Introduction: Adherence to medication is an important determinant of outcomes in chronic diseases like heart failure. Drug assays provide objective adherence biomarkers. Dried blood spots (DBS) are appealing samples for drug assays due to less demanding transportation and storage requirements.Objectives: To analytically validate a LC-MS/MS method for the simultaneous quantification of carvedilol, ena-laprilat, and perindoprilat in DBS and evaluate the feasibility of using the method as an adherence determining assay. To validate the assay further clinically by establishing correlation and agreement between plasma and DBS samples from a pharmacokinetic pilot study. Methods: The method was validated over a concentration range of 1.00-200 ng/mL according to FDA guidelines. Adherence tracking ability of the assay was evaluated using a pharmacokinetic pilot study. Correlation and agreement were evaluated through Deming regression and Bland-Altman analysis, respectively. Results: Accuracy, precision, selectivity, and sensitivity were proven with complete and reproducible extraction recovery at all concentrations tested. Stability of the analytes in the matrix and throughout sample processing was proven. The full range of concentrations of the pharmacokinetic pilot study could be quantified for ena-laprilat, but not for carvedilol and perindoprilat. The difference between the observed and calculated plasma concentrations was less than 20 % of their mean for >67 % of samples for all analytes.Conclusions: The assay is suitable as a screening tool for carvedilol and perindoprilat, while suitable as an adherence determining assay for enalaprilat. Equivalence between observed and predicted plasma concentra-tions proves DBS and plasma concentrations can be used interchangeably.

Background: Poor medication adherence leads to poor health outcomes and increased healthcare costs among patients with heart failure (HF). This study aimed to objectively assess medication adherence by measuring carvedilol and enalaprilat plasma concentrations among patients with HF. Methods: The present sub-study of the Safety, Tolerability, and Efficacy of Rapid Optimization, helped by NTproBNP testing, of Heart Failure therapies (STRONG-HF) study involved adult patients with acute HF admitted in two Mozambican and two Nigerian hospitals who were not optimally treated with oral enalapril and carvedilol. Patients in the high-intensity arm of the STRONG-HF study, and those not meeting the biomarker criteria for persistent congestion, were included in the "frequent visit" (FV) arm. In the FV arm, blood for bioanalysis of plasma enalaprilat or/and carvedilol was drawn at the 2,6,12th week post-discharge. Patients in the usual care arm of STRONG-HF were included in the "standard visit" (SV) arm, which followed the usual local practice with blood sampling in week 12. Results: The study involved 113 (79 FV and 34 SV) participants with a mean age of 48.6 years and a mean left ventricular (LV) ejection fraction of 33.1%. Theenalaprilat below the lower level of quantification (LLOQ) was documented in 7.7%, 11.9%, and 15.6% of participants in FV during the 2,6 and 12th weeks. Carvedilol concentration below LLOQ was documented in 37%, 30%, and 44.4% of participants in the FV arm during the 2,6 and 12th weeks, respectively. For the SV arm, enalaprilat and carvedilol concentrations below LLOQ in the twelfth week were documented in 37.3% and 42.9% of patients, respectively. Conclusion: Up to a third of patients using enalapril and carvedilol did not take any medication during the 12 weeks of follow-up. Non adherence was more common in patients who had less follow up, emphasizing the importance of close follow up to adherence. No adherence was also more common in medications know to have more side effects such as carvedilol.

A method for the extraction and quantification of carvedilol, enalaprilat, and perindoprilat in 50 µL human plasma, using high-performance liquid chromatography with tandem mass spectrometry (LC–MS/MS) detection was developed and validated. Samples were prepared via protein precipitation with chromatographic separation on a Restek Ultra II Biphenyl column using gradient elution at a corresponding flowrate of 300 µL/min. Electrospray ionisation with mass detection at unit resolution in the multiple reaction monitoring (MRM) mode on an AB Sciex API 5500 mass spectrometer was used. Accuracy, precision, selectivity, sensitivity, matrix effects, recovery, process efficiency, and stability were assessed over the validation period. The assay was validated over the calibration range 0.2–200 ng/mL for all three analytes. The inter- and intra-day precision expressed as the coefficient of variation (CV) and accuracy (%Nom) all fell within acceptable limits. The overall recovery was calculated as 72.9%, 77.1%, and 77.0% for carvedilol, enalaprilat, and perindoprilat respectively, with the recovery being shown to be reproducible at the low, medium and high end of the calibration range for all three analytes. The method proved to be specific for all three analytes with no significant matrix effects observed. The validated method facilitated the analysis of carvedilol, enalaprilat, and perindoprilat in human plasma collected from adults as part of a pilot pharmacokinetic study. This validated analytical method lays the foundation for determining adherence in heart failure patients prescribed with carvedilol, enalapril and perindopril.