Information comparison of the effects of drugs on laboratory tests in drug labels and Young’s book

Background: The effects of drugs on laboratory tests may lead to misinterpretation of laboratory data, unnecessary tests, higher costs and missed diagnoses. This study compared the information on drug-laboratory effects (DLE) described in 200 drug labels with that in Young’s book. Methods: Information on DLE was searched in the drug labels of 200 frequently prescribed drugs using the keywords ‘interfer*’, ‘influence’, and ‘laborator*’. This information was compared with the information in Young’s book. Each item of information scored 1 point if it was specific and exactly the same. Primary outcome was the percentage of DLE with completely the same information. Results: In 23 (11.5%) of the 200 drug labels 83 DLE were described. Most DLE were described in drug labels of contraceptives (71%) and antibacterials (15%). The most frequently affected laboratory tests were adrenal gland (17%), urine tests (15%), liver tests (10%) and renal function tests (10%). Comparison of six DLE with Young’s book was not possible because the information was not described in the book. Twelve (14.5%) DLE of the information in the drug label was identical to that in Young’s book. Detailed information about nature of the effect, strength of the effect and body fluid was not described in the drug labels. Conclusions: In a limited number of DLE in the drug labels the information was the same as in Young’s book. Overall, the information on DLE provided in drug labels is unclear, inconsistent and incomplete and does not support healthcare professionals in making evidence-based monitoring decisions.