Povidone‐Iodine in the Treatment of Metronidazole‐Resistant Trichomonas vaginalis

Abstract

EDITORIAL COMMENT: Resistance of Trichomonas vaginalis to metronidazole has been controversial because of the inability to confirm conclusively the resistance of strains isolated from patients with refractory vaginal trichomoniasis. Treatment failure has thus been attributed to reinfection by the sexual partner, noncompliance, poor absorption or inactivation by vaginal flora. The authors of this study do appear to have conclusively demonstrated resistance to metronidazole using an appropriate test method. They do not however, exclude noncompliance or possible poor absorption. The treatment of refractory trichomoniasis is usually to treat again with higher doses of metronidazole. This has sometimes been successful but in other cases has been unsuccessful despite high doses and prolonged courses of treatment. Povidone‐iodine (Betadine) has often been used successfully in the treatment of vaginal trichomoniasis, but treatment failures have occurred. It is believed that treatment failures are due to the inability of topical therapy to eradicate the organism from extravaginal sites, e.g. urethra, Bartholin glands. The fact that the authors of this paper found povidone‐iodine douches more effective on the second occasion could relate to the fact that povidone‐iodine releases iodine slowly. Antiprotozoal action is dependent upon the release of iodine. Thus a 10‐minute douche could be more effective than a 2‐minute douche. There remains the possibility of spontaneous resolution in the reported patient. Although povidone‐iodine douches are generally safe, it is possibly not a good idea to recommend such a practice unreservedly. There have been several reports of neonatal hypothyroidism following maternal use of povidone‐iodine in pregnancy (negative feedback in the fetus, the iodine causing inhibition of thyroid stimulating hormone release); also hypersensitivity reactions to iodine can be expected in approximately 1 in 3,000 patients.