TDM and adherence

Simon Collins, HIV i-Base

Perhaps the least effective use for drug level assays is for assessing patient adherence. Aside from overtones of ‘big brother’ surveillance, random testing only provides information about the ‘last dose’, and can be complicated by ‘white coat adherence’ – where a patients takes medication on the days s/he know they have a doctors appointment.

Reassuringly a similar reaction came from both clinicians and patient advocates in the audience although several other presentations detailed thorough and complicated methodologies from deriving adherence data from random sampling.

Nevertheless, John Urquart, Professor of Pharmco-epidemiology, Maastricht University, provided a plenary, aimed at establishing both the importance of adherence for successful treatment and many of the practical issues involved for doctors. Cross-referencing with adherence studies from other disease areas, HIV patients are actually remarkably compliant – a fact not attributable to the severity of the illness. Several studies in other disease areas show that success rates for adherence are apparently not related to the severity of symptoms or risk of future illness and studies for glucose intolerance, epilepsy and pain management were cited. intolerance, epilepsy and pain management were cited.

A recent article in the BMJ by Judith Jones showed that adherence rates drop to 40% after six months for patients prescribed other ‘lifelong’ medications. Diaries, histories and even TDM can overestimate adherence compared to electronic monitoring (MEMS). However, accurate feedback from patients to their doctor about actual adherence, will require allocating time to adherence issues in every consultation.

Doctors developing this area would also do well to bear in mind Dr Urquart opening remarks in his lecture, that pointed out that one of the key obstacles faced in improving adherence was the fact that ‘doctors strongly believe that their patients do what they tell them’. [1]


  1. Urquhart J – The Challenges of Patient Non-Compliance with Antiretroviral Drug Regimens. Plenary 2. First International Workshop on Clinical Pharmacology, 30-31 March 2000. Noordwijk, Netherlands.

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