FRCA Notes

Ephedrine

  • A naturally occurring sympathomimetic amine found in certain plants, although a synthetic version is used clinically

Presentation

  • It can exist as four isomers but only the L-ephedrine isomer is active
  • Presentations include:
    • A clear, colourless solution of 30mg/ml stored in glass vials at room temperature
    • Pre-filled 10ml syringes of 3mg/ml ephedrine
    • Tablets of 15 - 60mg
    • Elixir of 3mg/ml
    • 0.5 - 1% nasal drops

Uses

  • To treat hypotension associated with general, neuraxial or regional anaesthesia, including in the obstetric patient (IV or IM)
  • Others:

  • Has direct and indirect sympathomimetic actions

  • It inhibits action of MAO on noradrenaline
  • Owing to its indirect action it is prone to tachyphylaxis as noradrenaline stores in sympathetic nerves are depleted

  • It is unlikely to be efficacious in the management of hypotension caused by drugs that affect neuronal storage, uptake, metabolism or release of neurotransmitters, e.g.:
    • Reserpine - depletes noradrenaline in neuronal granules
    • Alpha-methyl dopa - acts as a false transmitter
  • Also less efficacious where there is block of adrenoreceptors e.g. due to alpha blockade (e.g. phenoxybenzamine) or beta blockade (e.g. propranolol)

Absorption

  • Well absorbed from PO, IM or SC routes

Metabolism

  • It is not metabolised by COMT or MAO and therefore has a longer duration (elimination half-life 4hrs)
  • Some metabolism to phenylpropanolamine which is a central stimulant

Excretion

  • 65% is excreted unchanged (with some metabolism in the liver)
  • Excretion enhanced under acidic conditions

Respiratory

  • Respiratory stimulant and bronchodilator

Cardiovascular

  • Increases HR and cardiac output
  • Increases BP
  • Increases coronary blood flow and myocardial oxygen consumption
  • May precipitate arrhythmias

Neurological

  • Rapidly crosses BBB
  • Increases MAC
  • Increases BIS value

Gastrointestinal

  • Splanchnic and renal blood flow is decreased and GFR falls
  • Can relax GI smooth muscle

Uteroplacental

  • Does not affect placental blood flow
  • Readily crosses the placental membrane; associated with poorer cord gas pH than phenylephrine

Interactions

  • Should be used with caution in those taking MAO-I's