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In the European Union, the European Medicines Agency (EMA) released the \u201c<jats:italic toggle=\"yes\">Guideline on the Investigation of Bioequivalence<\/jats:italic>.\u201d The bioequivalence (BE) of the generic (tested, T) versus original (reference, R) product should be confirmed by obtaining a 90% confidence interval (CI) for the T:R ratio of each of the 2 decisive pharmacokinetic parameters, namely, the area under the curve (AUC) between 90.00% and 111.11%. A similar approach (90.00%\u2013112.00%) for AUC was adopted by the Canadian Agency for Drugs and Technologies in Health (CADTH) for NTIDs; however, the US Food and Drug Administration is still based on classic acceptance criteria: 90% CI between 80.00% and 125.00% but with special requirements of BE testing. A discussion about long-expected global consensus was performed in this study based on the literature concerning BE testing in the case of NTIDs. The narrow acceptance criteria reduce the potential mean difference in bioavailability between generic and original products by a few percent. To identify this problem, special attention has been paid to switching drugs (generic\u2013generic, original\u2013generic) and therapeutic drug monitoring after conversion (TDM). There is no global consensus on the acceptance criteria for the BE of generic drugs; therefore, consensus and harmonization are strictly necessary. This study presents a review of the generic drug market and its classification by manufacturers, drug agencies, and dates of marketing authorization. Guidelines for TDM optimization (during switching\/conversion) have been proposed. Physicians and clinical pharmacists should pay special attention to switching immunosuppressive drugs between original versus generic formulations, and generic versus generic formulations. Patients and their families should be educated on the risks associated with uncontrolled conversion.<\/jats:p>","DOI":"10.1097\/ftd.0000000000001041","type":"journal-article","created":{"date-parts":[[2023,3,15]],"date-time":"2023-03-15T16:05:34Z","timestamp":1678896334000},"page":"173-190","update-policy":"https:\/\/doi.org\/10.1097\/lww.0000000000001000","source":"Crossref","is-referenced-by-count":2,"title":["Generic Medicinal Products in Immunosuppressive Therapy\u2014Should It be a Challenge for Therapeutic Drug Monitoring?"],"prefix":"10.1097","volume":"45","author":[{"given":"Arkadiusz","family":"Kocur","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pawe\u0142 K.","family":"Kunicki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9110-4312","authenticated-orcid":false,"given":"Tomasz","family":"Pawi\u0144ski","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"276","reference":[{"key":"R1-20250603","doi-asserted-by":"crossref","first-page":"771","DOI":"10.1111\/tri.12074","article-title":"Methods, strengths, weaknesses, and limitations of bioequivalence tests with special regard to immunosuppressive drugs","volume":"26","author":"van Gelder","year":"2013","journal-title":"Transpl Int."},{"key":"R2-20250603","first-page":"109","article-title":"Brand name and generic drugs in immunosuppression\u2014how to make a reasonable choice?","author":"B\u0105czkowska","year":"2011","journal-title":"Polish Nephrol Dial."},{"key":"R4-20250603","doi-asserted-by":"crossref","first-page":"221","DOI":"10.1111\/j.1742-7843.2009.00518.x","article-title":"The New European Medicines Agency guideline on the investigation of bioequivalence","volume":"106","author":"Morais","year":"2010","journal-title":"Basic Clin Pharmacol Toxicol."},{"key":"R5-20250603","first-page":"181","article-title":"Bioequivalence of generic formulations of immunosuppressive drugs\u2014pharmacokinetic differences and consequences for therapeutic drug monitoring","author":"Kunicki","year":"2012","journal-title":"Polish Nephrol Dial."},{"key":"R6-20250603","doi-asserted-by":"crossref","first-page":"708","DOI":"10.1111\/j.1600-6143.2009.03058.x","article-title":"Can generics be trusted?","volume":"4","author":"Pondrom","year":"2010","journal-title":"Am J Transpl."},{"key":"R7-20250603","doi-asserted-by":"crossref","first-page":"206","DOI":"10.1159\/000449020","article-title":"Bioavailability, efficacy and safety of generic immunosuppressive drugs for kidney transplantation: a systematic review and meta-analysis","volume":"44","author":"Tsipotis","year":"2016","journal-title":"Am J Nephrol."},{"key":"R9-20250603","doi-asserted-by":"crossref","first-page":"286","DOI":"10.1002\/cpt.28","article-title":"Novel bioequivalence approach for narrow therapeutic index drugs","volume":"97","author":"Yu","year":"2015","journal-title":"Clin Pharmacol Ther."},{"key":"R11-20250603","doi-asserted-by":"crossref","first-page":"657","DOI":"10.1097\/TP.0b013e3182445e9d","article-title":"Generic immunosuppression in solid organ transplantation: a Canadian perspective","volume":"93","author":"Harrison","year":"2012","journal-title":"Transplantation"},{"key":"R12-20250603","doi-asserted-by":"crossref","first-page":"659","DOI":"10.1586\/1744666X.2015.1026895","article-title":"Generic immunosuppression in transplantation: current evidence and controversial issues","volume":"11","author":"El Hajj","year":"2015","journal-title":"Expert Rev Clin Immunol."},{"key":"R13-20250603","doi-asserted-by":"crossref","first-page":"2269","DOI":"10.1097\/TP.0000000000000782","article-title":"What is the future of generics in transplantation?","volume":"99","author":"van Gelder","year":"2015","journal-title":"Transplantation"},{"key":"R14-20250603","doi-asserted-by":"crossref","first-page":"1654","DOI":"10.1016\/S0149-2918(03)80161-3","article-title":"CONSENT: consensus on substitution in European transplantation. 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