Usage
Mephentermine is prescribed for the treatment of hypotension (low blood pressure), particularly during or after spinal anesthesia, and other hypotensive states like circulatory failure caused by drug-induced hypotension. It’s classified as a sympathomimetic and vasopressor agent, specifically an alpha- and beta-adrenergic agonist. Its mechanism of action involves stimulating the release of norepinephrine, which leads to vasoconstriction (narrowing of blood vessels) and increased heart rate and contractility, thereby elevating blood pressure.
Alternate Names
Mephentermine sulfate is the chemical name. A common brand name is Wyamine (though this may no longer be marketed in many countries as of today’s date, February 16, 2025).
How It Works
Pharmacodynamics: Mephentermine primarily acts indirectly by releasing stored norepinephrine from nerve terminals. It also has some direct agonist activity at alpha- and beta-adrenergic receptors. This results in increased cardiac output, both by increasing heart rate (positive chronotropic effect) and the force of heart contractions (positive inotropic effect), and vasoconstriction. The net effect is an increase in blood pressure.
Pharmacokinetics: Mephentermine is administered intravenously or intramuscularly. Onset of action is rapid (almost immediate with IV administration, within 5-15 minutes with IM). The duration of effect is relatively short, typically around 30 minutes for IV and up to 4 hours for IM administration. Mephentermine is metabolized in the liver via N-demethylation followed by p-hydroxylation, and eliminated primarily through renal excretion. The half-life is approximately 17-18 hours.
Dosage
Standard Dosage
Adults:
- Hypotensive states: 30-45 mg IV as a single dose, which can be repeated as needed. Alternatively, a continuous IV infusion of 0.1% mephentermine in 5% dextrose can be administered, with the rate and duration adjusted based on patient response.
- Hypotension after spinal anesthesia (obstetric patients): 15 mg IV as a single dose, repeated if necessary. Maximum dose: 30 mg.
Children:
Mephentermine is generally not recommended for use in children under 18 years of age, as safety and efficacy have not been established. However, in certain life-threatening situations, a doctor may prescribe mephentermine if the benefits outweigh the risks.
Special Cases:
- Elderly Patients: Caution is advised due to potential for increased sensitivity to the drug’s effects. Start with a lower dose and titrate carefully.
- Patients with Renal Impairment: Dose adjustment may be necessary.
- Patients with Hepatic Dysfunction: Dose adjustment may be necessary.
- Patients with Comorbid Conditions (e.g., Cardiovascular Disease, Hyperthyroidism): Use with caution and close monitoring.
Clinical Use Cases
Dosage recommendations are as above for standard adult use (primarily hypotensive states and hypotension after spinal anesthesia). It can also be used in emergency situations when rapid correction of blood pressure is needed, though other vasopressors are often preferred.
Dosage Adjustments
Dosage should be adjusted based on the patient’s response and clinical condition. Factors to consider include renal and hepatic function, and the presence of other medical conditions.
Side Effects
Common Side Effects:
Headache, anxiety, restlessness, tremor, insomnia, dizziness, nausea, vomiting, and palpitations.
Rare but Serious Side Effects:
Systemic hypertension (high blood pressure), cardiac arrhythmias (irregular heartbeats), cerebral hemorrhage, pulmonary edema, seizures, psychosis.
Long-Term Effects:
No specific long-term effects have been identified with typical short-term use in acute settings.
Adverse Drug Reactions (ADR):
Severe hypertension, cardiac arrhythmias requiring immediate intervention.
Contraindications
- Hypersensitivity to mephentermine
- Pheochromocytoma (adrenal gland tumor)
- Hypotension caused by phenothiazines
- Concurrent use with MAO inhibitors
Drug Interactions
- MAO inhibitors: Can cause severe hypertension.
- Tricyclic antidepressants: May potentiate cardiovascular effects.
- Ergot alkaloids and oxytocin: Additive vasoconstricting effects.
- Halogenated anesthetics and cyclopropane: Increased risk of cardiac arrhythmias.
- Antihypertensive medications: Antagonizes their effects.
Pregnancy and Breastfeeding
Mephentermine is generally not recommended during pregnancy and breastfeeding unless absolutely necessary. If used during pregnancy, weigh the potential benefits against the potential risks to the fetus. It is unknown whether mephentermine is excreted in breast milk.
Drug Profile Summary
- Mechanism of Action: Indirect-acting sympathomimetic, primarily releases norepinephrine, some direct agonist activity at alpha- and beta-adrenergic receptors.
- Side Effects: Hypertension, palpitations, headache, anxiety, insomnia. Serious side effects include cardiac arrhythmias, cerebral hemorrhage, pulmonary edema.
- Contraindications: Hypersensitivity, pheochromocytoma, phenothiazine-induced hypotension, concurrent MAOI use.
- Drug Interactions: MAOIs, tricyclic antidepressants, ergot alkaloids, oxytocin, halogenated anesthetics, cyclopropane.
- Pregnancy & Breastfeeding: Not generally recommended.
- Dosage: Adults: 30-45 mg IV for hypotension; 15 mg IV for hypotension after spinal anesthesia. Pediatric use not established.
- Monitoring Parameters: Blood pressure, heart rate, cardiac rhythm.
Popular Combinations
Mephentermine is not typically used in combination therapies, as it’s primarily for acute management of hypotension.
Precautions
- Pre-existing cardiovascular disease, hyperthyroidism, chronic illnesses.
- Renal/hepatic impairment.
- Elderly patients.
- Avoid in pregnancy and breastfeeding unless absolutely necessary.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Mephentermine?
A: Adults: 30-45 mg IV for hypotension, 15 mg IV for hypotension after spinal anesthesia. Pediatric use not established.
Q2: How does Mephentermine work?
A: It stimulates norepinephrine release, causing vasoconstriction and increased heart rate/contractility, thus raising blood pressure.
Q3: What are the common side effects?
A: Headache, anxiety, palpitations, insomnia, dizziness, nausea, and vomiting.
Q4: What are the serious side effects?
A: Severe hypertension, cardiac arrhythmias, cerebral hemorrhage, pulmonary edema, and seizures.
Q5: Who should not take Mephentermine?
A: Individuals with pheochromocytoma, hypotension caused by phenothiazines, or those taking MAOIs.
Q6: What are the potential drug interactions?
A: MAOIs, tricyclic antidepressants, halogenated anesthetics, ergot alkaloids, oxytocin, and antihypertensives.
Q7: Can Mephentermine be used during pregnancy?
A: Generally not recommended unless absolutely necessary due to potential risks to the fetus.
Q8: Is Mephentermine safe during breastfeeding?
A: It’s unknown if mephentermine is excreted in breast milk. Use with caution or choose an alternative if possible.
Q9: How is Mephentermine administered?
A: Intravenously (IV) or intramuscularly (IM) injection.
Q10: How quickly does Mephentermine work?
A: Onset of action is rapid, almost immediate with IV administration and within 5-15 minutes with IM administration.
