Ketotifen fumarate is a benzocycloheptathiophene derivative that works through two complementary mechanisms: it stabilizes mast cells (preventing degranulation and the release of histamine, tryptase, and prostaglandins)^1,2 and blocks H1 histamine receptors.¹ This dual action makes it particularly useful for conditions involving mast cell activation.

Ketotifen also interferes with eosinophil chemotaxis, degranulation, and survival,^3,4 and inhibits platelet-activating factor (PAF)-mediated responses.^1,5 In a randomized controlled trial in patients with irritable bowel syndrome (IBS) with visceral hypersensitivity, ketotifen significantly reduced abdominal pain and improved quality of life compared to placebo.⁶

While ketotifen eye drops (Zaditor, Alaway) are available over-the-counter in the US, oral ketotifen is not commercially manufactured domestically. Patients who need oral ketotifen must obtain it through a compounding pharmacy with a valid prescription.

Ketotifen acts on multiple pathways relevant to allergic and inflammatory conditions:¹

• Mast cell stabilization — prevents release of histamine, leukotrienes, tryptase, and other inflammatory mediators by stabilizing calcium permeability in mast cell membranes^1,2
• H1 receptor antagonism — competitively blocks histamine H1 receptors at target tissues¹
• Eosinophil inhibition — inhibits eosinophil chemotaxis to eotaxin, IL-5, and fMLP; reduces leukotriene C4 release from eosinophils; and can induce eosinophil necrosis at clinically relevant concentrations^3,4,7
• PAF antagonism — inhibits PAF-mediated platelet activation in vitro and attenuates PAF-induced eosinophil chemotaxis^1,5

✓ Mast Cell Activation Syndrome (MCAS)

✓ Asthma prevention (prophylaxis)

✓ Allergic rhinitis & chronic urticaria

✓ Eosinophilic Esophagitis (EoE)