61-76-7

Description

R-(-)-Phenylephrine is an adrenergic α1A receptor agonist (Ki = 1.4 μM) that demonstrates selectivity against the α1B and α1C receptor subtypes (Kis = 23.9 and 47.8 μM, respectively). By stimulating adrenergic α1 receptors, L-phenylephrine can induce aortic smooth muscle contractions, although reported relative affinity and potency values in rabbit are 5-fold weaker compared to that of L-norepinephrine . This compound is frequently used to precontract smooth muscle in preparations designed to study the properties of various vasodilator agents.

Chemical Properties

white to almost white crystalline powder

Originator

Neosynephrine, Badrial, France ,1953

Uses

Phenylephrine hydrochloride is used medically as a vasoconstrictor and pressor drug. It is chemically related to epinephrine and ephedrine. Actions are usually longer lasting than the latter two drugs. The action of phenylephrine hydrochloride contrasts sharply with epinephrine and ephedrine, in that its action on the heart is to slow the rate and to increase the stroke output, inducing no disturbance in the rhythm of the pulse. In therapeutic doses, it produces little if any stimulation of either the spinal cord or cerebrum. The drug is intended for the maintenance of an adequate level of blood pressure during spinal and inhalation anesthesia and for the treatment of vascular failure in shock, shock-like states, and drug-induced hypotension, or hypersensitivity. It is also used to overcome paroxysmal supraventricular tachycardia, to prolong spinal anesthesia, and as a vasoconstrictor in regional analgesia. Caution is required in the administration of phenylephrine hydrochloride to elderly persons, or to patients with hyperthyroidism, bradycardia, partial heart block, myocardial disease, or severe arteriosclerosis. The brand name Neo-Synephrine? is also used to designate another product (nose drops) which does not contain phenylephrine hydrochloride. The nose drops contain xylometazoline hydrochloride.

Definition

ChEBI: A hydrochloride that is the monohydrochloride salt of phenylephrine.

Manufacturing Process

4.5 g of the hydrochloride of m-hydroxymethylaminoacetophenone aredissolved in a small amount of water; to the solution a solution of colloidal palladium obtained from palladiumchloride is added, and the mixture is treated with hydrogen.After diluting the reaction liquid with acetone it is filtered, and the residue obtained after the evaporation of the filtrate in vacuo, and complete drying over pentoxide of phosphorus is then dissolved in absolute alcohol, and to this is added about the same volume of dry ether, until turbidity just commences to occur. After a short time the hydrochloride of the m-hydroxyphenylethanolmethylamine will separate out as a colorless mass of crystals at a melting point of 142°C to 143°C.

Brand name

Afrin 4 Hour Nasal Spray (Schering-Plough Health Care); Biomydrin (Parke-Davis); Mydfrin (Alcon); Neo-Synephrine (Sterling Health U.S.A.); Nostril (Boehringer Ingelheim).

General Description

Odorless white microcrystalline powder. Bitter taste. pH (1% aqueous solution) about 5.

Reactivity Profile

Phenylephrine hydrochloride is incompatible with acids, acid chlorides, acid anhydrides and oxidizing agents. Phenylephrine hydrochloride is also incompatible with butacaine, alkalis and ferric salts.

Fire Hazard

Flash point data for Phenylephrine hydrochloride are not available; however, Phenylephrine hydrochloride is probably combustible.

Biological Activity

α 1 -adrenoceptor agonist; pK i values are 5.86, 4.87 and 4.70 for α 1D , α 1B and α 1A receptors respectively.

Contact allergens

Phenylephrine hydrochloride is an alpha-adrenergic agonist, used as a mydriatic and decongestant in eyedrops.

Safety Profile

Poison by ingestion, intraperitoneal, subcutaneous, intravenous,and intramuscular routes. Mutation data reported. When heated to decomposition it emits very toxic fumes of HCl and NOx.

Veterinary Drugs and Treatments

Phenylephrine is a vasoconstrictor used to differentiate conjunctival vascular injection (blanches with phenylephrine application) versus deep episcleral injection (blanches incompletely) associated with uveitis, glaucoma, or scleritis. It is also used prior to conjunctival surgery to reduce hemorrhage and in combination with atropine prior to cataract or other intraocular surgeries that require maximal pupillary dilation. Phenylephrine can be used to confirm the diagnosis of Horner’s syndrome. Dilution of 2.5% phenylephrine solution with saline (1:10) produces a 0.25% solution. Normal eyes will not demonstrate mydriasis in response to this low concentration of phenylephrine. Third order Horner’s syndrome of greater than two weeks duration is associated with receptor up regulation and therefore a response to 0.25% phenylephrine is noted. In this way, the diagnosis of Horner’s is confirmed and a suggestion as to whether or not the condition is 2nd or 3rd order in nature. In dogs, maximum mydriasis persists for about 2 hours and effects may last for up to 18 hours. Phenylephrine has significant alpha adrenergic effects (vasoconstriction and pupillary dilation) and minimal effects on beta receptors. When used alone, phenylephrine is reportedly not efficacious in the cat unless used with other mydriatics.