To clarify the absorption mechanism of baicalin and to investigate the interaction between baicalin and antibiotics, the pharmacokinetics of baicalin and its aglycone baicalein in normal rats and in antibiotic-treated (with a mixture of neomycin and streptomycin) rats were investigated. A method of liquid chromatography-tandem mass spectrometry with a selected reaction monitoring mode was used to determine the plasma concentrations of baicalin and baicalein. The plasma concentration of total baicalein was determined after treatment of beta-glucuronidase/sulfatase. Unpaired Student's t-test was used for statistical comparison. After oral administration of baicalin, the absolute bioavailability of baicalin, based on the AUC of the baicalin parent form, was 2.2+/-0.2% in normal rats, which decreased to 1.5+/-0.2% in antibiotic-treated rats. Based on the AUC of total baicalein after enzymatic hydrolysis, the absorption of baicalin was 28.0+/-5.7%, which significantly decreased to 7.7+/-1.2% in antibiotic-treated rats. After oral administration of baicalein, the glucuronides/sulfates of baicalein were predominant in plasma. Based on the AUC of total baicalein after enzymatic hydrolysis, the absorption of baicalein was 36.1+/-4.4% in normal rats, which did not differ markedly from that in antibiotic-treated rats (P>0.05). The presence of baicalin isomer in plasma after oral administration of baicalin indicated that baicalin was transformed, at least in part, to baicalein before absorption, then to its conjugated metabolites in rats. Aminoglycosides decreased the absorption of baicalin, but not of baicalein, which indicated that antibiotics decreased the decomposition of baicalin to baicalein by inhibiting intestinal flora, and further influenced the absorption, metabolism and efficacy of baicalin. These interactions should be paid attention to in clinical studies when baicalin is administered in combination with antibiotics.
A sensitive and high-throughput LC-MS-MS method was developed for simultaneous determination of nitrendipine (NIT) and its major metabolite, dehydronitrendipine (DNIT) in human plasma using nifedipine as the internal standard. Plasma samples were prepared based on a simple liquid-liquid extraction. The extracted samples were analyzed on a Zorbax SB C(18) column interfaced with a triple quadrupole tandem mass spectrometer. Positive atmospheric pressure chemical ionization was employed as the ionization source. The analytes were detected by use of selected reaction monitoring mode. Standard curves were linear (r > or = 0.995) over the concentration range of 0.4-40 ng/mL for NIT and 0.2-20 ng/mL for DNIT. The intra- and inter-run precision was measured to be below 8.5% for NIT and DNIT. The inter-run accuracy was less than 4% for the analytes. The overall extraction recoveries of NIT and DNIT were determined to be about 75% and 78% on average, respectively. The chromatographic run time was approximately 3 min. More than 120 samples could be assayed daily with this method, including sample preparation, data acquisition and processing. The method developed was successfully used to investigate plasma concentrations of NIT and DNIT in a pharmacokinetic study of volunteers who received NIT orally.
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