Determination of five antihypertensives in dried capillary plasma spots by LC-MS/MS: A novel method for monitoring pharmacotherapy adherence.

Adherence to hypertension treatment is crucial for therapeutic success, as noncompliance adversely affects quality of life and healthcare costs. Assessing adherence directly through plasma drug concentrations is particularly effective for patients with complex medication regimens. This study aimed to develop and validate an LC-MS/MS method for quantifying five antihypertensive drugs in dried capillary plasma obtained via a plasma separation device. The process involved incubating three 6 mm discs in 150 µL of 0.1% bovine serum albumin, followed by chloride analysis of a 20 µL aliquot after 45 min. The residual volume was precipitated using 25% trichloroacetic acid, then mixed with 500 µL methanol containing internal standards (losartan-D4 and atenolol-D7). The extract was dried, reconstituted with methanol, and combined with the supernatant from protein precipitation for analysis. An octadecylsilic column and gradient elution with 0.1% formic acid in water and acetonitrile were used, with positive electrospray ionization except for hydrochlorothiazide. The analytical run time was eight minutes, exhibiting linear ranges from 0.5 to 200 ng/mL for amlodipine and losartan and 5-2000 ng/mL for atenolol, hydrochlorothiazide, and losartan, with r² > 0.99 and 1/x weighting. Precision and accuracy were acceptable, with CV% ranging from 4.3% to 14.5% and accuracy from 86% to 112%, while extraction yields were between 75% and 101%. The analytes were stable at 23 ºC for 21 days in DPS samples. Comparison of drug concentrations in DPS and fresh plasma samples from 72 patients demonstrated high correlation (r = 0.93-0.98), indicating reliability in assessing therapy adherence. Lower concentrations of amlodipine, hydrochlorothiazide, and losartan were observed in patients exhibiting poor adherence (n = 21) compared to adherent patients (n = 51) with statistical significance (p < 0.05). The method is promising for assessing antihypertensive adherence using dried plasma spots.