Mouse pharmacokinetic analysis.

Mouse pharmacokinetic studies were conducted by using female CD-1 mice for compounds 1, 11, and 12, while BALB/c mice were used for compound 13. Mouse body weights were 19 to 28 g, and on the morning of dosing, mice were split randomly into 3 dosing groups to receive the test article by either intravenous (i.v.) tail vein injection or oral (p.o.) gavage. After dosing, blood samples were collected via cardiac puncture at specific time points (n = 3 mice/time point) through 24 h (K₂EDTA as an anticoagulant) and processed for plasma. Antibiotic concentrations in the plasma samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The LC-MS/MS analysis was conducted by using analyte/internal standard peak area methods. The internal standard was AN3365 (21), and the instrument used was an API4000 QTRAP instrument (AB Sciex). The limit of quantitation (LOQ) was 1 or 2 ng/ml. Pharmacokinetic analyses of the mean plasma concentration-time profiles were performed by using WinNonlin Pro version 5.2. A compartmental model was used for the data for i.v. dosing, and a noncompartmental model was used for the data for p.o. dosing. The concentration-time curve after an i.v. dose showed a biexponential decline with first-order elimination. Compounds 1 and 13 were formulated in saline (0.9% [wt/vol] NaCl) at 7.5 mg/ml, and the pH was adjusted to >5 by the addition of NaOH. Compound 11 was formulated to 6.5 mg/ml in water-dimethylacetamide-ethanol (EtOH) (76:19:5), and the pH was adjusted to >5 by the addition of NaOH. Compound 12 was formulated to 7.5 mg/ml in PEG 300-propylene glycol (PG)-water (55:25:20), and the pH was adjusted to >5 by the addition of NaOH.