Objective: To estimate the economic impact of using low dose polyethyene glycol 3350 (PEG 3350) plus electrolytes (PEG+E) compared with lactulose in the treatment of idiopathic constipation in ambulant patients. Design and perspective: This was a decision analytic modelling study performed from the perspective of the UK's National Health Service (NHS). Methods: The clinical outcomes from a previously reported single-blind, randomised, multicentre trial were used as the clinical basis for the analysis. These data were combined with resource utilisation estimates derived from a panel of six general practitioners (GPs) and four nurses enabling a decision model to be constructed depicting the management of idiopathic constipation with either PEG+E or lactulose over 3 months. The model was used to estimate the expected 3-monthly NHS cost of using either laxative to manage idiopathic constipation. Main outcome measures and results: The expected 3-monthly NHS cost of using PEG+E or lactulose to manage idiopathic constipation was estimated to be pound85 and pound96 per patient, respectively (1999/2000 values). However, significantly more patients were successfully treated with PEG+E than lactulose (53% versus 24%; p < 0.001) at 3 months. GP visits were the primary cost driver for both PEG+E- and lactulose-treated patients, accounting for 56% (2.9 visits) and 73% (4.4 visits), respectively, of the expected NHS cost per patient at 3 months. Among PEG+E-treated patients, the acquisition cost of PEG+E was the secondary cost driver, accounting for 30% of the expected NHS cost per patient at 3 months, whereas the acquisition cost of lactulose accounted for only 11% of the expected NHS cost per lactulose-treated patient. District nurse domiciliary visits accounted for 4% and thyroid function tests for 2%. The costs of switched laxatives, concomitant laxatives, and gastroenterologist and colorectal surgeon visits collectively accounted for up to 9% of the total. Conclusions: The true cost of managing idiopathic constipation is impacted on by a broad range of resources and not only laxative acquisition costs. This study indicated that managing idiopathic constipation with PEG+E instead of lactulose reduces the expected 3-monthly NHS cost by pound11 per patient. Moreover, using PEG+E instead of lactulose is expected to double the percentage of patients successfully treated at 3 months. Hence, PEG+E is a dominant treatment compared with lactulose. This suggests that the decision to use either PEG+E or lactulose to treat idiopathic constipation should be based on efficacy, safety, patient preferences and total management costs, and not drug acquisition costs.
