Cost–Effectiveness of Rivaroxaban Versus Heparins for Prevention of Venous Thromboembolism After Total Hip or Knee Surgery in Sweden

Lars Ryttberg; Alex Diamantopoulos; Fiona Forster; Michael Lees; Anina Fraschke; Ingela Björholt


Expert Rev Pharmacoeconomics Outcomes Res. 2011;11(5):601-615. 

In This Article

Costs & Resource Use

The unit costs included in the model are reported in Table 3. Prophylaxis-related monitoring or administration costs are only incurred post-discharge. With regards to LMWH administration, the analysis assumes that 10% of patients require nurse assistance for injection[7] and that such assistance is required for 3 days, even if treatment is indicated for a longer time period, because patients may learn to self-inject as they get some practice and start to regain their normal strength after the operation. The unit cost of nurse-administered prophylaxis was adjusted from published data.[21,22] Treatment with enoxaparin and dalteparin should be initiated on the day preceding surgery. However, dalteparin may also be started peri- or post-operatively.[102] Based on a structured interview in Swedish orthopedic clinics, it was assumed that 24% of patients receiving LMWH will require one additional preoperative hospital night stay [Ambring A, Björholt I, Data on File]. A total of 15 orthopedic clinics were invited to participate in the study and the head of the department was asked to appoint a nurse to represent the clinic. Two clinics declined to take part, and another three were excluded because the nurse was unavailable. Participating clinics had 22–48 beds and the clinics were well distributed across Sweden.

The costs of diagnosis and treatment of venous thromboembolic events were obtained from a study by Lundkvist et al.[6] It was assumed that the cost of treating recurrent VTE is the same as treating patients who developed their first DVT post-discharge. Lundkvist et al. also reported the cost of acute PTS (first quarter) and chronic PTS (subsequent quarters).[6] In this model, it was assumed that the difference between acute and chronic PTS was the cost of diagnosis. The cost of PTS treatment in the model was SEK6513, assuming that the quarterly costs are repeated evenly. The model combines costs of diagnosis and treatment for the first year and only used the cost of treatment in subsequent years.

Because of a lack of robust national unit cost data and clinical guidelines, the cost of diagnosing CTPH was estimated based on a test and procedures algorithm published in the European Society of Cardiology guidelines for the diagnosis and treatment of pulmonary arterial hypertension.[23] All unit costs for this input were identified from UK National Health Service reference costs and then converted to Swedish crowns (SEK; exchange rate: GBP£1 = SEK12.6253). The cost of treating CTPH was based on costs reported in a cost–effectiveness analysis for pulmonary artery hypertension in Australia;[24] the cost value was converted to SEK and inflated from 2001 prices.

All related costs and health outcomes were discounted at 3% in the base case analysis. Costs were inflated to 2008 levels using the Swedish consumer price index.[103]

The robustness of the economic model to changes in key parameters was tested by one-way sensitivity analysis. Moreover, parameter uncertainty was explored by probabilistic sensitivity analysis (PSA) using 1000 simulations. PSA involved a statistical distribution fitted to appropriate parameters in the model replacing its deterministic definition. These distributions reflected uncertainty around the model input; for event risk, transition probabilities and utility scores a beta-distribution is used; whereas for cost parameters the model assumes a gamma-distribution. Table 4 presents details of the sampled parameters, the respective measures of dispersion and distributions used.


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