Budesonide

Budesonide is a **locally acting, highly potent glucocorticoid** (approximately 15 times more potent than prednisolone) with weak mineralocorticoid activity. * **Targeted Delivery**: Oral formulations are typically enteric-coated (e.g., Entocort EC®) to delay dissolution until the drug reaches the duodenum. This allows the medication to exert concentrated, topical anti-inflammatory action directly within the intestines. * **Reduced Systemic Effects**: While absorbed into the portal circulation, budesonide undergoes extensive **first-pass hepatic metabolism**. The liver clears the vast majority of the drug before it reaches systemic circulation, significantly reducing the risk of classic systemic steroid side effects (such as polyuria, polydipsia, and polyphagia). * **Clinical Utility**: Primarily used off-label in veterinary medicine for **Inflammatory Bowel Disease (IBD)** in dogs and cats that are either refractory to, or intolerant of, traditional systemic corticosteroids. * **Cost & Formulation**: Expense can be a limiting factor, and because human capsules are often too large for small veterinary patients, the drug frequently requires compounding into smaller dosage strengths.

กลไกการออกฤทธิ์: Budesonide diffuses across cell membranes and binds with high affinity to cytosolic **glucocorticoid receptors (GR)**. * The receptor-ligand complex translocates to the nucleus → binds to glucocorticoid response elements (GREs) on DNA → alters gene transcription. * **Anti-inflammatory pathway**: Induces the production of **lipocortin-1 (annexin-1)** → inhibits **phospholipase A2** → blocks the release of arachidonic acid from membrane phospholipids → decreases the synthesis of potent inflammatory mediators (prostaglandins and leukotrienes). * Despite its high first-pass metabolism, it still causes significant suppression of the **hypothalamic-pituitary-adrenal (HPA) axis**.

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