(for veterinary information only)
5 mg, 10 mg, 25 mg, 50 mg
We normally think of urination as a voluntary activity but, in fact, there is a great deal more to it. In order to urinate, the bladder’s detrusor muscle must contract (squeezing the bladder empty) while simultaneously the lower sphincter must relax. These two activities must be coordinated or one will end up with the bladder squeezing against a closed sphinter or a dilated sphincter allowing passive leakage. The voluntary part is simply the “when” and “where.”
The coordination of these two muscles is disrupted by certain types of spinal injuries. The so-called “upper motor neuron” sign creates an increase in sphincter tone while “lower motor neuron signs” create a flaccid sphincter and a flabby bladder. (For more details on these injuries, see the Cats With Broken Tails page.)
Bethanechol chloride works to strengthen the detrusor muscle’s contraction. If the lower sphincter is too tight from an upper motor neuron injury, this medication will help the bladder to contract harder to overcome it. If the bladder is flabby, this medication will help it regain some shape and strength so that it can empty in a controlled fashion rather than just leaking.
Bethanechol chloride works neurologically stimulating what are called “muscarinic cholinergic receptors” in the autonomic nervous system. (Think of the autonomic system as the part of one’s nervous system concerned with automatic functions such as muscle coordinations of the bladder and its sphincter.) By stimulating these nerve receptors, this medication is able to provide a stronger contraction message to the muscles those receptors control.
One has many muscarinic cholinergic receptors besides those in the bladder and these will also be stimulated by bethanechol chloride. Increased peristalsis in the intestine and stomach is a side effect (which can lead to diarrhea). Excess salivation and tear production can occur. Increasing the bladder’s detrusor muscle tone leads to a tighter bladder which means less urine storage capacity and more frequent need to urinate.
The most common side effects at normal doses are diarrhea, appetite loss, vomiting, and drooling. The other side effects listed above tend to involve overdosing. Atropine is considered an antidote.
If the patient’s urinary tract is not obstructed but has excess tone, it is helpful to combine bethanechol with a medication to relax the lower sphincter and urethra: diazepam or phenoxybenzamine.
- Bethanechol should be stored at room temperature.
- Bethanechol is best given on an empty stomach.
Bethanechol should not be used in patients where urinary obstruction is an issue. There is no need to cause the bladder to contract against an obstructed outlet.
Patients with stomach ulcers may secrete more acid while on bethanchol and should not receive this medication.
Bethanechol is also considered contraindicated in hyperthyroidism, inflammatory bowel disease, epilepsy, asthma, low blood pressure, and certain heart rhythm disturbances.
Page last updated: 6/24/09
Page last reviewed: 3/12/2011