From Wikipedia, the free encyclopedia
Phenylephrine or Neo-Synephrine is an α1-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and to increase blood pressure. Phenylephrine has recently been marketed as a substitute for pseudoephedrine (e.g., Pfizer's Sudafed (Original Formulation)), but there are recent claims that oral phenylephrine may be no more effective as a decongestant than a placebo (see questions about effectiveness below).
Phenylephrine is used as a decongestant sold as an oral medicine, as a nasal spray, or as eye drops. Phenylephrine is now the most common over-the-counter (OTC) decongestant in the United States; oxymetazoline is a more common nasal spray. Pseudoephedrine was historically 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 , an enzyme that is present in the gastrointestinal tract and in the liver. Therefore, compared to orally-taken pseudoephedrine, it has a reduced and variable bioavailability of only up to 38 percent,. Because phenylephrine is a direct selective α-adrenergic receptor agonist, it does not cause the release of endogenous noradrenaline, as pseudoephedrine does. Therefore, phenylephrine is less likely to cause side-effects such as central nervous system stimulation, insomnia, anxiety, irritability, and restlessness.
Some popular cold remedies containing phenylephrine include:
- Codral Cold & Flu (New Formula)
- Lemsip Max Cold & Flu Hot Drink with decongestant
- Sudafed PE Sinus Non-Drowsy Nasal Decongestant
- Demazin PE
- Nyal Decongestant Nasal Spray
- Panadol Flu Strength Day & Night PE
- Panadol Cold & Flu Max + Decongestant
- Codral Cold & Flu (New Formula)
As a nasal spray, phenylephrine is available in 1 percent and 0.5 percent concentrations. It causes some rebound congestion effects, similar to oxymetazoline, although possibly to a lesser degree.
Phenylephrine is used as an eye drop to dilate the pupil in order to facilitate visualization of the retina. It is often used in combination with tropicamide. Narrow-angle glaucoma is a contraindication to phenylephrine use.
Phenylephrine is sometimes used as a vasopressor to increase the blood pressure in unstable patients with hypotension. Such use is more common in anesthesia or critical-care practices; phenylephrine is especially useful in counteracting the hypotensive effect of epidural and subarachnoid anesthetics. It also has the advantage of not being inotropic or chronotropic, and so it strictly elevates the blood pressure without increasing the heart rate or contractility (reflex bradycardia may result from the blood pressure increase, however). This is especially useful if the heart is already tachycardic and/or has a cardiomyopathy. The elimination half life of phenylephrine is about 2.5 to 3 hours.
The primary side-effect of phenylephrine is hypertension. Patients with congestion and hypertension are typically advised to avoid products containing phenylephrine. Prostatic hyperplasia can also be symptomatically worsened by use, and chronic use can lead to rebound hyperemia. Patients with a history of epilepsy and on anticonvulsant medication should not take this substance. The drug interaction might produce seizures. Some patients have been shown to have an upset stomach, severe abdominal cramping, and vomiting issues connected to taking this drug.
Substitute for pseudoephedrine
Pseudoephedrine and phenylephrine are both used as decongestants; and, until recently, pseudoephedrine was much more commonly available in the United States. This has changed because provisions of the Combat Methamphetamine Epidemic Act of 2005 placed restrictions on the sale of pseudoephedrine products in order to prevent the clandestine manufacture of methamphetamine. Since 2004, phenylephrine has been increasingly marketed as a substitute for pseudoephedrine; some manufacturers have changed the active ingredients of products to avoid the restrictions on sales. Phenylephrine has been off patent for some time, and there are many generic brands available.
Questions about effectiveness
Pharmacists Leslie Hendeles and Randy Hatton of the University of Florida suggested in 2006 that oral phenylephrine is ineffective as a decongestant at the 10-mg dose used, arguing that the studies used for the regulatory approval of the drug in the United States in 1976 were inadequate to prove effectiveness at the 10-mg dose and safety at higher doses. Other pharmacists have expressed concerns over phenylephrine's effectiveness as a nasal decongestant, and other clinicians have indicated concern for regulatory actions that reduced the availability of pseudoephedrine. A subsequent meta-analysis by the same researchers concluded that there is insufficient evidence for its effectiveness, though another meta-analysis published shortly thereafter by researchers from GlaxoSmithKline found the standard 10 mg dose to be significantly more effective than a placebo. Additionally, two studies published in 2009 examined the effects of phenylephrine on symptoms of allergic rhinitis by exposing sufferers to pollen in a controlled, indoor environment. Neither study was able to distinguish between the effects of phenylephrine or a placebo. Pseudoephedrine and loratadine-montelukast therapy were found to be significantly more effective than both phenylephrine and placebo.
The Food and Drug Administration has stood by its 1976 approval of phenylephrine for nasal congestion as the debate continues.
- ^ a b University of Florida (press release) (2006-07-19). "UF researchers question effectiveness of decongestant". http://news.ufl.edu/2006/07/19/decongensant/. Retrieved 2008-03-15.
- ^ Drug Properties
- ^ Pharmacogenetics and Pharmacogenomics Knowledge Base entry on phenylephrine
- ^ NZ Medicines and Medical Devices Safety Authority recommendation on phenylephrine (November 2004)
- ^ "Morepen acquires Lemolate The fifth largest brand in cough and cold Segment." Morepen Laboratories. 25 June 2002. Morepen Laboratories. 06 July 2009 <http://www.morepen.com/lemolate.htm>.
- ^ Decolgen Product Information, United Laboratories, Inc.
- ^ Bioflu Product Information, United Laboratories, Inc.
- ^ Shen, Howard (2008). Illustrated Pharmacology Memory Cards: PharMnemonics. Minireview. p. 3. ISBN 1-59541-101-1.
- ^ a b Hilenmeyer, K. (30 January 2007). "All stuffed up". Southwest Florida Herald-Tribune. http://www.heraldtribune.com/apps/pbcs.dll/article?AID=/FP/20070130/HEALTHMATTERS/70129001/1025/NEWS06.
- ^ Heldeles, L. and Hatton, R. (2006). "Oral phenylephrine: An ineffective replacement for pseudoephedrine?". Journal of Allergy and Clinical Immunology 118 (1): 279–280. doi:10.1016/j.jaci.2006.03.002. PMID 16815167.
- ^ Eccles R (May 2006). "Phenylephrine an ineffective replacement for pseudoephedrine in response to the methamphetamine problem in the USA". BMJ. http://www.bmj.com/cgi/eletters/332/7538/382-b.
Rapid Response to
Tanne JH (February 2006). "Methamphetamine epidemic hits middle America". BMJ 332 (7538): 382. doi:10.1136/bmj.332.7538.382-b. PMID 16484253.
- ^ Eccles, R. (2007). "Substitution of phenylephrine for pseudoephedrine as a nasal decongestant. An illogical way to control methamphetamine abuse". British Journal of Clinical Pharmacology 63 (1): 10–14. doi:10.1111/j.1365-2125.2006.02833.x. PMID 17116124. PMC 2000711. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2000711. (January 2007)
- ^ Hatton, R.C. et al. (2007). "Efficacy and Safety of Oral Phenylephrine: A Systematic Review and Meta-Analysis" (abstract). Annals of Pharmacotherapy 41 (3): 381–390. doi:10.1345/aph.1H679. PMID 17264159. http://www.theannals.com/cgi/content/abstract/aph.1H679v1. (published online Jan 2007)
- ^ Kollar C, Schneider H, Waksman J, Krusinska E. (2007). "Meta-analysis of the efficacy of a single dose of phenylephrine 10 mg compared with placebo in adults with acute nasal congestion due to the common cold". Clinical Therapeutics 29 (6): 1057–1070. doi:10.1016/j.clinthera.2007.05.021. PMID 17692721.
- ^ a b Horak, F; Zieglmayer, P; Zieglmayer, R; Lemell, P; Yao, R; Staudinger, H; Danzig, M (Feb 2009). "A placebo-controlled study of the nasal decongestant effect of phenylephrine and pseudoephedrine in the Vienna Challenge Chamber". Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology 102 (2): 116–20. ISSN 1081-1206. PMID 19230461.
- ^ a b Day, Jh; Briscoe, Mp; Ratz, Jd; Danzig, M; Yao, R (Apr 2009). "Efficacy of loratadine-montelukast on nasal congestion in patients with seasonal allergic rhinitis in an environmental exposure unit". Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology 102 (4): 328–38. ISSN 1081-1206. PMID 19441605.
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