AN IMPROVED MICROMETHOD FOR THE DETERMINATION OF ACETAMINOPHEN IN PLASMA BY VISIBLE SPECTROPHOTOMETRY: APPLICATION TO A PHARMACOKINETIC STUDY IN RABBITS
Objective: To report a simple and economic alternative spectrophotometric micro-method for the determination of acetaminophen using 200 Âµl of plasma sample.
Methods: The analyses were based on a simple colorimetric test in which p-aminophenol, after an acidic hydrolysis step, is reacted with phenol in an alkaline medium to form an indophenol dye which exhibits a maximum extintion at 625 nm. The micro method was validated according to the international criteria, and then it was used for the quantification of plasma levels of acetaminophen after rectal administration of 100 mg of the drug to male New Zealand rabbits.
Results: The analytical recovery was 100.97%, with solutions of 5âˆ’25 Âµg/ml (plasma/water). The linearity with plasma solutions was good (R2 = 0.995), at the same concentration levels. The within-run and between-run precision, as well as accuracy expressed as coefficient of variation, were less than 8%. The mean accuracy was 102.24%. The stability was proved for a one-week period at âˆ’20 Â°C. The pharmacokinetic parameters were computed by non-linear regression analysis. The non-compartment model analysis was used to fit the in vivo data.Conclusion: The validation parameters were within acceptable limits for clinical studies. The analysis was adequate for the determination of acetaminophen in small plasma samples, and it can be easily adapted by any hospital or clinical laboratory with non-special equipment.
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