Therapeutic drug monitoring: do the improved outcomes justify the costs?

In the 30 years that therapeutic drug monitoring (TDM) has moved from an abstract consideration to a routine intervention, issues remain over justifying the benefits in the light of the ever-increasing competition for budgetary resources. Resolving the issues is constrained by various methodological concerns. These include considerations such as: (i) the changed environment of knowledge and practice during the generation in which TDM has been used and evaluated; (ii) the predominance of studies using system-related rather than patient-centred outcomes; (iii) using a timeframe for analysis that is too short; (iv) a lack of rigour in many of the pharmacoeconomic analyses; and (v) excessive use of a site-specific rather than a societal perspective. Current observation suggests that the greatest benefit of TDM accrues from targeted or specialty populations: those with severely decompensated renal function, those at the extremes of age, and those using immunosuppressive, some antineoplastic, some psychotherapeutic and some anticonvulsant drugs. In these situations, safe and humane practice considers TDM a necessity without respect to cost. But for many routine situations with drugs for which TDM has commonly been used in the past, present reliance on the intervention may have become excessive in the light of today's knowledge base of practitioners.