Ephedrine

Ephedrine is a sympathomimetic amine acting directly on the alpha and beta receptors and indirectly by increasing the release of noradrenaline by the sympathetic nerve endings. As with any sympathomimetic agent, ephedrine stimulates the central nervous system, the cardiovascular system, the respiratory system, and the sphincters of the digestive and urinary systems.

Ephedrine hydrochloride is applied locally to relieve congestion of mucous membranes in acute sinusitis and hay fever. It has a stimulant action on the respiratory centre. Ephedrine releases norepinephrine from storage sites in the sympathetic nerves to the effector organ. It exhibits tachyphylaxis; repeated infusions become less effective as the releasable stores of norepinephrine are depleted.

Ephedrine redistributes the blood flow and causes cardiac stimulation, without markedly raising the blood pressure.

Sympathomimetic drugs exert their effect by vasoconstriction of the mucosal blood vessels, which in turn reduces the thickness of the nasal mucosa. However, they can give rise to a rebound phenomenon as their effects wear off, due to a secondary vasodilation with a subsequent temporary increase in nasal congestion.

After intravenous administration, ephedrine is completely biologically available, and after oral administration, the bioavailability of ephedrine has been reported to be above 90%.

Excretion depends on urine pH:

From 73 to 99% (mean: 88%) in acidic urine.

From 22 to 35% (mean: 27%) in alkaline urine.

After oral or parenteral administration, 77% of ephedrine is excreted in unchanged form in the urine.

The half-life depends on urine pH. When the urine is acidified at pH=5, the half-life is 3 hours; when the urine is rendered alkaline at pH=6.3, the half-life is approximately 6 hours.

There is no pre-clinical data.