The TABLE provides a summary of the clinical performance of the various tests for T vaginalis. 15-18
The 5-nitroimidazole agents, which include metronidazole and tinidazole, are the preferred agents for the treatment of trichomoniasis.
Dosing regimen. While a single oral dose of metronidazole 2 g has long been the mainstay of treatment for T vaginalis, this regimen recently has been questioned, at least in women, due to the high posttreatment positive rate of T vaginalis, which ranges from 5% to 37%.19,20 These cases may be due to reinfection by untreated sexual partners. They also may result from treatment failure, however, specifically inadequate treatment time.21 Overall, patients treated with single-dose metronidazole are 1.87 times more likely to experience treatment failure compared with those treated with a multidose regimen.19 Since many cases of T vaginalis infection are associated with bacterial vaginosis co-infection, recommending metronidazole 500 mg twice daily for 7 days is beneficial because this course provides optimal treatment for both infections.
Treatment during pregnancy. In the minds of some investigators, treatment of T vaginalis in asymptomatic pregnant women is problematic. One study demonstrated a similar to slightly increased risk of preterm delivery for metronidazole-treated patients compared with a placebo-treated group.22 Limitations of the study included atypical treatment dosing (2 doses of metronidazole 2 g given 48 hours apart at 16 to 23 weeks’ gestation and repeated at 24 to 29 weeks’ gestation) and a latency between the last dose of metronidazole and preterm delivery.22
We believe that all pregnant women, symptomatic or asymptomatic, should be treated because of the sexually transmitted nature of the infection and the probability that most asymptomatic carriers ultimately become symptomatic.
Cost of treatment. Generic oral metronidazole is very inexpensive. The approximate retail price for 14 metronidazole 500-mg tablets is $15.69 (www.goodrx.com). By contrast, a single-dose course of tinidazole (four 500-mg tablets) costs approximately $45. Accordingly, we reserve tinidazole for patients who have experienced a treatment failure with metronidazole or who cannot tolerate metronidazole.
Drug‒alcohol interaction. With both metronidazole and tinidazole, patients must abstain from alcohol during treatment and for 72 hours after completing therapy because these drugs have a disulfiram-like reaction with ethanol.