A sensitive method for the simultaneous UHPLC-MS/MS analysis of milrinone and dobutamine in blood plasma using NH4F as the eluent additive and ascorbic acid as a stabilizer

The purpose of this work was to develop and validate an HPLC-MS/MS method suitable for quantifying two important cardiovascular drugs, milrinone and dobutamine, in neonatal and paediatric patients' blood plasma samples. Sufficiently low LLOQ levels were required to obtain adequate pharmacokinetic data for the evaluation of optimal dosing. Since the specifics of the patient group set some restrictions on the available sample volume, the method was designed to use only 20 µL of plasma for the analysis. Analytes were separated chromatographically in a biphenyl column using a conventional water-methanol-formic acid eluent with the addition of ammonium fluoride. The latter provided a significant signal enhancement in positive ion mode detection for both analytes allowing the LLOQ to reach below 1 ng/mL. Matrix matched calibration was linear in the range of 1-300 ng/mL, between-run accuracy remained within 107-115%, and precision within 4.8-7.4% for both analytes over the calibration range (including LLOQ level). Dobutamine degradation in plasma samples was prevented by the usage of ascorbic acid. The method was applied to plasma samples of neonates from two pharmacokinetic/pharmacodynamics studies (n = 38).