Chlorpheniramine

# Chlorpheniramine ## Overview - **Classification**: First-generation antihistamine (alkylamine), H1 receptor antagonist. - **Mechanism**: Competitively blocks histamine H1 receptors, reducing effects of histamine. Possesses anticholinergic and sedative properties. ## Primary Indications 1. **Allergic Rhinitis**: Symptomatic relief of sneezing, runny nose, watery eyes, itching of nose or throat. 2. **Urticaria**: Relief of itching associated with hives. 3. **Allergic Conjunctivitis**: Alleviates itchy, watery eyes due to allergies. 4. **Common Cold Symptoms**: Temporary relief of sneezing and runny nose. ## Adult Dosing ### Standard Dosing **Allergic Conditions (e.g., Allergic Rhinitis, Urticaria)** - **Dose**: **4 mg** - **Frequency**: Every **4 to 6 hours** - **Route**: Oral - **Maximum**: **24 mg/day** (immediate release) ### Dose Adjustments - **Renal Impairment**: Use with caution. Consider lower starting dose or extended intervals in severe impairment (CrCl <30 mL/min) due to metabolite accumulation. - **Hepatic Impairment**: Use with caution. Consider lower starting dose due to impaired metabolism. - **Elderly Patients**: Start with lower dose (**2 mg**) due to increased sensitivity to anticholinergic effects and sedation. Higher risk of falls. ## Pediatric Dosing ### Neonates (0-28 days) - **Contraindicated.** High risk of serious adverse events (e.g., respiratory depression). ### Infants (1-12 months) - **Not recommended.** High risk of serious adverse events (e.g., respiratory depression, paradoxical excitation, central nervous system depression). ### Children (1-12 years) - **1-5 years**: **Not generally recommended** by major health organizations (e.g., FDA, AAP) for common cold. - If used under medical supervision for specific allergic conditions: - **Dose**: **1 mg** - **Frequency**: Every **4 to 6 hours** - **Maximum**: **6 mg/day** - **Special Notes**: Oral solution (syrup) is commonly available for accurate dosing. - **6-12 years**: - **Dose**: **2 mg** - **Frequency**: Every **4 to 6 hours** - **Maximum**: **12 mg/day** - **Special Notes**: Oral solution (syrup) is commonly available for accurate dosing. ### Adolescents (13-18 years) - **Dose**: **4 mg** - **Frequency**: Every **4 to 6 hours** - **Maximum**: **24 mg/day** (approach adult dosing). ## Safety Information ### Contraindications - **Absolute**: Newborns or premature infants, narrow-angle glaucoma, acute asthma attack, lower respiratory tract symptoms. - **Absolute**: Concurrent use or within 14 days of MAOI therapy. - **Relative**: Bladder neck obstruction, prostatic hypertrophy, pyloroduodenal obstruction. ### Common Adverse Effects - **Very Common (>10%)**: Drowsiness, sedation, dizziness. - **Common (1-10%)**: Dry mouth, blurred vision, urinary retention, constipation, thickened bronchial secretions. - **Serious but Rare**: Paradoxical excitation (especially in children), seizures, severe cardiovascular events (arrhythmias, hypotension), blood dyscrasias. ### Key Drug Interactions - **CNS Depressants (alcohol, opioids, benzodiazepines)**: Increased sedation and CNS depression. Avoid concurrent use or advise extreme caution. - **Anticholinergic drugs (tricyclic antidepressants, antipsychotics, atropine)**: Increased anticholinergic effects (dry mouth, urinary retention, constipation, blurred vision). - **Monoamine Oxidase Inhibitors (MAOIs)**: Intensified and prolonged anticholinergic effects and CNS depression. **Contraindicated.** ## Monitoring & Follow-up - **Before Treatment**: Assess for pre-existing conditions like glaucoma, prostatic hypertrophy, or asthma. - **During Treatment**: Monitor for excessive sedation, anticholinergic effects (e.g., urinary difficulty, dry mouth). - **Clinical Signs**: Watch for dizziness, cognitive impairment, or paradoxical excitation (agitation, restlessness) in children. ## Clinical Pearls - 💡 **Tip 1**: Causes significant drowsiness; advise patients against driving or operating heavy machinery until effects are known. - 💡 **Tip 2**: If sedation is an issue, consider taking the dose primarily at bedtime. - 💡 **Tip 3**: Not recommended for children under **2-6 years** by many guidelines due to risk of serious adverse effects. Always check specific product labeling. - 💡 **Tip 4**: Available in many OTC cold/allergy combination products; advise patients to check ingredients to avoid accidental overdose. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.