Hypothesis / aims of study
Following a spinal cord injury (SCI), disruption to the neural pathways to the bladder can result in Neurogenic Lower Urinary Tract Dysfunction (NLUTD). This can lead to reduced bladder capacity, neurogenic detrusor overactivity (NDO), incontinence and potential damage to the upper tracts. The first line treatment is anti-muscarinic medication (AM), however this can be associated with intolerable side effects such as dry mouth, blurred vision and constipation and has been implicated in the development of dementia in older patients. Additionally, AMs are contra-indicated in patients with glaucoma. A ß3 agonist, mirabegron has become available for treatment of OAB and NDO. We have been offering mirabegron (25 or 50 mg) as an alternative to AMs where the patient can no longer take them or as an additional treatment where AMs or botox are not effectively managing NDO. We present the effects of mirabegron treatment on urodynamic parameters in patients with NLTUD following SCI.
Study design, materials and methods
92 patients who had been prescribed mirabegron were identified from our records. 24 patients (15 male and 9 female) had undergone urodynamics before and after treatment with mirabegron. The average age of the patients was 51 years (range 23 – 82 years). 4 were voiding on urge, 9 performing intermittent catheters (ISC), 2 doing ISC and voiding, and 9 had a supra-pubic catheter (SPC). Maximum Cystometric Capacity (MCC) and Maximum Detrusor Pressure (MDP) were compared before and after treatment. Patients were classified into 3 groups; Group 1 - No previous treatment n=6, Group 2 - Mirabegron replaced usual treatment n=10, and Group 3 - Mirabegron given in addition to usual treatment n=8.
Results
Of the 92 patients who were prescribed mirabegron, 9 stopped due to inefficacy, 4 due to side effects (headache, constipation) and 1 was contra-indicated due to high BP. There was a statistically significant reduction in mean (±SD) MCC in patients in Group 2 who took mirabegron as an alternative to their usual treatment (390 (±250) ml to 244 (±155) ml). There was no significant change in MCC or MDP in the other 2 groups, however, there were trends towards increased bladder capacity and decreased in MDP.
Interpretation of results
Urodynamic results showed that in patients with NLUTD, mirabegron may be effective at increasing bladder capacity and reducing detrusor pressure when used in combination with other treatments including anti-muscarinic medication and botox (Group 3). This is in agreement with previous studies that have shown that mirabegron is effective in combination with anti-muscarinic medication and botox. However, we have shown that when used as an alternative to these treatments there is a decrease in bladder capacity (Group 2).