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Naphazoline is a medicine used as a decongestant, and a vasoconstrictor added to eye drops to relieve red eye. It has a rapid action in reducing swelling when applied to mucous membranes. It is a sympathomimetic agent with marked alpha adrenergic activity that acts on alpha-receptors in the arterioles of the conjunctiva to produce constriction, resulting in decreased congestion.

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It was patented in 1934 and came into medical use in 1942.

Medical uses

thumb|left|Red eyes can be treated with naphazoline.

Nasal administration

Nasal decongestant. However, continuous use is not recommended without knowing an underlying condition.

Side effects

A few warnings and contraindications that apply to all naphazoline-containing substances intended for medicinal use are:

  • Hypersensitivity to naphazoline
  • 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
  • A possible association with stroke has been suggested.

Nasal administration

  • Extended use may cause rhinitis medicamentosa, a condition of rebound nasal congestion.

Ophthalmic drug administration

Known side-effect:

  • Stinging
  • Discomfort
  • Irritation
  • Increased red eyes
  • Blurred vision
  • Mydriasis
  • Punctate keratitis
  • Lacrimation (tears)
  • Increased intraocular pressure

Contraindications

  • Patients taking MAO inhibitors can experience a severe hypertensive crisis if given a sympathomimetic drug such as naphazoline HCl
  • 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.

Pharmacology

Naphazoline is a mixed α<sub>1</sub>- and α<sub>2</sub>-adrenergic receptor agonist.

Chemistry

The non-hydrochloride form of Naphazoline has the molecular formula C<sub>14</sub>H<sub>14</sub>N<sub>2</sub> and a molar mass of 210.28 g/mol. The HCl salt form has a molar mass of 246.73 g/mol.

Society and culture

It is an active ingredient in several over-the-counter eye drop formulations including Clear Eyes, Rohto Cool, Eucool, and Naphcon-A.

Illicit use

The nasal or ophthalmic form of naphazoline has been abused by heroin or cocaine drug addicts. It's used as CNS stimulant and vasoconstrictor to enhance primary drug effects.