Masakazu Hayashibara

Simultaneous determination of ofloxacin, fenbufen and felbinac in rat plasma by high-performance liquid chromatography

Ofloxacin, fenbufen and its active metabolite, felbinac, were simultaneously extracted from 50 microliters of rat plasma and analysed by high-performance liquid chromatography on a reversed-phase column. Quantitative and reproducible determinations were possible for ofloxacin, fenbufen and felbinac over the concentration ranges 0.15-40, 0.3-80 and 0.45-45 micrograms/ml, respectively. The detection limits for all the drugs were lower than those reported previously. The recovery of ofloxacin, fenbufen and felbinac added to plasma was nearly 100% with a coefficient of variation of less than 3.0%. This method was found to be applicable to pharmacokinetic studies of each drug after the concomitant administration of ofloxacin and fenbufen.

Dihydrodiol dehydrogenases in guinea pig liver

Four major and four minor dihydrodiol dehydrogenases, with similar apparent molecular weights of 28,000 to 34,000 but with different charges, were purified from male guinea pig liver cytosol. One of the minor enzymes catalyzed only the oxidation of benzene dihydrodiol with a high Km value of 5.0 mM and was identified immunologically with aldehyde reductase. The other enzymes oxidized xenobiotic alicyclic alcohols and 17 beta-hydroxysteroids as well as benzene dihydrodiol. These enzymes exhibited higher affinity for 17 beta-hydroxysteroids than for alicyclic alcohols and benzene dihydrodiol, and immunologically cross-reacted with testosterone 17 beta-dehydrogenase purified from the same source. Four major enzymes and one minor with Km values for benzene dihydrodiol of about 0.2 mM, possessed specificity for 5 beta-androstane--17 beta-hydroxysteroids and dual cofactor requirement, whereas the other two minor enzymes with high Km values of over 5 mM showed apparent NADP and 5 alpha-androstane specificity. The dihydrodiol dehydrogenase activity was localized in the cytosol of liver. The results indicate that the hepatic oxidation of dihydrodiols in the guinea pig is mediated by cytosolic testosterone 17 beta-dehydrogenase isozymes and aldehyde reductase. Testosterone 17 beta-dehydrogenase immunologically identical to the liver enzymes was detected only in kidney, whereas aldehyde reductase was detected in all tissues of the guinea pig.

Effect of Fenbufen on the Entry of New Quinolones, Norfloxacin and Ofloxacin, into the Central Nervous System in Rats

Abstract— The entry of two new quinolone antibacterial agents, norfloxacin and ofloxacin, into the central nervous system (CNS) of rats, and the effect of fenbufen on this was investigated. At various times after the administration of a bolus intravenous dose of norfloxacin or ofloxacin (10 mg kg−1) with or without fenbufen (20 mg kg−1), serum and cerebrospinal fluid (CSF) samples and whole brain were collected from the rats and the concentration of norfloxacin or ofloxacin in each sample was determined. Serum concentrations of both quinolones declined biexponentially with time and were significantly elevated by coadministration with fenbufen at the terminal phase. The fractions of these quinolones bound to serum protein were not altered by coadministration with fenbufen. Coadministered fenbufen raised the brain concentrations of both quinolones but did not affect their brain to serum unbound concentration ratios. In contrast, CSF to serum unbound concentration ratios as well as CSF concentrations of norfloxacin and ofloxacin were elevated by coadministration with fenbufen. Apparent diffusional clearances between blood and CSF of norfloxacin and ofloxacin estimated by the physiological model analysis increased by 1·9 and 2·6 times, respectively, after coadministration with fenbufen. These findings suggest that coadministered fenbufen may facilitate the entry of norfloxacin and ofloxacin into the CNS.

Absence of pharmacokinetic interaction between ofloxacin and fenbufen in rats

The possible pharmacokinetic interaction between a new quinolone and fenbufen was investigated by comparing the plasma concentration‐time profiles and serum protein binding of ofloxacin, fenbufen and its active metabolite, felbinac, in rats. The rats were administered intravenous doses of ofloxacin (5 mg kg−1), fenbufen (10 mg kg−1) alone or concomitantly. The plasma elimination half‐lives were about 55 min in both groups. A slight elevation of plasma concentration of ofloxacin and a small decrease of its total body clearance were observed after its coadministration with fenbufen. The extent of ofloxacin binding to rat serum tended to be slightly reduced by fenbufen which coexisted at relatively high concentrations. Plasma concentration‐time curves, pharmacokinetic parameters and serum protein binding of fenbufen and felbinac were not affected by the coadministration with ofloxacin. These results suggest that any substantive pharmacokinetic interaction may be unlikely after the concomitant administration of ofloxacin and fenbufen.

Salivary excretion of mexiletine after bolus intravenous administration in rats

Abstract— Salivary excretion of mexiletine was investigated following bolus intravenous administration (10 mg kg−1) in rats. Parotid and mandibular saliva was collected separately by stimulating salivation with constant rate infusion of pilocarpine (3 mg kg−1 h−1). The mexiletine levels in blood plasma and parotid and mandibular saliva declined biexponentially with time in almost parallel fashion. Although the mexiletine levels in both types of saliva were lower than that in plasma, the drug level in parotid saliva was always higher than that in mandibular saliva. Significant correlations were observed when all data relating mexiletine concentration in plasma and saliva were included (P < 0·001). The saliva/plasma drug concentration ratios (S/P ratios) did not vary to a large extent (0·56 ± 0·10 for parotid saliva, 0·21 ± 0·06 for mandibular saliva), but there was a consistent tendency for the higher plasma drug levels in the distribution phase to produce relatively high S/P ratios for both parotid and mandibular saliva. Moreover, the plasma mexiletine levels calculated by the equation of Matin et al (1974) employing the observed values for the saliva drug level, saliva pH and free fraction of mexiletine in plasma were significantly higher than the observed drug levels. Therefore, it is suggested that the salivary excretion of mexiletine could not be explained quantitatively by simple, passive secretion based on pH‐partition theory.

Salivary excretion of mexiletine in normal healthy volunteers.

Abstract— To investigate the kinetics and correlation between serum and saliva levels of mexiletine, serum (total and unbound) and saliva drug concentration‐time courses have been analysed in five normal healthy volunteers after administration of a single oral dose (200 mg) of the drug. Mexiletine levels in saliva were always higher than those in serum. The drug concentration‐time curve in each sample was analysed according to the non‐linear least squares regression program MULTI, for a two‐compartment model with first‐order absorption. The saliva drug concentration in the post‐absorption phase was found to be well correlated with either corresponding serum total or serum unbound drug level in four of the subjects. Although there was a large inter‐individual variation in the ratio of saliva to serum drug concentrations as well as in the pharmacokinetic parameters, an almost consistent ratio was obtained in each individual.

A possible reduction in the renal clearance of ciprofloxacin by fenbufen in rats

Abstract— The change in plasma concentration‐time profile, serum protein binding and renal and biliary clearances of ciprofloxacin caused by coadministration of fenbufen has been studied in rats administered an intravenous dose of ciprofloxacin (5 mg kg−1) alone or with fenbufen (10 mg kg−1). Coadministered fenbufen significantly prolonged the plasma elimination half‐life of ciprofloxacin from 40.5 to 57.6 min and tended to reduce the total body clearance of this quinolone by about 20%. The extent of ciprofloxacin binding to rat serum protein was not affected by fenbufen, nor did it affect the biliary clearance of the quinolone. However, fenbufen tended to reduce renal clearance and significantly decreased the cumulative renal excretion of the quinolone during at least the first 3 h after drug administration. These results suggest a possible reduction of ciprofloxacin clearance owing to inhibition of renal excretion by fenbufen.

Simultaneous high-performance liquid chromatographic determination of ciprofloxacin, fenbufen and felbinac in rat plasma

Ciprofloxacin (CPFX) is a new quinolone agent with potent, broad antibacterial activity. It is well absorbed and widely distributed into various body tissues and fluids when given orally [1,2]. Recently, it was reported that severe convulsion was induced in some patients who were given new quinolone antibacterial agents and non-steroidal anti-inflammatory drugs, including fenbufen (FNB) [3,4], which was later reported to potentiate the convulsant activity of various quinolones in mice [5]. FNB is readily biotransformed into 4-biphenylacetic acid (felbinac, FLB), which possesses anti-inflammatory activity [6-81. Therefore, in order to investigate possible pharmacokinetic interaction between these drugs, it is necessary to develop a simple, sensitive, selective and simultaneous assay method for the quinolone, FNB and FLB in biological fluids. We have already developed high-performance liquid chromatographic (HPLC) methods for simultaneous determination of quinolone involving ofloxatin, enoxacin or norfloxacin with FNB and FLB [9-l 11, and examined the effects of FNB and FLB on the pharmacokinetics of these three quinolones [12-141. However, no investigation has been carried out on the pharmacokinetic interaction of the newer quinolone, CPFX, with FNB and FLB. This paper describes a novel analytical method for the simultaneous determination of CPFX, FNB and FLB in rat plasma.

Immunological identification of soluble carbonyl reductase with testosterone 17β-dehydrogenase (NADP+) in guinea pig liver and kidney

Antiserum was produced against one of two carbonyl reductases purified from guinea pig liver cytosol to identify the enzymes as testosterone 17 beta-dehydrogenase isozymes. Immunoelectrophoresis and immunoprecipitation with the antiserum indicated that the two reductases had common antigenic sites. The antiserum inhibited most of both carbonyl reductase and testosterone 17 beta-dehydrogenase activities in the purified reductases and in cytosols of liver and kidney.

High-performance liquid chromatographic determination of nalidixic acid in rat serum, brain and cerebrospinal fluid

A high-performance liquid chromatographic method for the determination of nalidixic acid (NA) in rat serum, brain and cerebrospinal fluid (CSF) was developed. NA in rat serum and brain homogenate was extracted and injected onto a reversed-phase column. CSF was directly analysed without extraction procedure. The limits of detection were 0.05 microgram ml-1 for serum, 0.07 microgram g-1 for brain and 0.02 microgram ml-1 for CSF, respectively. Calibration curves were linear over the concentration ranges 0.1-50 micrograms ml-1 for serum, 0.12-9 micrograms g-1 for brain and 0.05-10 micrograms ml-1 for CSF, respectively. The reproducibility of NA assay in rat biological media ranged from 1 to 4% relative standard deviations (RSD). The recoveries of NA added to serum and brain were higher than 96% with an RSD of less than 4%. The present method was found to be applicable to pharmacokinetic study of NA in rat serum, brain and CSF.