Lenka Kolářová

Comparative biotransformation and disposition studies of nabumetone in humans and minipigs using high-performance liquid chromatography with ultraviolet, fluorescence and mass spectrometric detection

The disposition of the non-steroidal anti-inflammatory drug (NSAID) nabumetone after a single oral dose administration of nabumetone tablets to humans and minipigs was investigated. Nabumetone is a prodrug, which is metabolized in the organism to the principal pharmacodynamically active metabolite -- 6-methoxy-2-naphthylacetic acid (6-MNA), and some other minor metabolites (carbonyl group reduction products, O-desmethylation products and their conjugates with glucuronic and sulphuric acids). Standards of the above-mentioned metabolites were prepared using simple synthetic procedures and their structures were confirmed by NMR and mass spectrometry. A simple HPLC method for the simultaneous determination of nabumetone, 6-MNA and the other metabolites was developed, validated and used for xenobiochemical and pharmacokinetic studies in humans and minipigs and for distribution studies in minipigs. Naproxen was chosen as the internal standard (I.S.), both UV (for higher concentrations) and fluorescence detection (for very low concentrations) were used. The identity of the nabumetone metabolites in biological samples was confirmed using HPLC-MS experiments. Pharmacokinetics of nabumetone, 6-MNA and 6-HNA (6-hydroxy-2-naphthylacetic acid) in human and minipig plasma was evaluated and compared. The concentration levels of nabumetone metabolites in urine, bile and synovial fluid were also evaluated.

Retention Behavior of Oligomers and Cooligomers in Reversed-phase and in Normal-phase Interactive Liquid Chromatographic Systems

Abstract Models describing the retention of small molecules combined with the additivity rules for the contributions to the retention can be used for prediction of the retention and resolution of oligomers, small synthetic polymers and copolymers in interactive liquid chromatography with dependency on the molar mass distribution and on the composition of the mobile phase, both in reversed-phase and in normal-phase chromatographic systems, for isocratic or gradient elution. Synthetic copolymers or cooligomers with two (or more) repeat monomer units show not only molar mass distribution, but also composition and sequence distribution of the individual repeat units. By combination of adequately selected separation conditions in normal-phase and in reversed-phase systems, the separation conditions can be adjusted to enhance or to suppress the chromatographic resolution according to each of the two distribution modes and to achieve the separation following the distribution of any of the two repeating groups under “critical conditions” of interactive HPLC. The sequence distribution, i.e., the distribution of the position of the blocks was found to affect significantly the retention behavior of the individual species in the block cooligomers. Based on the retention mechanism suggested, optimization of the conditions for isocratic and gradient-elution separations of cooligomers is possible.