Therapeutic drug monitoring - Do the improved outcomes justify the costs?

In the 30 years that therapeutic drug monitoring (TDM) has moved from an ab stract consideration to a routine intervention, issues remain over justifyi ng the benefits in the light of the ever-increasing competition for budgeta ry resources. Resolving the issues is constrained by various methodological concerns. These include considerations such as: (i) the changed environmen t of knowledge and practice during the generation in which TDM has been use d and evaluated; (ii) the predominance of studies using system-related rath er than patient-centred outcomes; (iii) using a timeframe for analysis that is too short; (iv) a lack of rigour in many of the pharmacoeconomic analys es; and (v) excessive use of a site-specific rather than a societal perspec tive. 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 immunosuppres sive, some antineoplastic, some psychotherapeutic and some anticonvulsant d rugs. In these situations, safe and humane practice considers TDM a necessi ty 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 inter vention may have become excessive in the light of today's knowledge base of practitioners.