The US Food and Drug Administration (FDA) has affirmed the use of letrozole (LTZ) combined with palbociclib (PLB) to treat breast malignant tumor growth in postmenopausal women. A straightforward and extremely sensitive reversed-phase high-performance liquid chromatography method with photodiode array detection (RP-HPLC–PDA) was created and validated for the simultaneous determination of LTZ and PLB in rat plasma. The parameters used to give the best separation were a C18 column (150 mm × 4.6 mm, 3.5 μm) as the stationary phase with an isocratic mobile phase composed of methanol–30 mM ammonium acetate at a ratio of 60:40 (v/v), pH = 5.5, a flow rate of 0.8 mL/min, and detection wavelengths of 240 and 220 nm for LTZ and PLB, respectively. The developed method was assessed by the FDA rules over a range of 10–600 ng/mL for LTZ and PLB. The mean of %recovery of LTZ and PLB extracted from rat plasma by acetonitrile-based deproteinization was 91.06 ± 2.73 and 90.30 ± 1.95%, respectively, and the limits of detection were 5 ng/mL for LTZ and 7 ng/mL for PLB in rat plasma. The mean values of Tmax and Cmax were 6 ± 0.00 h and 266.96 ± 21.23 ng/mL for LTZ and 4 ± 0.00 h and 508.75 ± 61.56 ng/mL for PBL, respectively, after intraperitoneal administration of both drugs to rats. The developed HPLC–PDA method was demonstrated to be robust and was effectively applied to study the pharmacokinetics of LTZ and PLB in rat plasma.

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A Microemulsion Electrokinetic Chromatography method coupled with diode array detector (MEEKC-DAD) was developed for the first time and found to be efficient, sensitive, and selective for the simultaneous analysis of Trifluridine (FTD), and its metabolites 5-(trifluoromethyl) uracil (FTY) and 5-carboxy-2′-deoxyuridine (5CDU), and Tipiracil (TIP) in rat plasma. Sample pre-treatment involved a simple protein precipitation from plasma using acetonitrile. The separation was achieved using a fused silica capillary (65 cm total length, 55 cm effective length and 50 µm i.d.) and a microemulsion solution consisted of 1.66% sodium dodecyl sulfate (SDS), 0.91% heptane, 6.61% 1-butanol, and 90.72% borate buffer (20 mM, pH 9.5). Electrophoretic separation was carried out at 20 °C and 20 kV. The samples were injected for 40 s at 20 mbar and detected simultaneously at 205 nm. The electrophoretic parameters indicated that the developed MEEKC-DAD method permitted complete resolution of the analytes within 13 min. The developed method was fully validated according to the FDA guidelines for bioanalytical method validation. The method was linear in the range 200–4000 ng/ml for FTD, FTY, 5CDU, and 100–1000 ng/ml for TIP. The intra/inter-day accuracy and precisions were ≤4% for all drugs. Extraction recovery and stability were also assessed and were within acceptable range. After being validated, the method was applied for the determination of the studied drugs in plasma samples collected from rats injected intraperitoneally with a combination of FTD and TIP. The results obtained were used to study the pharmacokinetics of FTD with its metabolite and TIP in rat plasma.

LE300 is a novel dopamine receptor antagonist used to treat cocaine addiction. In the current study, a sensitive and fast liquid chromatography–tandem mass spectrometry (LC-MS/MS) has been established and validated for the simultaneous analysis of LE300 and its N-methyl metabolite, MLE300, in rat plasma with an application in a pharmacokinetic study. The chromatographic elution of LE300, MLE300, and Ponatinib (IS, internal standard), was carried out on a 50 mm C18 analytical column (ID: 2.1 mm and particle size: 1.8 μm) maintained at 22 ± 2 °C. The run time was 5 min at a flow rate of 0.3 mL/min. The mobile phase consisted of 42% aqueous solvent (10 mM ammonium formate, pH: 4.2 with formic acid) and 58% organic solvent (acetonitrile). Plasma samples were pretreated using protein precipitation with acetonitrile. The electrospray ionization (ESI) source was used to generate an ion-utilizing positive mode. A multiple reaction monitoring mass analyzer mode was utilized for the quantification of analytes. The linearity of the calibration curves in rat plasma ranged from 1 to 200 ng/mL (r2 = 0.9997) and from 2 to 200 ng/mL (r2 = 0.9984) for LE300 and MLE300, respectively. The lower limits of detection (LLOD) were 0.3 ng/mL and 0.7 ng/mL in rat plasma for LE300 and MLE300, respectively. Accuracy (RE%) ranged from −1.71% to −0.07% and −4.18% to −1.48% (inter-day), and from −3.3% to −1.47% and −4.89% to −2.15% (intra-day) for LE300 and MLE300, respectively. The precision (RSD%) was less than 2.43% and 1.77% for the inter-day, and 2.77% and 1.73% for intra-day of LE300 and MLE300, respectively. These results are in agreement with FDA guidelines. The developed LC-MS/MS method was applied in a pharmacokinetic study in Wistar rats. Tmax and Cmax were 2 h and 151.12 ± 12.5 ng/mL for LE300, and 3 h and 170.4 ± 23.3 ng/mL for MLE300.