苯海拉明
苯海拉明是一種在獸醫學中廣泛使用的**第一代乙醇胺類抗組織胺藥物**。 * **主要適應症**：處理過敏反應（蕁麻疹、血管性水腫、異位性皮膚炎）、搔癢症及過敏性休克。 * **次要適應症**：預防動暈症、輕度鎮靜及作為止吐藥。 **臨床要點**： * 由於其容易穿透血腦屏障，與第二代抗組織胺（如西替利嗪、氯雷他定）相比，會引起更明顯的中樞神經抑制（鎮靜）作用。 * 在貓咪體內，組織胺被認為不是引發嘔吐的主要介質。因此，在治療貓咪的動暈症或嘔吐時，通常更傾向使用 NK-1 拮抗劑（如馬羅匹坦）或 M1-膽鹼能拮抗劑，而非苯海拉明。 * 有時也作為牛隻無菌性蹄葉炎及貓胰臟炎的輔助治療藥物。
作用機制: Diphenhydramine exerts its effects through multiple pathways: * **H1-Receptor Antagonism**: Competitively binds to and blocks **H1 receptors** on effector cells → prevents histamine-mediated capillary permeability, vasodilation, and smooth muscle spasms (bronchoconstriction). * **Central Effects**: Readily crosses the blood-brain barrier → blocks central **H1 receptors** → produces sedation and antiemetic effects. * **Anticholinergic Activity**: Non-selectively binds to **muscarinic receptors** → decreases exocrine secretions (drying effect) and can cause urinary retention or tachycardia. * **Additional Effects**: Possesses mild antitussive properties.
各物種劑量
- As an antihistamine · 0.5 mg/kg · PO · q12h · Liquid formulation is distasteful
- As an antihistamine · 2-4 mg (total dose) · PO · q12-24h
- As an antihistamine · 2-4 mg/kg · PO · q8h
- For severe urticaria and angioedema · 2 mg/kg · IM · twice daily as needed · Used with steroids (prednisone 2 mg/kg IM twice daily) and epinephrine 1:10,000 (0.5-2 mL SC)
- For adjunctive treatment of pancreatitis · 2-4 mg/kg · PO · q8h
- Prevaccination · 2 mg/kg · PO, IM or IV · 10 minutes prior to vaccination
- Pretreatment before doxorubicin · 5 mg (total dose) · IM · Single dose
- For adjunctive therapy of anaphylaxis · 0.5-1 mg/kg · IM or IV · Single dose · Used with epinephrine and steroids
- For adjunctive therapy of aseptic laminitis · 55-110 mg/100 kg body weight (0.55-1.1 mg/kg) · IV or IM · Single dose · During the acute phase · Used with corticosteroids
給藥途徑
禁忌症
- Hypersensitivity to diphenhydramine or other antihistamines in its class
- Angle closure glaucoma
- Prostatic hypertrophy
- Pyloroduodenal or bladder neck obstruction
- COPD (if mucosal secretions are a problem)
- Hyperthyroidism (use with caution)
- Cardiovascular disease or hypertension (use with caution)
- Seizure disorders (use with caution)
- Known hypersensitivity to diphenhydramine
- Glaucoma (due to anticholinergic effects)
- Prostatic hypertrophy or urinary retention
- Gastrointestinal obstruction
- Use with caution in working dogs due to sedation
不良反應
- CNS depression (lethargy, somnolence)
- Anticholinergic effects (dry mouth, urinary retention)
- GI effects (diarrhea, vomiting, anorexia)
- Paradoxical excitement (especially in cats)
- Sedation/lethargy
- Dry mouth (xerostomia)
- Urinary retention
- Tachycardia
- Gastrointestinal disturbances (diarrhea, vomiting, anorexia)
藥物相互作用
- Anticholinergic drugs (including tricyclic antidepressants) · May potentiate anticholinergic effects
- CNS depressant drugs · Increased sedation can occur
- CNS Depressants (e.g., opioids, benzodiazepines, barbiturates) · Additive sedation and central nervous system depression · moderate
- Anticholinergic drugs · Additive anticholinergic effects (dry mouth, tachycardia, urinary retention) · moderate
- Monoamine Oxidase Inhibitors (MAOIs) · May prolong and intensify the anticholinergic effects of antihistamines · major
- CNS Depressants (e.g., Diazepam, Phenobarbital, Gabapentin) · Additive CNS depression and sedation · moderate
- Anticholinergic drugs (e.g., Atropine, Glycopyrrolate) · Additive anticholinergic effects (tachycardia, dry mouth, ileus) · moderate
- Tricyclic Antidepressants (e.g., Amitriptyline) · Increased risk of anticholinergic toxicity and sedation · moderate
監測
- Clinical efficacy (reduction in pruritus, allergic signs, or vomiting)
- Adverse effects (excessive sedation, anticholinergic signs)
- Resolution of allergic signs or pruritus
- Degree of sedation
- Heart rate (monitor for tachycardia)
- Urination frequency (monitor for retention)
過量
Overdosage can cause **CNS stimulation** (ranging from excitement to seizures) or **CNS depression** (lethargy to coma), severe anticholinergic effects, respiratory depression, and death. **Treatment**: * Empty the gut after oral ingestion using standard protocols. * Induce emesis if the patient is alert and CNS status is stable. * Administer a saline cathartic and/or activated charcoal after emesis or gastric lavage. * Provide symptomatic and supportive therapies. * **Seizure management**: Phenytoin (IV) is recommended in humans for seizures caused by antihistamine overdose; **barbiturates and diazepam should be avoided**.
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