Zafirlukast

Zafirlukast is an oral **leukotriene-receptor antagonist** used off-label in veterinary medicine. While theoretically promising for conditions driven by leukotriene-mediated inflammation—such as **feline asthma**, **canine atopic dermatitis**, and **inflammatory bowel disease (IBD)**—clinical efficacy in veterinary patients has been largely disappointing, limited, or not fully studied. > **Clinical Pearl:** Leukotrienes are potent inflammatory mediators produced via the lipoxygenase pathway. While blocking them is highly effective in human asthma, cats and dogs may rely on different primary inflammatory pathways (such as histamine, interleukins, or prostaglandins), which likely explains the variable and often poor clinical response to zafirlukast in these species.

Mechanism: Zafirlukast selectively and competitively inhibits **leukotriene receptors**, specifically targeting the **LTD4** and **LTE4** receptors. * Arachidonic acid → 5-lipoxygenase pathway → Leukotrienes (LTC4, LTD4, LTE4) * By blocking these receptors, zafirlukast prevents the binding of slow-reacting substance of anaphylaxis (**SRS-A**). * This inhibition reduces smooth muscle contraction (bronchoconstriction), vascular permeability, and inflammatory cell infiltration associated with allergic and asthmatic responses.

VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.