Bias within economic evaluations – the impact of considering the future entry of lower-cost generics on currently estimated incremental cost-effectiveness ratios of a new drug

Figures & data

Figure 1 Undiscounted (A) and discounted (B) price of the two drug comparators over the model’s time horizon when the comparator drug is already a generic drug.

Notes: I: overestimation of the lifetime cost of the new drug; P₀: daily price of the generic comparator drug; P₁′: daily price of the new drug when considering the future introduction of generic versions of the molecule; P₁: daily price of the new drug when ignoring the future introduction of generic versions of the molecule; T₁*: timing of the introduction of generic versions of the new drug.

Figure 2 Undiscounted (A) and discounted (B) price of the two drug comparators over the model’s time horizon when both drugs are patented molecules.

Notes: I: overestimation of the lifetime cost of the new drug; II: overestimation of the lifetime cost of the comparator drug; P₀′: daily price of the comparator drug when considering the future introduction of generic versions of the molecule; P₀: daily price of the comparator drug when ignoring the future introduction of generic versions of the molecule; P₁′: daily price of the new drug when considering the future introduction of generic versions of the molecule; P₁: daily price of the new drug when ignoring the future introduction of generic versions of the molecule; T₀^*: timing of the introduction of generic versions of the comparator drug; T₁^*: timing of the introduction of generic versions of the new drug.

Table 1 Incremental cost of dabigatran etexilate compared to generic warfarin when ignoring and when considering the future introduction of generic dabigatran etexilate

Comparator	Cost (undiscounted), CAN$	Cost (discounted at 5%), CAN$
Generic warfarina	6,462	4,266
Ignoring the future entry of generic dabigatran etexilate
Dabigatran etexilate	17,685	11,675
Incremental cost compared to generic warfarin	11,223	7,409
Considering the future entry of generic dabigatran etexilate
Dabigatran etexilate	9,998	7,687
Incremental cost compared to generic warfarin	3,356	3,421

Note:

a Costs include international normalized ratio monitoring costs.

Table 2 Overestimation of the incremental cost based on different times to introduction of generic versions

Time to the introduction of generic versions	Overestimation of the ICER, CAN$ (%)
	Generic to brand-name drug cost ratio: 18%	Generic to brand-name drug cost ratio: 40%
5 years	5,588 (75.4)	4,089 (55.2)
6 years	4,949 (66.8)	3,621 (48.9)
7 years	4,361 (58.9)	3,191 (43.1)
8 years	3,822 (51.6)	2,797 (37.7)
9 years	3,330 (44.9)	2,437 (32.9)
10 years	2,884 (38.9)	2,110 (28.5)
11 years	2,479 (33.5)	1,814 (24.5)
12 years	2,116 (28.6)	1,548 (20.9)
13 years	1,790 (24.2)	1,310 (17.7)
14 years	1,502 (20.3)	1,099 (14.8)
15 years	1,247 (16.8)	912 (12.3)

Notes:

Table 2 only shows overestimations with future costs discounted at a 5% discount rate; an undiscounted overestimation would be greater. Values are shown as absolute and relative to the ICER estimated when ignoring the future introduction of generic dabigatran etexilate.

Abbreviation: ICER, incremental cost-effectiveness ratio.

Table S1 Base case parameters for the case study

Model parameter	Base case and two-way sensitivity analyses estimate	Source (reference)
Demographic characteristics
Male	60%
Age at diagnosis	70 years old
Survival data
Monthly mortality rate	Age- and sex-specific all-cause mortality rate	1
Costing parametera
Cost of brand-name dabigatran etexilate	CAN$3.20 per day	2
Cost of warfarin	CAN$0.06 per day	2
INR monitoring cost, yearly	CAN$405.16	2
Generic dabigatran etexilate
Time to introduction of generic versions	7 years (5 years–15 years)	2,3
Generic to brand-name cost ratio	25% (18%–40%)	4,5

Note:

a All costs are in 2010 Canadian values.

Abbreviation: INR, international normalized ratio.