Usage
- Medical Conditions: Chlorpheniramine maleate is primarily prescribed for the symptomatic relief of allergic conditions such as hay fever (seasonal allergic rhinitis), urticaria (hives), pruritus (itching), angioedema (swelling), allergic conjunctivitis (pink eye), and reactions to insect bites or stings. It is also used to alleviate cold symptoms like sneezing and runny nose. It can be used as an adjunct in the emergency treatment of anaphylactic shock.
- Pharmacological Classification: First-generation antihistamine.
- Mechanism of Action: Chlorpheniramine competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract. This competitive antagonism prevents histamine from binding to receptors and triggering allergic responses.
Alternate Names
- Chlorphenamine (International Nonproprietary Name)
- Brand Names: Chlor-Trimeton, Piriton, Aller-Chlor, and various others.
How It Works
- Pharmacodynamics: Chlorpheniramine effectively blocks the effects of histamine at H1 receptors. This action reduces vascular permeability, which minimizes edema and itching. It also decreases nasal and bronchial secretions, providing relief from runny nose and sneezing. Central nervous system (CNS) depression can occur, resulting in drowsiness. The anticholinergic properties of the medication can cause dry mouth, blurred vision, and urinary retention.
- Pharmacokinetics:
- Absorption: Chlorpheniramine is well-absorbed after oral administration.
- Metabolism: Primarily metabolized in the liver via the cytochrome P450 system.
- Elimination: Excreted mainly through the kidneys, with elimination dependent on urinary pH and flow rate.
- Mode of Action: Competitively binds to H1 histamine receptors, preventing histamine-mediated responses.
- Receptor Binding: Selective H1 receptor antagonist.
- Elimination Pathways: Primarily renal excretion, with some hepatic metabolism.
Dosage
Standard Dosage
Adults:
- Tablets/Syrup: 4 mg every 4-6 hours, not to exceed 24 mg/day.
- Extended-Release Tablets: 8 mg every 8-12 hours or 12 mg every 12 hours, not exceeding 24 mg/day.
- Extended-Release Capsules: 12 mg once daily, not to exceed 24 mg/day.
- Sustained-Release Capsules: 8-12 mg every 8-12 hours, up to 16-24 mg/day.
Children:
- Under 2 Years: Safety and efficacy not established.
- 2-6 years: 1 mg every 4-6 hours (max 6mg/day)
- 6-12 years: 2 mg every 4-6 hours, not to exceed 12 mg/day.
- Over 12 years: Same as adult dose.
Special Cases:
- Elderly Patients: Lower initial dose (e.g., 4 mg once daily or every 12 hours, or 8 mg sustained-release at bedtime) is recommended due to increased sensitivity to side effects, particularly anticholinergic and sedative effects. Maximum daily dose: 12 mg/day
- Patients with Renal Impairment: Dose adjustment may be needed. Consult medical resources for specific recommendations.
- Patients with Hepatic Dysfunction: Dose adjustment may be needed. Consult medical resources for specific recommendations.
- Patients with Comorbid Conditions: Caution advised in patients with cardiovascular disease, glaucoma, prostatic hypertrophy, urinary retention, and asthma.
Clinical Use Cases
The primary use of chlorpheniramine is management of allergic symptoms. Intravenous administration is possible, but not typically used in the specific clinical scenarios you mentioned (intubation, surgical procedures, mechanical ventilation, ICU use, emergency situations). For these, other faster acting antihistamines are preferred.
Dosage Adjustments
Adjustments based on renal/hepatic function should be made on a case-by-case basis, consulting relevant clinical guidelines and resources.
Side Effects
Common Side Effects:
- Drowsiness
- Dry mouth
- Blurred vision
- Dizziness
- Nausea
- Constipation
Rare but Serious Side Effects:
- Severe allergic reactions (anaphylaxis)
- Seizures
- Confusion
- Difficulty urinating
- Irregular heartbeats
- Blood disorders (e.g., agranulocytosis, hemolytic anemia)
- Liver dysfunction (e.g., cholestasis, hepatitis)
Long-Term Effects:
Chronic complications from prolonged use are rare but could potentially include cognitive impairment and anticholinergic tolerance.
Adverse Drug Reactions (ADR):
Any of the rare but serious side effects would qualify as an ADR needing immediate attention.
Contraindications
- Hypersensitivity to chlorpheniramine
- Narrow-angle glaucoma
- Urinary retention
- Severe asthma attack
- Pyloroduodenal obstruction
- Concomitant use or within 14 days of MAOI therapy
Drug Interactions
- CNS Depressants: Alcohol, opioids, sedatives, hypnotics can potentiate drowsiness.
- Anticholinergics: Atropine, tricyclic antidepressants can exacerbate anticholinergic effects.
- MAOIs: Contraindicated due to risk of severe hypertension.
- Other: May interact with various other medications, including some antihypertensives, anticonvulsants, and certain antibiotics. Consult a comprehensive drug interaction resource for specific details.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Generally considered low risk in pregnancy but ideally avoided, particularly in the third trimester.
- Breastfeeding: Small, occasional doses (2-4 mg) are generally considered acceptable. Larger doses or prolonged use may cause infant drowsiness or decrease milk supply. Non-sedating antihistamines are preferred if necessary.
Drug Profile Summary
- Mechanism of Action: H1 receptor antagonist.
- Side Effects: Drowsiness, dry mouth, blurred vision, dizziness, gastrointestinal upset.
- Contraindications: Hypersensitivity, narrow-angle glaucoma, urinary retention, MAOI use.
- Drug Interactions: CNS depressants, anticholinergics, MAOIs.
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: See detailed dosage section above.
- Monitoring Parameters: Observe for sedation, anticholinergic effects, and allergic reactions.
Popular Combinations
Chlorpheniramine is often combined with decongestants like pseudoephedrine for the treatment of cold and allergy symptoms. It is important to remember that these combinations increase the likelihood of experiencing side effects.
Precautions
- General Precautions: Assess for pre-existing conditions like glaucoma, prostatic hypertrophy, and renal/hepatic dysfunction.
- Specific Populations: See dosage adjustments for elderly, renally/hepatically impaired patients. Caution during pregnancy and breastfeeding.
- Lifestyle Considerations: Avoid alcohol and operating machinery due to sedative effects.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Chlorpheniramine Maleate?
A: See detailed dosage section above.
Q2: Can Chlorpheniramine be used in children?
A: Yes, but dosing is weight/age dependent and use is generally not recommended in children under 2 years of age.
Q3: What are the common side effects of Chlorpheniramine?
A: Drowsiness, dry mouth, blurred vision, dizziness, constipation.
Q4: Is Chlorpheniramine safe during pregnancy?
A: While generally considered low risk, it’s best to avoid it if possible, especially during the third trimester. Consult with an obstetrician for guidance.
Q5: What are the contraindications for Chlorpheniramine?
A: Hypersensitivity, narrow-angle glaucoma, urinary retention, concurrent MAOI use, pyloroduodenal obstruction.
Q6: Does Chlorpheniramine interact with other medications?
A: Yes, it can interact with CNS depressants, anticholinergics, MAOIs, and others. Consult a drug interaction resource for a comprehensive list.
Q7: Can Chlorpheniramine be used to treat anaphylaxis?
A: It can be used as an adjunct treatment, but adrenaline is the primary medication for anaphylaxis.
Q8: Can patients with renal impairment take Chlorpheniramine?
A: Dose adjustment may be needed. Consult with a nephrologist or relevant clinical guidelines.
Q9: What is the mechanism of action of Chlorpheniramine?
A: Chlorpheniramine is a competitive antagonist of histamine at the H1 receptor.
