Adrenergic Agonists: Ephedrine

EPHEDRINE

Clinical Considerations

The cardiovascular effects of ephedrine, a noncate-cholamine sympathomimetic, are similar to those of epinephrine: increase in blood pressure, heart rate, contractility, and cardiac output. Likewise, ephed-rine is also a bronchodilator. There are important differences, however: ephedrine has a longer dura-tion of action, is much less potent, has indirect and direct actions, and stimulates the central nervous system (it raises minimum alveolar concentration). The indirect agonist properties of ephedrine may be due to peripheral postsynaptic norepinephrine release, or by inhibition of norepinephrine reuptake.Ephedrine is commonly used as a vasopressor during anesthesia. As such, its administration should be viewed as a temporizing measure while the cause of hypotension is determined and reme-died. Unlike direct-acting α1-agonists, ephedrine is believed not to decrease uterine blood flow, and thus was regarded as the preferred vasopressor for most obstetric uses. Recently, however, phenylephrine has been argued to be a better vasopressor in obstetric patients undergoing neuroaxial anesthesia due its faster onset, shorter duration of action, and better titratability and maintenance of fetal pH. Ephedrine has also been reported to possess antiemetic prop-erties, particularly in association with hypotension following spinal anesthesia. Clonidine premedica-tion augments the effects of ephedrine.

Dosing & Packaging

In adults, ephedrine is administered as a bolus of 2.5–10 mg; in children, it is given as a bolus of 0.1 mg/kg. Subsequent doses are increased to offset the development of tachyphylaxis, which is probably due to depletion of norepinephrine stores. Ephed-rine is available in 1-mL ampules containing 25 or 50 mg of the agent.