Piriton (Chlorphenamine) Oral Dosing for Adults
For adults, the recommended oral dose of Piriton (chlorphenamine maleate) is 4 mg every 4 to 6 hours, with a maximum of 24 mg (6 tablets) in 24 hours. 1
Standard Dosing Regimen
- Adults and children ≥12 years: 1 tablet (4 mg) every 4 to 6 hours 1
- Maximum daily dose: Do not exceed 6 tablets (24 mg) in 24 hours 1
Pharmacokinetic Considerations
The traditional frequent dosing schedule (every 4-6 hours) may not be necessary for all adults due to chlorphenamine's pharmacokinetic profile:
- Elimination half-life: Ranges from 19-43 hours (mean 28 hours) after oral administration, suggesting less frequent dosing may be adequate 2
- Peak plasma concentration: Occurs at 2-4 hours after oral administration 2
- Bioavailability: Oral tablets have 25-44% absolute bioavailability due to extensive first-pass metabolism 2
Important Clinical Considerations
Accumulation with frequent dosing: Due to the long half-life, frequent daily dosing (every 4-6 hours) leads to significant drug accumulation, with accumulation ratios ranging from 4.1 to 9.4 (mean 6.5) 2. This suggests the current practice of frequent dosing may need reconsideration in clinical practice.
Subsensitivity development: Adults develop true subsensitivity to chlorphenamine during chronic therapy (3 weeks), which is not explained by changes in drug metabolism 3. This means the drug becomes less clinically effective over time even when blood levels are maintained.
Common side effects: Drowsiness is frequently reported and may require individualized dosing adjustments 3
Practical Pitfalls to Avoid
- Compliance issues: Poor compliance is significantly worse during prolonged therapy (3 weeks vs 3 days), which may contribute to subtherapeutic results 3
- Avoid excessive dosing frequency: Given the 19-43 hour half-life, dosing every 4-6 hours may lead to unnecessary accumulation and increased side effects 2