Pheniramine maleate is a first-generation (classical) ethanolamine-derivative antihistamine with pronounced sedative and anticholinergic properties. It is a potent, competitive, and reversible antagonist of the histamine H1 receptor. In the Indian market, it is widely used for symptomatic relief of allergic conditions, primarily as a short-term treatment due to its significant central nervous system (CNS) depressant effects. The 25mg strength is a common adult dose for conditions requiring potent antihistaminic action.
Adult: 25mg to 50mg orally every 4 to 6 hours. Maximum: 150mg per day. The 25mg dose is typical for initiation or in patients sensitive to sedation.
Note: Administer orally 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. For sleep induction, take 30 minutes before bedtime.
Pheniramine competitively and reversibly blocks the action of histamine at the H1 receptor sites on effector cells (e.g., in the gastrointestinal tract, blood vessels, and respiratory smooth muscle). This blockade inhibits the vasodilatory, bronchoconstrictive, and secretory effects of histamine released during allergic reactions.
Pregnancy: Category B (US FDA). Animal studies have not shown risk, but no adequate, well-controlled studies in pregnant women. Use only if clearly needed, especially in the first trimester. Should be avoided near term due to potential anticholinergic effects in the neonate.
Driving: STRONGLY DISCOURAGED. Pheniramine significantly impairs alertness, reaction time, and motor coordination. Patients must be warned not to drive or operate heavy machinery for at least 8-10 hours after a dose.
| Alcohol, Benzodiazepines, Opioids | Potentiates CNS depression, sedation, and 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 side effects (dry mouth, constipation, urinary retention, confusion). | Major |
| CNS Stimulants (e.g., Amphetamines) | Pheniramine may counteract the stimulant effect. | Moderate |
| Hepatic Enzyme Inhibitors (e.g., Cimetidine, Fluoxetine) | May increase pheniramine plasma levels, increasing toxicity risk. | Moderate |
| Hepatic Enzyme Inducers (e.g., Phenobarbital, Rifampicin) | May decrease pheniramine plasma levels, reducing efficacy. | Moderate |
Same composition (Pheniramine (25mg)), different brands: