What is the recommended dosage and usage of Chlorpheniramine (antihistamine) maleate?

Chlorpheniramine Maleate Dosage and Usage Guidelines

The recommended oral dosage of chlorpheniramine maleate for adults and children 12 years and over is 4 mg (1 tablet) every 4-6 hours, not exceeding 24 mg (6 tablets) in 24 hours; for children 6-12 years, the dosage is 2 mg (1/2 tablet) every 4-6 hours, not exceeding 12 mg (3 tablets) in 24 hours, while it is not recommended for children under 6 years of age. 1

Oral Dosing by Age Group

• Adults and children 12 years and over: 4 mg every 4-6 hours, maximum 24 mg in 24 hours 1
• Children 6-12 years: 2 mg every 4-6 hours, maximum 12 mg in 24 hours 1
• Children under 6 years: Not recommended for oral use 1

Parenteral Dosing for Anaphylaxis Management

When used parenterally (IM or IV) for anaphylaxis management, the following doses apply:

• Adults and children over 12 years: 10 mg IM or IV slowly 2
• Children 6-12 years: 5 mg IM or IV slowly 2
• Children 6 months to 6 years: 2.5 mg IM or IV slowly 2
• Children under 6 months: 250 μg/kg IM or IV slowly 2

Pharmacokinetic Considerations

• Chlorpheniramine has a long half-life of approximately 15-28 hours 3, 4
• Absorption begins after a lag time of approximately 0.7 hours with peak plasma levels occurring at about 2.8 hours after oral administration 4
• Bioavailability from oral solution ranges from 34-59%, and from tablets 25-44%, indicating extensive first-pass metabolism 4
• Due to its long half-life, significant accumulation can occur with frequent daily dosing, with estimated accumulation ratios of 4.1 to 9.4 (mean 6.5) 4

Special Populations

Renal Impairment

• Use with caution in moderate renal impairment (creatinine clearance 10-20 mL/min) 2
• Avoid in severe renal impairment (creatinine clearance <10 mL/min) 2

Hepatic Impairment

• Should be avoided in severe liver disease due to potential sedating effects 2

Pregnancy

• Best to avoid during pregnancy, especially in the first trimester, although no teratogenic effects have been demonstrated in humans 2
• When antihistamine therapy is necessary during pregnancy, chlorpheniramine is often chosen by clinicians due to its long safety record 2

Clinical Applications

• Primary use is for allergic conditions including allergic rhinitis, urticaria, and as adjunctive treatment in anaphylaxis 5
• Can be used in combination with other medications for symptomatic relief of cough and cold 5
• In anaphylaxis management, chlorpheniramine is used as adjunctive therapy after epinephrine administration 2

Common Side Effects and Precautions

• Sedation is the most common adverse effect, particularly in younger children 3
• Other potential adverse effects include dizziness, impaired coordination, dry mouth, and blurred vision 5
• First-generation antihistamines like chlorpheniramine can cause reduced concentration and performance 2
• May be combined with non-sedating antihistamines (daytime use of non-sedating, nighttime use of chlorpheniramine) to improve sleep while maintaining daytime alertness 2

Important Clinical Considerations

• For anaphylaxis, epinephrine remains the first-line treatment, with chlorpheniramine serving as adjunctive therapy 2
• In urticaria management, non-sedating antihistamines are generally preferred for daytime use, with chlorpheniramine potentially added at night 2
• The long half-life suggests that less frequent dosing may be appropriate, contrary to common practice of frequent daily dosing 4