Ketotifen (Ketotifen Hydrogen Fumarate)

Ketotifen is an antihistamine that acts on allergic pathways to reduce symptoms in several related conditions, offering both H1‑receptor blockade and mast‑cell stabilization.

• Allergic rhinitis: reduces nasal congestion, sneezing, itching and watery discharge, improving overall nasal comfort and sleep quality.
• Allergic conjunctivitis: alleviates eye itching, redness, swelling and tearing, providing clearer vision and comfort.
• Bronchial asthma: contributes to asthma control by stabilizing mast cells, decreasing inflammatory mediator release and reducing bronchospasm frequency, potentially lowering the need for rescue inhalers.

• Ketotifen acts as a selective H1‑receptor antagonist, preventing histamine from binding to mast cells and other target cells. In addition, it stabilizes mast cell membranes, inhibiting the release of histamine, leukotrienes and other inflammatory mediators. This dual action reduces the early and late phases of allergic reactions, decreasing vascular permeability, smooth‑muscle contraction and mucus secretion. The drug’s effect on H1 receptors also diminishes itching and vasodilation associated with allergic responses.

Ketotifen may cause a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Drowsiness: mild sedation or sleepiness.
• Dry mouth: reduced salivation causing thirst.
• Weight gain: modest increase in body weight.
• Gastrointestinal discomfort: nausea, abdominal pain or dyspepsia.
• Headache: mild to moderate head pain.
• Dizziness: sensation of light‑headedness.

Serious or Rare Side Effects

• Severe allergic reaction: anaphylaxis or angioedema requiring immediate medical attention.
• Hepatotoxicity: signs of liver injury such as jaundice, dark urine or elevated enzymes.
• Cardiac arrhythmia: irregular heartbeat, especially in patients with pre‑existing heart conditions.
• Blood dyscrasias: rare cases of neutropenia or agranulocytosis.
• Severe skin reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.

When prescribing or dispensing Ketotifen, several safety considerations should be observed to minimize risk.

• Assess patient history: evaluate for asthma severity, liver disease or hypersensitivity.
• Monitor sedation: advise caution when operating machinery or driving due to possible drowsiness.
• Avoid alcohol: concurrent alcohol may enhance central nervous system depression.
• Use in pregnancy: only if clearly needed; benefits must outweigh potential risks.
• Use in lactation: consider infant exposure through breast milk and assess necessity.
• Store at ambient temperature: keep below 25 °C in original packaging, protect from moisture and direct sunlight.

Ketotifen can interact with other medicines, altering its effectiveness or increasing adverse effects.

Major Interactions (Avoid)

• CYP3A4 inhibitors: strong inhibitors may increase ketotifen plasma levels, raising toxicity risk.
• CNS depressants: concurrent use with sedatives or antihistamines can intensify drowsiness.
• Monoamine oxidase inhibitors: may increase risk of hypertensive reactions.

Moderate Interactions (Monitor Closely)

• Anticholinergic agents: may worsen dry mouth and constipation.
• Alcohol: can potentiate sedation and impair coordination.
• Other antihistamines: additive antihistaminic effects may increase side‑effect burden.
• Theophylline: may reduce bronchodilator response.
• Beta‑blockers: may mask tachycardia symptoms.