Hyoscyamine
**Hyoscyamine** is a belladonna alkaloid and the highly active levo-isomer of racemic atropine. Because it is the active enantiomer, it is significantly more potent than atropine in both its central and peripheral anticholinergic effects. In veterinary medicine, its use is relatively limited but it serves as a valuable alternative to other anticholinergics (like glycopyrrolate or atropine). It is primarily utilized for: * **Gastrointestinal hypermotility:** Managing conditions like irritable bowel syndrome (IBS) by reducing spasms. * **Cardiovascular support:** Treating symptomatic bradycardia or sinus node disease. * **Perioperative use:** Potentially reducing hypersalivation, urinary spasms, and respiratory secretions, though clinical data in animals is sparse. > **Clinical Pearl:** Because hyoscyamine crosses the blood-brain barrier more readily than quaternary anticholinergics like glycopyrrolate, patients should be monitored closely for central nervous system (CNS) side effects, such as paradoxical excitement or sedation.
กลไกการออกฤทธิ์: 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).
ขนาดยาตามชนิดสัตว์
- 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.
ขนาดยาเป็นข้อมูลอ้างอิงทางคลินิกสำหรับสัตวแพทย์ผู้มีใบอนุญาต โปรดตรวจสอบกับฉลากล่าสุดและผู้ป่วยแต่ละรายเสมอ
วิธีการให้ยา
ข้อห้ามใช้
- 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
อาการไม่พึงประสงค์
- Mydriasis (pupil dilation)
- Xerostomia (dry mouth)
- Constipation
- Urinary retention
- Xerophthalmia (dry eyes)
- Tachycardia
- CNS effects (somnolence, delirium, or paradoxical excitement at higher doses)
อันตรกิริยาระหว่างยา
- 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.
การติดตาม
- 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)
การได้รับยาเกินขนาด
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.
ข้อมูลอ้างอิงยาของ VetSheet มีไว้สำหรับสัตวแพทย์ผู้มีใบอนุญาตเพื่อช่วยในการตัดสินใจทางคลินิก ไม่ใช่สิ่งทดแทนการวินิจฉัยของผู้เชี่ยวชาญหรือฉลากล่าสุดของผู้ผลิต