Ephedrine (EPH) is a sympathomimetic amine commonly used as a decongestant. Chemically, it is an alkaloid derived from various plants in the genus Ephedra (family Ephedraceae). The salt ephedrine hydrochloride has found various uses which utilise its sympathomimetic effect.

The traditional Chinese herb Ma Huang (Ephedra sinica) contains ephedrine as its principal active constituent. The same is true of other herbal products containing extracts from Ephedra species.

Chemistry

Ephedrine exhibits optical isomerism and has two chiral centres. By convention the enantiomers with opposite stereochemistry around the chiral centres are designated ephedrine, while pseudoephedrine has same stereochemistry around the chiral carbons. That is, (1R,2R)- and (1S,2S)-enantiomers are designated pseudoephedrine; while (1R,2S)- and (1S,2R)-enantiomers are designated ephedrine.

The isomer which is marketed is (-)-(1R,2S)-ephedrine. (Reynolds, 1988)

As with other phenylethylamines, it is also somewhat chemically similar to methamphetamine, although the methamphetamines are more potent and have additional biological effects which are absent from ephedrine.

Ephedrine may also be referred to as: (αR)-α-[(1S)-1-(methylamino)ethyl]benzenemethanol, α-[1-(methylamino)ethyl]benzyl alcohol, or L-erythro-2-(methylamino)-1-phenylpropan-1-ol. Ephedrine hydrochloride has a melting point of 187-188°C. (Budavari, 1996)

Mode of Action

Ephedrine is a sympathomimetic amine - that is, its principal mechanism of action relies on its indirect action on the adrenergic receptor system. Whilst it may have weak agonist activity at α- and β-adrenergic receptors, the principal mechanism is to displace noradrenaline from storage vesicles in presynaptic neurons. The displaced noradrenaline is released into the neuronal synapse where it is free to activate the aforementioned postsynaptic adrenergic receptors.

Indications

In traditional Chinese medicine, ephedrine has been used in the treatment of asthma and bronchitis for centuries (Ford, 2001). In Western medicine ephedrine was once widely used as a nasal decongestant and as a bronchodilator in the treatment for asthma. It continues to be used for these indications, though the popularity is waning due to the availability of more selective agents for these indications which exhibit fewer adverse effects (Joint Formulary Committee, 2004). The role in nasal congestion has largely been replaced by more potent α-adrenergic receptor agonists (e.g. oxymetazoline). Similarly the role of ephedrine in asthma has been almost entirely replaced by β₂-adrenergic receptor agonists (e.g. salbutamol).

Ephedrine continues to be used intravenously in the reversal of hypotension from spinal/epidural anaesthesia (Joint Formulary Committee, 2004). It is also used in other hypotensive states, including overdose with ganglionic blocking agents, antiadrenergic agents, or other medications that lower blood pressure (Bicopoulous, 2002).

An ECA stack is a component found in thermogenic weight loss pills, composed of ephedrine, caffeine and aspirin working to speed up the metabolism and thus cause calories to burn faster.

Safety issues

Ephedrine is found in many popular weight control products, in the form of Ephedra, some of which have been banned by the United States Food and Drug Administration (FDA). Some of the serious adverse effects associated with ephedrine include hypertension, stroke and myocardial infarction.

Misuse/Illicit-use

Anectodal reports have suggested that ephedrine helps thinking or studying to a greater extent than caffeine. Some students and some white-collar workers have used ephedrine (or Ephedra-containing herbal supplements) for this purpose. Such misuse of ephedrine has been associated with stimulant dependence.

As a phenylethylamine, ephedrine has a similar chemical structure to amphetamines. Ephedrine can be used in the synthesis of methamphetamine by chemical reduction; this has made ephedrine a highly sought-after chemical precursor in the illicit manufacture of methamphetamine. Following a much easier process, ephedrine can be used as a direct precursor to synthesise methcathinone.

References

• Bicopoulos, D (Ed.) (2002). AusDI. Drug Information for the Healthcare Professional (2 ed.). Castle Hill: Pharmaceutical Care Information Services
• Budavari, S (Ed.) (1996). The Merck Index. An encyclopedia of chemicals, drugs, and biologicals (12 ed.). Whitehouse Station: Merck Research Laboratories ISBN 0-91191-012-3
• Ford MD, Delaney KA, Ling LJ, Erickson T (Eds.) (2001). Clinical Toxicology. Philadelphia: WB Saunders. ISBN 0-72165-485-1
• Joint Formulary Committee (2004). British National Formulary (47 ed.). London: British Medical Association and Royal Pharmaceutical Society of Great Britain. ISBN 0-85369-854-9
• Reynolds, JEF (Ed.) (1989). Martindale. The Extra Pharmacopoeia (29 ed.). London: The Pharmaceutical Press. ISBN 0-85369-210-6
• "Weight loss with Ephedrine article" (April 4, 2005).

See also

• phenethylamines
• pseudoephedrine
• methamphetamine
• methcathinone
• ECA stack