Description
R-(-)-Phenylephrine is an adrenergic α
1A receptor agonist (K
i = 1.4 μM) that demonstrates selectivity against the α
1B and α
1C receptor subtypes (K
is = 23.9 and 47.8 μM, respectively). By stimulating adrenergic α
1 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
Chemical Properties
Phenylephrine Hydrochloride is white or nearly white crystalline substance, odorless, bitter taste. Solutions are acid to litmus paper, freely soluble in water and in alcohol. Levorotatory in solution.
Originator
Neosynephrine, Badrial, France ,1953
Uses
(R)-Phenylephrine Hydrochloride is an α-Adrenergic agonist. Mydriatic; decongestant.
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).
Therapeutic Function
Adrenergic
General Description
Odorless white microcrystalline powder. Bitter taste. pH (1% aqueous solution) about 5.
Air & Water Reactions
May be sensitive to prolonged exposure to air and light. Water soluble.
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.
