Promethazine

# Promethazine ## Overview - **Classification**: Phenothiazine derivative, First-generation H1-antihistamine - **Mechanism**: Competitively blocks H1 receptors. Also has anticholinergic, sedative, and antiemetic effects by blocking dopaminergic and alpha-adrenergic receptors. ## Primary Indications 1. **Nausea and Vomiting** - Prevention and treatment 2. **Allergic Reactions** - Symptomatic relief of perennial/seasonal allergic rhinitis, conjunctivitis, urticaria 3. **Sedation** - Pre-operative, post-operative, or for insomnia ## Adult Dosing ### Standard Dosing **Nausea and Vomiting** - **Dose**: **12.5 mg** to **25 mg** - **Frequency**: Every 4 to 6 hours as needed - **Route**: Oral (PO), Intramuscular (IM), Intravenous (IV), Rectal (PR) - **Maximum**: **100 mg** per day **Allergic Reactions** - **Dose**: **12.5 mg** every 4 to 6 hours PRN, or **25 mg** - **Frequency**: Once daily at bedtime for perennial allergy - **Route**: Oral (PO) - **Maximum**: **100 mg** per day **Sedation** - **Dose**: **25 mg** to **50 mg** - **Frequency**: Once at bedtime or pre-operatively - **Route**: Oral (PO), Intramuscular (IM), Intravenous (IV), Rectal (PR) - **Special Considerations**: Administer 30-60 minutes pre-op. ### Dose Adjustments - **Renal Impairment**: Use with caution. No specific dose adjustments provided; monitor for increased sedation. - **Hepatic Impairment**: Use with caution. Extensively metabolized by the liver; monitor for increased sedation. - **Elderly Patients**: Start with lower doses (e.g., **12.5 mg**). Increased risk of sedation, anticholinergic effects, and orthostatic hypotension. ## Pediatric Dosing ### Neonates (0-28 days) - **Contraindicated**: **ABSOLUTELY CONTRAINDICATED** due to fatal respiratory depression risk. ### Infants (1-12 months) - **Contraindicated**: **ABSOLUTELY CONTRAINDICATED** due to fatal respiratory depression risk. - **Special Notes**: Black Box Warning for respiratory depression in children younger than 2 years. ### Children (2-12 years) **Nausea and Vomiting (only if > 2 years)** - **Dose**: **0.5 mg/kg** - **Frequency**: Every 4 to 6 hours as needed - **Route**: Oral (PO), Intramuscular (IM), Rectal (PR) - **Maximum**: **25 mg** per dose. Total daily dose should not exceed **50 mg**. **Allergic Reactions (only if > 2 years)** - **Dose**: **0.1 mg/kg** - **Frequency**: Every 4 to 6 hours PRN, or **0.5 mg/kg** at bedtime - **Route**: Oral (PO), Rectal (PR) - **Maximum**: **12.5 mg** per dose or **25 mg** at bedtime. **Sedation (only if > 2 years)** - **Dose**: **0.5 mg/kg** to **1 mg/kg** - **Frequency**: Once, typically at bedtime or pre-operatively - **Route**: Oral (PO), Intramuscular (IM), Rectal (PR) - **Maximum**: **50 mg** per dose. - **Special Notes**: Use lowest effective dose. Monitor closely for respiratory depression. ### Adolescents (13-18 years) - **Dose**: Follow adult dosing guidelines. - **Maximum**: **100 mg** per day. - **Special Notes**: Consider starting with lower adult doses in younger adolescents due to potential increased sensitivity. ## Safety Information ### Contraindications - **Absolute**: Children younger than **2 years** due to fatal respiratory depression risk. - **Absolute**: Severe CNS depression, comatose states. - **Absolute**: Known hypersensitivity to promethazine or other phenothiazines. - **Absolute**: Lower respiratory tract symptoms (e.g., asthma, COPD) due to thickening of bronchial secretions. - **Absolute**: Subcutaneous or intra-arterial administration (risk of severe tissue injury). ### Common Adverse Effects - **Very Common (>10%)**: Drowsiness, sedation (can be significant). - **Common (1-10%)**: Dry mouth, blurred vision, urinary retention, dizziness, confusion, excitability (paradoxical in children). - **Serious but Rare**: Neuroleptic Malignant Syndrome (NMS), agranulocytosis, seizures, severe tissue injury with IV extravasation (e.g., "chemical gangrene"), respiratory depression. ### Key Drug Interactions - **CNS Depressants (e.g., opioids, benzodiazepines, alcohol)**: Potentiates sedation and respiratory depression. **Avoid concurrent use** or significantly reduce doses of both. - **Anticholinergics (e.g., TCAs, atropine, ipratropium)**: Increased anticholinergic effects (dry mouth, urinary retention, constipation, blurred vision). **Monitor for toxicity**. - **QT-prolonging drugs (e.g., antiarrhythmics, some antipsychotics)**: May increase risk of QT prolongation and arrhythmias. **Use with caution**, monitor ECG. - **Dopamine Agonists (e.g., bromocriptine)**: Promethazine's anti-dopaminergic effects may antagonize. ## Monitoring & Follow-up - **Before Treatment**: Assess for contraindications (age < 2 years, severe CNS depression, respiratory issues, narrow-angle glaucoma, prostatic hypertrophy). - **During Treatment**: Monitor for excessive sedation, respiratory depression (especially in children > 2 years), anticholinergic effects, and paradoxical excitation in children. - **Clinical Signs**: Observe for changes in mental status, difficulty breathing, unresponsiveness, or signs of extravasation (pain, swelling, blistering at injection site). ## Clinical Pearls - 💡 **Administration**: For IV use, dilute well with normal saline (e.g., **25 mg/10-20 mL**) and administer into a large, patent vein (not hand/wrist) at max rate of **25 mg/min**. Deep IM injection is preferred for parenteral administration. - 💡 **Extravasation Risk**: IV promethazine carries a **black box warning** for severe tissue injury, including "chemical gangrene," requiring amputation, due to extravasation. **DO NOT** administer subcutaneously or intra-arterially. - 💡 **Photosensitivity**: Advise patients to use sun protection as promethazine can increase sensitivity to sunlight. - 💡 **Alertness**: Counsel patients about significant drowsiness. Avoid driving or operating machinery until effects are known. - 💡 **Paradoxical Excitation**: In children, promethazine can cause agitation, nightmares, and delirium instead of sedation. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.