Sign Out
Pharmacology: Pharmacodynamics: Phenylephrine hydrochloride is a synthetic sympathomimetic amine. After topical application to the conjunctiva, phenylephrine acts directly on α-adrenergic receptors in the eye producing contraction of the dilator muscle of the pupil and constriction of arterioles in the conjunctiva. Phenylephrine hydrochloride is used for local ocular disorders because of its vasoconstrictor and mydriatic action. There is almost no cycloplegic effect.
Pharmacokinetics: Phenylephrine is a weak base at physiological pH. The extent of ocular penetration is determined by the condition of the cornea. A healthy cornea presents a physical barrier, in addition to which, some metabolic activity may occur. Where the corneal epithelium is damaged, the effect of the barrier and the extent of metabolism are reduced, leading to greater absorption.
Administration of a 10% solution of Phenylephrine hydrochloride produces maximal mydriasis within 10-90 minutes; recovery occurs within 3-7 hours.
Occasionally, enough Phenylephrine may be absorbed following topical application to the conjunctiva to cause systemic sympathomimetic effects. Circulating drug is metabolized in the liver by the enzyme monoamine oxidase (MAO).
