Also Known As: Phenylephrine, AH-Chew D, 001 Neo-synephrine
Phenylephrine is a selective Î±1-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., Sudafed (Original Formulation)), but there are 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 IV pseudoephedrine, it has a reduced and variable bioavailability; 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. 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.