Chlorphenamine Maleate Dosage for Adults
For adults, the standard dose of chlorphenamine maleate is 4 mg every 4 to 6 hours, with a maximum of 24 mg (6 tablets) in 24 hours. 1
Standard Oral Dosing
- Adults and children ≥12 years: 4 mg (1 tablet) every 4 to 6 hours 1
- Maximum daily dose: 24 mg (6 tablets in 24 hours) 1
- Children 6 to <12 years: 2 mg (half tablet) every 4 to 6 hours, not exceeding 12 mg (3 whole tablets) in 24 hours 1
Clinical Context-Specific Dosing
For Urticaria Management
- Nighttime dosing: 4-12 mg at bedtime when added to a non-sedating antihistamine during the day 2
- This approach helps patients sleep better, though it provides minimal additional antihistamine effect if H1 receptors are already saturated 2
For Anaphylaxis (Parenteral Route)
While chlorphenamine is not specifically mentioned in the anaphylaxis guidelines provided, the related first-generation antihistamine diphenhydramine is dosed at 25-50 mg parenterally in adults 2. Important caveat: H1 antihistamines are second-line therapy to epinephrine and should never be administered alone in anaphylaxis treatment 2.
Pharmacokinetic Considerations
- Half-life: Approximately 21-28 hours (range 19-43 hours), which is considerably longer than the typical dosing interval 3, 4
- Bioavailability: 25-59% due to extensive first-pass metabolism 4
- Peak plasma concentration: Occurs at approximately 2.8 hours after oral administration 4
- Accumulation: Significant drug accumulation occurs with frequent daily dosing, with accumulation ratios of 4.1 to 9.4 (mean 6.5) 4
Special Populations and Precautions
Hepatic Impairment
- Avoid in severe liver disease due to inappropriate sedating effects 2
Renal Impairment
- Dose adjustments may be needed as reduced plasma clearance occurs in renal patients 4
Pregnancy
- Use with caution, particularly in the first trimester 2
- Chlorphenamine is often chosen in the UK when antihistamine therapy is necessary during pregnancy due to its long safety record 2
Common Pitfalls to Avoid
Do not use chlorphenamine as monotherapy for anaphylaxis - it is only adjunctive therapy to epinephrine 2. The sedating effects can impair concentration and performance, making non-sedating second-generation antihistamines preferable for daytime use 2. Given the long half-life and significant accumulation with frequent dosing, the current practice of dosing every 4-6 hours may lead to excessive drug accumulation over time 4.