What are the recommended oral and injectable doses of Avil (chlorpheniramine maleate) for children, including weight‑based dosing for ages 6‑12 years, adult dosing for ≥12 years, and contraindications for infants under 6 months or those with hepatic/renal impairment?

Chlorpheniramine (Avil) Dosing in Children

For children 6-12 years, give chlorpheniramine 2 mg (half tablet) every 4-6 hours, not exceeding 12 mg (6 half-tablets) in 24 hours; for children ≥12 years, use adult dosing of 4 mg every 4-6 hours, not exceeding 24 mg daily; chlorpheniramine is contraindicated in children under 6 years of age. 1

Age-Based Oral Dosing

Children Under 6 Years

• Do not use chlorpheniramine in children under 6 years of age 1
• This contraindication is absolute per FDA labeling 1

Children 6 to Under 12 Years

• Dose: 2 mg (1/2 tablet of 4 mg tablet) every 4-6 hours 1
• Maximum daily dose: 12 mg (not more than 3 half-tablets in 24 hours) 1
• Weight-based dosing studies suggest 4.4-8.8 mg/kg/day range, though specific chlorpheniramine pediatric weight-based recommendations are limited 2

Children ≥12 Years (Adult Dosing)

• Dose: 4 mg (1 tablet) every 4-6 hours 1
• Maximum daily dose: 24 mg (not more than 6 tablets in 24 hours) 1

Injectable Dosing Considerations

Injectable chlorpheniramine formulations exist but lack specific pediatric dosing guidelines in the provided FDA labeling. 1 The evidence focuses primarily on oral administration, which is the standard route for pediatric use 3. Injectable routes (intravenous, intramuscular, subcutaneous) have been documented but require individualized dosing based on clinical judgment and are typically reserved for situations where oral administration is not feasible 3.

Important Clinical Caveats

Pharmacokinetic Considerations in Children

• Children aged ≥2 years are pharmacokinetically similar to adults and differ primarily in size, not maturation 4
• Chlorpheniramine has a long elimination half-life of approximately 23-28 hours in adults, suggesting potential for significant accumulation with frequent dosing 5
• Pediatric studies show similar maximum concentrations (Cmax) across age groups when using age/weight-based dosing, with a terminal half-life of approximately 15 hours in children 2

Contraindications and Precautions

• Absolute contraindication: Children under 6 years 1
• Hepatic impairment: Chlorpheniramine undergoes extensive hepatic first-pass metabolism (extraction ratio 0.06-0.07), requiring dose reduction in hepatic dysfunction 5
• Renal impairment: Reduced plasma clearance occurs in renal patients, necessitating dose adjustment 5
• Sedation is the most common adverse effect and appears more prevalent in younger children (2-5 years in research studies) 2

Dosing Frequency Warning

The long half-life of chlorpheniramine (15-28 hours) raises concerns about the appropriateness of every 4-6 hour dosing schedules, as this may lead to drug accumulation with accumulation ratios ranging from 4.1 to 9.4 5. However, the FDA-approved labeling maintains the every 4-6 hour schedule 1.

Route-Specific Guidance

Oral Administration (Preferred Route)

• Standard tablets and oral solutions are the primary formulations 1, 3
• Oral bioavailability ranges from 25-59% due to extensive gut first-pass metabolism 5
• Absorption lag time averages 0.7 hours with peak concentrations at 2.8 hours 5

Alternative Routes

• Intranasal routes have been explored recently, particularly for antiviral properties, but are not standard for pediatric allergic conditions 3
• Injectable routes lack established pediatric dosing protocols in current labeling 1