Stability of Aspirin in Different Media Aspirin rapidly hydrolyzes in various aqueous, organic, andbiological media. The purpose of this investigation was to study the decomposition of aspirin in the media that comes in contact with it duringanalysis in biological fluids for pharmacokinetic studies. These mediaincluded water, water-polyethylene glycol 400,water-methanol-aceticacid, phosphate buffer, freshly drawn blood and plasma from control ratsand rats deprived of water for 36 hr, and blood precipitated with acetonitrile. Studieswere also conducted to determine the decomposition asa functionof temperature and pH. Of the varioussolvent systems studied,aspirin was found most stable in water-polyethylene glycol (4:1, v/v),which provides an excellent medium for preparation of intravenousdosage forms. Phosphate buffer showed significant catalysis of aspirinhydrolysis. A more than fivefold increasein the hydrolysisof aspirin wasnoted when the temperature was raised to 37' from 22.5'. The hydrolysisof aspirin in rat blood was 13times faster than that in plasma, with anaverage half-life in blood of -13 min. This creates significant problemsin aspirin disposition kinetic studies. Mixingthe blood sample immediately after collection with twice the volume of acetonitrile and thencentrifuginggives a plasma-acetonitrile mixture in which no lysisof bloodcells is observed
Stability of Aspirin in Different Media<br> Aspirin rapidly hydrolyzes in various aqueous, organic, and<br>biological media. The purpose of this investigation was to study the decomposition of aspirin in the media that comes in contact with it during<br>analysis in biological fluids for pharmacokinetic studies. These media<br>included water, water-polyethylene glycol 400,water-methanol-acetic<br>acid, phosphate buffer, freshly drawn blood and plasma from control rats<br>and rats deprived of water for 36 hr, and blood precipitated with acetonitrile. Studieswere also conducted to determine the decomposition as<br>a functionof temperature and pH. Of the varioussolvent systems studied,<br>aspirin was found most stable in water-polyethylene glycol (4:1, v/v),<br>which provides an excellent medium for preparation of intravenous<br>dosage forms. Phosphate buffer showed significant catalysis of aspirin<br>hydrolysis. A more than fivefold increasein the hydrolysisof aspirin was<br>noted when the temperature was raised to 37' from 22.5'. The hydrolysis<br>of aspirin in rat blood was 13times faster than that in plasma, with an<br>average half-life in blood of -13 min. This creates significant problems<br>in aspirin disposition kinetic studies. Mixingthe blood sample immediately after collection with twice the volume of acetonitrile and then<br>centrifuginggives a plasma-acetonitrile mixture in which no lysisof blood<br>cells is observed
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