Naphazoline

Absorption

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

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.

Originator

Privine,Ciba,US,1942

The Uses of Naphazoline

Naphazoline is used in severe rhinitis associated with colds, allergic reactions, and severe and chronic inflammatory conditions, in particular for inflammation of the antrum of Highmore as well as for stopping nosebleeds.

The Uses of Naphazoline

Adrenergic (vasoconstrictor).

Background

Naphazoline is a rapid acting imidazoline sympathomimetic vasoconstrictor of ocular or nasal artierioles. It acts to decrease congestion and is found in many over the counter (OTC) eye drops and nasal preparations.
Naphazoline was first developed in 1942 as a nasal formulation for congestion.

Indications

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

Definition

ChEBI: 2-(1-naphthalenylmethyl)-4,5-dihydro-1H-imidazole is a member of naphthalenes.

Manufacturing Process

2.7 parts of naphthyl-(1)-acetiminoethylether hydrochloride of the formula (produced from naphthyl-(1)-acetonitrile and methanol) are dissolved in 12 parts of absolute alcohol. 1 part of ethylenediamine is then added and the whole is heated to gentle boiling while passing nitrogen through it and simultaneously stirring until ammonia escapes no longer. The alcohol is then distilled and the residue mixed with 40 parts of benzene and 1.8 parts of caustic potash. Stirring is continued for some time whereby the imidazoline base is dissolved in benzene. The benzene residue is recrystallized several times from toluene.

brand name

Albalon (Allergan); Nafazair (Bausch & Lomb); Nafazair (Pharmafair); Naphcon (Alcon); Opcon (Bausch & Lomb); Vasocon (Novartis).

Therapeutic Function

Nasal decongestant

Pharmacokinetics

Naphazoline is a sympathomimetic alpha adrenergic agonist that acts to vasoconstrict nasal or ocular arterioles, resulting in reduced congestion at the site of administration.

Synthesis

Naphazoline, 2-(1-naphthylmethyl)-2-imidazoline (11.1.36), is synthesized from (1-naphthyl)acetonitrile, which upon reaction with ethanol transforms into iminoester (11.1.35), and undergoes further heterocyclization into the desired imidozoline derivative (11.1.36) upon reaction with ethylendiamine [40].

Metabolism

Metabolism data for naphazoline are scarce. Imidazoline compounds undergo some hepatic metabolism but a large fraction of the dose may be excreted unchanged in the urine.