Chlorpheniramine Maleate Dosage and Usage
For oral administration in adults and children ≥12 years, chlorpheniramine maleate should be dosed at 4 mg every 4-6 hours, not exceeding 24 mg in 24 hours, while children 6-12 years should receive 2 mg every 4-6 hours, not exceeding 12 mg in 24 hours. 1
Standard Oral Dosing
Adults and Children ≥12 Years
- 4 mg every 4-6 hours (maximum 6 tablets/24 hours = 24 mg daily) 1
- The FDA-approved labeling specifies this as the standard dosing regimen for allergic conditions 1
Children 6-12 Years
- 2 mg every 4-6 hours (maximum 3 tablets/24 hours = 12 mg daily) 1
Children <6 Years
- Not recommended for oral tablet formulation 1
- Consult product-specific data sheets for liquid formulations in younger children 2
Parenteral Dosing for Acute Allergic Reactions/Anaphylaxis
Chlorpheniramine serves only as adjunctive therapy after epinephrine administration—never as monotherapy for anaphylaxis. 3, 4
Adults and Children >12 Years
- 10 mg IM or IV slowly 3
Children 6-12 Years
- 5 mg IM or IV slowly 3
Children 6 Months to 6 Years
- 2.5 mg IM or IV slowly 3
Infants <6 Months
- 250 μg/kg IM or IV slowly 3
Clinical Applications and Timing
Urticaria Management
- Nighttime dosing (4-12 mg) can be added to daytime non-sedating antihistamines to improve sleep, though this provides minimal additional urticaria control if H1 receptors are already saturated 2
- The sedating effects make chlorpheniramine less suitable for daytime monotherapy due to concerns about reduced concentration and performance 2
Anaphylaxis Protocol
- Administer only after epinephrine (0.3-0.5 mg IM for adults; 0.01 mg/kg for children) has been given 4
- Consider adding H2-antihistamine (ranitidine 50 mg IV or famotidine 20 mg IV) for superior symptom control compared to H1-antihistamine alone 4
- Chlorpheniramine takes significantly longer to work than epinephrine and cannot reverse life-threatening symptoms 5
Special Populations and Contraindications
Renal Impairment
- Use with caution in moderate renal impairment (creatinine clearance 10-20 mL/min) 3
- Avoid in severe renal impairment (creatinine clearance <10 mL/min) 3
Hepatic Impairment
- Avoid in severe liver disease because sedating effects are inappropriate and may worsen hepatic encephalopathy 2, 3
Pregnancy
- Avoid, especially in first trimester, though no teratogenic effects have been demonstrated in humans 2, 3
- Chlorpheniramine is often chosen by UK clinicians when antihistamine therapy is necessary during pregnancy due to its long safety record 2
Pediatric Use
- No contraindications exist for children ≥12 years 2
- For younger children, consult specific product data sheets as dosing and age restrictions vary 2
Pharmacokinetic Considerations
- Terminal half-life: 23-28 hours with significant accumulation occurring with frequent daily dosing (accumulation ratios 4.1-9.4) 6
- Absolute oral bioavailability: 34-59% due to extensive first-pass metabolism 6
- Peak plasma levels: 2-4 hours after oral administration 6
- These pharmacokinetic properties suggest current frequent dosing practices may lead to substantial drug accumulation 6
Critical Safety Warnings
Common Pitfalls
- Never use as monotherapy for anaphylaxis—any delay in epinephrine administration increases mortality risk 5
- Sedation and anticholinergic effects limit daytime use and require caution in activities requiring alertness 2, 3
- Reduced concentration and performance are significant concerns with first-generation antihistamines like chlorpheniramine 3
Drug Accumulation Risk
- The long half-life (23-28 hours) means significant accumulation occurs with standard every-4-6-hour dosing, potentially increasing sedation and anticholinergic side effects 6