An Evaluation of the Dose-Dependent Inhibition of CYP1A2 by Rofecoxib Using Theophylline as a CYP1A2 Probe

This study was undertaken to determine whether rofecoxib can interfere with CYP1A2 activity in humans using theophylline as a probe substrate. Single oral doses of theophylline were administered to each of three panels of 12 healthy subjects receiving daily doses of rofecoxib for 7 days to examine the effect of rofecoxib administration on the absorption and disposition of theophylline. Each panel was administered doses of 12.5, 25, or 50 mg of rofecoxib or a matching placebo in a two-way, randomized, crossover fashion and administered a single oral 300-mg dose of theophylline on day 7 of rofecoxib or placebo administration. Plasma concentrations of theophylline were monitored for 48 hours postdose to assess differences in pharmacokinetics. All three commercially marketed doses of rofecoxib were found to slow the clearance of theophylline with no detectable effect on absorption. CL/F values for theophylline were estimated from AUC infinity and by point estimates from the concentrations of drug in plasma at 12 and 24 hours postdose. The point estimates of CL/F were found to be in agreement with those derived from AUC.

A non-radioactive in situ hybridization method that does not require RNAse-free conditions

This report describes a quick and versatile method to perform non-radioactive in situ hybridization in which none of the hybridization steps are performed under RNAse-free conditions. This study demonstrates that in situ hybridization can be performed without an RNAse-free environment provided that the concentration of RNAse introduced during the experiment does not reach 0.1 microg/ml, a concentration that is unlikely to be achieved through an accidental contamination. Moreover, evidence is provided that the only step sensitive to RNAse degradation is the pretreatment since degradation during the hybridization step can not occur due to a very efficient protective effect exerted by formamide. Finally, our data suggest that endogenous RNAse activity might be readily neutralized through paraformaldehyde fixation. A feature of this method is the strong fixation that ensures a perfect tissue preservation, even at level of the fine structure of the cell processes. The method allows a uniform tissue penetration by sodium periodate and sodium borohydride treatment and can be easily used in combination with diaminobenzidine immunohistochemistry for double labeling experiments.