Influence of a latent period in QALY analysis: pilot study of intrathecal drug delivery systems for chronic non-malignant pain.

Cost effectiveness of a treatment is an important factor in decision making in the United Kingdom. Preceding most interventional health care treatments there is a waiting period between decision and procedure where health care costs may be lessened. Intrathecal drug delivery systems (IDDS) are a recognised pain management therapy for chronic non-malignant pain. To our knowledge, the period of time between being placed on a waiting list for IDDS and the implant (latent period) has not been taken into consideration for cost effectiveness analysis. A retrospective longitudinal analysis of all pain related costs for a period no less than 4 years was undertaken by assessment of medical records of 12 consecutive patients implanted with IDDS for chronic non-malignant pain. The total cost of patient care for 2 years before latent, the latent period itself and 2 years after the implant of an IDDS was computed, according to the National Health Service tariff. An EQ-5D questionnaire was filled by all participants before and after IDDS implant. Total costs were converted to cost per day for comparison with latent period. The average duration of the latent period was 263 ± 176 days (range 3-489). The cost of conventional treatments during the pre-implant phase excluding the latent period was significantly higher (M = £ 5,005.86, SE = £ 918.56) compared with the costs of the same phase including the latent period (M = £ 4,086.35, SE = £ 959.09, t(11) = 2.23, p = 0.05, r = 0.56). The cost per day changed significantly over the different periods (χ(2)(2) = 24.00, p < 0.05). The variability and significantly lower costs of the latent period may influence cost effectiveness evaluations and consequently decision making, if not considered. Further studies analysing the influence of a latent period on the cost effectiveness of other treatments are warranted.