Effects of competitive red blood cell binding and reduced hematocrit on the blood and plasma levels of [14C]Indapamide in the rat.
The effects of chlorthalidone and acetazolamide on the red blood cell binding of indapamide were investigated. Both drugs caused a substantial decrease in the amount of indapamide bound to the erythrocytes in vitro. This effect was demonstrated by a change in the indapamide blood/plasma ratio from approximately 6 in control samples, to a value of 1 when either of the displacing agents was added. Coadministration of acetazolamide with 14C-labeled indapamide to rats, resulted in a 5-fold drop in the blood levels of total radioactivity, relative to rats dosed with [14C]indapamide alone. Concomitantly, there was a 2-fold increase in the plasma levels of total radioactivity after acetazolamide coadministration. In rats whose hematocrits had been reduced by extensive bleeding, there were only minor alterations in the blood/plasma partitioning of [14C]indapamide. Thus, chlorthalidone and acetazolamide were able to displace indapamide from erythrocytes in vitro and in vivo, possibly by competition at a carbonic anhydrase binding site. The pharmacokinetics of drugs which are extensively bound to erythrocytes may be significantly altered by the presence of other agents capable of competitive binding.[1]References
- Effects of competitive red blood cell binding and reduced hematocrit on the blood and plasma levels of [14C]Indapamide in the rat. Lettieri, J.T., Portelli, S.T. J. Pharmacol. Exp. Ther. (1983) [Pubmed]
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