Neosayomol (Diphenhydramine Hydrochloride)

• Diphenhydramine Hydrochloride acts on histamine‑mediated skin reactions, providing antiallergic and antipruritic effects for various dermatologic conditions.
• Allergic skin reactions (pruritus): reduces itching and redness, offering symptomatic relief for conditions such as contact dermatitis and seasonal allergies.
• Insect bite reactions: alleviates localized itching, swelling and discomfort caused by mosquito, flea or other arthropod bites.
• Minor skin irritations and rashes: soothes mild dermatitis, heat rash or other non‑infectious eruptions, improving patient comfort.

• Diphenhydramine Hydrochloride exerts its effect by competitively blocking histamine H1 receptors on peripheral sensory nerves and vascular endothelial cells, preventing histamine‑induced vasodilation, increased vascular permeability and nerve stimulation. The molecule also possesses anticholinergic activity, which contributes to its antipruritic properties but may affect cholinergic pathways. By reducing the release of inflammatory mediators, it helps to diminish the sensation of itch and the associated erythema.

Topical diphenhydramine may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Drowsiness: feeling of sleepiness or reduced alertness, may affect daily activities.
• Dry mouth: reduced salivation causing oral discomfort and difficulty swallowing.
• Blurred vision: temporary visual disturbance that usually resolves after discontinuation.
• Constipation: slowed gastrointestinal motility leading to infrequent bowel movements.

Serious or Rare Side Effects

• Anaphylaxis: severe, potentially life‑threatening allergic reaction with hives, swelling and breathing difficulty.
• Cardiac arrhythmia: irregular heart rhythm that may cause palpitations, dizziness or require medical intervention.
• Stevens‑Johnson syndrome: rare, serious skin disorder with blistering, detachment and possible mucosal involvement.

When using topical diphenhydramine, consider the following precautions to ensure safe and effective application.

• Hypersensitivity: discontinue use if signs of allergic reaction such as rash or swelling appear.
• Glaucoma: avoid or use with caution in patients with narrow‑angle glaucoma due to anticholinergic effects.
• Urinary retention: monitor individuals with prostate enlargement or bladder outlet obstruction.
• Concomitant CNS depressants: limit use with alcohol, sedatives or opioids as additive drowsiness may occur.
• Pediatric use: apply only under medical supervision for children under two years of age.
• Store at room temperature: keep in original packaging, protect from moisture and direct sunlight.

Diphenhydramine may interact with other medicines; awareness of major and moderate interactions helps prevent adverse outcomes.

Major Interactions (Avoid)

• MAO inhibitors: risk of hypertensive crisis or severe CNS effects.
• Other antihistamines: additive anticholinergic and sedative effects.
• Alcohol: potentiates drowsiness and impairment.
• CNS depressants (e.g., benzodiazepines, opioids): may cause excessive sedation.
• Tricyclic antidepressants: increased anticholinergic burden.

Moderate Interactions (Monitor Closely)

• CYP450 inhibitors (e.g., cimetidine, erythromycin): may raise diphenhydramine levels.
• Anticholinergic drugs (e.g., atropine, ipratropium): combined effect on dry mouth and urinary retention.
• SSRIs (e.g., fluoxetine): possible increased sedation.