Benzodiazepines
Diazepam
Diazepam is a benzodiazepine used for relaxation of primarily skeletal muscle in the urethra in dogs with functional urethral obstruction.
Formulation → Oral, injectable
Dose (dogs) → 2-10 mg/dog PO 30 minutes before voiding (≤3 times a day)1
Key Points
- Serum half-life in dogs and cats is significantly shorter than in humans.1
- Adverse effects include CNS depression, appetite stimulation, and sedation.
- May cause disinhibition in aggressive patients
- Oral form should not be used in cats, as there is significant potential for hepatotoxicity.
- Should be used carefully in debilitated patients or those with liver dysfunction
Alprazolam
Alprazolam is a benzodiazepine that produces sedation, anxiolysis, and skeletal muscle relaxation. It may be used to relax the skeletal muscle of the urethra in patients with urethrospasm; however, no data on its use in this manner in either dogs or cats has been published.
Formulation → Oral
Dose (dogs) → 0.02-0.05 mg/kg PO q6-12h1
Dose (cats) → 0.125-0.25 mg/cat PO q8-24h1
Doses extrapolated from anxiolytic use
Acepromazine
Acepromazine is a phenothiazine that has antispasmodic and α-adrenergic blocking effects. It is used in dogs and cats with functional urethral obstruction.
Formulation → Oral, injectable
Dose (dogs, cats) → 0.55-2.2 mg/kg PO q6-12h or to effect1
Key Points
- Has been shown to significantly decrease preprostatic and prostatic urethral pressures in intact male cats18
- Adverse effects include hypotension and prolapse of the nictitans.
- Should not be used in patients with hypotension, volume depletion, or shock
- Should be used carefully in patients with cardiac disease or hepatic dysfunction
- Caution: Dose should be reduced in patients with possible breed-related MDR1 mutations (eg, collies, Shetland sheepdogs, Australian shepherds).1,19
Baclofen
Baclofen is a skeletal muscle relaxant that appears to act at the level of the spinal cord. It has been shown to reduce urethral striated (skeletal) muscle sphincter tone in dogs.20
Formulation → Oral
Dose (dogs only) → 1-2 mg/kg PO q8h
Key Points
- Should be gradually discontinued to reduce risk for psychomotor effects (eg, seizures, hallucinations)
- Adverse effects include sedation, weakness, or GI cramping.
- Narrow margin of safety in dogs and should not be used in cats
- Should be used with caution in patients with seizure disorders
Dantrolene
Dantrolene is a direct-acting muscle relaxant that has been used to treat patients that have functional urethral obstruction. Because of the availability of more effective and safer muscle relaxants, dantrolene is not recommended as a first-line treatment for detrusor-urethral dyssynergia.
Formulation → Oral; injectable is available but not practical for veterinary use
Dose (dogs) → 1-5 mg/kg PO q8-12h1
Dose (cats) → 0.5-2 mg/kg PO q12h1
Key Points
- May be less effective than baclofen
- Several studies have indicated its effect on striated muscle is poor.21
- Adverse effects include hepatotoxicity, weakness, and sedation.
- Should not be used in patients with hepatic dysfunction
- Should be used with caution in patients with cardiac disease