1. Clinical Overview
Pheniramine maleate is a first-generation (classical) ethanolamine-derivative antihistamine with pronounced sedative and anticholinergic properties. The 22.75mg strength is a common oral tablet formulation in India, equivalent to 15mg of the pheniramine base. It is primarily used for symptomatic relief of allergic conditions, pruritus, and as a sedative in various over-the-counter (OTC) and prescription combinations.
| Onset | Duration | Bioavailability |
|---|---|---|
| 15 to 30 minutes (oral) | 4 to 6 hours | Not well documented for oral form; high but variable. |
2. Mechanism of Action
Competitively and reversibly inhibits histamine at the H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract. This blockade prevents histamine-mediated allergic responses such as vasodilation, increased capillary permeability, and bronchoconstriction.
3. Indications & Uses
- Symptomatic relief of allergic conditions: Allergic rhinitis (seasonal/perennial), Urticaria (hives)
- Pruritus (itching) of allergic or non-allergic origin
- As a sedative component in cough and cold preparations
4. Dosage & Administration
Adult Dosage: 22.75mg (one tablet) every 4 to 6 hours. Maximum: 4 tablets (91mg) in 24 hours. Often used as a single dose at night for sedation.
Administration: Oral administration. Can be taken with or without food. Taking with food may reduce GI upset. Tablet should be swallowed whole with a glass of water. Avoid crushing/chewing unless advised (bitter taste).
5. Side Effects
Common side effects may include:
- Drowsiness, sedation, somnolence
- Dry mouth, nose, and throat
- Dizziness, disturbed coordination
- Gastrointestinal disturbances (epigastric distress, nausea)
- Thickening of bronchial secretions
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Alcohol, Benzodiazepines, Opioids, Barbiturates | Potentiation of CNS depression (additive sedation, impaired psychomotor performance). | Major |
| Monoamine Oxidase Inhibitors (MAOIs) - e.g., Phenelzine, Tranylcypromine | Increased anticholinergic and CNS depressant effects; risk of hypertensive crisis. | Contraindicated |
| Other Anticholinergics (e.g., Atropine, TCAs, Antipsychotics) | Additive anticholinergic toxicity (dry mouth, constipation, urinary retention, confusion, hyperthermia). | Major |
| CNS Stimulants (e.g., Amphetamines) | Mutual antagonism of therapeutic effects. | Moderate |
| Hepatic Enzyme Inhibitors (e.g., Cimetidine, Fluoxetine, Quinidine) | Increased plasma levels and toxicity of pheniramine due to inhibited metabolism (CYP2D6). | Moderate |
7. Patient Counselling
- DO take exactly as prescribed, usually at bedtime if sedation is desired.
- DO inform your doctor about all other medicines, including OTC and herbal products.
- DO stay well-hydrated to counter dry mouth.
- DO NOT consume alcohol or sleep-inducing OTC medicines.
- DO NOT drive, operate machinery, or perform hazardous tasks until you know how the drug affects you.
- DO NOT take a double dose to make up for a missed one.
8. Toxicology & Storage
Overdose: Manifests as an extension of its pharmacological effects: CNS depression (somnolence progressing to coma, respiratory depression), CNS stimulation (hallucinations, tremors, convulsions - especially in children), anticholinergic crisis (flushed dry skin, hyperthermia, dilated pupils, tachycardia, urinary retention, ileus), cardiovascular collapse.
Storage: Store below 30°C (86°F), in a cool, dry place. Protect from light and moisture. Keep in the original container, tightly closed. Keep out of reach and sight of children.