Similar-appearing press-through package (PTP) sheets (also known as blister packs) that contain different medicines may result in incorrect medication due to confusion errors. To evaluate the significance of this problem and to identify the factors that may lead to such errors, we conducted a questionnaire survey for pharmacists. Three hundred and eighty-two pairs of PTP sheets with similar appearance were included in the questionnaire. Factors related to color (sheet color at the front of the sheet 90.9％, color of tablet/capsule 57.1％, print color at the front of the sheet 45.9％) were most frequently selected as infiuencing the perceived similarity of the reported pairs, followed by tablet/capsule shape (46.2％), sheet size (32.4％), and mark and character positioning on sheets (6.8％). In the pairs of similar PTP sheets, pairs manufactured by the same pharmaceutical company accounted for 15％. The frequency of confusion errors or near-errors due to similar appearance of PTP sheets was highest at the time of collecting PTP sheets from the medicine shelf and returning the sheets to the medicine shelf, followed by the time of inspection of prepared medicines and medication instructions. The questionnaire results also indicate that patients themselves can confuse similar PTP sheets and take the wrong medicine. Further quantitative studies are needed to clarify the key factors that cause confusion errors due to similar appearance and to identify potential remedial measures.
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