Naphazoline hydrochloride
[CAS# 550-99-2]

Identification

• Classification: API >> Nervous system medication >> Cholinergic
• Name: Naphazoline hydrochloride
• Synonyms: 2-(1-Naphthylmethyl)imidazoline hydrochloride
• Molecular Formula: C₁₄H₁₄N₂.HCl
• Molecular Weight: 246.74
• CAS Registry Number: 550-99-2
• EC Number: 208-989-2
• SMILES: C1CN=C(N1)CC2=CC=CC3=CC=CC=C32.Cl

Properties

• Melting point: 254-260 °C
• Water solubility: 170 g/L (20 °C)

Safety Data

• Hazard Symbols: GHS06 Danger
• Risk Statements: H300
• Safety Statements: P264-P270-P301+P316-P321-P330-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	2	H300
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	3	H301
Acute toxicity	Acute Tox.	3	H311
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332

• Transport Information: UN 2811

Discovery and Applications

Naphazoline hydrochloride is a widely used drug known for its vasoconstrictive and decongestive properties. Naphazoline hydrochloride, chemically known as 2-(1-naphthylmethyl)-2-imidazoline hydrochloride, was first synthesized in the mid-20th century as a derivative of imidazoline. It relieves nasal congestion and eye irritation by constricting blood vessels in the nasal and ocular mucosa.

Naphazoline hydrochloride belongs to the imidazoline class of compounds, which are characterized by a naphthalene ring structure and an imidazoline moiety. The hydrochloride form enhances its water solubility, facilitating formulation into nasal sprays, eye drops, and topical solutions.

Naphazoline hydrochloride acts topically to constrict blood vessels in the nasal mucosa, reducing swelling and congestion, helping to relieve symptoms of nasal congestion caused by allergies, colds, or sinusitis, making breathing easier. When used as eye drops, naphazoline hydrochloride constricts conjunctival blood vessels, reducing redness and irritation caused by minor eye irritants or environmental factors. It temporarily relieves eye discomfort and allergic conjunctivitis.

Naphazoline hydrochloride is commonly used in nasal sprays and drops to relieve nasal congestion symptoms associated with the common cold, hay fever, or sinusitis. Its rapid onset of action quickly relieves nasal congestion, allowing patients to breathe more comfortably.

In ophthalmic preparations, naphazoline hydrochloride is used in the eye to relieve redness and discomfort caused by minor irritations, dust, smoke, or pollen. It is effective for temporary relief of eye irritation and allergic reactions affecting the conjunctiva.

Naphazoline hydrochloride should be used as directed to avoid potential side effects such as rebound congestion or eye irritation. Long-term use beyond the recommended use period may lead to tolerance or dependence on nasal congestion relief medications. People with certain medical conditions, such as narrow-angle glaucoma or cardiovascular disease, should use naphazoline hydrochloride with caution or under medical supervision because naphazoline hydrochloride can have systemic effects on blood pressure and heart rate.

References

2022. Naphazoline enhances cutaneous analgesia of lidocaine in rats. Fundamental & Clinical Pharmacology, 37(1).
DOI: 10.1111/fcp.12853

2024. Photodegradation of naphazoline: analytical study of degradation products. Molecules, 29(17).
DOI: 10.3390/molecules29174122

2020. Green HPTLC and HPLC methods for analysis of naphazoline in pharmaceuticals. Chromatographia, 83(6).
DOI: 10.1007/s00764-020-00024-1