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RESPIRATORY SYSTEM › ANTIHISTAMINES FOR SYSTEMIC USE › ANTIHISTAMINES FOR SYSTEMIC USE › Phenothiazine derivatives
isothipendyl
R06AD09
Forms & Strengths
- Oral tablets 10 mg
- Oral syrup 1 mg/mL
Adult Dosing
- Allergic rhinitis/urticaria: 10 mg 2–3 times daily (max 30 mg)
- Pruritus: 10 mg 2–3 times daily
- Insomnia: 10 mg at bedtime
Pediatric Dosing
- Not recommended <12 y; if used, 0.25 mg/kg per dose (max 10 mg) up to 30 mg/day
Indications
- Allergic rhinitis
- Seasonal allergy
- Urticaria
- Pruritus of dermatologic disorders
- Atopic dermatitis adjunct
- Sedation/insomnia
Mechanism of Action
- Competitive H1‑receptor antagonist (central and peripheral)
- Anticholinergic (muscarinic) blockade contributes to sedation
Contraindications
- Hypersensitivity to isothipendyl or related antihistamines
- Narrow‑angle glaucoma
- Severe urinary retention or prostate hypertrophy
- Severe hepatic impairment
- Infants and young children
Adverse Reactions
- Somnolence and fatigue
- Dry mouth, blurred vision, constipation, urinary retention
- Tachycardia, postural hypotension
- Dizziness, headache
- Weight gain, increased appetite
- Photosensitivity
- Rare extrapyramidal symptoms
Drug Interactions
- Additive CNS depression with alcohol, benzodiazepines, opioids, other sedatives
- Enhanced anticholinergic effects with other anticholinergics (e.g., atropine)
- CYP2D6 inhibitors may increase plasma levels
- Cautious use with other antihistamines (additive sedation)
- Concurrent QT‑prolonging drugs may increase arrhythmia risk
Curated Content: Needs Vetting Before Put to Clinical Use