High-level Review: Updated STI Guidelines Part 2

Dr. Jonathan Ryder, 2nd year UNMC ID fellow

In July 2021 the Center for Disease Control and Prevention (CDC) released their sexually transmitted infections (STI) treatment guideline, an update from 2015.1 Below, senior ID fellow Dr. Jonathan Ryder highlights significant (but by no means comprehensive) changes in this new guideline that can be incorporated into clinical practice and some of the evidence supporting these changes. Part 2 – Bacterial Vaginosis, Trichomonas, Pelvic Inflammatory Disease

Bacterial Vaginosis (BV)

Photomicrograph of vaginal smear with normal epithelia cell and epithelia cell covered with bacteria, known as a clue cell. Image Source: CDC Public Health Image Library https://phil.cdc.gov/Details.aspx?pid=14574

            In a fairly interesting and somewhat controversial recommendation given current medical teachings, the CDC guidelines reversed course on counseling against alcohol consumption during treatment with metronidazole. Citing a Norwegian study, the guideline authors comment that no studies have demonstrating convincing evidence of a clear interaction between alcohol and metronidazole causing a disulfiram-like reaction.6 A study supporting this recommendation from 2002 included 12 healthy volunteers randomized to either oral metronidazole 200mg three times daily or placebo followed by drinking 0.4g/kg of ethanol found no difference in blood acetaldehyde levels or any subjective or objective evidence of a disulfiram-type reaction.7

            Treatment recommendations for BV remain the same with oral metronidazole 500mg twice daily for 7 days or either topical metronidazole gel or clindamycin cream being the preferred options.


Trichomonas vaginalis protozoan parasites. Image Source: CDC Public Health Image Library https://phil.cdc.gov/Details.aspx?pid=14500

            New guidelines recommend a 7-day course of oral metronidazole 500mg twice daily for women with trichomonas, which differs from the prior recommendation of one dose of oral metronidazole 2g. However, in men, the single dose of oral metronidazole 2g is still recommended. The evidence for this change comes from a randomized controlled trial in women with HIV showing increased effectiveness of the 7-day treatment course compared to single dose as well as a meta-analysis including women without HIV showing the same.8 A single dose of oral tinidazole 2g remains an alternative treatment for both men and women.

Pelvic Inflammatory Disease (PID)

            The recommended treatment for PID now includes anaerobic coverage, specifically with metronidazole. Based on a randomized controlled trial comparing ceftriaxone and doxycycline with or without metronidazole, the metronidazole group was found to have decreased presence of endometrial anaerobes, less Mycoplasma genitalium, and reduced pelvic tenderness.10 Therefore, the preferred regimen for PID is ceftriaxone 1g daily plus doxycycline 100mg twice daily plus oral metronidazole 500mg twice daily. Cefotetan or cefoxitin with doxycycline are also recommended. Notably, the higher dose ceftriaxone used for gonorrhea above should be used for PID as well when given as an outpatient.

For another summary of the changes, Ina Park, MD has an excellent Twitter thread:


  1. Fjeld H, Raknes G. Er det virkelig farlig å kombinere metronidazol og alkohol? [Is combining metronidazole and alcohol really hazardous?]. Tidsskr Nor Laegeforen. 2014;134(17):1661-1663. Published 2014 Sep 16. doi:10.4045/tidsskr.14.0081
  2. Visapää JP, Tillonen JS, Kaihovaara PS, Salaspuro MP. Lack of disulfiram-like reaction with metronidazole and ethanol. Ann Pharmacother. 2002;36(6):971-974. doi:10.1345/aph.1A066
  3. Kissinger P, Mena L, Levison J, et al. A randomized treatment trial: single versus 7-day dose of metronidazole for the treatment of Trichomonas vaginalis among HIV-infected women. J Acquir Immune Defic Syndr. 2010;55(5):565-571. doi:10.1097/QAI.0b013e3181eda955
  4. Howe K, Kissinger PJ. Single-Dose Compared With Multidose Metronidazole for the Treatment of Trichomoniasis in Women: A Meta-Analysis. Sex Transm Dis. 2017;44(1):29-34. doi:10.1097/OLQ.0000000000000537
  5. Wiesenfeld HC, Meyn LA, Darville T, Macio IS, Hillier SL. A Randomized Controlled Trial of Ceftriaxone and Doxycycline, With or Without Metronidazole, for the Treatment of Acute Pelvic Inflammatory Disease. Clin Infect Dis. 2021;72(7):1181-1189. doi:10.1093/cid/ciaa101

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