Oxymetazoline Hydrochloride (Intranasal)

Mechanism

Pharmacological Class and Group

Topical intranasal direct-acting sympathomimetic decongestant. Selective agonist of alpha-1 and alpha-2 adrenergic receptors.

Mechanism of Action

Oxymetazoline is an imidazole derivative designed to potently mimic the effects of catecholamines on the vasculature of the nasal turbinates:

Molecular Mechanism of Mucosal Vasoconstriction

1. Stimulation of Postsynaptic Alpha-1 Receptors: It binds directly to the alpha-1 receptors expressed in the smooth muscle fibers of the resistance arterioles of the nasal mucosa. This activates the Gq protein, stimulating phospholipase C, which increases intracellular calcium levels and causes powerful arteriolar vasoconstriction of immediate onset (in less than 5 to 10 minutes).

2. Stimulation of Presynaptic Alpha-2 Receptors: It binds to the alpha-2 receptors located in the capacitance venules of the nasal turbinate, decreasing the volume of the erectile venous sinusoids:

Oxymetazoline Emptying of the erectile cavernous tissue of the turbinates ↑ Nasal aerial cross-sectional area

As a direct consequence of the reduction in arterial perfusion and capillary venous emptying, mucosal edema drastically decreases, the obstruction disappearing almost completely.

Pharmacokinetics

High Resolution Pharmacokinetics

• Onset of Action: Extremely fast, less than 5-10 minutes.
• Duration of Effect: Prolonged, decongestion remaining between 8 and 12 hours after a single application.
• Systemic Absorption: Low if administered at the recommended doses and for periods of time. However, if the dose is exceeded or the drug is swallowed, it can be absorbed from the upper digestive tract, inducing systemic sympathomimetic cardiovascular or neurological effects (especially in children).

Indicators and dose

Clinical Indications and Off-Label Uses

• Acute Nasal Congestion: Symptomatic relief of nasal obstruction in cases of acute infectious rhinitis (common cold), acute rhinosinusitis and seasonal allergic rhinitis.
• Instrumental Management in ENT: Vasoconstriction of the nasal mucosa prior to performing nasal endoscopies (nasofibrolaryngoscopy) to facilitate the passage of instruments and improve anatomical visualization.
• Control of Active Previous Epistaxis: Hemostatic adjuvant to stop bleeding from the vessels of the Kiesselbach plexus through induced local ischemia.
• Acute Tubal Dysfunction (off-label): To facilitate deflation of the Eustachian tube orifice in the cavum in situations of barotrauma or air travel.

Dosage and Clinical Adjustment

Adults and Children over 6 years old:

• 1 or 2 sprays of the 0.05% solution in each nostril.
• Frequency: Maximum every 12 hours (2 times a day), preferably before going to bed to facilitate a night's rest.
• Duration Limit: It should not be administered under any circumstances for more than 3 to 5 consecutive days.

Adjustment in Renal or Hepatic Failure: Does not require adjustment due to the topical nature of the route.

Security

Absolute and Relative Contraindications

Absolute Contraindications

• Known hypersensitivity to oxymetazoline or decongestants of the imidazole group.
• Rinitis Seca (Atrophic Rhinitis): Severely aggravates mucosal ischemia and nasal scab.
• Patients who recently underwent transsphenoidal pituitary surgery.
• Children under 6 years of age (high risk of neurological and systemic cardiovascular depression).

Relative Contraindications

• Severe or uncontrolled arterial hypertension, ischemic heart disease, cardiac arrhythmias or hyperthyroidism.
• Angle closure glaucoma.
• Symptomatic prostatic hyperplasia (increased risk of acute urinary retention due to stimulation of alpha receptors in the bladder neck).

Adverse Effects (ADR) and Specific Toxicity

• Frequent (1%-10%): Itching or temporary dryness of the nasal mucosa, sneezing, rebound hyperemia when the decongestant effect ceases.
• Uncommon (0.1%-1%): Epistaxis due to dryness or prolonged ischemia, palpitations, elevated blood pressure, insomnia, nervousness.
• Rare (<0.1%): Rhinitis Medicamentosa, dependence on nasal spray, necrosis of the anterior nasal septum in cases of massive and uninterrupted use.

Critical Toxicity: Drug Rhinitis and Vasomotor Rebound

Uninterrupted use of oxymetazoline for more than 5 to 7 consecutive days causes a decrease by down-regulation of alpha adrenergic receptors in the arterioles of the nasal mucosa, along with a lower endogenous release of norepinephrine. The turbinate undergoes intense compensatory rebound vasodilation, forcing the patient to apply the spray more frequently, inducing a vicious cycle of physical addiction and chronic epithelial ischemic damage.

Chronic use Down-regulation of alpha receptors Irreversible obstructive vasomotor hypertrophy

Treatment requires immediate and radical suspension of the drug, temporarily replacing it with hypertonic salt water washes, topical nasal corticosteroids in high doses and even short-course systemic corticosteroid therapy to attenuate rebound obstruction.

Drug Interactions of Clinical Relevance

• Monoamine Oxidase Inhibitors (MAOIs): Critical interaction. Coadministration can trigger severe acute hypertensive crises due to the accumulation of circulating vasopressor amines.
• Tricyclic antidepressants (Amitriptyline, Clomipramine): They enhance the systemic pressor effect of oxymetazoline in case of systemic absorption.

Safety in Pregnancy and Breastfeeding

• Pregnancy: Not recommended. The potential systemic vasoconstrictor effect and uterine adrenergic stimulation, although unlikely with moderate topical use, advise against its use in underlying gestational rhinitis. Prefer saline nasal washes.
• Breastfeeding: Avoid. It is unknown if it passes into breast milk; Infants are highly sensitive to the cardiovascular and neurological effects of direct sympathomimetics.