Effect of Different Dosage Frequency of Polymyxin B on Rat Nephrotoxicity.

BACKGROUND: Polymyxin B, as the final treatment against multidrug-resistant Gram-negative bacilli, is widely used in clinical practice. However, little is known about the nephrotoxicity of polymyxin B. The purpose of this study was to elucidate the relationship between polymyxin B nephrotoxicity and daily administration frequency. METHODS: Sprague-Dawley rats were randomly divided into three groups: 18 mg/kg/q24 h group (Group A, once daily), 9 mg/kg/q12 h group (Group B, twice daily), and normal saline control group (Group C). The rats were injected subcutaneously for 5 consecutive days with the same daily total dose and different frequency of administration. The serum creatinine (SCr) and blood urea nitrogen (BUN) of each group before administration (0 h), and 8 and 24 h after administration, were measured by tail vein blood sampling. On the sixth day, the rats in each group were killed, the left kidney was taken for pathological section observation, and the results of each group were compared. RESULTS: After 96 h of administrated polymyxin B, the total average level of SCr in Group A was 56.98±12.42 µmol/L, that of Group B was 52.02±8.68 µmol/L, and that of Group C was 34.36±5.39 µmol/L. BUN was 9.86±4.58, 10.54±4.08, and 3.55±0.73 mmol/L in Groups A, B, and C, respectively. The daily urinary protein excretion was 5004.45±1333.84 µg in Group A, 4608.04±1444.42 µg in Group B, and 2096.33±215.28 µg in Group C. In addition, according to the observation of pathological slices, compared with Group A, the number of exfoliated and necrotic cells of renal tubules in Group B was higher, and the morphological changes were more serious. CONCLUSION: The experimental results showed that the renal toxicity in rats treated with a twice-daily subcutaneous dose of polymyxin B was higher than that in rats treated with once-daily dose of polymyxin B.

Pharmacokinetic and metabolic profiling studies of sennoside B by UPLC-MS/MS and UPLC-Q-TOF-MS.

Sennoside B is a specific dianthrone compound extracted from senna, which is widely used as a stimulant laxative but has potential side effects. This study aimed to obtain the metabolic and pharmacokinetic data of sennoside B. The metabolic profiles of sennoside B were obtained from rat plasma, urine, bile and feces by an ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). As a result, 14 metabolites were structurally identified and the proposed metabolic pathways of sennoside B included hydrolysis to aglycones, release of rhein-type anthrone, and extensive conjugation. As the only compound detected in the plasma samples after intravenous and intragastric administrations, the prototype was selected as the plasma marker in the pharmacokinetic study. A simple and sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the quantitation of sennoside B in rat plasma. The linear range of sennoside B was 5-1000 ng/mL (R2 ≥ 0.991) and the lowest limit of quantification (LLOQ) was 5 ng/mL. The intra- and inter- precisions of the assay were less than 10%, whereas accuracy ranged from 85.80% to 103.80%. The extraction recovery, matrix effect and stability of sennoside B were within acceptable limits. The established method was well validated and successfully applied to the pharmacokinetic study of sennoside B. The oral absolute bioavailability of sennoside B was calculated as 3.60% and the value apparent volume of distribution of intravenous and intragastric administrations were 32.47 ±â€¯10.49 L/kg and 7646 ±â€¯1784 L/kg, respectively. The maximum plasma concentrations were 212.6 ±â€¯50.9 µg/L and 14.06 ±â€¯2.73 µg/L for intravenous and intragastric dosing groups, respectively. According to the current results of pharmacokinetic and metabolic profiling studies, metabolites with high abundance in tissues would be the next object in the pharmacokinetic study of sennoside B.