Benadryl

# Benadryl ## Overview - **Classification**: First-generation Antihistamine (H1 blocker), Ethanolamine derivative - **Mechanism**: Blocks H1 histamine receptors, preventing histamine's effects. Also has significant anticholinergic and sedative properties. ## Primary Indications 1. **Allergic Reactions** - Treatment of seasonal/perennial allergic rhinitis, urticaria, angioedema. 2. **Insomnia** - Short-term management of sleep difficulties. 3. **Motion Sickness** - Prevention and treatment of nausea/vomiting associated with motion. 4. **Extrapyramidal Symptoms (EPS)** - Adjunct treatment for drug-induced EPS. ## Adult Dosing ### Standard Dosing **Allergy / Motion Sickness / EPS** - **Dose**: **25-50 mg** - **Frequency**: Every 4-6 hours PRN - **Route**: Oral (PO), Intramuscular (IM), Intravenous (IV) - **Maximum**: **300 mg** in 24 hours **Insomnia (Short-term)** - **Dose**: **50 mg** - **Frequency**: Once daily at bedtime - **Route**: Oral (PO) - **Duration**: Do not exceed 7-10 days for insomnia ### Dose Adjustments - **Renal Impairment**: Use with caution. Lower doses or extended intervals may be needed for CrCl <30 mL/min due to prolonged half-life. - **Hepatic Impairment**: Use with caution. Lower doses may be needed due to altered metabolism. - **Elderly Patients**: Start with lower doses (**25 mg**) due to increased sensitivity to anticholinergic effects and sedation. Avoid chronic use (BEERS Criteria). ## Pediatric Dosing ### Neonates (0-28 days) - **Contraindicated**: Due to high risk of severe adverse effects, including respiratory depression and CNS effects. ### Infants (1-12 months) - **Indication**: Generally *not recommended* for cold/cough symptoms. Use only under medical supervision for specific allergic reactions. - **Dose**: **1 mg/kg/dose** - **Frequency**: Every 6 hours PRN - **Route**: PO, IM, IV - **Maximum**: **6.25 mg/dose** - **Special Notes**: Monitor closely for sedation and respiratory depression. ### Children (1-12 years) - **Indication**: Allergic reactions, motion sickness. - **Dose**: **1 mg/kg/dose** - **Frequency**: Every 4-6 hours PRN - **Route**: PO, IM, IV - **Maximum**: **50 mg/dose** (single dose). Total daily maximum: **5 mg/kg/day** or **300 mg/day**, whichever is less. - **Age-specific Examples**: * 2-5 years: **6.25 mg** PO q4-6h. Max **37.5 mg/day**. * 6-12 years: **12.5-25 mg** PO q4-6h. Max **150 mg/day**. ### Adolescents (13-18 years) - **Indication**: Allergic reactions, motion sickness, insomnia. - **Dose**: **25-50 mg** - **Frequency**: Every 4-6 hours PRN (allergy/motion sickness); Once daily at bedtime (insomnia) - **Route**: PO, IM, IV - **Maximum**: **300 mg** in 24 hours (adult dose equivalent) ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to diphenhydramine or other antihistamines with similar structure. - **Absolute**: Neonates and premature infants. - **Absolute**: Acute asthma exacerbation. - **Absolute**: Narrow-angle glaucoma. - **Absolute**: Prostatic hypertrophy with urinary retention. - **Absolute**: Concomitant use with MAOIs (within 14 days). ### Common Adverse Effects - **Very Common (>10%)**: Drowsiness, sedation, dizziness. - **Common (1-10%)**: Dry mouth, blurred vision, urinary retention, constipation. - **Serious but Rare**: Paradoxical excitation (especially in children), severe allergic reactions (e.g., anaphylaxis). ### Key Drug Interactions - **CNS Depressants (Alcohol, Opioids, Benzodiazepines)**: Increased sedation and CNS depression. Avoid concomitant use or use with extreme caution. - **Anticholinergic Drugs (TCAs, Antipsychotics)**: Exacerbated anticholinergic effects (dry mouth, blurred vision, urinary retention). - **MAO Inhibitors**: Potentiates anticholinergic effects; use is contraindicated. ## Monitoring & Follow-up - **Before Treatment**: Assess for contraindications (e.g., glaucoma, prostatic hypertrophy) and concurrent CNS depressants. - **During Treatment**: Monitor for sedation, dizziness, and anticholinergic side effects. - **Clinical Signs**: Watch for paradoxical excitation (agitation, restlessness, insomnia) in children and elderly. ## Clinical Pearls - 💡 **Sedation**: Benadryl is highly sedating. Advise patients against driving or operating machinery. - 💡 **Pediatric Use**: Avoid in children <2 years old for cough/cold symptoms due to risk of serious side effects. Always calculate dose carefully by weight. - 💡 **Elderly**: Generally avoided in the elderly due to high anticholinergic burden and risk of falls (BEERS Criteria). - 💡 **Paradoxical Effect**: Can cause hyperactivity or agitation instead of sedation, especially in young children. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.