Effects of Verapamil and Diltiazem on the Pharmacokinetics and Pharmacodynamics of Rivaroxaban

Concomitant use of rivaroxaban with non-dihydropyridine calcium channel blockers (non-DHPs) might lead to an increase of systemic rivaroxaban exposure and anticoagulant effects in relation to the inhibition of metabolic enzymes and/or transporters by non-DHPs. This study was designed to evaluate the effects of verapamil and diltiazem on the pharmacokinetics and the prolongation of prothrombin time of rivaroxaban in rats. The data were analyzed using a pharmacokinetic/pharmacodynamics (PK/PD) modeling approach to quantify the influence of verapamil. Verapamil increased the systemic exposure of rivaroxaban by 2.8-fold (p <0.001) which was probably due to the inhibition of efflux transportation rather than metabolism. Prothrombin time was also prolonged in a proportional manner; diltiazem did not show any significant effects, however. A transit PK model in the absorption process comprehensively describes the double-peaks of rivaroxaban plasma concentrations and the corresponding change of prothrombin time with a simple linear relationship. The slope of prothrombin time vs. rivaroxaban plasma concentration in rats was retrospectively found to be insensitive by about 5.4-fold compared to than in humans. More than a 67% dose reduction in rivaroxaban is suggested in terms of both a pharmacokinetic point of view, and the sensitivity differences on the prolongation of prothrombin time when used concomitantly with verapamil

Stereo-Selective Pharmacokinetics of Ilimaquinone Epimers Extracted from a Marine Sponge in Rats

An ilimquinone (IQ) mixture isolated from Hippiospongia metachromia, consisting of IQ and epi-ilimaquinone (epi-IQ), exerts anti-HIV, anti-microbial, anti-inflammatory, and anti-cancer effects. An HPLC-MS/MS method was developed for simultaneous determination of the two epimers in rat plasma, separating them using a biphenyl column. Ascorbic acid is added during the sample preparation to ensure the stability of both isomers. The plasma concentrations of the isomers were monitored following intravenous and oral administration of the IQ mixture in rats as well as the individual epimers that were separately orally administered. Compare to IQ, epi-IQ was much more stable in rat plasma, likely due to its configurations of decalin. Both substances decayed in more than bi-exponential pattern, with an elimination rate constant of 1.2 h−1 for IQ and 1.7 h−1 for epi-IQ. The epi-IQ was distributed more widely than IQ by about two-fold. Consequently, the clearance of epi-IQ was greater than that of IQ by about three-fold. The oral absolute bioavailability for IQ was 38%, and, that for epi-IQ, was 13%. Although the systemic exposure of IQ was greater than that of epi-IQ by ~8.7-fold, the clearance of each isomer was similar when administered either orally or intravenously, when normalized for bioavailability. The stereo-specific behavior of the isomers appears to originate from differences in both their tissue distribution and gastrointestinal permeability