Interspecies pharmacokinetic comparisons and allometric scaling of napsagatran, a low molecular weight thrombin inhibitor.

The objective of this work was to assess the pharmacokinetics of napsagatran, a low molecular weight thrombin inhibitor, after intravenous administration in a variety of laboratory animals, and prospectively to help design the first pharmacokinetic studies in man. Napsagatran is actively excreted into the bile and urine of various species and pronounced species-differences in its pharmacokinetics are observed. It is, therefore, an interesting compound to use in tests of the limitations of presently available inter-species scaling methods. The present data suggest that allometric exponent values which are consistent with the values expected for physiological processes and small organic molecules are not necessarily associated with successful predictions in man when active transport processes are involved in the disposition of the compounds. For example, compared with the values observed in man, the clearance (CL), non-renal clearance (CL(nr)) and the volume of distribution at steady state (Vd(ss)) were over-predicted by 3-, 7- and 2-fold, respectively, by use of allometry. Of the species tested, the cynomolgus monkey seemed to be the most useful for predicting kinetics in man when the approach based on concentration-time transformations was used. Thus, for half-life (t(1/2)), CL and Vd(ss), the observed mean values of 1.7 h, 459 mL min(-1) and 24 L kg(-1) in man were very close to the values predicted from the cynomolgus monkey (1.7 h, 652 mL min(-1) and 22 L kg(-1), respectively). The results show that there are large inter-species differences for kidney and liver excretion of napsagatran. This is probably because of the involvement of active transport processes, which compromised the kinetic extrapolation from animal to man, although a more thorough investigation of the transporters involved in the disposition of napsagatran is necessary to enable better understanding of the species differences observed.

Antimalarial activity of the bisquinoline trans-N1,N2-bis (7-chloroquinolin-4-yl)cyclohexane-1,2-diamine: comparison of two stereoisomers and detailed evaluation of the S,S enantiomer, Ro 47-7737.

The S,S enantiomer of the bisquinoline trans-N1,N2-bis(7-chloroquinolin-4-yl)cyclohexane-1,2-diamine, Ro 47-7737, is significantly more potent against chloroquine-resistant Plasmodium falciparum than the R,R enantiomer and the previously described racemate. Both the enantiomers and the racemate are more potent inhibitors of heme polymerization than chloroquine, and their activities are probably mediated by inhibition of this parasite-specific process. The S,S enantiomer, Ro 47-7737, was studied in more detail and proved to be a potent antimalarial in the treatment of P. vivax ex vivo and P. berghei in vivo. Its suppression of P. berghei growth in a mouse model (50% effective dose, 2.3 mg/kg of body weight) was equal to that of chloroquine and mefloquine, and Ro 47-7737 was found to be more potent than these two drugs in the Rane test, in which the curative effect of a single dose is monitored. The dose at which 50% of animals were permanently cured (34 mg/kg) was markedly superior to those of chloroquine (285 mg/kg) and mefloquine (> 250 mg/kg). When administered orally at 50 mg/kg, Ro 47-7737 also showed a faster clearance of parasites than either chloroquine or mefloquine, and unlike the other two compounds, Ro 47-7737 showed no recrudescence. In a study to compare prophylactic efficacies of oral doses of 50 mg/kg, Ro 47-7737 provided protection for 14 days compared to 3 days for mefloquine and 1 day for chloroquine. The good curative and prophylactic properties of the compound can be explained in part by its long terminal half-life. The ability to generate parasite resistance to Ro 47-7737 was also assessed. With a rodent model, resistance could be generated over eight passages. This rate of resistance generation is comparable to that of mefloquine, which has proved to be an effective antimalarial for many years. Toxicity liabilities, however, ruled out this compound as a candidate for drug development.

4-aminoquinoline analogs of chloroquine with shortened side chains retain activity against chloroquine-resistant Plasmodium falciparum.

We have synthesized several 4-aminoquinolines with shortened side chains that retain activity against chloroquine-resistant isolates of Plasmodium falciparum malaria (W. Hofheinz, C. Jaquet, and S. Jolidon, European patent 94116281.0, June 1995). We report here an assessment of the activities of four selected compounds containing ethyl, propyl, and isopropyl side chains. Reasonable in vitro activity (50% inhibitory concentration, < 100 nM) against chloroquine-resistant P. falciparum strains was consistently observed, and the compounds performed well in a variety of plasmodium berghei animal models. However, some potential drawbacks of these compounds became evident upon in-depth testing. In vitro analysis of more than 70 isolates of P. falciparum and studies with a mouse in vivo model suggested a degree of cross-resistance with chloroquine. In addition, pharmacokinetic analysis demonstrated the formation of N-dealkylated metabolites of these compounds. These metabolites are similarly active against chloroquine-susceptible strains but are much less active against chloroquine-resistant strains. Thus, the clinical dosing required for these compounds would probably be greater for chloroquine-resistant strains than for chloroquine-susceptible strains. The clinical potential of these compounds is discussed within the context of chloroquine's low therapeutic ratio and toxicity.

Animal pharmacokinetics and metabolism of the new antimalarial Ro 42-1611 (arteflene).

Ro 42-1611 (arteflene) is a new synthetic structural analogue of yingzhaosu, a Chinese traditional herbal drug, now under development for treatment of malaria. The in vivo activity of arteflene in a mouse animal model was 4-5 fold higher after parenteral than after oral administration. Pharmacokinetics of the drug were investigated in mice, rats, dogs, marmosets and cynomolgus monkeys. Plasma concentrations of arteflene were determined using a specific HPLC-UV method; the limit of quantification was 45 ng/ml using 0.5 ml plasma. The oral bioavailability was very low and variable (0.6% in mice, 4-5% in rats, 2.5 +/- 1% in dogs, < or = 0.5% in marmosets and < 0.5% in cynomolgus) as expected from the high metabolic clearance and the relative short apparent half-life (1.4-4.7 h). However, a metabolite (MA) was observed in plasma of all species indicating that drug was absorbed but underwent extensive first-pass metabolism. MA was also detected in samples of human plasma, collected during an oral tolerability study in healthy volunteers. After incubation of 14C-arteflene with liver microsomes of mice, rats, dogs and humans, the same major metabolite was detected and both samples were identical to Ro 47-6936 which was chemically synthesized as a reference compound. The in vitro activity of Ro 47-6936 was tested against Plasmodium falciparum and found to be about 1/4 that of the parent drug. Therefore, this metabolite makes a significant contribution to the biological activity in vivo, partially explaining the high activity of arteflene after oral administration in spite of its low bioavailability. Moreover, comparison of the metabolic patterns from human, rat and dog microsomes indicated that the dog is an appropriate species for toxicological evaluations.

High-performance liquid chromatographic determination of the mucoregulatory drug CO/1408 in rat plasma and urine.

A sensitive and selective high-performance liquid chromatographic (HPLC) method was developed for the determination of the mucoregulatory drug CO/1408 in plasma and urine. Samples containing an internal standard were prepared for analysis using a simple clean-up procedure based on Extrelut solid-phase extraction and chromatographed using a reversed-phase analytical column. Isocratic elution with a mobile phase consisting of 25 mM phosphate buffer (pH 2.5)-acetonitrile-methanol [85:10:5 or 87:9:4 (v/v) for plasma or urine analysis, respectively] was effected at a flow-rate of 0.8 ml/min. The eluate was monitored with an ultraviolet-visible variable-wavelength detector at 200 nm. The limit of quantification for the assay of CO/1408 was 80 ng/ml for plasma and 1 per 0.1 ml for urine samples. In spite of the high solubility of CO/1408 in water, the recovery from plasma and urine was very good and reproducible. The method was found to be applicable to pharmacokinetic studies of the drug in the rat.

Capillary gas chromatographic determination of epomediol in human plasma and urine using a rapid solid-phase extraction.

A simple and precise method for the quantitation of epomediol in human plasma and urine is described. Each biological sample is added with the internal standard and applied directly to an Extrelut-1 solid-phase column. After absorption the column is eluted with chloroform and the eluate is evaporated to dryness. The residue, reconstituted in ethanol, is analysed by capillary gas chromatography. No interferences from possible metabolites or endogenous constituents can be noted. The method has been applied to human pharmacokinetic studies: the results of a subacute administration to volunteers are presented.

High-performance liquid chromatographic assay of nesosteine in human plasma and urine.

A high-performance liquid chromatographic method for the quantitation of the mucoactive drug sodium 2-(3-thiazolidinylcarbonyl)benzoate in plasma and urine was developed, involving liquid-liquid extraction under acidic conditions and reversed-phase chromatography using ultraviolet detection at 210 or 235 nm. The extraction efficiency, linearity, limit of detection, precision and accuracy were determined. Products of the main biotransformation of the drug, involving hydrolysis of the amidic bond, do not interfere. The method is selective, precise, reproducible and applicable to studies of the pharmacokinetic behaviour of the drug in humans. Pharmacokinetic parameters derived from six healthy subjects following acute intravenous administration of the drug (150 mg) are presented.

Quantitation of hexaprazol in human plasma and urine by capillary gas chromatography with nitrogen-sensitive detection.

A selective and sensitive gas chromatographic assay for hexaprazol, a new antiulcer drug, in human plasma and urine has been developed. The method involves liquid-liquid extraction and capillary gas chromatography with nitrogen-sensitive detection. The limit of quantitation of plasma hexaprazol is ca. 25 ng/ml. The assay procedure permits the measurement of the levels of the unchanged drug following its clinical administration to humans.