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P2.082 Post-Treatment Detection of Azithromycin in High-Vaginal Swabs Using Liquid Chromatography and Tandem Mass Spectrometry (LC-MS/MS)
  1. L A Vodstrcil1,2,
  2. T Rupasinghe3,
  3. D Tull3,
  4. K Worthington1,4,
  5. M Y Chen1,4,
  6. W M Huston5,
  7. C K Fairley1,4,
  8. M McConville3,
  9. S N Tabrizi2,6,7,
  10. J S Hocking1
  1. 1Melbourne School of Population and Global Health, University of Melbourne, Parkville, Australia
  2. 2Murdoch Children’s Research Institute, Parkville, Australia
  3. 3Metabolomics Australia, Bio21 Institute, University of Melbourne, Parkville, Australia
  4. 4Melbourne Sexual Health Centre, Carlton, Austria
  5. 5Faculty of Health - Biomedical Sciences, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
  6. 6Department of Microbiology and Infectious Diseases, The Royal Women’s Hospital, Parkville, Australia
  7. 7Department of Obstetrics and Gynaecology, University of Melbourne, Parkville, Australia


Introduction Recent data have raised questions over the efficacy of azithromycin 1g for the treatment of chlamydia infection. In order to measure effective absorption, we developed a protocol to quantify the concentration of azithromycin using liquid chromatography and tandem mass spectrometry (LC-MS/MS) in self-collected high-vaginal swabs.

Methods Ten healthy women were asked to self-collect a high-vaginal swab (baseline) prior to taking a 1g dose of azithromycin. A blood sample was collected four hours later to determine plasma concentrations of azithromycin. Participants then self-collected a high vaginal swab each day for a further 9 days. All swabs were preserved in 1ml of 100% Methanol and stored at –80°C prior to analysis. One ml of chloroform containing 10mg/ml of Leucine enkephalin as an internal standard was added to extract azithromycin. Azithromycin concentrations were calculated using a validated LC-MS/MS method. Data were normalised to the internal standard and to membrane lipid concentrations, measured in the same samples using LC-MS/MS.

Results Azithromycin was detected at varying concentrations in all 10 women in all post-treatment samples. The highest average normalised azithromycin concentration of 953ng/ml (range = 267–2200ng/ml, standard error of mean (sem) = 181ng/ml) was detected on day 2 post-treatment. The lowest average azithromycin concentration was 164ng/ml (range = 51–387ng/ml, sem = 42ng/ml), 9 days post-treatment. The average concentration of azithromycin detected in blood samples was 339ng/ml (range = 107–628ng/ml, sem = 57ng/ml). In 9/10 women azithromycin concentrations remained above 64ng/ml, the hypothesised mean inhibitory concentration (MIC) of azithromycin for chlamydia, for the entire 9 days.

Conclusion We have validated a method for detecting the azithromycin concentration in self-collected high-vaginal samples using LC-MS/MS. Azithromycin concentrations remained above the reported MIC of 64ng/ml for up to 9 days post-treatment in high-vaginal swabs from 10 healthy women.

  • antimicrobials
  • azithromycin
  • chlamydia

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