Assessment of patients' and physicians compliance to an ACE inhibitor treatment based on urinary N-acetyl Ser-Asp-Lys-Pro determination in the noninsulin-dependent diabetes, hypertension, microalbuminuria, proteinuria, cardiovascular events, and Ramipril (DIABHYCAR) study

OBJECTIVE - The purpose of this study was to assess patients' and physicians' compliance with ACE inhibitor treatment, by measuring an endogenous biomarker of ACE inhibition, urinary N-acetyl-Ser-Asp-Lys-Pro (AcSDKP), in the Noninsulin-Dependent Diabetes, Hypertension, Microalbuminuria, Proteinuria, Cardiovascular Events, and Ramipril (DIABHYCAR) trial, which compared ramipril (1.25 mg o.d.) with placebo in 4,912 patients with type 2 diabetes and microalbuminuria/proteinuria. RESEARCH DESIGN AND METHODS - The urine AcSDKP-to-creatinine ratio was measured blind to treatment in all participants who completed follow-up and provided spot urine samples (n = 1,871). RESULTS - The median urinary AcSDKP-to-creatinine ratio was six times higher for ramipril than for placebo. Urinary AcSDKP-to-creatinine ratios displayed a bimodal distribution in both groups, with a very large intergroup overlap. Based on cluster analysis, we defined truly adherent. ramipril patients as those with a ratio >= 4 nmol/mmol and truly adherent placebo patients as those with a ratio < 4 nmol/mmol. After excluding patients withdrawing prematurely from the study or known to have used a nonstudy ACE inhibitor, 27.3% of the 597 ramipril patients had ratios < 4, indicating poor compliance, and 9.7% of the 621 placebo patients had ratios >= 4, indicating intake of a nonstudy ACE inhibitor. Correcting for compliance by using AcSDKP-guided analysis affected surrogate outcome results (decrease in systolic blood pressure and urinary albumin excretion) only slightly. CONCLUSIONS - The systematic use of spot urinary AcSDKP determination facilitated the detection of defects in compliance with ACE inhibitor treatment in both patients and physicians. Urinary AcSDKP measurement could be a useful biomarker for assessing compliance with ACE inhibition in the routine care of diabetic patients.