EPHEDRINE

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Ephedrine is a sympathomimetic amine that has both direct and indirect actions on adrenergic receptors. It is an important medication in the field of anesthesia due to its ability to counteract hypotension (low blood pressure) and support the cardiovascular system. Some of the reasons for its importance in anesthesia include:

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1. Prevention and treatment of hypotension: Hypotension is a common side effect of general anesthesia and spinal or epidural anesthesia. It can lead to decreased perfusion of vital organs, which can be dangerous for the patient. Ephedrine is often used to prevent or treat hypotension by increasing blood pressure through its vasoconstrictive and inotropic effects.

2. Bronchodilation: Ephedrine can cause bronchodilation by stimulating β2-adrenergic receptors, which can help in cases of bronchospasm or reactive airway disease during anesthesia.

3. Stimulating the central nervous system (CNS): Ephedrine has central nervous system-stimulating effects, which can help counteract the sedating effects of anesthetics.

4. Rapid onset and short duration of action: Ephedrine has a rapid onset of action and a relatively short half-life, making it suitable for use in acute situations, such as intraoperative hypotension.

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The mechanism of action of ephedrine involves both direct and indirect actions on adrenergic receptors:

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1. Direct action: Ephedrine binds to and activates α- and β-adrenergic receptors on target cells, including vascular smooth muscle cells, cardiac muscle cells, and bronchial smooth muscle cells.

2. Indirect action: Ephedrine promotes the release of endogenous norepinephrine from presynaptic nerve terminals, which further stimulates adrenergic receptors.

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                                                                                         Key points about Ephedrine

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• It is a noncatecholamine sympathomimetic used in anesthesia for hypotension and bradycardia. Ephedrine is an agonist at α, β1, and β2 receptors with both direct and indirect actions.

 

• Easily titrated, fast-acting pressor and inotrope that can be administered via peripheral vein.

 

• It binds directly to both alpha and beta receptors, but its principal mechanism of action is achieved INDIRECTLY by displacing more norepinephrine from storage vesicles.

 

• Ephedrine produces dose-related increases in blood pressure, cardiac output, heart rate, and systemic vascular resistance.

 

• The duration of action of ephedrine is longer than epinephrine, because it lacks a catechol structure; this makes it resistant to metabolism by monoamine oxidase (MAO).

 

• Ephedrine is often used for alleviation of hypotension related to cardiac-depressant effects of anesthetic agents or vasodilation resulting from spinal anesthesia.

 

• Ephedrine had long been considered the drug of choice for maternal hypotension after regional anesthesia because of maintenance of uterine blood flow. However, recent data recommends phenylephrine over ephedrine.

 

• Newer evidence suggests that ephedrine produces an increased fetal metabolic rate leading to fetal acidosis due to beta stimulation and phenylephrine does not.

 

• Tachyphylaxis may develop with subsequent dosing, because catecholamine stores become depleted.

       Risk of malignant hypertension with MAO inhibitors or cocaine.

 

• Ephedrine is up to 40% excreted unchanged by the kidneys.

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