Antihistamines (H1-receptor antagonists) competitively inhibit histamine at H1 receptor sites. They do not inactivate, nor prevent the release of histamine, but can prevent histamine’s action on the cell. Besides their antihistaminic activity, these agents also have varying degrees of anticholinergic and CNS activity (sedation). Pyrilamine is considered to be less sedating and have fewer anticholinergic effects when compared to most other antihistamines.
Antihistamines are used in veterinary medicine to reduce or help prevent histamine mediated adverse effects; predominantly used in horses.
劑量數字暫停提供：VetPro 的劑量改依 DRUGAPI 藥物資料庫對外的內容，DRUGAPI 目前不提供可直接計算的劑量。下方列出 DRUGAPI 的審查結論與劑量審查引用的來源；計算機可手動輸入劑量換算。
現行 API 無法同時強制 NADA、20 mg/mL 濃度、成年馬／幼駒、產品特定途徑、適應症、非食用馬、美國法域與監測條件。即使 21 CFR 支持四張具名馬用注射產品參考卡，所有 19 張數值卡仍不得由通用計算器或飼主端執行。
DRUGAPI 劑量審查引用的獸醫官方標示（各標示只適用於其產品、物種與法域，不可互換）
依出現頻率分組；嚴重副作用獨立列出，臨床上需立即辨識。
3-5 days