Tetrahydrozoline hydrochloride
[CAS# 522-48-5]

Identification

• Classification: API >> Nervous system medication >> Cholinergic
• Name: Tetrahydrozoline hydrochloride
• Synonyms: 2-Tetralin-1-yl-4,5-dihydro-1H-imidazole hydrochloride
• Molecular Formula: C₁₃H₁₆N₂.HCl
• Molecular Weight: 236.74
• CAS Registry Number: 522-48-5
• EC Number: 208-329-3
• SMILES: C1CC(C2=CC=CC=C2C1)C3=NCCN3.Cl

Properties

• Solubility: 12 mg/mL (DMSO), 48 mg/mL (water) (Expl.)

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302-H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	3	H335

Discovery and Applications

Tetrahydrozoline hydrochloride is a synthetic chemical compound recognized primarily for its vasoconstrictive properties. Structurally, it is a member of the imidazoline class, characterized by a nitrogen-containing heterocyclic ring, which enables its interaction with adrenergic receptors in the body. First developed in the mid-20th century, tetrahydrozoline hydrochloride was introduced as an effective agent for reducing eye redness caused by minor irritation, allergies, or fatigue. Its unique structure allows it to selectively bind to alpha-adrenergic receptors in the smooth muscle of blood vessels, prompting vasoconstriction and thus reducing redness and swelling.

The primary application of tetrahydrozoline hydrochloride is in ophthalmic solutions formulated for over-the-counter (OTC) eye drops. Its vasoconstrictive action works rapidly to reduce visible blood vessels in the eye, providing temporary relief from redness without causing significant side effects at typical dosages. This compound has become a common ingredient in eye drop formulations marketed for relieving redness and dryness associated with mild ocular irritation. Additionally, it has been employed in nasal sprays to relieve nasal congestion, leveraging the same mechanism of constricting blood vessels to decrease swelling in nasal tissues.

Beyond its use as an OTC remedy, tetrahydrozoline hydrochloride has been studied for its potential application in drug formulations targeting local delivery within ophthalmology and nasal treatments. Researchers continue to investigate its extended use and effect on adrenergic receptors for potential development of novel treatments with improved efficacy or broader therapeutic applications. However, as with other vasoconstrictors, long-term or excessive use of tetrahydrozoline-based products can lead to rebound redness or dependency, limiting its use to short-term relief under guidance.

References

1955. THE SYMPATHOMIMETIC AND OTHER PHARMACOLOGICAL PROPERTIES OF DL 2-(1 ,2 ,3 ,4-TETRAHYDRO-1-NAPHTHYL)-IMIDAZOLINE (TETRAHYDROZOLINE). The Journal of Pharmacology and Experimental Therapeutics, 113(3).
DOI: 10.1016/s0022-3565(25)11519-x

2023. More than meets the eye: a scoping review on the non-medical uses of THZ eye drops. Forensic science, medicine, and pathology, 19(4).
DOI: 10.1007/s12024-023-00680-9

2020. In vitro-in vivo evaluation of tetrahydrozoline-loaded ocular in situ gels on rabbits for allergic conjunctivitis management. Drug Development Research, 81(6).
DOI: 10.1002/ddr.21677