Phenerazoline

Uses

Naphazoline is a sympathomimetic vasoconstrictor used for the symptomatic relief of redness and itching of the eye, and nasal congestion.

Naphazoline is indicated for use as OTC eyedrops for ocular vasoconstriction or as a nasal preparation for nasal congestion.

Phenerazoline is also used to associated treatment for these conditions: Bacterial Conjunctivitis, Blepharoconjunctivitis, Conjunctivitis, Conjunctivitis allergic, Dacryocystitis, Dacryostenosis, Dermatitis, Eczematous of the Eyelid, Eye Pain, Eye redness, Iritis, Lacrimation, Nasal Allergies, Nasal Congestion, Noninfective conjunctivitis, Otitis Media (OM), Photophobia, Foreign body sensation in eye, Ocular bacterial infections, Ocular vasoconstriction

How Phenerazoline works

Naphazoline is a vasoconstrictor that functions by stimulating alpha adrenergic receptors in arterioles leading to decreased congestion at the site of administration.

Naphazoline causes the release of norepinephrine in sympathetic nerves. Norepinephrine binds to alpha adrenergic receptors and causes vasoconstriction. Naphazoline is also a mild beta adrenergic receptor agonist, which can cause rebound vasodilation after the alpha adrenergic stimulation has ended. Naphazoline's release of norepinephrine also triggers a negative feedback loop which decreases production of norepinephrine, which can lead to rhinitis medicamentosa after long term use when naphazoline is stopped.

Toxicity

In high doses or when ingested, naphazoline can lead to central nervous system depression (which can progress to coma and death), hypothermia, bradycardia, and death. This effect is especially pronounced in children under 6 years.

Long term use of naphazoline can lead to rhinitis medicamentosa once naphazoline is stopped. This condition is a result of norepinephrine release by naphazoline triggering a negative feedback loop.

Safety and effectiveness in children under 12 has not been established. Studies in elderly patients have yet to be performed. Risk in pregnancy, breast feeding, and on overall fertility have not been established, though pregnant and breast feeding patients should consider the risk and benefit before starting naphazoline treatment.

Volume of Distribution

Distribution data for naphazoline are scarce but imidazoline compounds are distributed throughout the body, and can cross the blood-brain barrier.

Elimination Route

Absorption data for naphazoline are scarce but imidazoline compounds in general are weakly basic and lipophilic, with high bioavailability from the gastrointestinal tract.

Half Life

Half life has not been determined but effects last for 4 to 8 hours. Other imidazoline compounds have half lives varying from 2 to 12 hours.

Clearance

Clearance data for naphazoline is unavailable.

Elimination Route

Imidazoline compounds undergo some hepatic metabolism but a large fraction of the dose may be excreted unchanged in the urine. Urinary excretion is higher with more acidic urine.

Innovators Monograph

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