Pharmacokinetics of an indomethacin pro-drug: apyramide after intravenous administration in dog

Chronobiological variations of indomethacin pharmacokinetic parameters in sheep

A two-phase study to investigate the influence of administration time on pharmacokinetics of indomethacin in sheep was performed. In phase I, 12 animals were allocated to four groups, each corresponding to a different time: 08:00, 14:00, 20:00, 02:00 h. Sheep received an intravenous administration of 1 mg/kg indomethacin. In phase II, each group was administered indomethacin with a 12-h difference compared to Phase I. The trial was performed in autumn, and animals were subjected to a natural light:dark cycle of 10:14 h. Blood samples were taken and processed by high performance liquid chromatography (HPLC) with ultraviolet detection. For each pharmacokinetic parameter, an analysis of variance was performed to outline the existence of chronobiological variations. Concentration at zero time (C0), hybrid constant for distribution and its half life, hybrid constant for elimination and its half-life, volume of distribution (V(d)), area under the curve (AUC(infinity)) and clearance rate (Cl), presented chronobiological variations (P < 0.05) and were fitted to a cosine equation. The following parameters adjusted to circadian rhythms: C(0) (acrophase: 13.9788 h); AUC(infinity) (acrophase: 13.4377 h); V(d) (acrophase: 0.8245 h) and Cl (acrophase: 1.4965 h). It was concluded that pharmacokinetic parameters of intravenously injected indomethacin in sheep would behave in a different, though predictable, manner according to the animal's biological clock.

Pharmacokinetics of indomethacin in sheep after intravenous and intramuscular administration

The pharmacokinetics of indomethacin (1 mg/kg) was determined in six adult sheep after intravenous (i.v.) and intramuscular (i.m.) injection. Plasma concentrations were maintained within the therapeutic range (0.3-3.0 microg/mL) from 5 to 50 min after i.v. and from 5 to 60-90 min after i.m. administration. After two trials, indomethacin best fitted an open two-compartment model. The mean (+/- SD) volumes of distribution at steady state (Vd(ss)) were 4.10 +/- 1.40 and 4.21 +/- 1.93 L/kg and the mean clearance values (ClB) were 0.17 +/- 0.06 and 0.22 +/- 0.12 L/h x kg for i.v. and i.m. routes, respectively. The elimination phase half-lives did not show any significant difference between routes of injection (t1/2beta = 17.4 +/- 4.6 and 21.25 +/- 4.44 h, i.v. and i.m. respectively). After i.m. administration, plasma maximum concentration (Cmax = 1.10 +/- 0.68 microg/mL) was reached 10 min after dosing; the absorption phase was fast (Kab = 26 +/- 18 h(-1)) and short (t1/2ab = 2.33 +/- 1.51 min) and the mean bioavailability was 91.0 +/- 32.8%, although there was considerable interanimal variation. In some individuals, bioavailability was higher than 100%. This fact combined with the slower elimination phase after i.m. than after i.v. administration, could be related with enterohepatic recycling.

Influence of poly(DL-lactide) nanocapsules on the biliary clearance and enterohepatic circulation of indomethacin in the rabbit

Following intravenous administration, the uptake of colloidal drug carriers by cells of the mononuclear phagocyte system, mainly the Kuppfer cells, may concentrate an encapsulated drug close to the liver parenchymal cells and facilitate its biliary excretion and enterohepatic circulation. To test this hypothesis indomethacin was administered (10 mg/kg) in four groups of 10 rabbits each by intravenous infusion at a constant rate over 2 hr, either in its free form (aqueous solution) or as nanocapsules prepared from preformed poly(DL-lactide). Unchanged drug was assayed in plasma of the two control (sham-operated) groups and in both plasma and bile of the two bile-cannulated groups. Pharmacokinetic analysis led to the conclusion that the uptake of nanocapsules by liver macrophages reduces the concentration of the drug by enhancing its total clearance. This enhancement was due to an increase in biliary clearance, as a result of parallel increases in bile concentration and biliary excretion of the drug. It was also demonstrated that nanocapsules enhance the enterohepatic circulation of indomethacin.