馬來酸吡拉明 (美吡拉敏)
**馬來酸吡拉明**（又稱美吡拉敏）是一種第一代乙二胺類抗組織胺藥物，在獸醫學中主要用於減少或預防組織胺介導的不良反應。 主要臨床重點： * **主要用途**：主要用於**馬匹**，以控制過敏性疾病，如昆蟲叮咬過敏、蕁麻疹，並作為馬氣喘（heaves）等呼吸道疾病的輔助治療。 * **優點**：與其他第一代抗組織胺藥物（如苯海拉明）相比，吡拉明的**鎮靜作用較弱**，且**抗膽鹼能副作用較少**。 * **劑型**：通常以複方產品（例如與偽麻黃鹼或癒創甘油醚結合）的口服顆粒劑形式用於馬匹，或作為注射液使用。 * **法規注意事項**：在馬術運動中，它被歸類為 ARCI 第 3 類藥物，在比賽前需要適當的停藥期。
作用機制: Pyrilamine acts as a **competitive antagonist (inverse agonist)** at **H1-receptors**. * **Mechanism**: Allergic trigger → Mast cell degranulation → Histamine release. Pyrilamine competes with free histamine for binding sites on **H1-receptors** located on smooth muscle, endothelium, and in the CNS. * **Effects**: By blocking these receptors, it prevents histamine-induced bronchoconstriction, vasodilation, and increased capillary permeability (which leads to edema/hives). * **Limitations**: It does **not** inhibit the release of histamine from mast cells, nor does it inactivate histamine that is already bound. Therefore, it is more effective as a preventative rather than a rescue treatment during acute anaphylaxis. * **Secondary Actions**: Like other first-generation antihistamines, it can cross the blood-brain barrier, leading to mild CNS depression (sedation) or paradoxical CNS stimulation, and possesses mild anticholinergic properties.
各物種劑量
- Antihistamine · 0.25-0.5 gram IM · IM · Unknown
- Antihistamine · 0.5-1.5 grams IM · IM · Unknown
- Adjunctive treatment of aseptic laminitis · 55-110 mg/100 kg IV or IM · IV, IM · Unknown
- Antihistamine · 0.88-1.32 mg/kg (2-3 mL of 20 mg/mL solution per 100 lbs body weight) IV (slowly), IM or SC · IV, IM, SC · q6-12h · May repeat in 6-12 hours if necessary. NOTE: ARCI UCGFS CLASS 3 DRUG
- Antihistamine (Foals) · 0.44 mg/kg (1 mL of 20 mg/mL solution per 100 lbs. body weight) IV (slowly), IM or SC · IV, IM, SC · q6-12h · May repeat in 6-12 hours if necessary.
- Antihistamine · 1 mg/kg IV , IM or SC · IV, IM, SC · Unknown
- Antihistamine · 0.5-1.5 grams IM · IM · Unknown
- Antihistamine · 0.25-0.5 gram IM · IM · Unknown
- Antihistamine · 12.5-25 mg PO four times a day · PO · q6h
給藥途徑
禁忌症
- Should not supersede the use of other emergency drugs and procedures (e.g., epinephrine for acute anaphylaxis)
不良反應
- CNS stimulation (nervousness, insomnia, convulsions, tremors, ataxia)
- Palpitation
- GI disturbances
- CNS depression (sedation)
- Muscular weakness
- Anorexia
- Lassitude
- Incoordination
藥物相互作用
- Anticoagulants (heparin, warfarin) · Antihistamines may partially counteract the anticoagulation effects of heparin or warfarin.
- CNS Depressant Drugs · Increased sedation can occur if pyrilamine is combined with other CNS depressant drugs.
- Epinephrine · Pyrilamine may enhance the effects of epinephrine.
監測
- Clinical efficacy (reduction in allergic signs, hives, or respiratory effort)
- Adverse effects (monitor for signs of CNS stimulation or excessive sedation)
過量
Treatment of overdosage is **supportive and symptomatic**. * **Seizure Management**: Phenytoin (IV) is recommended in the treatment of seizures caused by antihistamine overdose in humans. Most toxicologists recommend **avoiding** barbiturates and diazepam, though one veterinary manufacturer historically suggested 'careful titration' of barbiturates. * **CNS Depression**: Avoid the use of CNS stimulants (analeptics like caffeine, ephedrine, or amphetamines) to treat CNS depression, as this can exacerbate toxicity.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。