Pharmacology

Ephedrine

Ephedrine is primarily an indirect sympathomimetic which causes the release of endogenous catecholamines (ie, norepinephrine). Its uses extend from traditional Chinese medicine as an anti-asthmatic to recreational use due to its structural similarity to methamphetamine.
I administer ephedrine boluses of 5-10 mg intravenously to offset hypotension in the ICU and OR. Often times this medication is given in addition to or as a substitute for phenylephrine when the heart rate is “low” as ephedrine tends to increase the blood pressure and heart rate.

Because of its mechanism, prolonged use of ephedrine can result in diminished efficacy over time (tachyphylaxis). This is due to a depletion of norepinephrine-containing vesicles from their usual storage sites at the neuronal synaptic cleft.

I also give 20-30 mg of intramuscular ephedrine prior to spinal anesthetics to promote hemodynamic stability as parts of the sympathetic outflow are knocked out by the neuraxial anesthetic. I always give this injection in the thigh since any residual discomfort should disappear once the spinal is in place.

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