Bethanechol

Bethanechol is a direct muscarinic cholinergic agonist used primarily to increase urinary bladder contraction in selected small-animal patients. Its role is most relevant when poor detrusor activity contributes to incomplete emptying and the urinary outflow tract is patent. Evidence for efficacy is limited, and stimulation of the bladder cannot compensate for every neurologic or mechanical cause of retention.

It also stimulates gastrointestinal smooth muscle, but historical use for motility disorders has a less secure clinical role. Its cholinergic effects extend beyond the intended organ, which can limit useful exposure.

Group

Muscarinic agonist

Mechanism of Action

Bethanechol directly activates muscarinic acetylcholine receptors and is relatively resistant to breakdown by acetylcholinesterase. Compared with acetylcholine, this resistance prolongs the duration of receptor stimulation. At usual therapeutic exposure it has little nicotinic activity.

Muscarinic stimulation increases detrusor smooth-muscle contraction and can reduce functional bladder capacity. Successful emptying still requires sufficiently low urethral resistance and intact coordination; contraction against an obstructed or tightly closed outlet can increase pressure without producing effective voiding.

In the gastrointestinal tract, receptor stimulation increases tone, peristaltic activity and secretions. Related effects in other tissues include salivation and bronchial smooth-muscle contraction. These shared receptor actions explain why escalating the dose may produce generalized cholinergic effects rather than a selective improvement in bladder or bowel function.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Urinary bladder atony	5–15 mg/animal	PO	Every 8 h	Empirical size-related doses: small dogs 2.5 mg, medium dogs 5 mg, large dogs 15 mg. The general range is not a validated weight-band table.
Urinary bladder atony	2.5 mg/animal	PO	Every 8 h	Small-dog alternative.
Urinary bladder atony	5–25 mg/animal	PO	Every 8–12 h
Urinary bladder atony	2.5–25 mg/animal	PO	Every 8 h
Reduced esophageal sphincter tone	0.5–1 mg/kg	PO	Every 8 h
Dysautonomia	1.25–5 mg/animal	PO	Every 24 h
Divided-dose dysautonomia treatment	Reference only	PO		2.5–7.5 mg total orally divided every 8–12 hours; the passage does not unambiguously distinguish the daily total from the amount per administration.
Dysautonomia	0.05 mg/kg	SC	Every 12 h	Increase slowly according to response; have atropine available for cholinergic toxicity.
Dysautonomia	1.25–5 mg/animal	PO	Every 12 h

Cats

Use / stage	Dose	Route	Schedule	Instructions
Urinary bladder atony	1.25–5 mg/animal	PO	Every 8 h
Urinary bladder atony	1.25–7.5 mg/animal	PO	Every 8–12 h
Urinary bladder atony	1.25–7.5 mg/animal	PO	Every 8 h
Dysautonomia	1.25–5 mg/animal	PO	Every 24 h
Divided-dose dysautonomia treatment	Reference only	PO		2.5–7.5 mg total orally divided every 8–12 hours; the passage does not unambiguously distinguish the daily total from the amount per administration.

Horses

Use / stage	Dose	Route	Schedule	Instructions
Gastrointestinal motility stimulation	0.025 mg/kg	SC	Once	Historical regimen; efficacy for gastrointestinal stasis is questionable.
Urinary bladder atony	0.025–0.075 mg/kg	SC	Every 8 h
Urinary bladder atony	0.25–0.75 mg/kg	PO	Every 6–12 h	Only if weak detrusor contractions remain; dose differs substantially from SC administration.
Postoperative bladder atony	0.4 mg/kg	PO	Every 8–12 h	Foals only; withdraw gradually as bladder function returns.

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Gastrointestinal motility stimulation	0.07 mg/kg	SC	Once	Historical regimen; efficacy for gastrointestinal stasis is questionable.
Cecal dilation without torsion	0.07 mg/kg	SC	Every 8 h	Up to 2 days; Only for stable or mildly affected cattle still passing feces, without rectal evidence of torsion or retroflexion. Combine fluids and other indicated care; no improvement in 24 hours requires reassessment for surgery.

Indications

Selected urinary bladder atony or detrusor hypocontractility in small animals with a patent outflow tract, including postoperative atony.
Adjunctive stimulation of bladder emptying in selected neurologic or autonomic dysfunction cases; efficacy evidence is limited.
Historical stimulation of esophageal or gastrointestinal motility; controlled veterinary efficacy evidence is limited.

Contraindications

Suspected urinary or gastrointestinal obstruction.
Compromised bladder integrity, recent gastrointestinal anastomosis, peritonitis, peptic ulceration or inflammatory gastrointestinal lesions.
Severe bradycardia, hypotension, asthma, epilepsy or hyperthyroidism.
Hypersensitivity to bethanechol.

Interactions

Atropine and other anticholinergics oppose its effects.
Other cholinergic drugs can produce additive cholinergic toxicity.
Quinidine and procainamide may oppose the response; ganglionic blockers can increase gastrointestinal and hypotensive effects.

Adverse effects

Abdominal cramping and diarrhea
Circulatory depression

Toxicity

Cholinergic excess causes salivation, diarrhea, bradycardia, bronchospasm and potentially circulatory collapse. Atropine antagonizes muscarinic toxicity; maintain airway and cardiovascular support.

Preparations

Preparation	Form	Strength	Route
Bethanechol 5 mg tablet	Tablet	5 mg / tablet	PO
Bethanechol 10 mg tablet	Tablet	10 mg / tablet	PO
Bethanechol 25 mg tablet	Tablet	25 mg / tablet	PO
Bethanechol 50 mg tablet	Tablet	50 mg / tablet	PO
Bethanechol 5 mg/mL injection	Injection	5 mg / mL	SC
Compounded bethanechol chloride 5 mg/mL oral suspension Specific Ora-Plus/Ora-Sweet formulation; 60-day reported potency at 5°C or 25°C protected from light.	Oral Liquid	5 mg / mL	PO

Monitoring and Administration

Exclude obstruction before treatment. Monitor urination, gastrointestinal function and cardiovascular response.

Only subcutaneous injection is described. Oral treatment is generally preferred in small animals. Large-animal use for gastrointestinal stasis has uncertain efficacy and is not recommended routinely.

Follow voided volume, bladder size, urination frequency and gastrointestinal tolerance. Exclude mechanical obstruction; increased urethral tone may require a separate outflow-relaxing drug. Give oral doses on an empty stomach unless this is poorly tolerated.

Compounding stability is vehicle-specific: twelve 50 mg tablets in 60 mL Ora-Plus, made to 120 mL with Ora-Sweet or Ora-Sweet SF, gives 5 mg/mL and has reported 60-day potency at 5°C or 25°C protected from light. Do not generalize this to other aqueous vehicles.