Background: Medical tablets and capsules are superior with regard to portability and are the most common dosage form in Japan. However, their large size often results in difficulties during ingestion, sometimes leading to reduced medication adherence. Objective: The authors used postmarketing surveillance data to determine the threshold size of medical tablets and capsules that patients feel are too large to ingest. Patients and Methods: The marketing specialists of Toho Pharmaceutical Co., Ltd. collected opinions of patients and medical workers (November 2014–April 2016). Regarding 709 reports from patients stating that the tablet or capsule for too large for ingestion, a dataset was prepared from package inserts of the reported drugs. Two analyses were conducted: histogram analysis of size distribution and geometric analysis using linear approximation. Six indices of tablet/capsule size were considered: length; length + width; length + width + depth; length × width; length × width × depth; and weight. Results: Histogram analysis revealed that length + width + depth is an excellent index of tablet/capsule size, and negative reports on tablet/capsule size drastically increase when this index is ≥21 mm. Geometric analysis using linear approximation also revealed similar results. Conclusion: The threshold size of tablets/capsules that patients feel are too large to ingest is length + width + depth = 21 mm. Therefore, when designing or altering tablets/capsules, if length + width + depth is ≥21 mm, the drug should be scored, split into smaller doses, or redesigned as an orally disintegrating formulation.
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