Nonoxynol 9 (non-9) is the active ingredient in a wide variety of vaginal contraceptive preparations. The manufacturer recommendation for optimal contraceptive practice is repeated application every 6 h. We studied the in vitro activity of non-9 against Chlamydia trachomatis (E/UW-5/Cx) and its toxicity against HeLa 229 cells and monkey cervical epithelial cells. With a contact time of 6 h, non-9 was toxic to HeLa cells at concentrations of 50 micrograms/ml or greater and to monkey cervical cells at 100 micrograms/ml or greater. Inhibitory effects of non-9 on extracellular chlamydiae were observed at concentrations of 50 micrograms/ml or greater. Inhibition of intracellular growth of chlamydiae in monkey cervical cells was observed at a nontoxic concentration of 50 micrograms/ml. Our studies show that non-9 has antichlamydial activity. However, owing to its toxicity to cervical cells in vitro, the effects of prolonged use of non-9 in vivo should be further studied
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