莨菪鹼
**莨菪鹼（Hyoscyamine）**是一種顛茄生物鹼，為外消旋阿托品（atropine）的高活性左旋異構物。由於它是具活性的對映異構體，其中樞與周邊的抗膽鹼作用明顯強於阿托品。 在獸醫學中，其應用相對有限，但可作為其他抗膽鹼藥物（如格隆溴銨或阿托品）的有效替代品。主要用於： * **胃腸道蠕動過速：** 透過減少痙攣來控制大腸激躁症（IBS）等疾病。 * **心血管支持：** 治療有症狀的心搏過緩或竇房結疾病。 * **圍手術期使用：** 潛在可用於減少唾液分泌過多、尿道痙攣及呼吸道分泌物，儘管動物的臨床數據較少。 > **臨床要點：** 由於莨菪鹼比格隆溴銨等四級抗膽鹼藥物更容易穿透血腦屏障，應密切監測病患是否出現中樞神經系統（CNS）副作用，如矛盾性興奮或鎮靜。
作用機制: Hyoscyamine acts as a competitive, reversible antagonist of acetylcholine at **muscarinic receptors** (M1-M5) located on smooth muscle, cardiac muscle, and glandular cells. * **Gastrointestinal/Urinary:** Blocks parasympathetic stimulation → relaxes smooth muscle → decreases GI and urinary tract motility and spasms. * **Secretions:** Inhibits glandular muscarinic receptors → dose-dependent reduction in salivary, bronchial, pharyngeal, and gastric secretions. * **Cardiovascular:** Blocks vagal (parasympathetic) tone at the sinoatrial (SA) node → increases heart rate. * **Ocular:** Paralyzes the pupillary sphincter muscle → causes mydriasis (pupil dilation).
各物種劑量
- Irritable bowel syndrome · 0.003-0.006 mg/kg PO two to three times a day · PO · q8-12h · Assumed to be for immediate release oral dosage forms.
- Long-term management of symptomatic patients with sinus node disease · 0.003-0.006 mg/kg PO q8h · PO · q8h · Long-term · Assumed to be for immediate release oral dosage forms.
劑量為合格獸醫專業人員的臨床參考。請務必對照最新藥品仿單及個別病患確認。
給藥途徑
禁忌症
- Hypersensitivity to hyoscyamine or other belladonna alkaloids
- Glaucoma (narrow or wide angle)
- Intestinal obstruction or intestinal atony
- Toxic megacolon
- Severe ulcerative colitis
- Obstructive uropathy
- Acute hemorrhage with cardiovascular instability
不良反應
- Mydriasis (pupil dilation)
- Xerostomia (dry mouth)
- Constipation
- Urinary retention
- Xerophthalmia (dry eyes)
- Tachycardia
- CNS effects (somnolence, delirium, or paradoxical excitement at higher doses)
藥物相互作用
- Antacids (magnesium, aluminum, calcium salts) · May interfere with the gastrointestinal absorption of hyoscyamine.
- Other Anticholinergics (e.g., atropine, glycopyrrolate) · Additive anticholinergic actions and increased risk of adverse effects.
- First-Generation Antihistamines (e.g., diphenhydramine) · Additive anticholinergic actions and increased risk of adverse effects.
- Prokinetic Agents (e.g., cisapride, metoclopramide) · Hyoscyamine may antagonize and counteract their gastrointestinal prokinetic effects.
監測
- Clinical efficacy (resolution of GI spasms or improvement in heart rate)
- Heart rate and rhythm
- Bowel elimination (monitor for constipation/ileus)
- Urinary elimination (monitor for urinary retention)
過量
Significant overdosage can be life-threatening; contacting an animal poison control center is strongly advised. The LD50 in rats is 375 mg/kg. **Clinical Signs of Toxicity:** * Intensified anticholinergic effects: severe tachycardia, mydriasis, urinary retention, and absent gut sounds (ileus). * CNS signs: behavioral changes, severe depression, delirium, or seizures. **Treatment:** * **Decontamination:** Protocols to decrease oral absorption (e.g., emesis, activated charcoal) should be considered if the overdose was recent and the patient is asymptomatic. * **Antidote:** Severe anticholinergic effects can be treated with **physostigmine** or **neostigmine**, but this should *only* be done under the strict guidance of a poison control center due to the risk of cholinergic crisis. * **Supportive Care:** Delirium or excitement can be managed with small doses of short-acting barbiturates or benzodiazepines. Hyoscyamine can be removed by hemodialysis.
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