric settings due to lower fetal acidosis risk compared to other vasopressors. - 💡 **Tip 3**: Avoid extravasation as it can cause local tissue irritation; administer via central line if possible for infusions. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.