Instructions on laboratory monitoring in 200 drug labels

Monitoring drug treatment is important to assess the therapeutic effects and to prevent adverse drug reactions. Unfortunately, the clinical evidence for monitoring is often missing. To attain evidence-based laboratory monitoring and to improve patient safety it is mandatory for the clinical chemist to develop effective and rational methods for monitoring. The legal source for this evidence-based information is the drug label. We analysed frequency, nature, and applicability of instructions on laboratory monitoring described in 200 drug labels.

The applicability of instructions was assessed with an adapted Systematic Information for Monitoring score. Seven items of information were evaluated: why to monitor, what to monitor (essential), when to start or stop monitoring, how frequently to monitor, critical value (essential) and how to respond (essential). Each item scored one point when information was described specifically, otherwise the score was zero. Instructions were applicable if all three essential items scored.

In 131 drug labels, 566 instructions on laboratory monitoring were identified, an average of 2.8 per drug label. Kidney, liver, electrolyte, and drug monitoring were important biomarker categories (71%). The median applicability score was 2.1 (0-6) and 95 (17%) instructions were applicable. Six determinants were associated with applicable instructions: kidney (OR 7.0; 95% CI 4.4-11.3), creatine phosphokinase (4.5; 1.5-13.6), drug selection (6.8; 4.0-11.7), dose adjustments (2.4; 1.5-3.7), year on the market 2000-2007 (2.6; 1.1-6.1) and statins (4.8; 2.5-9.0).

Drug labels frequently describe instructions on laboratory monitoring, but these are ambiguous and incomplete and clinical applicability for the professional is limited.