Concentrations of medetomidine enantiomers and vatinoxan, an α2-adrenoceptor antagonist, in plasma and central nervous tissue after intravenous coadministration in dogs

Abstract

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A quick approach for medetomidine enantiomer determination in dog plasma by chiral liquid chromatography–tandem mass spectrometry and application to a pharmacokinetic study

“…In our study, the addition of 0.1% diethylamine, besides 20‐mM ammonium formate, to the aqueous phase brought the pH to around 8.5, which turned out to be a key factor to obtain optimal resolution of DEX and LEVO. After performing multiple tests under both isocratic and programmed LC conditions, we concluded that a mobile phase with a constant composition of methanol (55%) and 20‐mM ammonium formate 0.1% diethylamine aqueous solution (45%) provided the best results, as also described by Honkavaara et al 8 Increased content of water or methanol in the mobile phase negatively affected peak shape or peak separation, respectively.…”

“…A concentration of 0.1 ng/mL, considered largely sufficient for the method to be used in a PK study, was set as target LLOQ at the beginning of the experiment. This goal was easily reached for both enantiomers (as shown in Figure 3), resulting lower compared with the LLOQ reported in previous works 7,8 . In addition, during further extra‐validation experiments, a plasma sample spiked at 0.05 ng/mL was processed, providing a chromatographic trace with an S/N ratio still greater than 10.…”

“…However, chiral columns specifically designed for such technology have only recently been introduced on the market; therefore, we preferred to opt for the well‐known (and previously used with success in our laboratory) Phenomenex Lux 3 μ Cellulose‐3 HPLC column. Although this configuration did not allow to take full advantage of UHPLC capabilities, it provided optimal peak resolution in a relatively short total run time (9.5 min), making this approach faster compared with similar previously published techniques 7,8 . It has been highlighted how different mobile phase modifiers, such as ammonium acetate, ammonium formate, formic acid and diethylamine, can play a pivotal role in the chiral separation of the optical isomers of some compounds 7,9 .…”

“…The quick and simple extraction procedure proved to be a strength point of the proposed method, requiring only small amounts of chemical reagents and sample and allowing to process 24 samples in less than 45 min. This is an advantage compared with other published approaches for the quantification of medetomidine enantiomers in plasma, based on more expensive and time-consuming solid phase extraction techniques 8,10 or on liquid-liquid extraction with larger volume of a chemically hazardous solution containing chloroform. 7 Before opting for the extraction with ethyl acetate, protein precipitation with methanol was also tested during method development.…”

Investigation of the effects of vatinoxan on somatic and visceral antinociceptive efficacy of medetomidine in dogs

“…16 The peripheral selectivity of vatinoxan has also been recently found in dogs. 17 Vatinoxan has been used experimentally and clinically to prevent or attenuate the undesired peripheral effects of medetomidine and dexmedetomidine in dogs, [18][19][20][21][22] and reductions in the unwanted effects of the latter drugs are dose dependent. 18,21 Centrally mediated dexmedetomidine-induced sedation is not substantially reversed by the administration of vatinoxan in dogs, 19,23 although the duration of sedation is slightly shortened.…”