Naphazoline

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.

Naphazoline

Clinical data
Trade names	Clear Eyes, Cleari, Naphcon-A, Rohto
AHFS/Drugs.com	Monograph
Routes of administration	Ophthalmic drug administration, nasal administration
ATC code	R01AA08 (WHO) S01GA01 (WHO)
Legal status
Legal status	In general: Over-the-counter (OTC)
Identifiers
IUPAC name 2-(naphthalen-1-ylmethyl)-4,5-dihydro-1H-imidazole
CAS Number	835-31-4 N
PubChem CID	4436
IUPHAR/BPS	5509
DrugBank	DB06711 Y
ChemSpider	4283 Y
UNII	H231GF11BV
KEGG	D08253 Y
ChEMBL	ChEMBL761 Y
CompTox Dashboard (EPA)	DTXSID3048449
ECHA InfoCard	100.011.492
Chemical and physical data
Formula	C14H14N2
Molar mass	210.280 g·mol−1
3D model (JSmol)	Interactive image
SMILES N\1=C(\NCC/1)Cc2cccc3c2cccc3
InChI InChI=1S/C14H14N2/c1-2-7-13-11(4-1)5-3-6-12(13)10-14-15-8-9-16-14/h1-7H,8-10H2,(H,15,16) Y Key:CNIIGCLFLJGOGP-UHFFFAOYSA-N Y
NY (what is this?)  (verify)

It was patented in 1934 and came into medical use in 1942.^[1]

Medical uses

Red eyes can be treated with naphazoline.

Nasal administration

Nasal decongestant.^[2]

Ophthalmic drug administration

Eye drops (brand names Clear Eyes, and Cleari) narrowing swollen blood vessels (ophthalmic arteries, and ophthalmic veins) to relieve red eye.^[2]

Temporary red eye can safely be treated when the cause of the redness is established (e.g. cannabis induced conjunctival vasodilation).^[3] 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.^[4]

Nasal administration

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

Ophthalmic drug administration

Known side-effect:^[5][6]

• 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 α₁- and α₂-adrenergic receptor agonist.^[2]

Chemistry

The non-hydrochloride form of Naphazoline has the molecular formula C₁₄H₁₄N₂ 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.^[7]

Illicit use

The nasal or ophthalmic form of naphazoline has been abused by heroin or cocaine drug addicts.^[8][9] It's used as CNS stimulant and vasoconstrictor to enhance primary drug effects.^[9]