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Artemisinin (ART) drugs showed declining plasma concentrations after repeated oral dosing, known as time-dependent pharmacokinetics (PK). ART and dihydroartemisinin (DHA) were adopted as representatives to evaluate the roles of first-pass effects and systemic metabolism in time-dependent PK by comparison of oral versus intravenous administration and 1 dose versus 5 consecutive doses PK in rats and dogs, respectively. The hepatic extraction ratio (ER h) and the intestinal elimination changes were further investigated in rats to distinguish the roles of hepatic first-pass effect or intestinal first-pass effect. The induction capacities of ARTs to cytochrome P450 (CYP450) in rats and human cells were evaluated as well. For ART, only the oral groups showed time-dependent PK. A fairly high ER h that obtained for ART was not sensitive to multiple oral doses. An increased elimination and CYP450 expression have also been found in the intestine. For DHA, though a significant CYP450 induction was observed, neither time-dependent PK nor changes in the first-pass effects was found. In conclusion, time-dependent PK of ART was mainly caused by the increased intestinal first-pass effect rather than hepatic first-pass effect or systemic metabolism. DHA was not involved in auto-induction elimination, thus showing no time-dependent PK. [ABSTRACT FROM AUTHOR]

Montmorillonite (Mt) plays a very important role in controlling drug delivery. In this paper, the hydrochloric acid (HCl) treated Mt. was exploited to obtain composites, which were able to enhance dexibuprofen (IBU) loading and achieve to sustain release drug. The textural properties of the Mt. were strongly dependent on the treatment of HCl. The drug loading of pristine Mt. was 190 mg/g, while it was increased to 298 mg/g for Acid-Mt. In vitro release showed that the IBU was released about 92% from IBU/Acid-Mt within 12 h, while the pure IBU was released all within 4 h in simulated intestinal fluid, which meant that the IBU/Acid-Mt were able to retard the drug release with a controlled manner. The release profiles of IBU from composites were fitted by Higuchi and Korsmeyer-Peppas equations, which manifested that diffusion sustained release dominated the main mechanism. Meanwhile, in vivo pharmacokinetics studies in rats displayed that the IBU/Acid-Mt exhibited better gradual drug release than the commercial IBU suspension. For the IBU/Acid-Mt composites, the area under the plasma concentration-time curve from 0 to 24 h ( AUC 0–24 ) and mean residence time ( MRT 0–24 ) were 644.49 ± 73.26 μg/h/mL and 7.65 ± 0.48 h, both of which were significantly larger than commercial IBU suspension ( AUC 0–24 of 439.88 ± 84.41 μg/h/mL and MRT 0–24 of 3.10 ± 0.38 h), respectively ( P  < 0.05). The relative bioavailability of IBU/Acid-Mt was 154.11% ± 27.41% compared to commercial IBU suspension. As a result, the IBU/Acid-Mt is expected to achieve sustained release and extend residence time in plasma. [ABSTRACT FROM AUTHOR]