Phenylephrine
Overview
Phenylephrine is a selective α1-adrenergic receptor
Alpha-1 adrenergic receptor
The alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic...

 agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

 used primarily as a decongestant
Decongestant
A decongestant or nasal decongestant is a type of drug that is used to relieve nasal congestion.-Pharmacology:The vast majority of decongestants act via enhancing norepinephrine and epinephrine or adrenergic activity by stimulating the α-adrenergic receptors...

, as an agent to dilate the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...

, and to increase blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

. Phenylephrine has recently been marketed as a substitute for pseudoephedrine
Pseudoephedrine
Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

 (e.g.,Sudafed
Sudafed
Sudafed is a brand name and registered trademark for over the counter decongestants manufactured by McNeil Laboratories for sale in Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States...

 (Original Formulation)
), but there are claims that oral phenylephrine may be no more effective as a decongestant than a placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

 (see questions about effectiveness below).
Phenylephrine is used as a decongestant sold as an oral medicine, as a nasal spray
Nasal spray
Nasal sprays come in a variety of forms. Medicated such as Astelin, Afrin and Nasonex and natural such as Sinusoothe and Sterimar. Although delivery methods vary, most nasal sprays function by instilling a fine mist into the nostril by action of a hand-operated pump mechanism.-Antihistamine nasal...

, or as eye drops.
Encyclopedia
Phenylephrine is a selective α1-adrenergic receptor
Alpha-1 adrenergic receptor
The alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic...

 agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

 used primarily as a decongestant
Decongestant
A decongestant or nasal decongestant is a type of drug that is used to relieve nasal congestion.-Pharmacology:The vast majority of decongestants act via enhancing norepinephrine and epinephrine or adrenergic activity by stimulating the α-adrenergic receptors...

, as an agent to dilate the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...

, and to increase blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

. Phenylephrine has recently been marketed as a substitute for pseudoephedrine
Pseudoephedrine
Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

 (e.g.,Sudafed
Sudafed
Sudafed is a brand name and registered trademark for over the counter decongestants manufactured by McNeil Laboratories for sale in Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States...

 (Original Formulation)
), but there are claims that oral phenylephrine may be no more effective as a decongestant than a placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

 (see questions about effectiveness below).

Decongestant

Phenylephrine is used as a decongestant sold as an oral medicine, as a nasal spray
Nasal spray
Nasal sprays come in a variety of forms. Medicated such as Astelin, Afrin and Nasonex and natural such as Sinusoothe and Sterimar. Although delivery methods vary, most nasal sprays function by instilling a fine mist into the nostril by action of a hand-operated pump mechanism.-Antihistamine nasal...

, or as eye drops. Phenylephrine is now the most common over-the-counter
Over-the-counter drug
Over-the-counter drugs are medicines that may be sold directly to a consumer without a prescription from a healthcare professional, as compared to prescription drugs, which may be sold only to consumers possessing a valid prescription...

 (OTC) decongestant
Decongestant
A decongestant or nasal decongestant is a type of drug that is used to relieve nasal congestion.-Pharmacology:The vast majority of decongestants act via enhancing norepinephrine and epinephrine or adrenergic activity by stimulating the α-adrenergic receptors...

 in the United States; oxymetazoline
Oxymetazoline
Oxymetazoline is a selective alpha-1 agonist and partial alpha-2 agonist topical decongestant, used in the form of Oxymetazoline hydrochloride, in products such as Afrin, Dristan, Nasivin, Logicin, Vicks Sinex, Visine L.R., Sudafed OM, and Zicam. It was developed from Xylometazoline at E.Merck...

 is a more common nasal spray. Pseudoephedrine
Pseudoephedrine
Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

 was historically more common, although its notoriety as a methamphetamine
Methamphetamine
Methamphetamine is a psychostimulant of the phenethylamine and amphetamine class of psychoactive drugs...

 precursor has led some governments to restrict its sale.

Oral phenylephrine is extensively metabolised
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 by monoamine oxidase
Monoamine oxidase
L-Monoamine oxidases are a family of enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. The enzyme was originally discovered by Mary Bernheim in the liver and was named tyramine oxidase...

, an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that is present in the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

 and in the liver. Therefore, compared to IV pseudoephedrine, it has a reduced and variable bioavailability
Bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...

; only up to 38 percent. Because phenylephrine is a direct selective α-adrenergic receptor agonist, it does not cause the release of endogenous noradrenaline
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...

, as pseudoephedrine does. Therefore, phenylephrine is less likely to cause side effects such as central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 stimulation, insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...

, anxiety
Anxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...

, irritability, and restlessness. Phenylephrine's effectiveness as a decongestant stems from its vasoconstriction of nasal blood vessels, thereby decreasing blood flow to the sinusoidal vessels, leading to decreased mucosal edema.

Some popular cold
Common cold
The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...

 remedies containing phenylephrine include:

Australia
  • Codral
    Codral
    Codral is a brand name of cold and flu medication manufactured by Johnson & Johnson and sold primarily in Australia & New Zealand. Codral is the highest-selling cold and flu medication in Australia....

     Cold & Flu (New Formula)
  • Lemsip
    Lemsip
    Lemsip is a brand of cold and flu remedies in Ireland, the United Kingdom, Australia and New Zealand. It is manufactured by Reckitt Benckiser...

     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
  • Dimetapp PE Adult Strength Nasal Decongestant


Austria
  • Visadron Augentropfen (i.e. eye drops)
  • Neo Citran


Brazil
  • Coristina


China
  • Pharmaceutical Raw Material

Shenzhen Oriental Pharmaceutical co.,Ltd.

Canada
  • Hot lemon Neo Citran
  • Tylenol
    Tylenol
    Tylenol is a North American brand of drugs advertised for reducing pain, reducing fever, and relieving the symptoms of allergies, cold, cough, and flu. The active ingredient of its original, flagship product, paracetamol , is marketed as an analgesic and antipyretic...

     Cold Rapid Release
  • Sudafed PE


India
  • Crocin Cold n' Flu (GSK)
  • Kapryl (Kaptab Pharmaceuticals)
  • Lemolate
  • D-Cold Total
  • Solvin


Iran
  • Adult Cold (fa:قرص سرماخوردگی بزرگسالان)


Israel
  • Coldex


Italy
  • Tachiflu-dec


Mexico
  • Histiacil Flu
  • Next
  • Capsiflu


New Zealand
  • Panadol Cold & Flu Max + Decongestant
  • Codral
    Codral
    Codral is a brand name of cold and flu medication manufactured by Johnson & Johnson and sold primarily in Australia & New Zealand. Codral is the highest-selling cold and flu medication in Australia....

     Cold & Flu (New Formula)
  • Coldrex PE Phenylephrine
  • Nurofen Cold & Flu PE


Philippines
  • Decolgen
  • Bioflu
  • Neozep


South Africa
  • Corenza C
  • Demazin
  • Flutex


South Korea
  • Happynose Tab


United Kingdom
  • Lemsip
    Lemsip
    Lemsip is a brand of cold and flu remedies in Ireland, the United Kingdom, Australia and New Zealand. It is manufactured by Reckitt Benckiser...

  • Sudafed
    Sudafed
    Sudafed is a brand name and registered trademark for over the counter decongestants manufactured by McNeil Laboratories for sale in Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States...

     Non-Drowsy capsules
  • Beechams Flu-plus
  • Benylin
    Benylin
    Benylin is a brand name owned by Johnson & Johnson for a range of cough, cold and flu medications. The flagship cough syrup and cold care brand is marketed in several countries as Benylin DM, for its active ingredient, dextromethorphan...

     Cold & Flu Day & Night


United States
  • Advil
    Advil
    Advil is a brand of ibuprofen, a nonsteroidal anti-inflammatory drug . Advil is manufactured by Pfizer and has been on the market since 1984.-History:...

     Congestion Relief
  • Alka-Seltzer
    Alka-Seltzer
    Alka-Seltzer is an effervescent antacid and pain reliever first marketed by the Dr. Miles Medicine Company. It was developed by Treneer in Elkhart Indiana. Alka-Seltzer is marketed for relief of minor aches, pains, inflammation, fever, headache, heartburn, sour stomach, indigestion, and hangovers,...

     Cold Effervescent formula
  • Sudafed
    Sudafed
    Sudafed is a brand name and registered trademark for over the counter decongestants manufactured by McNeil Laboratories for sale in Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States...

     PE Non-Drowsy Nasal Decongestant
  • Robitussin
    Robitussin
    Robitussin is a line of cold and cough medicines currently produced by Pfizer. Robitussin is available in various formulations. Robitussin contains an expectorant ; Robitussin DM adds a cough suppressant to the expectorant ; Robitussin CF is a cold formula that adds an expectorant and a nasal...

     CF
  • DayQuil
    DayQuil
    DayQuil is a medicine intended to relieve symptoms of the common cold and flu. Made by Vicks, it is available in syrup and capsule form. DayQuil's night time counterpart is NyQuil, which contains sedative antihistamines. Because DayQuil lacks antihistamines, it does not cause drowsiness, and thus...

     Capsules
  • Tylenol
    Tylenol
    Tylenol is a North American brand of drugs advertised for reducing pain, reducing fever, and relieving the symptoms of allergies, cold, cough, and flu. The active ingredient of its original, flagship product, paracetamol , is marketed as an analgesic and antipyretic...

     Sinus
  • Tylenol
    Tylenol
    Tylenol is a North American brand of drugs advertised for reducing pain, reducing fever, and relieving the symptoms of allergies, cold, cough, and flu. The active ingredient of its original, flagship product, paracetamol , is marketed as an analgesic and antipyretic...

     Sinus Congestion & Pain
  • Theraflu
    Theraflu
    Theraflu is a brand of over-the-counter cold and flu medicines from Novartis that contain different groupings of various cold and flu symptom medications. The original version of Theraflu contained Acetaminophen , Chlorpheniramine maleate , Dextromethorphan hydrobromide , and Pseudoephedrine...

  • Benadryl
    Benadryl
    Benadryl is a brand name allergy medicine marketed over-the-counter by Johnson & Johnson subsidiary McNeil Consumer Healthcare. Prior to 2007, Benadryl was marketed by Pfizer Consumer Healthcare...

     Allergy & Sinus Headache
  • Excedrin Sinus Headache
  • Dristan
  • Entex
  • Neo-Synephrine


As a nasal spray, phenylephrine is available in 1 percent and 0.5 percent concentrations. It causes some rebound congestion
Rhinitis medicamentosa
Rhinitis medicamentosa is a condition of rebound nasal congestion brought on by extended use of topical decongestants that work by constricting blood vessels in the lining of the nose.-Presentation:This condition typically occurs after 5 to 7 days of use of such medications...

 effects, similar to oxymetazoline
Oxymetazoline
Oxymetazoline is a selective alpha-1 agonist and partial alpha-2 agonist topical decongestant, used in the form of Oxymetazoline hydrochloride, in products such as Afrin, Dristan, Nasivin, Logicin, Vicks Sinex, Visine L.R., Sudafed OM, and Zicam. It was developed from Xylometazoline at E.Merck...

, although possibly to a lesser degree.

Mydriatic

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
Tropicamide
Tropicamide is an anticholinergic used as a mydriatic. In Russia, it is used to some degree as an inexpensive recreational drug...

. Narrow-angle glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

 is a contraindication
Contraindication
In medicine, a contraindication is a condition or factor that serves as a reason to withhold a certain medical treatment.Some contraindications are absolute, meaning that there are no reasonable circumstances for undertaking a course of action...

 to phenylephrine use.

Vasopressor

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
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

 effect of epidural
Epidural
The term epidural is often short for epidural analgesia, a form of regional analgesia involving injection of drugs through a catheter placed into the epidural space...

 and subarachnoid anesthetics. It also has the advantage of not being inotropic
Inotrope
An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions...

 or chronotropic
Chronotropic
Chronotropic effects are those that change the heart rate.Chronotropic drugs may change the heart rate by affecting the nerves controlling the heart, or by changing the rhythm produced by the sinoatrial node...

, and so it strictly elevates the blood pressure without increasing the heart rate or contractility (reflex bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

 may result from the blood pressure increase, however). This is especially useful if the heart is already tachycardic and/or has a cardiomyopathy
Cardiomyopathy
Cardiomyopathy, which literally means "heart muscle disease," is the deterioration of the function of the myocardium for any reason. People with cardiomyopathy are often at risk of arrhythmia or sudden cardiac death or both. Cardiomyopathy can often go undetected, making it especially dangerous to...

. The elimination half life of phenylephrine is about 2.5 to 3 hours.

Detumescent

Phenylephrine is used by Urologists to abort priapism
Priapism
Priapism is a potentially harmful and painful medical condition in which the erect penis or clitoris does not return to its flaccid state, despite the absence of both physical and psychological stimulation, within four hours. There are two types of priapism: low-flow and high-flow. Low-flow...

. It is diluted significantly and injected directly into the corpora cavernosa. The mechanism of action is to cause constriction of the blood vessels entering into the penis thus breaking the pathophysiologic cycle that continues the priapism.

Side effects

The primary side effect of phenylephrine is hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

. Patients with 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.

Extended use may cause rhinitis medicamentosa
Rhinitis medicamentosa
Rhinitis medicamentosa is a condition of rebound nasal congestion brought on by extended use of topical decongestants that work by constricting blood vessels in the lining of the nose.-Presentation:This condition typically occurs after 5 to 7 days of use of such medications...

, a condition of rebound
Rebound effect
The rebound effect, or rebound phenomenon, is the tendency of some medications, when discontinued suddenly, to cause a return of the symptoms it relieved, and that, to a degree stronger than they were before treatment first began...

 nasal congestion
Nasal congestion
Nasal congestion is the blockage of the nasal passages usually due to membranes lining the nose becoming swollen from inflamed blood vessels. It is also known as nasal blockage, nasal obstruction, blocked nose, stuffy nose, or stuffed up nose.Nasal congestion has many causes and can range from a...

.

Substitute for pseudoephedrine

Pseudoephedrine and phenylephrine are both used as decongestants; and, until recently, pseudoephedrine
Pseudoephedrine
Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

 was much more commonly available in the United States. This has changed because provisions of the Combat Methamphetamine Epidemic Act of 2005
Combat Methamphetamine Epidemic Act of 2005
The Combat Methamphetamine Epidemic Act of 2005 is federal legislation enacted in the United States on March 9, 2006, to regulate, among other things, retail over-the-counter sales of ephedrine, pseudoephedrine, and phenylpropanolamine products because of their use in the manufacture of illegal...

 placed restrictions on the sale of pseudoephedrine products in order to prevent the clandestine manufacture
Clandestine chemistry
Clandestine chemistry is chemistry carried out in secret, and particularly in illegal drug laboratories. Larger labs are usually run by gangs or organized crime intending to produce for distribution on the black market...

 of methamphetamine
Methamphetamine
Methamphetamine is a psychostimulant of the phenethylamine and amphetamine class of psychoactive drugs...

. 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
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

 for some time, and there are many generic brands available.

Questions about effectiveness

Pharmacists Leslie Hendeles and Randy Hatton of the University of Florida
University of Florida
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...

 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
GlaxoSmithKline
GlaxoSmithKline plc is a global pharmaceutical, biologics, vaccines and consumer healthcare company headquartered in London, United Kingdom...

 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
Allergic rhinitis
Allergic rhinitis, also known as pollenosis or hay fever, is an allergic inflammation of the nasal airways.It occurs when an allergen, such as pollen, dust or animal dander is inhaled by an individual with a sensitized immune system...

 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
Loratadine
Loratadine is a second-generation H1 histamine antagonist drug used to treat allergies. Structurally, it is closely related to tricyclic antidepressants such as imipramine, and distantly related to the atypical antipsychotic quetiapine. It is marketed by Schering-Plough under several trade names...

-montelukast
Montelukast
Montelukast is a leukotriene receptor antagonist used for the maintenance treatment of asthma and to relieve symptoms of seasonal allergies. It is usually administered orally...

 therapy were found to be significantly more effective than both phenylephrine and placebo.

The Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

has stood by its 1976 approval of phenylephrine for nasal congestion as the debate continues.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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