PubMed · 8990763
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W E Golden, N Sanchez, B Pitts. 1996. Pseudomembranous colitis.. https://pubmed.ncbi.nlm.nih.gov/8990763/
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Gels formed in situ following oral administration of 1% (w/v) aqueous solutions of gellan to rats and rabbits were evaluated as sustained-release vehicles. The formulation contained calcium ions in complexed form, the release of which in the acidic environment of the stomach caused gelation of the gellan gum. The in vitro release of theophylline from the rigid gellan gels followed root-time kinetics over a period of 6 h. Plasma levels of theophylline after oral administration of gellan solutions and a commercial oral sustained-release liquid dosage form containing an identical drug concentration were compared in both rats and rabbits. Bioavailability of theophylline from gellan gels formed by in situ gelation in the animal stomach was increased by four-fivefold in rats and threefold in rabbits compared with that from the commercial oral formulation. There was no significant difference in the mean residence times of theophylline when administered by these two vehicles.
Effects of renal insufficiency and of aging on the pharmacokinetics of NS-49, a newly developed phenethylamine class alpha(1A)-adrenoceptor agonist eliminated mainly by renal excretion, were investigated in rats after a single administration of (14)C-NS-49. The gromerular filtration rate (GFR) in the partially nephrectomized rats was about half that in the sham-operated rats, and the plasma creatinine concentration in the former was well above the normal limit. Plasma concentrations of radioactivity after intravenous or oral administration of (14)C-NS-49 were much higher in the nephrectomized rats than in the intact and sham-operated rats. As a result, the areas under the plasma concentration-time curve (AUC(0-infinity)) after intravenous and oral administrations respectively increased 5-fold and 7-fold after partial nephrectomy. The elimination half-life (t(1/2,beta)) was increased about 2-fold by partial nephrectomy. The systemic availability for the partially nephrectomized rats remained unchanged, indicative that partial nephrectomy does not affect the absorption of NS-49. Plasma concentrations of radioactivity after intravenous or oral administration of (14)C-NS-49 to 88-week-old rats were higher than in 7-week-old rats, the AUC(0-infinity) value for the aged rats being about two times higher. The aged rats, unlike the nephrectomized rats, showed no marked difference in the t(1/2,beta), value, whereas their V(ss) value was about half that for the young rats. These findings are considered to be caused by physiologic age-related changes; decrease in renal function and loss of body water. Systemic availability in the aged rats did not differ from that in the young, indicative that aging has no effect on the extent of absorption of this drug.
Recombinant human erythropoietin (Epo) is frequently administered by intravenous (i.v.) injection for the clinical treatment of renal anemia. Oral (per os; p.o.) administration is desired as an alternative route to i.v. administration, and liposomes have been chosen as a drug carrier. We found previously that after a p.o. administration to rats of Epo entrapped in liposomes before gel filtration, the Epo was absorbed, but variability in the number of days of appearance and in the levels of pharmacological effects, i.e. , the peak of circulating reticulocyte counts (RTC), was observed. The purpose of the present study was to examine the distribution characteristics of Epo in liposomes and intestinal absorption of liposomal Epo in rats by using purified Epo entrapped in liposomes after gel filtration (Epo/liposomes). The distribution characteristics of Epo/liposomes were determined by measuring the Epo in liposomes by a radioimmunoassay, high-performance liquid chromatography and zeta potential measurements. We observed that the protein part of Epo was mostly entrapped in liposomes, and was not adsorbed by the liposomal membrane at middle and high Epo p.o. doses, but the zeta potential of the Epo/liposomes increased negatively with the increase in the Epo p.o. doses. These results suggest that the sialic acid part of Epo entrapped in liposomes may project out from liposomes, depending on the entrapped Epo concentration. Little Epo was adsorbed or penetrated into liposomes when it was added to empty liposomes. After the p. o. administration of Epo/liposomes, the peak of RTC appeared at a 2-day delay on day 6, without variation and without dose dependency in comparison with that after i.v. administration. These results suggest that one of the reasons for the variability may be because the non-entrapped Epo and/or Epo/liposomes itself affected the intestinal absorption of Epo/liposomes. In conclusion, Epo/liposomes without nonentrapped Epo may be clinically useful for the oral administration of Epo.