Comparative pharmacokinetics and tissue distribution of norfloxacin-glycine acetate in flounder, (Paralichthys olivaceus) at two different temperatures

Clinical pharmacokinetics of norfloxacin-glycine acetate after intravenous and oral administration in pigs

The pharmacokinetics and dosage regimen of norfloxacin-glycine acetate (NFLXGA) was investigated in pigs after a single intravenous (i.v.) or oral (p.o.) administration at a dosage of 7.2 mg/kg body weight. After both i.v. and p.o. administration, plasma drug concentrations were best fitted to an open two-compartment model with a rapid distribution phase. After i.v. administration of NFLXGA, the distribution (t_1/2α) and elimination half-life (t_1/2β) were 0.36 ± 0.07 h and 7.42 ± 3.55 h, respectively. The volume of distribution of NFLXGA at steady state (Vd_ss) was 4.66 ± 1.39 l/kg. After p.o. administration of NFLXGA, the maximal absorption concentration (C_max) was 0.43 ± 0.06 µg/ml at 1.36 ± 0.39 h (T_max). The mean absorption (t_1/2ka) and elimination half-life (t_1/2β) of NFLXGA were 0.78 ± 0.27 h and 7.13 ± 1.41 h, respectively. The mean systemic bioavailability (F) after p.o. administration was 31.10 ± 15.16%. We suggest that the optimal dosage calculated from the pharmacokinetic parameters is 5.01 mg/kg per day i.v. or 16.12 mg/kg per day p.o.

The power of size. 1. Rate constants and equilibrium ratios for accumulation of organic substances related to octanol-water partition ratio and species weight

Most of the thousands of substances and species that risk assessment has to deal with are not investigated empirically because of financial, practical, and ethical constraints. To facilitate extrapolation, we have developed a model for accumulation kinetics of organic substances as a function of the octanol-water partition ratio (Kow) of the chemical and the weight, lipid content, and trophic level of the species. The ecological parameters were obtained from a previous review on allometric regressions. The chemical parameters, that is, resistances that substances encounter in water and lipid layers of organisms, were calibrated on 1,939 rate constants for absorption from water for assimilation from food and for elimination. Their ratio was validated on 37 laboratory bioconcentration and biomagnification regressions and on 2,700 field bioaccumulation data. The rate constant for absorption increased with the hydrophobicity of the substances with a Kow up to about 1,000 and then leveled off, decreasing with the weight of the species. About 39% of the variation was explained by the model, while deviations of more than a factor of 5 were noted for labile, large, and less hydrophobic molecules as well as for algae, mollusks, and arthropods. The efficiency for assimilation of contaminants from food was determined mainly by the food digestibility and thus by the trophic level of the species. A distinction was made between substances that are stable, that is, with a minimum elimination only, and those that are labile, that is, with an excess elimination probably largely due to biotransformation. The rate constant for minimum elimination decreased with the hydrophobicity of the substance and the weight of the species. About 70% of the variation was explained by the model, while deviations of more than a factor of 5 were noted for algae, terrestrial plants, and benthic animals. Labile substances were eliminated faster than isolipophilic stable compounds, but differences in laboratory elimination and accumulation were small compared with those in field accumulation. Excess elimination by vertebrates was faster than by invertebrates. Differences between terrestrial and aquatic species were attributed to water turnover rates, whereas differences between trophic levels were due to the food digestibility. Food web accumulation, expressed as organism-organic solids and organism-food concentrations ratios could be largely explained by ecological variables only. The model is believed to facilitate various types of scientific interpretation as well as environmental risk assessment.

Comparative pharmacokinetic profiles of two norfloxacin formulations after oral administration in rabbits

The pharmacokinetics and tissue distribution of two norfloxacin (NFLX) formulations, norfloxacin-glycine acetate (NFLXGA) and norfloxacin nicotinate (NFLXN), were compared after single oral administration with a dose of 5 mg equivalent NFLX base/kg of body weight in twenty rabbits. The pharmacokinetic characteristics of all formulations were fitted by a two-compartment open model. The elimination half-life (T1/2beta) of NFLX (3.37+/-1.37 hr) was not significant as compared with those of NFLXN (3.61+/-0.65 hr) and NFLXGA (3.93+/-1.54 hr). The absolute bioavailability (F) of NFLX, NFLXN and NFLXGA was calculated as 29%, 45% and 40%. In addition, tissue distribution of NFLXN and NFLXGA did not show any differences of NFLX concentrations in liver, kidney, serum and muscle. From the present results, it could be suggested that NFLXN and NFLXGA are considered to be bioequivalent when they use oral medication for rabbits.