Novel contribution to the simultaneous monitoring of pramipexole dihydrochloride monohydrate and levodopa as co-administered drugs in human plasma utilizing UPLC–MS/MS

An efficient, selective, sensitive, and rapid ultra-performance liquid chromatography tandem mass spectrometry method was established and validated for the quantification of pramipexole dihydrochloride monohydrate and levodopa simultaneously in human plasma with the aid of diphenhydramine as an internal standard. A simple protein precipitation technique with HPLC grade acetonitrile was efficiently utilized for the cleanup of plasma. The analysis was performed using a Hypersil gold 50 mm × 2.1 mm (1.9 µm) column and a mobile phase of 0.2% formic acid and methanol (90: 10 v/v). The triple-quadrupole mass spectrometer equipped with an electrospray source operated in the positive mode was set up in the selective reaction monitoring mode (SRM) to detect the ion transitions m/z 212.15 →153.01, m/z 198.10→ 135.16, and m/z 255.75 → 166.16 for pramipexole dihydrochloride monohydrate, levodopa, and diphenhydramine, respectively. The method was thoroughly validated according to FDA guidelines and proved to be linear, accurate, and precise over the range 100–4000 pg/mL for pramipexole dihydrochloride monohydrate and 60–4000 ng/mL for levodopa. The proposed method was effectively applied for monitoring both drugs in plasma samples of healthy volunteers.