Naphazoline

Chemical structure and classification

By its chemical structure, naphazoline (Naphtysinum) belongs to imidazoline derivatives. Drugs such as oxymetazoline, xylometazoline, and tetryzoline belong to the same structural group.

In the framework of pharmacological classification, the drug is included in the extensive group of agents regulating the functions of the peripheral nervous system. According to its mechanism of action, it is a predominantly local $\alpha_2$-adrenergic agonist.

Pharmacodynamics and mechanism of action

The main target of the drug is peripheral $\alpha_2$-adrenergic receptors.

Upon stimulation of these receptors, naphazoline causes a pronounced vasoconstrictor effect (vasoconstriction).

Pharmacological comparison: it is important to note that the vasoconstrictor effect of imidazoline derivatives (including naphazoline) is more prolonged than that of classical $\alpha_1$-adrenergic agonists, such as phenylephrine.

Use in ENT practice

The drug is available in various forms for topical application: drops, sprays, and emulsions. The main clinical application is intranasal administration for rhinitis.

The mechanism of the therapeutic effect represents a sequential cascade:

1. Local constriction of the blood vessels of the nasal mucosa.
2. Reduction of local tissue edema.
3. Improvement of mucus drainage from the paranasal sinuses.
4. Decreased blood flow to the venous sinuses.

Clinical result: rapid and effective relief of nasal breathing.

Systemic (central) effects of $\alpha_2$-adrenergic agonists

Although naphazoline is used as a topically acting drug, students need to know the systemic effects of the entire $\alpha_2$-adrenergic agonist group. Centrally acting drugs from this group include clonidine, guanfacine, methyldopa, and tizanidine.

Upon resorptive action (absorption into the systemic circulation) and stimulation of $\alpha_2$-adrenergic receptors in the CNS, the following effects develop:

• Hypotensive — a clinically significant decrease in blood pressure.
• Sedative — a pronounced calming effect on the nervous system.
• Analgesic — systemic pain relief.
• Hypothermic — lowering of body temperature.

Formulations and prescription guidelines

According to the prescription reference guide, the drug is prescribed in the form of solutions of various concentrations.

• Dosage form: Solution in 0.05% and 0.1% vials with a volume of 10 ml.
• Method of administration: 2–3 drops into the nasal passages 3–4 times a day.

Prescription example:

`Rp.: Sol. Naphtysini 0.1% - 10 ml` `D.S. 2-3 drops into each nasal passage 3-4 times a day.`

Class and exam questions

What else to study on this topic

• Comparative pharmacokinetics of topically acting imidazoline derivatives (naphazoline, oxymetazoline, xylometazoline).
• The mechanism of rhinitis medicamentosa (tachyphylaxis) development upon prolonged use of local vasoconstrictors.
• Differences between $\alpha_1$- and $\alpha_2$-adrenergic receptors: localization in organs and tissues, post-receptor mechanisms.
• The danger of the resorptive action of local $\alpha_2$-adrenergic agonists in pediatric practice.
• Pharmacodynamics of central $\alpha_2$-adrenergic agonists (clonidine, methyldopa) in the treatment of arterial hypertension.

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Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.