Tab chlorpheniramine maleate 40
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chlorpheniramine maleate 4mg tablet pharmacology dosage indications
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Chlorpheniramine Maleate 4 mg Tablet (Qty: 40)
Drug Class
First-generation H1-receptor antagonist (antihistamine). Available as generic only.
Mechanism of Action
Competitively blocks H1 histamine receptors on target tissues - it does not prevent histamine formation or release, but blocks its receptor-mediated response. It is much more effective at preventing symptoms than reversing them once established.
Additional receptor activity (due to low specificity):
- Antimuscarinic (anticholinergic) effects
- Anti-alpha-adrenergic effects
- Weak serotonin receptor blockade
Indications
| Condition | Notes |
|---|---|
| Allergic rhinitis | Reduces rhinorrhea, itching, sneezing - does NOT help nasal congestion |
| Urticaria (hives) | Drug of choice along with other antihistamines |
| Allergic conjunctivitis | |
| Contact dermatitis / pruritus | |
| Food allergies | |
| Insect sting reactions | |
| Angioedema (Quincke's edema) | |
| Anaphylaxis (adjunct) | IV chlorpheniramine + IV hydrocortisone alongside IM adrenaline |
| Insomnia (off-label) | Due to sedative properties |
NOT indicated in bronchial asthma - histamine is only one of several bronchoconstricting mediators. Epinephrine remains the drug of choice for systemic anaphylaxis.
Dosage
| Population | Dose | Frequency | Max/24 hr |
|---|---|---|---|
| Adults & children ≥12 yr | 4 mg | Every 4-6 hrs | 24 mg |
| Children 6-11 yr | 2 mg | Every 4-6 hrs | 12 mg |
| Children 2-5 yr (under physician supervision) | 1 mg | Every 4-6 hrs | 6 mg |
| Extended-release (adults) | 8-12 mg | Twice daily | 24 mg |
40 tablets = 10-day supply at the standard adult dosing of 4 tablets/day (4 mg every 6 hrs).
Pharmacokinetics
- Onset: 1-3 hours after oral dose
- Peak serum level: 1-2 hours
- Duration: 4-6 hours (justifying every 4-6 hr dosing)
- Distribution: All tissues including CNS (explains CNS side effects)
- Metabolism: Hepatic cytochrome P450 system
- Absorption: Well absorbed orally
Adverse Effects
CNS (most common - due to BBB penetration):
- Sedation/drowsiness (most prominent) - ranging from slight drowsiness to deep sleep
- Lassitude, dizziness, incoordination
- Paradoxical stimulation may occur, especially at high doses or in children/elderly
Anticholinergic (antimuscarinic):
- Dry mouth, blurred vision
- Urinary retention
- Constipation
- Tachycardia
Other:
- Psychomotor impairment (affects ability to drive/operate machinery)
Contraindications / Precautions
- Glaucoma (raised intraocular pressure)
- Prostatic hypertrophy (urinary retention risk)
- Severe hypertension or cardiovascular disease
- Asthma/bronchitis/bronchiectasis
- Epilepsy
- Hepatic or renal impairment
- Avoid alcohol and CNS depressants - enhanced sedation
Pregnancy
Considered safe (Category B) - one of the preferred antihistamines in pregnancy alongside diphenhydramine and cetirizine.
Key Comparison: 1st vs 2nd Generation
| Feature | Chlorpheniramine (1st gen) | Cetirizine/Loratadine (2nd gen) |
|---|---|---|
| CNS penetration | Yes - sedating | Minimal |
| Duration | 4-6 hrs | 12-24 hrs (once daily) |
| Anticholinergic | Yes | No |
| Driving impairment | Yes | Less so |
Sources: Lippincott Illustrated Reviews: Pharmacology, Chapter 39 (Histamine and Serotonin); DailyMed label; MedCentral dosing data
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