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

Figures & data

Figure 1.  Schematic of Markov model. Diagram adapted from Speakman et al.15.

Table 1.  Utility values used in the Markov model. Adapted from Kobelt et al.14*.

	Health states
	1	2	3	4	5	6 (drop-out)
OAB symptoms/day†	<9	≥9, <12	≥12, <15	≥15, <18	≥18	N/A
Baseline distribution
Solifenacin	10%	6%	41%	32%	10%	0%
Oxybutynin IR	11%	3%	38%	38%	11%	0%
Utilities	0.742	0.712	0.676	0.640	0.598	0.674‡
Pads used/day§	0.67	1.39	2.20	3.05	4.66	1.34‡

*Based on a self-administered, willingness-to-pay survey in OAB patients, which demonstrated that incontinence episodes and frequency of micturitions correlated with EuroQol scores16.

†Composite score of (micturition episodes/day) + (incontinence episodes/day).

‡Weighted average of 52 week distribution excluding the drop-out state.

§Based on pad use data [Data on file, Astellas] from two clinical studies17,18.

Table 2.  Unit costs used in each analysis.

Product	Units	Unit cost (CAN$) (except for wholesaler mark-up as %)
Medications
Oxybutynin IR	5 mg	0.1973*
Tolterodine	4 mg	1.8200*
Solifenacin	5 mg	1.6400†
Mark-ups
Dispensing fee	per 4 week cycle	7.00*
Wholesaler	per 4 week cycle	8.00%*
Adult incontinence pads
Tena medium adult pads‡	1 pad	1.4000§

*Ontario Drug Benefit Formulary and Comparative Drug Index (accessed February 2009).

†Astellas Pharma Canada Inc.

‡Tena is a registered trademark.

§Classic Care Pharmacy Price List, Pack of 64 (2009).

Table 3.  Sensitivity analyses performed.

Sensitivity analysis	Base case	One-way sensitivity analysis
		Range		Distribution
		Low	High	Mean (SD)
Unit cost per pad	0 CAN$	CAN$1.40	CAN$1.80	Lognormal
				CAN$1.40 (0.78) (for probabilistic analysis with pads only)
Cost of tolterodine ER 4 mg provided to drop-outs	1.82 CAN$	CAN$0	Not applicable	Normal
				CAN$0.910 (0.091)
Utility for drop-outs	See Table 1	−10%	Health state 2	Not applicable
Utility for all health states	See Table 1	−10%	+10%	Beta (α = 2, β = 3)

Figure 2.  Distribution of patients in health states 1–5 after treatment with solifenacin 5 mg/day or oxybutynin IR 15 mg/day, estimated over a 1-year period. See Table 1 for the distribution at baseline.

Table 4.  Summary of costs, QALYs, and ICUR results at 1 year with solifenacin 5 mg/day and oxybutynin IR 15 mg/day, with and without the cost of incontinence pads. Costs are in CAN$.

Treatment	Total costs ($)	Incremental costs ($)	Total QALYs	Incremental QALYs	Cost-utility ($)	ICUR ($)
Without incontinence pads
Solifenacin	695.10	145.24	0.696	+0.010	999	14,092
Oxybutynin	549.95		0.686		802
With incontinence pads
Solifenacin	2,555.58		0.696	+0.010	3,672	Dominant*
Oxybutynin	4,386.63	1,831.04	0.686		6,398

ICUR, incremental cost-utility ratio; QALY, quality-adjusted life-years.

*Defined as an intervention which has lower costs and the same or greater benefits than an alternative.

Figure 3.  Cost-effectiveness acceptability curve of solifenacin 5 mg/day versus oxybutynin IR 15 mg/day, with and without the cost of incontinence pads.

Table 5.  Summary of results of sensitivity analyses, in which the cost of incontinence pads was excluded from the base case (costs in CAN$).

Sensitivity analyses	Model inputs		ICUR
	Base case ($)	Sensitivity analysis ($)
Unit cost per pad	0	1.40	Dominant
		1.80	Dominant
Tolterodine ER provided to drop-outs	1.82	0	$30,149
Utility for drop-outs	See Table 1	−10%	$5,265
		Health state 2	$318,117
Utility for all health states	See Table 1	−10%	$5,850
		10%	Dominant

ICUR, incremental cost-utility ratio.

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