Objective: To determine whether dose titration based on therapeutic response is superior to standard dosing of oral trospium chloride in patients with neurogenic detrusor overactivity and, moreover, to investigate the possible underlying causes of differences in efficacy at equal doses in some patients.
Patients and methods: Using a double-blind approach, two groups (standard dose and adjustable dose) with a total of 80 patients were treated with trospium chloride coated tablets for a period of 3 - 5 weeks. Treatment duration and daily doses varied depending on change ofurodynamic parameters defined as therapeutic response. In Week 1, both groups started on 45 mg/day (3 x 15 mg). In the adjustable dose group, it was permissible to increase the daily dose to 90 or 135 mg/day depending on the urodynamic treatment response. In contrast, doses remained unchanged in the standard dose group although a need for dose adjustment had been recognized under the double-blind conditions. Therapeutic response was defined as improvement of at least two of the following three urodynamic parameters: bladder compliance 2 20 ml/cmH20, maximum cystometric capacity > 250 ml and maximum detrusor pressure < 40 cmH20. Changes in individual urodynamic parameters were defined as secondary efficacy variables. Primary and secondary parameters were assessed by comparing baseline values with those at the end of treatment. Therapeutic response was analyzed by using the Fisher-Yates test, and the Mann-Whitney U-test was used for secondary parameters. Trospium plasma concentration was measured to assess patient's compliance and as a tool to elucidate possible factors influencing treatment efficacy. Safety and tolerability were evaluated based on withdrawal rates and adverse events.
Results: Both dose groups had comparable baseline characteristics. Therapeutic response was achieved in 58% of patients in the adjustable dose group (ADG) and in 72% of those in the standard dose group (SDG, p -0.23). Clinically relevant increases in maximum cystometric capacity and bladder compliance were observed, and there was a clear decrease in detrusor pressure. After Day 7, the daily dose was increased in 52.8% of all patients in the adjustable dose group and (seemingly) in 32.5% of those of the standard dose group. Further dose escalation after Day 14 was assessed as necessary in 15% of the standard dose group and 22% of the adjustable dose group. The main changes in urodynamic parameters occurred during the first 7 days of treatment, but in some patients it takes a longer time. No statistically significant differences between plasma trospium chloride levels in the two dose groups were observed at any time, but increase of plasma concentration with higher doses became obvious when patients were differentiated to individual dose stages. In both groups, the most common treatment-related adverse event was dry mouth (ADG 35%, SDG 37%), which never led to discontinuation of treatment. Rates of other adverse events such as dry skin, dysopia, increased heart rate and gastrointestinal disorders were much lower.
Conclusion: Generally, in patients with neurogenic detrusor overactivity daily doses of 45 mg trospium chloride can be considered as being the standard dose, and dose adjustment, e.g. due to increased body weight, might usually not be necessary. However, increased daily doses of up to 135 mg appear to be safe when prescribed in individual patients less responsive to the drug.