貝膽鹼
**貝膽鹼 (Bethanechol)** 是一種合成的膽鹼酯，屬於直接作用的副交感神經致效劑（膽鹼能藥物）。 - **主要獸醫用途**：主要用於刺激小動物的膀胱收縮，是治療**逼尿肌無力**（膀胱鬆弛、過度擴張且無法正常收縮）的首選藥物。這種情況通常繼發於嚴重的膀胱過度擴張或神經系統疾病（如下運動神經元病變）。 - **臨床要點**：在刺激膀胱收縮之前，確保尿道括約肌放鬆至關重要。因此，貝膽鹼經常與 α-1 拮抗劑（如 prazosin 或 phenoxybenzamine）或骨骼肌鬆弛劑（如 diazepam）合併使用，以防止膀胱破裂。 - **胃腸道用途**：過去曾用作食道或一般胃腸道刺激劑，但目前這些用途已大多被 metoclopramide 和 neostigmine 所取代。 - **藥理特性**：它對乙醯膽鹼酯酶的分解具有高度抵抗力，因此與天然乙醯膽鹼相比，其作用時間顯著更長。
作用機制: Bethanechol directly stimulates **muscarinic (M) cholinergic receptors**, with a strong affinity for the **M3 receptors** located on the smooth muscle of the detrusor (bladder wall) and gastrointestinal tract. - **Mechanism Pathway**: Binds to M3 receptor → activates Gq-protein → stimulates Phospholipase C (PLC) → increases Inositol triphosphate (IP3) and Diacylglycerol (DAG) → triggers release of intracellular calcium (Ca2+) → **smooth muscle contraction**. - **Receptor Specificity**: At usual therapeutic doses, it has negligible effects on nicotinic receptors, which minimizes skeletal muscle and ganglionic side effects. - **Physiological Effects**: Increases detrusor muscle tone, decreases bladder capacity, increases GI peristalsis, and increases gastric/pancreatic secretions.
給藥途徑
禁忌症
- Bladder neck or urinary outflow obstruction
- Questionable bladder wall integrity (e.g., recent bladder surgery)
- Hyperthyroidism
- Peptic ulcer disease or inflammatory GI lesions
- Recent GI surgery with resections/anastomoses
- GI obstruction or peritonitis
- Hypersensitivity to bethanechol
- Epilepsy
- Asthma
- Coronary artery disease or occlusion
- Hypotension
- Severe bradycardia
- Vagotonia or vasomotor instability
不良反應
- Salivation
- Lacrimation
- Urination
- Defecation
- Vomiting
- Diarrhea
- Anorexia
- Bradycardia (high dose/SC)
- Arrhythmias (high dose/SC)
- Hypotension (high dose/SC)
- Asthma/Dyspnea (high dose/SC)
- Abdominal pain (horses)
藥物相互作用
- Anticholinergic drugs (e.g., atropine, glycopyrrolate, propantheline) · Can antagonize bethanechol's effects
- Other cholinergic drugs · Additive toxicity and increased risk of cholinergic crisis · major
- Atropine · Antagonizes the effects of bethanechol · moderate
監測
- Clinical efficacy (successful urination, reduction in residual bladder volume)
- Signs of cholinergic toxicity (SLUD: salivation, lacrimation, urination, defecation)
- Heart rate and rhythm (if given parenterally)
過量
Clinical signs of overdosage are basically cholinergic in nature. - **Mild/Moderate Toxicity**: Muscarinic effects (salivation, urination, defecation, vomiting) are usually seen with oral or SC administration. - **Severe Toxicity**: If given IM or IV, a full-blown **cholinergic crisis** can occur, characterized by circulatory collapse, bloody diarrhea, shock, and possible cardiac arrest. - **Treatment**: **Atropine** is the specific antidote for bethanechol toxicity. Epinephrine may also be employed to treat clinical signs of severe bronchospasm.
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