Canadian cost-effectiveness analysis of solifenacin compared to oxybutynin immediate-release in patients with overactive bladder.

ABSTRACT

OBJECTIVE: To estimate the cost effectiveness of solifenacin 5 mg/day compared to oxybutynin immediate-release (IR) 15 mg/day in patients with overactive bladder, from the perspective of the Canadian healthcare (payer) system. RESEARCH DESIGN AND METHODS: A Markov model was adapted to estimate the incremental cost per quality-adjusted life-year (QALY) of solifenacin and oxybutynin IR over a 1-year time horizon, based on efficacy and discontinuation data from the Canadian VECTOR (VEsicare in Comparison To Oxybutynin for oveRactive bladder patients) study. In the model, patients who discontinued treatment were offered tolterodine extended release 4 mg/day as second-line. Model robustness was tested using various sensitivity analyses. Utility values were derived from published literature; incontinence pads were included in a secondary analysis. RESULTS: In the base-case analysis, total costs over 1 year were CAN$695 and CAN$550 in the solifenacin and oxybutynin IR groups, respectively. When including incontinence pad costs, there was an incremental saving of CAN$1,831 per patient with solifenacin. Solifenacin was associated with an incremental QALY gain of 0.01 over 1 year. In the base-case analysis without incontinence pads, the incremental cost-utility ratio for solifenacin was CAN$14,092. Probabilistic analyses showed no overlap in the 95% confidence intervals for total costs or QALYs with or without incontinence pads. Solifenacin was cost effective in >90% of cases, based on a willingness-to-pay threshold of CAN$50,000 per additional QALY, irrespective of whether pad costs were included in the model. The most influential variables were the discontinuation rates and the cost of incontinence pads. Limitations of the analysis relate mainly to the fact that data in the VECTOR study were collected using a direct questioning approach, which might have increased the reporting of dry mouth. CONCLUSIONS: Solifenacin 5 mg/day was a cost-effective treatment compared with oxybutynin IR 15 mg/day. TRIAL REGISTRATION NCT00431041 (of the VECTOR study, upon which the analysis in this paper was based).