Dosage of Injectable Chlorpheniramine for Adults
The standard dose of injectable chlorpheniramine for adults is 10 mg administered intramuscularly or intravenously (slowly). 1
Dosing Guidelines
Adult Dosing
- Intravenous (IV) administration: 10 mg given slowly
- Intramuscular (IM) administration: 10 mg
Age-Based Dosing
| Age Group | Dosage (IM or IV slowly) |
|---|---|
| > 12 years | 10 mg |
| 6 to 12 years | 5 mg |
| 6 months to 6 years | 2.5 mg |
| < 6 months | 250 µg/kg |
Administration Considerations
IV Administration
- Administer slowly to minimize adverse effects
- Rapid IV administration may cause:
- Hypotension
- Dizziness
- Sedation
- Cardiac arrhythmias
Clinical Context
Injectable chlorpheniramine is primarily used in emergency situations such as:
- Anaphylactic reactions
- Severe allergic reactions
- Acute urticaria
- Angioedema
Pharmacokinetic Considerations
Chlorpheniramine has a longer half-life than many clinicians realize:
- Terminal half-life: approximately 20-28 hours in adults 2
- Extensive first-pass metabolism with oral administration
- Significant accumulation occurs with frequent dosing
Important Precautions
- Sedation: Chlorpheniramine is a first-generation antihistamine with significant sedative effects
- Anticholinergic effects: May cause dry mouth, urinary retention, and blurred vision
- Elderly patients: Use with caution due to increased sensitivity to anticholinergic effects
- Renal dysfunction: Half-life is increased in patients with renal impairment 3
Clinical Pearls
- In anaphylaxis management, chlorpheniramine is considered an adjunctive therapy and should never delay epinephrine administration
- While effective for cutaneous symptoms (urticaria, pruritus), chlorpheniramine does not address the life-threatening aspects of anaphylaxis
- Subsensitivity may develop with chronic use 4
- Monitor for respiratory depression when combined with other sedative medications
Common Pitfalls
- Delayed epinephrine: Using antihistamines as first-line treatment for anaphylaxis instead of epinephrine
- Rapid administration: Administering IV chlorpheniramine too quickly, which can cause adverse effects
- Overuse: Prescribing frequent daily dosing despite the long half-life
- Underestimating sedation: Failing to warn patients about potential sedation and impaired driving ability
Remember that while chlorpheniramine is effective for managing allergic symptoms, it should be used as part of a comprehensive treatment approach in severe allergic reactions, with epinephrine remaining the first-line treatment for anaphylaxis.