Sun28November0440PM 16

Are the following true or false of phenylephrine?

True / False

Gives a favourable blood gas umbilical cord gas profile compared with ephedrine Correct

May be given as intramuscular injection Correct

Acts on both alpha and beta adrenergic receptors Incorrect answer selected

Duration of action after intravenous injection can last up to one hour Correct

Is a directly-acting sympathomimetic Incorrect answer selected

Explanation

Phenylephrine is a direct acting sympathomimetic. It acts only on alpha-adrenergic receptors leading to vasoconstriction, rise in blood pressure and reflex bradycardia.

It can be given as intravenous boluses of 50-100 mcg leading to a rapid rise in blood pressure that lasts for five to 10 minutes. Intramuscular or subcutaneous administration has a slower onset but effects last for up to one hour.

Phenylephrine is associated with a better umbilical cord gas profile when used in obstetrics compared with ephedrine.

Reference:

Peck TE, Hill SA, Williams M. Pharmacology for Anaesthesia and Intensive Care. 3rd ed. Edinburgh: Cambridge University Press; 2008.

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