Mephentermine

Hypotension caused by phenothiazines. Hypertension. Phaeochromocytoma.

Patient on MAOIs. For shock due to loss of blood or fluid, give fluid replacement therapy primarily, CVS disease, hypertension, hyperthyroidism, chronic illnesses. Lactation, pregnancy.

Drowsiness, incoherence, hallucinations, convulsions, tachycardia. Fear, anxiety, restlessness, tremor, insomnia, confusion, irritability and psychosis. Nausea, vomiting, reduced appetite, urinary retention, dyspnoea, weakness.
Potentially Fatal: AV block, CNS stimulation. Cerebral haemorrhage and pulmonary oedema, ventricular arrhythmias.

Antagonises effect of hypotensive agents. Severe hypertension with MAOIs and possibly TCAs. Additive vasoconstricting effects with ergot alkaloids, oxytocin.
Potentially Fatal: Risk of arrhythmia in patients undergoing anesthesia with cyclopropane and halothane.

Description:
Mechanism of Action: Mephentermine appears to act by indirect stimulation of β-adrenergic receptors causing the release of norepinephrine from its storage sites. It has a positive inotropic effect on the myocardium. AV conduction and refractory period of AV node is shortened with an increase in ventricular conduction velocity. It dilates arteries and arterioles in the skeletal muscle and mesenteric vascular beds, leading to an increase in venous return.
Onset: 5-15 minutes (IM), immediate (IV).
Duration: 4 hr (IM), 30 minutes (IV).
Pharmacokinetics:
Metabolism: Rapidly demethylated in the body followed by hydroxylation.
Excretion: Via urine (as unchanged and metabolites); more rapid in acidic urine.

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