An investigation of package inserts was performed for 794 oral prescription drugs, in order to assess the package inserts as an information resource regarding the timing of drug intake which is important for rational usage of medicine. As a result, the number of package inserts which described the proper timing of drug intake was only 157 (20%). The timings of drug intake could be classified into five categories, i.e., before a meal, immediately before a meal, immediately after a meal, after a meal and between meals (at a hunger state). Evidence for the timing of drug intake is written in only 9% of the package inserts. However, such evidence could be provided from interview forms and original articles for 24% and 44% of the drugs, respectively. Furthermore, most of the evidence for the timing of drug intake (94%) was shown to be meant for either the appropriate onset of therapeutic actions (58%) or the prevention of adverse reactions (36%). On the other hand, there was a clear tendency that more evidence is provided for drugs which were put on market more recently. From these results, the information only from package inserts was found to be insufficient for the rational usage of medicine and that the timing of drug intake should thus be explained to patients based on additional investigation from interview forms and original articles as described in this study in order to achieve an improved efficacy and safety of drug administration.
