Phenylephrine
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Phenylephrine
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| Systematic (IUPAC) name | |
| 3-(1-hydroxy-2-methylamino-ethyl)phenol | |
| Identifiers | |
| CAS number | 59-42-7 61-76-7 (hydrochloride) |
| ATC code | C01CA06 R01AA04, R01AB01, R01BA03, S01FB01, S01GA05 |
| PubChem | 6041 |
| DrugBank | APRD00365 |
| Chemical data | |
| Formula | C9H13NO2 |
| Mol. weight | 167.205 g/mol |
| Pharmacokinetic data | |
| Bioavailability | 38% through GI tract |
| Protein binding | 95% |
| Metabolism | Hepatic (monoamine oxidase) |
| Half life | 2.1 to 3.4 hours |
| Excretion | ? |
| Therapeutic considerations | |
| Pregnancy cat. | |
| Legal status |
OTC(US) |
| Routes | Oral, intranasal, ophtalmic |
Phenylephrine or neosynephrine is an α-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and rarely to increase blood pressure.
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[edit] Uses
[edit] Decongestant
Phenylephrine is used as a decongestant, available as an oral medicine or as a nasal spray. Phenylephrine is not the most common over-the-counter (OTC) decongestant; oxymetazoline is a more common nasal spray. Pseudoephedrine has generally been more common, although its notoriety as a methamphetamine precursor has led some governments to restrict its sale.
Oral phenylephrine is extensively metabolised by monoamine oxidase [1], an enzyme which is present in the gastrointestinal tract and the liver. Therefore, compared to orally-taken pseudoephedrine, it has a reduced and variable bioavailability of only up to 38 percent [2] [3], and is therefore less effective as a nasal decongestant. Because phenylephrine is a direct selective alpha-adrenergic receptor agonist, it does not cause the release of endogenous noradrenaline like pseudoephedrine does. Therefore, phenylephrine is less likely to cause side-effects like central nervous system stimulation, insomnia, anxiety, irritability and restlessness.
Some popular cold remedies containing phenylephrine: Canada's hot lemon Neocitran, the United Kingdom's Lemsip, and the United States' Alka-Seltzer Cold Effervescent formula, Sudafed PE Non-Drowsy Nasal Decongestant, and DayQuil Capsules.
As a nasal spray, phenylephrine is available in 1% and 1/2% concentrations. It suffers some rebound congestion effects, although to a lesser degree than oxymetazoline.
Several studies suggests that the 10 mg dose of phenylephrine used as a substitute for pseudoephedrine is no more effective than a placebo [1][2]
[edit] Mydriatic
Phenylephrine is used as an eye drop to dilate the pupil to facilitate visualization of the retina. It is often used in combination with tropicamide. Narrow angle glaucoma is a contraindication to phenylephrine use.
[edit] Vasopressor
Phenylephrine is rarely used as a vasopressor to increase the blood pressure in unstable patients with hypotension. Such use is more common in anesthesia practices; phenylephrine is especially useful in counteracting the hypotensive effect of epidural and subarachnoid anesthetics.
[edit] Side effects
The primary side effect of phenylephrine is hypertension. Patients with congestion and hypertension are typically advised to avoid phenylephrine containing products.
[edit] Pregnancy
Phenylephrine is in the FDA pregnancy category C.
[edit] Legal issues
Pseudoephedrine and phenylephrine are both used as decongestants; and until recently, pseudoephedrine was much more commonly available in the United States. This is changing, because pseudoephedrine can be used in various straightforward reactions for the clandestine manufacture of methamphetamine, while production of methamphetamine from phenylephrine is much more difficult.
Since 2004, phenylephrine has been increasingly marketed as a substitute, although there is strong evidence that it is ineffective at the doses used [1][2]. In addition to selling a variety of medicines containing pseudoephedrine under the name brand Sudafed, Pfizer introduced "Sudafed PE" containing phenylephrine. Phenylephrine has been off patent for a long time; there are many generic brands available.
[edit] References
- ^ a b Oral phenylephrine: An ineffective replacement for pseudoephedrine? Journal of Allergy and Clinical Immunology, Volume 118, Issue 1, Pages 279-280, L. Hendeles, R. Hatton
- ^ a b http://starbulletin.com/2006/11/29/editorial/editorial01.html
[edit] See Also
| Adrenergic and dopaminergic agents (C01CA)edit | ||
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Dobutamine, Dopamine, Epinephrine, Fenoldopam, Isoprenaline, Metaraminol, Midodrine, Norepinephrine, Octopamine, Phenylephrine |
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