Azithromycin persists for a week in vagina
Azithromycin is present at high levels in the vagina for up to a week after administration of a 1-gram dose, a new study shows. Poor absorption of the antibiotic is thus not the cause of treatment failure.
The study involved self-collected vaginal swabs from 21 women; 11 (median age 30 [24 to 38] years)of which repeatedly collected samples within 24 hours after azithromycin treatment, while 10 (median age 34 [20 to 48] years) swabbed repeatedly over 9 days post-treatment. Only those without Chlamydia were included while those with contraindications to azithromycin and who were pregnant were excluded.
Blood samples were also collected from the participants. Liquid chromatography-mass spectrometry was used to measure azithromycin levels from the sample. Phosphatidylcholine and leucine enkephalin were used as internal standards.
Each of the 11 women provided 12 vaginal swabs over the course of a 24-hour period, while each of the 10 women provided 10 swabs over the course of a 9-day period.
Of the 24-hour swabs, concentrations of the leu-enkephalin internal controls remained consistent across all runs and samples, suggesting consistency in sample preparation. The mean normalized concentration of azithromycin an hour after treatment was 136 (1 to 1,453) mcg/mg of lipid.
The highest mean dose was observed 5 hours post-treatment and was calculated to be 1,031 (173 to 2,693) mcg/mg. The increase was statistically significant (p<0.001). Mean plasma azithromycin concentration was 915 (388 to 1,406) ng/mL 4 hours after treatment.
The mean normalized azithromycin was highest at 2 days after treatment (2,206 [721 to 5,791] mcg/mg of lipid) in the 9-day swab samples. The lowest mean concentration was 384 (139 to 1,024) mcg/mg reported 9 days after treatment. The decline was statistically significant (p=0.01).Finally, mean plasma concentration of azithromycin after 4 hours was 930 (408 to 1,518) ng/mL.