Phenylephrine Totally Explained

Everything about Phenylephrine totally explained

(hydrochloride) | ATC_prefix = C01 | ATC_suffix = CA06 | ATC_supplemental =,,,, | PubChem = 6041 | DrugBank = APRD00365 | C=9 | H=13 | N=1 | O=2 | | molecular_weight = 167.205 g/mol | bioavailability = 38% through GI tract | protein_bound = 95% | metabolism = Hepatic (monoamine oxidase) | elimination_half-life = 2.1 to 3.4 hours | pregnancy_AU = B2 | pregnancy_US = C | legal_US = OTC | routes_of_administration = Oral, intranasal, ophthalmic, intravenous, intramuscular }} Phenylephrine or Neo-Synephrine is an α-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, (for example Pfizer's Sudafed (Original Formulation)) but there are recent claims that oral phenylephrine may be no more effective as a decongestant than placebo.

Uses

Decongestant

Phenylephrine is used as a decongestant, available as an oral medicine or as a nasal spray. Phenylephrine is now the most common over-the-counter (OTC) decongestant; 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 (External Link

), 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, and is therefore less effective as a nasal decongestant than pseudoephedrine. Because phenylephrine is a direct selective α-adrenergic receptor agonist, it doesn't 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: Australia

Codral Cold & Flu (New Formula)

Canada

Hot lemon Neocitran, United Kingdom

Lemsip, United States

Alka-Seltzer Cold Effervescent formula

Sudafed PE Non-Drowsy Nasal Decongestant

Robitussin CF, Tylenol Sinus

DayQuil Capsules. As a nasal spray, phenylephrine is available in 1% and 0.5% concentrations. It suffers some rebound congestion effects, although to a lesser degree than oxymetazoline.

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.

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 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 2.5-3hours.

Side effects

The primary side effect of phenylephrine is hypertension. Patients with congestion and hypertension are typically advised to avoid products containing phenylephrine.
Patients with a history of epilepsy and on anticonvulsant medication shouldn't take this substance. The drug interaction might produce seizures.

Legal issues

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 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. Other pharmacists have expressed concerns over phenylephrine's effectiveness as a nasal decongestant, A subsequent meta-analysis by the same researchers concluded that there's insufficient evidence for its effectiveness, though another meta-analysis published shortly thereafter by researches from GlaxoSmithKline found the standard 10mg dose to be significantly more effective than a placebo.
The matter is still under debate, though the Food and Drug Administration has stood by its 1976 approval.

Further Information

Get more info on 'Phenylephrine'.

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