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Naphazoline (in the hydrochloride form) is the common name for 2-(1-naphthylmethyl)-2-imidazoline hydrochloride. It is a sympathomimetic agent with marked alpha adrenergic activity. It is a vasoconstrictor with a rapid action in reducing swelling when applied to mucous membrane. It acts on alpha-receptors in the arterioles of the conjunctiva to produce constriction, resulting in decreased congestion. It is an active ingredient in several over-the-counter formulations including Clear Eyes and Naphcon eye drops.
Warnings and contraindications
A few warnings and contraindications that apply to all naphazoline-containing substances intended for medicinal use are:
- Hypersensitivity to naphazoline
- Patients taking MAO inhibitors can experience a severe hypertensive crisis if given a sympathomimetic drug such as naphazoline HCl
- Use in infants and children can result in central nervous system depression, leading to coma and marked reduction in body temperature
- Should be used with caution in patients with severe cardiovascular disease including cardiac arrhythmia and in patients with diabetes, especially those with a tendency toward diabetic ketoacidosis
- Drug interactions can occur with anaesthetics that sensitize the myocardium to sympathomimetics (e.g. cyclopropane or halothane cautiously)
- Exercise caution when applying prior to use of phenylephrine.
- Extended use may cause rhinitis medicamentosa, a condition of rebound nasal congestion.
A possible association with stroke has been suggested.
Naphazoline can be synthesized from (1-naphthyl)acetonitrile, which upon reaction with ethanol transforms into iminoester, and undergoes further heterocyclization into the desired imidazoline derivative upon reaction with ethylene diamine.
- Green, S. M. (2008). "Ophthalmology: Naphazoline". Tarascon Pocket Pharmacopoeia 2009. Jones and Bartlett. ISBN 0-7637-6572-4.
- Zavala, J. A.; Pereira, E. R.; Zétola, V. H.; Teive, H. A.; Nóvak, E. M.; Werneck, L. C. (2004). "Hemorrhagic stroke after naphazoline exposition: case report". Arquivos de Neuro-Psiquiatrica 62 (3B): 889–891. PMID 15476091. doi:10.1590/S0004-282X2004000500030.
- A. Sonn, U.S. Patent 2,161,938 (1939)