Potential cost effectiveness of therapeutic drug monitoring (TDM) of protease inhibitors in the treatment of HIV

Abstract

Objectives: To quantify the value of TDM of dual PIs (IDV and RTV 800/100 bid) as cost per additional person with undetectable viral load<50 copies per mL (UVL) at 6 months from a government payer perspective. Methods: We developed a theoretical model (DATA 3.5) to estimate the costs and outcomes of usual care with genotyping (UC) compared to genotyping + TDM in HIV+ and ART experienced patients beginning a new regimen. Based on previous studies, we estimated a 20% difference in the proportion of patients achieving UVL who had therapeutic vs subtherapeutic PI concentrations. Approximately 15% to 40% of patients receiving dual PIs have subtherapeutic concentrations (STC). We assumed 15% of TDM and UC would switch the PI at 3 months due to adverse events (AE) and cost an extra CDN$238.06 in physician visits and labs. TDM patients had a minimum of one peak/trough measurement per PI, costing CDN$100. We assumed TDM patients with STC required 3 peak/trough assays per PI, two physician visits and a 20% increase in indinavir dose to attain therapeutic concentrations. Results: If at least 15% of the population had STC with dual PI use, and 85% tolerated the TDM dose increase, management with TDM would cost an additional CDN$178 per patient (UC:$6954 vs TDM: $7132) and achieve UVL in 1 additional patient per 100 (UC: 74.5$109 and achieve UVL in 8 additional patients per 100 by 6 months. Conclusions: If TDM proves to be efficacious, knowing the cost of implementing TDM in Canada will be as equally as important. Given this preliminary data, TDM potentially provides an important improvement at a reasonable additional cost