| Azithromycin is a semisynthetic 15-membered macrolide antibiotic, and it was widely used for bacterical infections in clinical therapy. The liquid chromatography-tandem mass spectrometry had been applied to the pharmacokinetic study of azithromycin in human, and the liquid chromatography-electrospray ion trap mass spectrometry had been applied to the metabolic study of azithromycin in mammals (rat, beagle dog, and human).1. The pharmacokinetic study of azithromycin in humanA selective and sensitive liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for the determination of azithromycin in human plasma was developed, and this method was applied to the bioequivalence investigation of azithromycin in human. After a liquid-liquid extraction, the post-treatment samples were analyzed on a Zorbax Eclipse XDB C8 column interfaced with a triple quadrupole tandem mass spectrometer, and clarithromycin was used as the internal standard. Positive electrospray ionization was employed as the ionization source. The mobile phase consisted of methanol-water-formic acid (75:25:0.5, v/v/v). Selected reaction monitoring (SRM) using the precursorâ†'product ion combinations of m/z 375â†'m/z 591 and m/z 748â†'m/z 158 were used to quantify the azithromycin and clarithromycin, respectively. The linear range of azithromycin was 1.0-1000 ng/mL, and the lower limit of quantification (LLOQ) was 1.0 ng/mLThe method was applicated to the bioequivalence investigation of 25 healthy volunteers after oral administration of 0.5 g azithromycin granules (test formulationâ… ), azithromycin tablets (test formulationâ…¡) and azithromycin tablets (reference formulation), the main pharmacokinetic parameters of testâ… , testâ…¡and reference formulation were:Tmax(1.9±0.6), (1.9±0.7) and (1.8±0.6) h, Cmax(441.0±129.5), (421.7±142.8) and (426.2±128.1) ng/mL, t1/2(48.0±10.7), (44.8±8.0) and (45.6±9.8) h, AUC0-t (4564.6±1312.0), (4743.1±1616.1) and (4654.6±1489.4) ng-h/mL, AUC0-∞(5224.6±1529.7), (5373.4±1854.7) and (5278.7±1675.9) ng·h/mL, respectively. According to AUC0-t, the relative bioavailability of azithromycin granules and tablets were (99.7±14.0) and (101.8±13.8)%. According to the two one-side tests, azithromycin of tests and reference formulation were bioequivalent. 2. The metabolism of azithromycinThree reference substances of azithromycin metabolites came from the chemical synthesis, and a reference substance bought from a company. The four reference substances were Descladinose Azithromycin,3’-N-desmethyl Azithromycin,9a-N-desmethyl Azithromycin,9a-N-desmethyl descladinose Azithromycin, and they were identified by NMR and ESI-MS". The mass spectometric characteristics of azithromycin and its metabolites were summarized to conjecture the unknown chemical structure of azithromycin metabolites.The metabolism of azithromycin in mammals (rat, dog, and human) were investigated by the LC/ESI-MS" method, among which human was the first time. A total of 11 metabolites were found, 10 metabolites had been known,1 metabolite was new and 4 metabolites were identified, among which 3 metabolites were identified for the first time (Descladinose Azithromycin,3’-N-desmethyl Azithromycin and 9a-N-desmethyl descladinose Azithromycin). A total of 8 metabolites were found in urine sample of healthy volunteers after oral administration of 500 mg azithromycin tablets. The metabolites of azithromycin in human were 3’-N-desmethyl descladinose Azithromycin, 3’-N-desmethyl,9a-N-desmethyl Azithromycin,3’-N-didesmethyl Azithromycin,9a-N-desmethyl Azithromycin,3"-O-desmethyl Azithromycin,3’-N-desmethyl Azithromycin, Hydroxy azalide Azithromycin and Hydroxy desosamine Azithromycin, except for the original drug azithromycin. The major metabolic pathways of azithromycin in human were O-demethylation, N-demethylation, N-desmethyl descladinose and hydroxylation. The metabolites in rat were similar with those in human, only an additional metabolite was Descladinose Azithromycin. Two additional metabolites were found in beagle dog, including 9a-N-desmethyl descladinose Azithromycin and Sulfated desosamine Azithromycin, phase II metabolites of Sulfated desosamine Azithromycin was a new one. |
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