Rational Use of Bethanechol in Dogs and Cats with Bladder Dysfunction.

Bethanechol chloride, a nonselective muscarinic agonist, is the most frequently employed drug in dogs and cats to induce detrusor smooth muscle contraction under conditions characterized by poor or absent bladder emptying. Although this drug has minimal or absent nicotinic activity, at higher doses, weak stimulation of neuronal nicotinic receptors may occur, causing the release of noradrenaline, which induces contraction of the urethral smooth muscle by activating α-adrenergic receptors. In the presence of total or partial suprasacral lesions, the elaboration and initiation phase of the urination process is absent due to an interruption of afferent signals from the bladder to the brainstem. In such cases, hypertonicity of the urethral sphincters is expected, and bethanechol is contraindicated. Bethanechol is also not indicated for reflex dyssynergia. In the presence of complete injuries involving the sacral segments, cauda equina, or pelvic nerve, both reflex and voluntary micturition are abolished, and bethanechol is usually ineffective. However, in cases of partial injuries, bethanechol is likely to be effective, as partial integrity of the micturition reflex is required to produce sustained bladder contraction. Bethanechol may benefit patients with myopathic decompensated bladder, although its effectiveness depends on the severity of detrusor damage.