AIMS: To evaluate medication adherence in patients with type 2 diabetes (T2D) using plasma drug measurements and assess the clinical impact of partial non-adherence on glycemic control and complications. MATERIALS AND METHODS: This cross-sectional study included 641 T2D outpatients attending routine follow-up visits. After overnight fasting, blood samples were collected and analysed by LC-MS to quantify plasma concentrations of 13 oral antidiabetic drugs. Adherence was defined as the detection of a prescribed drug above the limit of quantification. Self-reported lifestyle factors, dosing regimens, and clinical outcomes were assessed in relation to drug presence. RESULTS: Metformin adherence was very high, with the drug undetected in only 1.9% of patients. In contrast, adherence rates were lower for sulfonylureas (94%), DPP-4 inhibitors (90%), pioglitazone (82%), and SGLT2 inhibitors (73%). Non-adherence was predominantly partial: only one of the analysed antidiabetics taken by patients was not detected in 93% of non-adherent patients. Adherence declined with increasing numbers of prescribed agents and daily doses, suggesting treatment complexity as a key factor. No other tested lifestyle or drug management parameters were significantly associated with adherence. Glycemic control was worse in non-adherent patients: 63% did not reach target glucose and HbA1c levels, compared to 37% of fully adherent patients. Non-adherence was also associated with a higher prevalence of diabetic kidney disease. CONCLUSIONS: Partial non-adherence is common in T2D and strongly associated with treatment complexity and poor glycemic outcomes. These findings emphasize the need for individualized strategies to support adherence and improve long-term diabetes care. Our study further indicates that plasma analysis using LC-MS methods may serve as a robust tool for adherence assessment.

Centre for Experimental Medicine Institute for Clinical and Experimental Medicine Prague Czech Republic

Department of Biochemistry and Microbiology University of Chemistry and Technology Prague Czech Republic

Department of Social and Clinical Pharmacy Faculty of Pharmacy in Hradec Králové Charles University Hradec Králové Czech Republic

Diabetes Centre Institute for Clinical and Experimental Medicine Prague Czech Republic

Institute of Physiology of the Czech Academy of Sciences Prague Czech Republic

Institutional Pharmacy Institute for Clinical and Experimental Medicine Prague Czech Republic

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