Legal status: Prescription Only (S4) (AU) Schedule VI (CA) P (UK) OTC (US)
Routes: oral, IV, IM, SC
Main: Ephedrine (pronounced /ɨˈfɛdrɪn/ or /ˈɛfɨdriːn/) (not to be confused with ephedrone) is a sympathomimetic amine commonly used as a stimulant, appetite suppressant, concentration aid, decongestant, and to treat hypotension associated with anaesthesia. Ephedrine is similar in structure to the (semi-synthetic) derivatives amphetamine and methamphetamine. Chemically, it is an alkaloid derived from various plants in the genus Ephedra (family Ephedraceae). It works mainly by increasing the activity of noradrenaline on adrenergic receptors. It is most usually marketed in the hydrochloride and sulfate forms. In traditional Chinese medicines, the herb má huáng (麻黄, Ephedra sinica) contains ephedrine and pseudoephedrine as its principal active constituents. The same is true of other herbal products containing extracts from Ephedra species.
Nagayoshi Nagai, a Japanese chemist, was the first person to isolate ephedrine from Ephedra distachya (syn. Ephedra vulgaris) in 1885.
The four stereoisomers of ephedrine.
Ephedrine exhibits optical isomerism and has two chiral centres, giving rise to four stereoisomers. By convention the enantiomers with opposite stereochemistry around the chiral centres (1R,2S and 1S,2R) are designated ephedrine, while pseudoephedrine has same stereochemistry around the chiral carbons (1R,2R and 1S,2S). Ephedrine is a substituted amphetamine and a structural methamphetamine analogue. It differs from methamphetamine only by the presence of a hydroxyl (OH). Amphetamines, however, are more potent and have additional biological effects. The isomer which is marketed is (-)-(1R,2S)-ephedrine. Ephedrine hydrochloride has a melting point of 187-188°C.
The dextrorotary (+)- or d- enantiomer is (1S,2R)-Ephedrine, whereas the levorotating (−)- or l- form is (1R,2S)-Ephedrine. In the outdated d/l system (+)-Ephedrine is also referred to as l-Ephedrine and (—)-Ephedrine as d-Ephedrine (in the Fisher projection then the phenylring is drawn at bottom). Often the d/l system (with small caps) and the d/l system (with lower-case) are confused. The result is that the levorotary l-Ephedrine is wrongly named l-Ephedrine and the dextrorotary d-Pseudoephedrine (the diastereomer) wrongly d-Pseudoephedrine. The IUPAC names of the two enantiomers are (1R,2S)- respectively (1S,2R)-2-methylamino-1-phenylpropan-1-ol. A synonym is erythro-Ephedrine.
Raw materials for the production of ephedrine and traditional Chinese medicine are produced in China on a large scale. In 2007, companies produced for export extract US$13 million worth of ephedrine from 30,000 tons of ephedra annually, 10 times the amount that is used in traditional Chinese medicine.
Mechanism of action
Ephedrine is a sympathomimetic amine. The principal mechanism of its action relies on its indirect stimulation of the adrenergic receptor system, which is part of the sympathetic nervous system (SNS), by increasing the activity of noradrenaline at the post-synaptic α- and β-receptors. The presence of direct interactions with α-receptors is unlikely, but still controversial. Action upon the central nervous system (CNS) is limited because ephedrine only crosses the blood-brain barrier weakly and not very efficiently. The presence of an N-methyl group decreases binding affinities at α-receptors, compared with norephedrine. On the other hand ephedrine binds better than N-methylephedrine, which has an additional methyl group at the N-atom. Also the steric orientation of the hydroxyl group is important for receptor binding and functional activity.