Reduction and glucuronidation of naftazone by human and rat liver microsomes

Reduction and glucuronidation of the vasoprotectant drug, naftazone, by human and rat liver microsomes and by recombinant UDP-glucuronosyltransferases (UGT) stably expressed in V79 cells were studied. The oxo group was first reduced in the presence of NADPH or NADH, and was subsequently readily glucuronidated on the phenolic moiety leading to a 1 beta-O-glucuronide, as revealed from MS and by proton and 13C-NMR. Glucuronide extracted from the urine of rats treated with the drug presented the same structure. In all enzyme systems tested, NADH was the most efficient electron donor, when compared with NADPH. The reaction was strongly inhibited by quercitrin, a specific inhibitor of carbonyl reductase. Attempts to isolate the reduced intermediate were unsuccessful because of its marked instability. In humans, a large interindividual variation for the formation of glucuronide was observed with microsomes of seven different liver samples (3.98 +/- 3.22 nmol/min.mg). In rat, glucuronidation of reduced naftazone was strongly induced (12-fold) by 3-methylcholanthrene and, to a lesser extent (2.6-fold) by phenobarbital, but was not affected by clofibrate. In addition, liver microsomes from Gunn rats, which present a genetic defect in bilirubin and phenol UGTs could not form glucuronide of reduced naftazone. The drug, after addition of NADH, was a substrate of the human liver recombinant UGT1*6 that presents a strict specificity toward planar phenolic substances, but not that of UGT2B4 and UGT2B1 expressed in V79 fibroblasts. The reducing step by the endogenous V79 cellular reductase was rate-limiting. In conclusion, the powerful inducing effect exerted by 3-methylcholanthrene, the lack of glucuronidation in the Gunn rat and the ability of UGT1*6 encoded by the UGT1 gene to glucuronidate reduced naftazone suggest that, in humans and in the rat, the compound is metabolized by a UGT isoform (UGT1*6 and the rat orthologous form) belonging to family 1, with a restricted specificity toward the drug.

Pharmacokinetics of cutaneous Sulconazole nitrate in the hairless rat: absorption, excretion, tissue concentrations

After cutaneous application of radioactive solutions of Sulconazole nitrate in the hairless rat, the total absorption of the substance by the skin, estimated from the sum of the cumulative urinary and fecal excretions over 96 h, was 2.4% of the dose administered. The elimination reached a maximum between 6 and 24 h and was virtually complete after 96 h. The excretion was almost equally distributed between the urine and the feces, which corresponds to an intense elimination via the biliary tract. The quantities present in the stratum corneum, epidermis and dermis at the end of the period of contact constituted another estimation of the total absorption of the substance which confirmed the previous estimation (3.6% of the dose). The measurement of the concentrations of Sulconazole and its metabolites in the various layers of the skin revealed a high affinity of the substance for the stratum corneum, where it remained present in large quantities for more than 48 h. This affinity is due to the very intense lipophilia of the molecule. The concentrations in the other tissues were inversely proportional to the distance from the surface of the skin and were virtually nil in the circulating blood. These results suggest the absence of risk of systemic effects after cutaneous administration of Sulconazole and support the recommended therapeutic protocol in man (one administration per day).

The pharmacokinetics of tiopronin and its principal metabolite (2-mercaptopropionic acid) after oral administration to healthy volunteers

We have studied the pharmacokinetics of tiopronin and its principal metabolite, 2-mercaptopropionic acid (2-MPA) in healthy volunteers after the oral administration of 500 mg (2 Acadione tablets), followed by simultaneous assay of the two compounds in plasma over a period of 48 h using a new method (emission of fluorescence after HPLC and post-column derivatization by pyrene-maleimide). The absorption of tiopronin was slow (tmax between 4 and 6 h) and the plasma concentrations subsequently fell biexponentially. The principal metabolite 2-MPA appeared later in the plasma (tmax between 10 and 12 h after a lag-time of 3 h) then disappeared monoexponentially. About 15% of the tiopronin was metabolized to 2-MPA.

Determination of 2-mercaptopropionylglycine and its metabolite, 2-mercaptopropionic acid, in plasma by ion-pair reversed-phase high-performance liquid chromatography with post-column derivatization

A simple and fast high-performance liquid chromatographic method was developed for the simultaneous measurement of 2-mercaptopropionylglycine (Tiopronine) and its metabolite (2-mercaptopropionic acid) in human plasma after the administration of a pharmaceutical dosage form (Acadione). The sample treatment before high-performance liquid chromatographic analysis consisted of the reduction of the corresponding disulphides by tri-n-butylphosphine and protein precipitation with ethanol. Separation was achieved by ion-pair high-performance liquid chromatography on a reversed-phase column (LiChrospher RP 18e) with cetrimonium bromide as counter ion and detection by fluorimetry after post-column derivatization with a selective thiol reagent, i.e. pyrenemaleimide. The high frequency of the analyzed samples and validation results make the method suitable for pharmacokinetic studies, and this was demonstrated by the first results obtained after the administration of an oral dose of 500 mg of Tiopronine to two healthy subjects.

[Serum, synovial and intra-articular pharmacokinetics of naproxen after one-gram oral administration in patients with rheumatoid polyarthritis]

After a reminder of the major points of the pharmacokinetics of non-steroid anti-inflammatory drugs, the authors report the results of a multicentric study of the kinetics of naproxen after oral intake of one single dose of 1 gram in patients with rheumatoid arthritis. The half-life is longer in the synovial fluid than in the serum, 23 hours versus 17 hours. The balance point is obtained at the 24th hour and, at that time, the naproxen level in the synovium and the joint fluid are 32 and 60 p. cent, respectively, of the corresponding maximum concentrations.

[Course of the diffusion of cefotiam in infected ascitic fluid]

The cefotiam (CFT) penetration in infected ascitic fluid was investigated in 12 cirrhotic patients. CFT (1 g every 8 h) was given intravenously and measured by HPLC in plasmatic and ascitic samples. The mean ascitic concentrations (+/- SEM), 1 h, 3 h and 8 h after the first injection (J1) were 14.6 +/- 4.6, 11.8 +/- 3 and 8.4 +/- 2.9 micrograms/ml respectively. These values were 38, 62 and 88% of the corresponding mean plasmatic concentrations and higher than the MIC's for the organisms most commonly involved. The mean plasmatic and ascitic concentrations, a few days later (4.5 or 6 days) (Jn) were not significantly different from the corresponding values at J1. A significant decrease of polymorphonuclear cell count was observed between J1 and Jn. These results suggest that CFT diffusion into ascitic fluid is independent of inflammation and CFT is an adequate antibiotic in cirrhotic patients with infected ascitic fluid.

[Diffusion of cefotiam into ascitic fluid]

The large apparent volume of distribution of cefotiam (reported by Fourtillan et al. [4]), prompted an investigation of cefotiam diffusion into ascitic fluid. Eight patients with non-infected ascites were each given a single intravenous bolus of 2 gr cefotiam. Samples of blood and ascitic fluid were collected 0.5, 1, 2, 3, 4, 6 and 8 hours after the injection. Plasma and ascitic fluid concentrations of unchanged cefotiam were determined using HPLC. Peak concentration in ascitic fluid averaged 18 micrograms/ml and was reached at two hours. Concentrations were still high (approximately 13 micrograms/ml) at 8 hours, leading to further assays 12 and 24 hours after the injection in three subjects. Cefotiam concentrations achieved in ascitic fluid seem adequate for the treatment of infected ascites, given the antibiotic's MICs for the organisms most commonly involved.

[Clometacin--1. Metabolism and bioavailability of clometacin and its metabolites in the rat]

The metabolism and bioavailability of 14C clometacin was studied in the rat. The drug is rapidly excreted in the urine and in the feces. It is not detected in any tissues of the treated animals 48 hours after administration. The metabolism of clometacin is very limited under the experimental conditions used in our study. More than 85% of the drug is excreted in an unchanged from. One metabolite, representing 4 to 10% of the excreted radioactivity, was found in the urine and identified as 1-(2-methyl-3-p-chloro phenylcarbinol-6-hydroxy) indol acetic acid. This metabolite was not detected in the feces, nor in the different tissues 4 or 48 hours after i.v. or oral administration of the drug.