Phenylephrine

Image:Phenylephrine.png Phenylephrine hydrochloride is an α-agonist used medically to increase blood pressure, as a decongestant, and also to dilate the pupil.

Decongestant

Phenylephrine is used as a decongestant, available as an oral medicine or as a nasal spray. Phenylephrine is not the most common OTC decongestant; oxymetazolineis a more common nasal spray, pseudoephedrineis a more common oral decongestant.

Oral phenylephrine is rather extensively metabolised by monoamine oxidase, an enzyme which is present in the stomach and liver. Therefore, it has a rather reduced bioavailability, and hence, is less effective as an oral nasal decongestant, compared to orally taken pseudoephedrine. However, because phenylephrine is a direct selective alpha-adrenergic receptor agonist, it does not cause the release of endogeneous noradrenaline like the pseudoephedrine does. This also means that phenylephrine is less likely to cause side-effects like CNS stimulation, insomnia, anxiety, irritability and restlessness.

The popular Canadian hot lemon cold remedy Neo Citran, the US Alka-Seltzer Cold Effervescent formula, Nyquil Day Caps and the UK Lemsipall contain phenylephrine.

As a nasal spray, phenylephrine is available in 1% and 1/2% concentrations. It suffers some rebound congestion effects, although to a somewhat lesser degree than oxymetazoline.

Phenylephrine is in the FDA pregnancy category C.

Legal Issues

Because pseudoephedrine can be used in the illegal manufacture of methamphetamine, it is expected that phenylephrine will become more common. In particular, Pfizer, who manufactures the name brand decongestant Sudafedintroduced a new formulation in late 2004, "Sudafed PE," that uses phenylephrine instead of pseudoephedrine. Because it has been on the market for several years, phenylephrine is not legally patented by any drug company. Thus, many generic forms are available in addition to Pfizer's formula.

Pfizer was a strong opponent of strict pseudoephedrine laws previous to their introduction of "Sudafed PE", but now that their product is widely available (and currently the primary non-pseudoephedrine decongestant formula), they have changed their position to support legal changes severely restricting the sale of pseudoephedrine products.

References

• Drugs.com - Phenylephrine
• MedlinePlus - Phenylephrine (nasal drops)

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It uses material from the http://en.wikipedia.org/wiki/Phenylephrine Wikipedia article Phenylephrine.