Usage
Pheniramine maleate is an antihistamine primarily used to relieve symptoms associated with allergies, such as hay fever, rhinitis, urticaria, and angioedema. It can also be prescribed for motion sickness, allergic conjunctivitis, drug rashes, serum sickness, food allergy, and itching skin conditions (e.g., eczema, neurodermatitis, lichen planus). Its pharmacological classification is antihistamine (H1-receptor antagonist). Pheniramine works by blocking the effects of histamine, a substance released by the body during allergic reactions.
Alternate Names
Pheniramine maleate is the generic name. A popular brand name is Avil.
How It Works
Pharmacodynamics: Pheniramine competitively antagonizes the H1-receptor. Besides its antihistaminic activity, it also possesses anticholinergic and sedative properties.
Pharmacokinetics:
- Absorption: Pheniramine is well-absorbed from the gastrointestinal tract.
- Metabolism: It is metabolized in the liver primarily via CYP450 enzymes, to N-desmethylpheniramine and N-didesmethylpheniramine.
- Elimination: Pheniramine is excreted mainly through the kidneys, both as the parent drug and its metabolites.
Mode of Action: Pheniramine competes with histamine for binding at H1-receptor sites, effectively reducing the effects of histamine on tissues and organs. This reduces vasodilation, capillary permeability, and smooth muscle contraction caused by histamine, alleviating the symptoms of allergic reactions.
Dosage
Standard Dosage
Adults: The usual starting dose is 25 mg every 4 to 6 hours, with a maximum daily dose of 150 mg.
Children (5-10 years): 12.5 mg (half a 25 mg tablet) every 4 to 6 hours, as needed.
Children (under 5 years): Not recommended.
Special Cases:
- Elderly Patients: Start with lower doses and monitor closely.
- Patients with Renal Impairment: Dose adjustment is needed. The exact amount should be determined by a physician based on the degree of impairment.
- Patients with Hepatic Dysfunction: Dose reduction may be necessary.
- Patients with Comorbid Conditions: Caution is needed in patients with asthma, glaucoma, cardiovascular disease, diabetes, BPH, or hyperthyroidism.
Clinical Use Cases
Pheniramine’s use in intubation, surgical procedures, mechanical ventilation, ICU, or emergency situations is not routinely indicated. Its primary applications are the management of allergic reactions and motion sickness.
Dosage Adjustments
Adjustments should be made in the presence of renal or hepatic impairment and may be necessary in individuals with other comorbid conditions. Always consider the patient’s overall condition and consult with specialists when necessary.
Side Effects
Common Side Effects
Drowsiness, dizziness, dry mouth/nose/throat, headache, upset stomach, constipation, blurred vision.
Rare but Serious Side Effects
Confusion, hallucinations, ringing in the ears, difficulty urinating, fast/irregular heartbeat, seizures, allergic reactions (rash, itching/swelling, trouble breathing).
Long-Term Effects
No specific long-term side effects have been routinely reported, but prolonged use should be monitored by a physician.
Adverse Drug Reactions (ADR)
Severe allergic reactions, including anaphylaxis and angioedema, require immediate medical intervention.
Contraindications
Hypersensitivity to pheniramine, concomitant use of MAOIs (or within two weeks of MAOI discontinuation), narrow-angle glaucoma, urinary retention, severe cardiovascular disease, symptomatic prostatic hypertrophy.
Drug Interactions
Alcohol, sedatives, opioids, barbiturates, hypnotics, MAOIs, atropine, tricyclic antidepressants (TCAs), other antihistamines (especially topical ones), and drugs metabolized by CYP450 enzymes.
Pregnancy and Breastfeeding
Pregnancy Safety: Safety is not well established, use only if clearly needed and under the guidance of a physician.
Breastfeeding: Excreted in breast milk, may cause drowsiness in infants; non-sedating antihistamines are preferred during breastfeeding.
Drug Profile Summary
- Mechanism of Action: H1-receptor antagonist.
- Side Effects: Drowsiness, dizziness, dry mouth, blurred vision.
- Contraindications: Hypersensitivity, MAOI use, narrow-angle glaucoma.
- Drug Interactions: Alcohol, CNS depressants, MAOIs.
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: 25 mg every 4-6 hours (adults); adjust for children and special populations.
- Monitoring Parameters: Observe for adverse reactions, especially drowsiness and anticholinergic effects.
Popular Combinations
Pheniramine is sometimes combined with other medications, like phenylephrine (a decongestant) for treating cold symptoms. However, such combinations should be used with caution due to potential additive effects.
Precautions
Pre-existing conditions, particularly glaucoma, asthma, cardiovascular disease, prostatic hypertrophy, or diabetes, should be carefully assessed before prescribing pheniramine.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Pheniramine?
A: Adults: 25 mg every 4-6 hours, maximum 150mg/day. Children (5-10 years): 12.5 mg every 4-6 hours. Adjust for special populations.
Q2: What are the common side effects?
A: Drowsiness, dry mouth, dizziness, and blurred vision.
Q3: Is Pheniramine safe during pregnancy?
A: Safety is not well established. Consult a physician.
Q4: Can I take Pheniramine while breastfeeding?
A: It’s excreted in breast milk. Non-sedating antihistamines are preferred.
Q5: What are the contraindications?
A: Hypersensitivity, concurrent MAOI use, narrow-angle glaucoma.
Q6: Does Pheniramine interact with alcohol?
A: Yes, alcohol may potentiate the sedative effects of pheniramine.
Q7: Can Pheniramine be used in children under 5?
A: It is not recommended for children under 5 years of age.
Q8: What should I do if a patient experiences an allergic reaction to Pheniramine?
A: Discontinue the drug immediately and administer appropriate treatment, including epinephrine if necessary.
Q9: How does Pheniramine affect elderly patients?
A: Elderly patients may be more sensitive to the side effects, particularly drowsiness, dizziness, and confusion. Lower starting doses are recommended.
Q10: Can Pheniramine be used to treat acute asthma attacks?
A: No, pheniramine is not indicated for the treatment of acute asthma attacks.
