Quantitative determination of pidotimod in human plasma by liquid chromatography tandem mass spectrometry: application to a bioequivalence study.

A highly sensitive and simple LC-MS/MS method after one-step protein precipitation was developed and validated for determination of pidotimod (CAS 121808-62-6) in human plasma using dextrophan (CAS 125-73-5) as internal standard (IS). Pidotimod and IS were separated on a YMC-ODS-AQ C18 column using 0.5% formic acid and methanol as a mobile phase at a flow rate of 0.3 mL/min. Detection was performed on positive ion mode of the transitions at 245.0→134.0 for pidotimod and 258.1→157.0 for IS by selected reaction monitoring (SRM). The assay exhibited a linear range of 0.05-10.0 µg/mL. The lower limit of quantification were 0.05 µg/mL. Validation results indicated that the accuracy as determined from quality control samples was in the range of  - 4.00-6.48%. Intra-day and inter-day precision was ≤  8.35% and ≤  8.00%, respectively. The developed method was successfully applied to a bioequivalence study in 20 healthy Chinese volunteers following a single oral dose of 800 mg pidotimod. The simple, inexpensive protein precipitation and high-throughput method makes it a suitable and valuable tool in the investigation of the clinical pharmacokinetics and bioequivalence.