Development and Validation of an HPLC Method for Simultaneous Detection and Quantification of Paracetamol and Etodolac in Human Plasma and Its Application to a Pharmacokinetic Study

A simple, reproducible, and feasible RP-HPLC method has been developed for simultaneous determination of two commonly used drugs, paracetamol (PCM) and etodolac (EDL), in human plasma. In this specific and accurate method, tinidazole was used as an internal standard. Chromatographic separation was achieved on a Hiber C18 250 × 4.6 mm id, 5 μm particle size, column using the isocratic mobile phase 10 mM potassium phosphate buffer (adjusted to pH 7.5)–acetonitrile (70 : 30, v/v) at a flow rate of 1 mL/min. Detection was at 235 nm. The linear concentration range of the assay was 0.100 to 50.00 μg/mL for both analytes, and the linear regression correlation coefficient was (r2 > 0.99). The recovery of PCM and EDL were 94.03 and 88.27%, respectively. The method was validated for specificity, linearity, precision, accuracy, reproducibility, and stability. The intraday and interday precision and accuracy values for PCM and EDL met the acceptance criteria of U.S. Food and Drug Administration guidelines. PCM and EDL were stable in a battery of stability studies, viz., bench top, dry extract, and freeze-thaw cycles. This developed and validated method was successfully applied to quantitatively assess the PCM and EDL for the first time in human plasma obtained from a pharmacokinetic study performed with 12 healthy human volunteers.