Ketotifen is a benzocycloheptathiophene derivative with potent, long-acting, non-competitive H1-antihistaminic and mast cell stabilizing properties. It is a second-generation antihistamine used primarily for the prophylactic management of allergic conditions, including allergic conjunctivitis and allergic rhinitis. It inhibits the release of histamine and other mediators from mast cells and also acts as a leukotriene antagonist.
Adult: 1 mg (one tablet) orally twice daily, preferably in the morning and evening. May be increased to 2 mg twice daily in some cases under medical supervision.
Note: Can be taken with or without food. Swallow tablet whole with a glass of water. For long-term prophylaxis, consistent timing is important. Do not crush or chew. For ophthalmic use (separate formulation), follow specific eye drop instructions.
Ketotifen exerts a dual mechanism: 1) Potent, long-acting, non-competitive antagonism of histamine H1-receptors, blocking the effects of released histamine. 2) Stabilization of mast cell membranes, inhibiting the degranulation and release of preformed mediators (histamine, tryptase) and newly synthesized mediators (leukotrienes, prostaglandins, platelet-activating factor). It also exhibits anti-eosinophilic activity.
Pregnancy: Category C (US FDA). Animal studies have shown fetal risk; no adequate, well-controlled studies in humans. Use only if potential benefit justifies potential risk to the fetus. Avoid in first trimester unless clearly needed.
Driving: May impair alertness, especially during initial therapy. Patients should not drive or operate heavy machinery until their individual response is known (usually 3-5 days after starting or dose increase).
| CNS Depressants (Alcohol, Benzodiazepines, Opioids) | Additive sedation and impaired psychomotor performance. | Major |
| Anticholinergic drugs (Atropine, TCAs, Antipsychotics) | Increased risk of dry mouth, urinary retention, constipation, blurred vision. | Moderate |
| Oral Antidiabetics (e.g., Glimepiride) | Ketotifen may enhance hypoglycemic effect; monitor blood glucose. | Moderate |
| Enzyme Inducers (Phenobarbital, Phenytoin, Rifampicin) | May increase metabolism of ketotifen, reducing its efficacy. | Moderate |
| Enzyme Inhibitors (Ketoconazole, Erythromycin, Cimetidine) | May decrease metabolism of ketotifen, increasing its plasma levels and side effects. | Moderate |
| MAO Inhibitors (Phenelzine, Tranylcypromine) | Increased anticholinergic and CNS depressant effects. Contraindicated. | Major |