Kenji Ohtsubo

Influence of Additional Therapy with Zonisamide (Excegran) on Protein Binding and Metabolism of Carbamazepine

Summary: The influence of comedication with zonisamide (ZNS) on protein binding and carbamazepine (CBZ) metabolism was studied in 16 pediatric epileptic patients. Correlations were evaluated between ZNS daily dose and individual change of level per dose ratio (L/D ratio), free fraction, and carbamazepine‐10,11‐epoxide/CBZ level ratio (CBZEKBZ). Statistical significant negative correlation was observed between LID ratio and ZNS daily dose. Despite alteration in the L/D ratio, the free fraction of CBZ was unaltered in combination with ZNS. To assess the effect of addition of ZNS on CBZ metabolism, the CBZE/CBZ level ratio was compared; this ratio showed a tendency to increase with increase in ZNS dose. Consequently, ZNS is considered to have a significant effect on CBZ metabolism but not on protein binding.

Drug interactions of zonisamide with phenytoin and sodium valproate: serum concentrations and protein binding.

The influence of co-medication with zonisamide (ZNS) on the serum concentration and protein binding of phenytoin (PHT) and sodium valproate (VPA) was studied in 21 pediatric patients. No significant correlation between the daily ZNS dose, and total serum concentrations, free concentrations or free fractions (FF) of PHT or VPA was observed. The patient study showed that changes in the FF of PHT and VPA were correlated more closely with the serum protein and bilirubin levels than changes in the ZNS dosage. An in vitro study revealed that the addition of ZNS caused decreases in the FF of PHT and VPA. However, these decreases were within the range of measurement error and were negligible. In conclusion, no significant effect of ZNS on the serum concentration or protein binding of PHT or VPA was demonstrated.

COMPARISON OF SINGLE‐POINT PHENYTOIN DOSAGE PREDICTION TECHNIQUES

To dose the anticonvulsant phenytoin (PHT) in a clinical situation is difficult because of the non‐linear metabolism of the drug. Therefore many techniques have been advocated to aid dosage adjustments based on a single‐point PHT concentration determined at steady‐state (ss). We retrospectively investigated six methods in a population of 130 out‐patients treated with PHT. The dose needed to achieve a desired PHT concentration at ss was calculated based on an observed 55 dose‐concentration pair using a Bayesian feedback method (B), the Richens and Dunlop nomogram (RD), the Rambeck nomogram (R), the Martin nomogram (M), a population clearance equation (PC), and the Wagner equation (W).

Effect of 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) enantiomers, major metabolites of phenytoin, on the occurrence of chronic-gingival hyperplasia: in vivo and in vitro study.

The purpose of this study was to assess the possible role of the (R)- and (S)- enantiomers of the phenytoin metabolite p-HPPH in the pathogenesis of gingival hyperplasia (GH). About 98% of circulating p-HPPH is in the (S)-form. There were significant differences between patients with and without GH in (R)-p-HPPH level (0.055 vs 0.042 μg·ml−1), both enantiomer/racemate level ratios, and R/S enantiomeric ratio (0.0313 vs 0.0232); an increase in serum (R)-p-HPPH level was observed in patients with GH. In separate experiments, the effect of p-HPPH enantiomers on the proliferation of the normal human dermal fibroblast was studied. The in vitro study showed that (R)-p-HPPH selectively stimulated fibroblast growth. The results suggest that the least abundant metabolite, (R)-p-HPPH, is the most toxic with respect to gingival hyperplasia.

Sensitive determination of ambenonium chloride in serum from patients with myasthenia gravis using ion-exchange resin extraction and reversed-phase ion-pair chromatography

An effective and selective procedure for the extraction of ambenonium chloride (AMBC) from serum using a weak cation-exchange extraction cartridge has been developed. The solid-phase extraction procedure permitted the extraction of AMBC from serum without adhesion to materials such as the containers. A 200-microliter volume of the eluate could be directly injected on to a reversed-phase ion-pair high-performance liquid chromatographic column. The recovery was in the range 97-100%. The limit of detection for AMBC was 0.5 ng/ml in serum (signal-to-noise ratio = 3). The method was used to determine the serum concentration of AMBC in patients with myasthenia gravis. The method would be useful for monitoring AMBC in serum in order to study its pharmacokinetic behaviour in patients under oral administration therapy.

The fluorescent reaction product in the determination of aromatic aldehydes with 2,2'-dithiobis(1-amino-naphthalene)

The fluorescent product formed from benzaldehyde or p-hydroxybenzaldehyde with the reagent in the presence of tri-n-butylphosphine, phosphite and sulphite has been characterized by elemental and structural analysis as the corresponding 2-arylnaphtho [1,2-d ] thiazole.

Assay for dopamine β-hydroxylase in rat serum and adrenal medulla by high-performance liquid chromatography with fluorescence detection

Abstract A highly sensitive method for the assay of dopamine β-hydroxylase in rat serum and in sample solution prepared from rat adrenal medulla is described which employs high-performance liquid chromatography with fluorescence detection. Octopamine, formed enzymatically from the substrate tyramine, is separated by Dowex 50W-X4 column chromatography and oxidized with periodate to p-hydroxybenzaldehyde, which is then converted into a fluorescent compound with 2,2′-dithiobis(1-aminonaphthalene). The derivative, after extraction with n-hexane—chloroform, is separated by normal-phase chromatography on Alox T. The limit of detection for octopamine formed enzymatically is 10 pmol. This method requires as little as 5 μl of rat serum.