Chlorpheniramine Maleate is a first-generation antihistamine that competitively blocks histamine H₁ receptors, preventing histamine-mediated allergic responses. Its key actions include:

1. Peripheral Effects: Inhibits histamine-induced vasodilation, bronchoconstriction, and mucous secretion.
2. Central Nervous System (CNS) Effects: Crosses the blood-brain barrier, causing sedation by blocking H₁ receptors in the brain (Lippincott).
3. Anticholinergic Activity: Blocks muscarinic receptors, leading to dry mouth, blurred vision, and urinary retention.

Chlorpheniramine is indicated for:

1. Allergic Conditions:
   • Allergic rhinitis (hay fever).
   • Urticaria (hives) and pruritus (itching).
   • Conjunctivitis due to allergies.
2. Adjunctive Therapy:
   • Anaphylaxis (combined with adrenaline and steroids).
3. Symptomatic Relief:
   • Common cold (to reduce rhinorrhea and sneezing).

Adults:

• Oral: 4 mg every 4–6 hours; maximum 24 mg/day (BNF).
• Parenteral (Rare): 10–20 mg intramuscularly or intravenously under medical supervision.

Children:

• 1–2 years: 1 mg twice daily.
• 2–6 years: 1 mg every 4–6 hours (max 6 mg/day).
• 6–12 years: 2 mg every 4–6 hours (max 12 mg/day).

Special Populations:

• Renal/Hepatic Impairment: Use with caution; consider dose reduction.
• Elderly: More susceptible to anticholinergic effects; lower doses advised.

• Common: Drowsiness, dry mouth, blurred vision, dizziness, constipation.
• Serious (Rare):
  • Hypotension, palpitations.
  • Urinary retention (risk in prostatic hypertrophy).
  • CNS depression (confusion, hallucinations).
  • Severe allergic reactions (e.g., rash, anaphylaxis).

1. Contraindications:
   • Angle-closure glaucoma.
   • Severe urinary retention or pyloroduodenal obstruction.
   • Concurrent use of MAO inhibitors (BNF).
2. Pregnancy/Lactation:
   • Category B: Use only if clearly needed; limited human data.
   • Excreted in breast milk; may cause sedation in infants.
3. Activities Requiring Alertness: Avoid driving or operating machinery.

• CNS Depressants: Alcohol, benzodiazepines, opioids—enhanced sedation.
• MAO Inhibitors: Increased anticholinergic and CNS effects (avoid combination).
• Anticholinergics: Atropine, tricyclic antidepressants—additive dry mouth/urinary retention.
• Hypertensive Agents: May counteract efficacy of certain blood pressure medications.

• Generic: Chlorpheniramine Maleate.
• Brand Names:
  • UK: Piriton® (combination with other agents).
  • US: Chlor-Trimeton®, Aller-Chlor®.
  • Others: Avil® (India), Polaramine® (varies by region).