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

Risebrough, N. and Phillips, E.J. (2001) Potential cost effectiveness of therapeutic drug monitoring (TDM) of protease inhibitors in the treatment of HIV. In: 2nd International Workshop on Clinical Pharmacology of HIV Therapy, 2 - 4 April 2001, Noordwijk, The Netherlands.


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% vs TDM: 75.6%). If AE drop-out was reduced to 7.5% with TDM guided dose reduction, TDM strategy would cost an additional CDN$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.

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