Effects of medetomidine and its active enantiomer dexmedetomidine on N-demethylation of ketamine in canines determined in vitro using enantioselective capillary electrophoresis.

Cytochrome P450 (CYP) enzymes catalyze the metabolism of both, the analgesic and anesthetic drug ketamine and the α2 -adrenergic receptor-agonist medetomidine that is used for sedation and analgesia. As racemic medetomidine or its active enantiomer dexmedetomidine are often coadministered with racemic or S-ketamine in animals and dexmedetomidine together with S- or racemic ketamine in humans, drug-drug interactions are likely to occur and have to be characterized. Enantioselective CE with highly sulfated γ-cyclodextrin as chiral selector was employed for analyzing in vitro (i) the kinetics of the N-demethylation of ketamine mediated by canine CYP3A12 and (ii) interactions occurring with racemic medetomidine and dexmedetomidine during coincubation with ketamine and canine liver microsomes (CLM), canine CYP3A12, human liver microsomes (HLM), and human CYP3A4. For CYP3A12 without an inhibitor, Michaelis-Menten kinetics was determined for the single enantiomers of ketamine and substrate inhibition kinetics for racemic ketamine. Racemic medetomidine and dexmedetomidine showed an inhibition of the N-demethylation reaction in the studied canine enzyme systems. Racemic medetomidine is the stronger inhibitor for CLM, whereas there is no difference for CYP3A12. For CLM and CYP3A12, the inhibition of dexmedetomidine is stronger for the R- compared to the S-enantiomer of ketamine, a stereoselectivity that is not observed for CYP3A4. Induction is observed at a low dexmedetomidine concentration with CYP3A4 but not with CYP3A12, CLM, and HLM. Based on these results, S-ketamine combined with dexmedetomidine should be the best option for canines. The enantioselective CE assay with highly sulfated γ-cyclodextrin as chiral selector is an effective tool for determining kinetic and inhibition parameters of metabolic pathways.

Therapeutic drug monitoring of cefepime with micellar electrokinetic capillary chromatography: Assay improvement, quality assurance, and impact on patient drug levels

The improvement and performance of a micellar electrokinetic capillary chromatography assay for cefepime in human serum and plasma with a 50 μm id fused-silica capillary elongated from 40 to 60 cm is reported. Sample preparation with dodecylsulfate protein precipitation at pH 4.5, the pH 9.1 separation medium and the applied voltage were as reported previously[16]. The change resulted in a significant lower current, higher resolution and increased detection time intervals. The performance of the assay with multi-level internal calibration was assessed with calibration and control samples. Quality assurance data of a two year period assessed under the new conditions demonstrated the robustness of the assay. In serum samples of patients who received both cefepime and sulfamethoxazole, cefepime could not be detected due to the inseparability of the two compounds. The presence of an interference can be recognized by an increased peak width (width > 0.2 min), the appearance of a shoulder or an unresolved double peak. The patient data gathered during a three year period reveal that introduction of therapeutic drug monitoring led to a 50% reduction of the median drug level. The data suggest that therapeutic drug monitoring can help to minimize the risk of major adverse reactions and to increase drug safety on an individual basis. This article is protected by copyright. All rights reserved.