Validated HPLC Method for the Pharmacokinetic Study of Linezolid in Rats

Linezolid is an oxazolidinone with potent antibacterial activity against multidrug resistant Gram‐positive bacteria. This study aimed to develop and validate a sensitive, rapid and reliable high‐performance liquid chromatography‐photodiode array detector method for determining linezolid concentrations in the plasma and urine and to further characterize the pharmacokinetics of linezolid in rats. Chromatographic separation was performed using a SinoPak BEH C18 column with isocratic elution (acetonitrile: water, 28:72, v/v). The retention times of linezolid and the internal standard are 3.30 and 5.20 min, respectively. The calibration curve for linezolid was linear over the concentration range of 0.25–50.0 μg/mL in rat plasma and 1.00–100.0 μg/mL in rat urine. Intra‐ and inter‐assay precision values were below 9.00%, with accuracy ranging from 0.67% to 8.34%. Plasma samples were extracted using acetonitrile‐mediated protein precipitation, and the recovery was > 93%. Following intragastric (63 mg/kg) and intravenous (25 mg/kg) administration of linezolid to rats, the area under the plasma concentration–time profile from time 0 to infinity were 224.5 and 86.4 μg·h/mL, total clearance were 0.29 and 0.30 L/h/kg, respectively. The cumulative urinary excretion rates of linezolid were 26.2%–27.5% for both administration routes. The presented method can certainly be used for routine analysis of linezolid in plasma and urine.