OBJECTIVES : Generic imatinib mesylate (IM) is an effective therapy and is the least costly option for patients with chronic myeloid leukemia (CML). Therapeutic drug monitoring (TDM) has the potential to improve the adherence to IM therapy allowing patients to stay in remission and avoid switching to more toxic and expensive tyrosine kinase inhibitors (TKI). The objective of this study was to determine the cost effectiveness of TDM for generic IM administration in CML patients.

METHODS : We built a Markov model depicting multiple CML states including normal IM dose (400mg), IM dose escalation (600mg), secondary TKI and post TKI phases to calculate an incremental cost effectiveness ratio (ICER) for TDM in reference to non-TDM monitoring . We assumed all patients were followed by molecular monitoring. Transition from normal IM dose to either dose escalation or secondary TKI was determined by the patient response and known plasma concentration (Cp) of IM. The response and Cp were a function of adherence. CML related healthcare costs and quality adjusted life years (QALY) were calculated over a lifetime. Probabilistic sensitivity analyses conditional on multiple levels of generic IM price were performed.

RESULTS : TDM was associated with higher cost ($3,344) and an increase in QALY (0.085) compared to non-TDM with an ICER of $39,126 per QALY gained. The ICER was sensitive to the dose-Cp association and the price of IM. TDM achieved a 60% likelihood of being cost-effective at willingness to pay (WTP) threshold $100,000 per QALY gained at the current price. The acceptability at $100,000/QALY increased to 66% when the price of generic IM was reduced by 50%.

CONCLUSIONS : TDM is likely cost-effective compared to non-TDM. However, the likelihood of acceptance of TDM was less than 70% at the conventional level of the WTP, $100,000 per QALY gained.