Pharmacokinetics of E-6087, a new anti-inflammatory agent, in rats and dogs.

The pharmacokinetics of E-6087, a newly developed cyclooxygenase-2 inhibitor, was studied in rats and dogs after single oral and intravenous doses. In both animal species, E-6087 was characterized by a long elimination half-life (20-35 h), a low plasma clearance (0.10-0.22 l h(-1) kg(-1)) and a relatively large volume of distribution (2-6 l kg(-1)). Oral bioavailability was lower in dogs than in rats whereas a faster elimination was found in rats. Multiple peaks were present regardless of administration route and animal species, suggesting the existence of enterohepatic circulation. Gender effect on the pharmacokinetics of E-6087 was only found in rats, with greater exposure and longer elimination in females than in males. Food intake reduced the bioavailability (approximately 22%) with no apparent changes in the absorption rate. After oral dosing of 1, 5 and 25 mg kg(-1) to rats, linearity was lost at the highest dose due to the low aqueous solubility of E-6087. Drug absorption was improved by micronization. E-6087 and E-6132, (a pharmacologically active metabolite), showed different pharmacokinetics. The higher percentage of E-6087 at early times suggests that E-6087 is the main compound responsible for in vivo activity, although E-6132 would contribute to the activity at later times.

Development and validation of two chromatographic methods for the quantification of E-6087 and one of its metabolites, E-6132, in rat plasma.

E-6087 is a nonsteroidal anti-inflammatory compound under development that selectively inhibits cyclooxygenase-2. In vitro studies have shown that one of its metabolites, E-6132, also inhibits this enzyme. Due to chromatographic reasons, two reverse phase HPLC methods were developed and validated in order to elucidate which compound is responsible for the pharmacological activity in vivo. Chromatographic separation of E-6087 was achieved using acetonitrile-phosphate buffer (pH 2.5; 25 mM) (60:40, v/v) as mobile phase and two 4.6 x 150 mm x 5 microm Inertsil ODS-2 columns. For E-6132, two Inertsil ODS-3 columns and 52% of acetonitrile were used instead. Internal standards and fluorescence detection differed between both methods. The same on-line solid-phase extraction method was used. Mean retention times for E-6087 and E-6132 were 15.2 (+/-1.3) and 36.1 (+/-0.6) min, respectively. The methods were selective and linear over the concentration range of 10--500 ng ml(-1) (r(2)>0.996) for E-6087 and 5--200 ng ml(-1) (r(2)>0.997) for E-6132. The limits of quantitation were 10 ng ml(-1) (E-6087) and 5 ng ml(-1) (E-6132) with a precision and accuracy <16% (E-6087) and <11% (E-6132). Mean recoveries from plasma were 43.2-61.9% (E-6087) and 60.4--65.2% (E-6132). For both compounds, both inter-assay and intra-assay precision and accuracy were within acceptable limits (<15%). As an example of the suitability of these methods, the results from a pharmacokinetic study are reported. After single oral administration of 5 mg kg(-1) of E-6087 to rats, plasma concentrations of E-6087 at peak time were higher than those of E-6132, suggesting that activity is mainly due to E-6087.

Validation of a chromatographic method to determine E-6006 and its metabolite E-6332 in rat and dog plasma by solid-phase extraction and capillary gas chromatography. Application in pharmacokinetics.

E-6006, 5-(alpha-[2-(dimethylamino)ethoxy]-2-thienylmethyl)-1-methyl-1H-pyrazole is a new antidepressive compound and E-6332, 5-(alpha-[2-(methylamino)ethoxy]-2-thienylmethyl)-1-methyl-1H-pyrazole is its desmethylate metabolite. With the aim of quantifying E-6006 and E-6332, simultaneously in rat or dog plasma, a method of analysis based on solid-phase extraction coupled with capillary gas chromatographic system with N-P detection was developed and validated. E-6006, E-6332 and its internal standard (E-4018) were isolated from plasma using an off-line semiautomatic solid-phase extraction method. Gas chromatography separations were carried out by means of 12 m length, 0 2 mm (i.d.) and 0.33 microm (f.t.) ULTRA 1 type capillary column in splitless mode of injection at 190 degrees C, with a TSD or specific nitrogen--phosphorus detector. No peaks interfering with the quantification of E-6332 and E-6006 were observed. The limit of quantification was 5 ng/ml with a precision and accuracy <17%. The peak height ratios were proportional to E-6332 and E-6006 concentration over the range from 5 to 600 ng/ml (r(2)>0.998). Mean recoveries of E-6332, E-6006 and internal standard from rat plasma were between 57.1 and 82.6. Intra-assay precision coefficients were <8.0 and <11.8%, respectively, for E-6332 and E-6006, with an accuracy <12.6 and <9.7%. Both inter-assay precision and accuracy were within acceptable limits (<15%). In dog, the results were very similar to those obtained in rat. To show an example of the suitability of the method to determine E-6332 and E-6006, plasma profiles obtained after single oral and intravenous administration of 20 mg/kg to rats and 25 mg/kg to dogs are reported.

Absorption, distribution, metabolism and excretion of cizolirtine, a new analgesic compound, in rat and dog.

1. The pharmacokinetics of cizolirtine citrate, a new analgesic compound, were studied in the rat and dog following single oral and intravenous doses. 2. Absorption of radioactivity was fast and complete regardless of the species, and no dose and food-related differences were found. However, the elimination half-life of unchanged cizolirtine was shorter in rat than in dog. 3. Tissue distribution of total radioactivity in rat differed widely and a high affinity for liver, kidney, gastrointestinal and pigmented tissues was observed. In blood and almost all tissues the highest concentrations were reached at 20 min; beyond that time the decline of radioactivity in most tissues was parallel to that in blood. 4. The percentage of radioactivity excreted in the rat was 68% in urine and 21% in faeces, the latter being apparently due to drug enterohepatic circulation. In the dog, 92 and 4% of the radioactivity was found in urine and faeces respectively. The contribution of renal excretion to cizolirtine elimination was <5% in rat and 20% in dog. Twelve metabolites were detected in rat and six in the dog by radio-hplc analysis of urine.

Absorption, distribution and excretion of [14C]-Lesopitron after single and repeated administration in rats and dogs.

Disposition of [14C]-lesopitron was investigated in male rats and dogs after single and repeated oral administration. Radioactivity was rapidly and efficiently absorbed from gastrointestinal tract following oral administration. After 7 days, the radioactivity was mainly excreted into feces via bile. The cumulative urinary and fecal excretion was 99% and 75% of the administered dose in rats and dogs, respectively. [14C]-Lesopitron was widely distributed in rats, with the highest concentrations in liver and kidney, while the concentration in brain was similar to that in plasma. Radioactivity in most tissues decreased essentially in parallel with that in plasma. In rats, plasma levels of [14C]-lesopitron radioactivity achieved steady state on day 2 of repeated administration. The distribution pattern obtained after 7 consecutive daily oral doses was similar to that in the single-dose study. At 72 h after the last administration, tissue radioactivity was fully eliminated and no accumulation occurred. After i.v. administration in rats and dogs, plasma concentrations of lesopitron decreased biphasically with an apparent elimination half-life of 100 min. The absolute bioavailability of lesopitron was about 10%, suggesting an important first-pass effect. In rats, the lesopitron plasma concentrations were similar to those obtained for its metabolites (5-hydroxylesopitron and PmP), whereas in dogs, the PmP plasma concentrations were higher than those for lesopitron and 5-hydroxylesopitron.