Bethanechol
**Bethanechol** is a synthetic choline ester and a direct-acting parasympathomimetic (cholinergic) agent. - **Primary Veterinary Use**: It is primarily used to stimulate bladder contractions in small animals, making it the drug of choice for treating **detrusor atony** (a flaccid, overstretched bladder that cannot contract properly). This condition is often secondary to severe overdistension or neurologic disease (e.g., lower motor neuron lesions). - **Clinical Pearl**: It is crucial to ensure the urinary sphincter is relaxed before stimulating the bladder to squeeze. Therefore, bethanechol is frequently prescribed alongside alpha-1 antagonists (like prazosin or phenoxybenzamine) or skeletal muscle relaxants (like diazepam) to prevent bladder rupture. - **GI Uses**: Historically used as an esophageal or general GI stimulant, though metoclopramide and neostigmine have largely supplanted it for these purposes. - **Pharmacologic Profile**: It is highly resistant to hydrolysis by acetylcholinesterase, giving it a significantly longer duration of action compared to natural acetylcholine.
Mecanismo: 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.
Vías de administración
Contraindicaciones
- 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
Efectos adversos
- 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)
Interacciones farmacológicas
- 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
Monitoreo
- 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)
Sobredosis
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.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.