The prophylaxis module reflects the incidence of events observed in the clinical trials; VTE, PE and prophylaxis-related bleeding for rivaroxaban versus enoxaparin in THR and TKR, respectively (Table 1).
An analysis of the event rate of rivaroxaban versus enoxaparin revealed that the incidence of major bleeding (major bleeding was defined as bleeding that was fatal, was into a critical organ [e.g., retroperitoneal, intracranial, intraocular or intraspinal], required re-operation, or clinically overt extra-surgical-site bleeding associated with a fall in hemoglobin of 20 g/l or more, calculated from the day 1 postoperative baseline value, or requiring infusion of two or more units of whole blood or packed cells) and PE events in each study was either low or very similar, with no statistically significant difference shown. The baseline analysis conservatively assumed parity between comparators for events showing no statistically significant difference, with the impact of using the observed event rates tested in sensitivity analyses. The model assumes that the cohort had the same risk of fatal bleeding following prophylaxis-related bleeding, regardless of the prophylaxis arm.
The economic analysis assumes that patients with an asymptomatic venous thromboembolic event incurred no costs or disutility, reflecting the silent nature of the condition. Nevertheless, the model applies an extension to the clinical trial results representing the risk of patients developing a symptomatic event at a later time.
The post-prophylaxis module extends the risk of symptomatic VTE up to 90 days post-surgery by extrapolating asymptomatic VTE to symptomatic VTE based on a study by Quinlan et al. It was assumed that a proportion of patients with asymptomatic VTE, ranging from 4.7% (TKR) to 20.5% (THR), would develop a symptomatic event between the end of the clinical trial and the first 90 days. In the absence of data differentiating between comparators beyond the clinical trial duration, the economic model assumes the same risk of progression from asymptomatic to symptomatic VTE for both prophylaxis strategies.
Expert Rev Pharmacoeconomics Outcomes Res. 2011;11(5):601-615. © 2011 Expert Reviews Ltd.
Cite this: Cost–Effectiveness of Rivaroxaban Versus Heparins for Prevention of Venous Thromboembolism After Total Hip or Knee Surgery in Sweden - Medscape - Oct 01, 2011.