Metronidazole (Flagyl) versus ...

Metronidazole vs. Vancomycin (Vancocin)

Clostridium difficile-associated diarrhea

Metronidazole and vancomycin are equally effective for mild Clostridium difficile-associated diarrhea (CDAD), but vancomycin is superior for treating severe CDAD5, 7. Vancomycin therapy can significantly reduce the risk of 30-day mortality among patients with severe Clostridium difficile infection8.

So vancomycin may be preferable to metronidazole for severe disease. However, metronidazole is still currently recommended as first-line treatment, mainly because it is less expensive and because of concern of vancomycin-resistant organisms in the intestinal lumen.

Comparative clinical trials

In the prospective observational study among the patients with mild CDAD, treatment with metronidazole or vancomycin resulted in clinical cure in 90% and 98% of the patients. However, in severe CDAD clinical cure was 76% in metronidazole group and 97% in vancomycin group.

Results from 2 randomized, controlled trials of vancomycin, metronidazole, or tolevamer for Clostridium difficile Infection (CDI) 7 Metronidazole Vancomycin
Clinical success 72.7% 81.1%
Clinical success in patients with severe CDI 66.3% 78.5%

Note: Combination therapy of metronidazole and vancomycin is not superior to monotherapy because it is associated with an increased risk of side effects9.


Metronidazole vs. Ciprofloxacin (Cipro)


Ciprofloxacin is preferable to metronidazole1, because treatment with ciprofloxacin eradicates both pathogens (Clostridium perfringens and E. coli) and results in an optimal restoration of normal pouch flora. Also, ciprofloxacin is better tolerated than metronidazole2.

Metronidazole vs. Albendazole


Albendazole and metronidazole are equally effective in the treatment of giardiasis3-4. Albendazole is better tolerated than metronidazole.

Results of randomized, double-blind, clinical trial of albendazole versus metronidazolefor adult giardiasis 6 Metronidazole Albendazole
Regimen 250 mg 3 times daily for 5 days 400 mg daily for 5 days
Efficacy rate 85.3% 82.6%
Most common side effects bitter taste, headache, vomiting and dizziness abdominal pain

Further reading

  • 1. Gosselink MP, Schouten WR, van Lieshout LM, Hop WC, Laman JD, Ruseler-van Embden JG. Eradication of pathogenic bacteria and restoration of normal pouch flora: comparison of metronidazole and ciprofloxacin in the treatment of pouchitis. Dis Colon Rectum. 2004 Sep;47(9):1519-25. Jul 8. PubMed
  • 2. Shen B, Achkar JP, Lashner BA, Ormsby AH, Remzi FH, Brzezinski A, Bevins CL, Bambrick ML, Seidner DL, Fazio VW. A randomized clinical trial of ciprofloxacin and metronidazole to treat acute pouchitis. Inflamm Bowel Dis. 2001 Nov;7(4):301-5. PubMed
  • 3. Romero-Cabello R, Robert L, Munoz-Garci'a R, Tanaka J. Randomized study comparing the safety and efficacy of albendazole and metronidazole in the treatment of giardiasis in children. Rev Latinoam Microbiol. 1995 Oct-Dec;37(4):315-23. PubMed
  • 4. Misra PK, Kumar A, Agarwal V, Jagota SC. A comparative clinical trial of albendazole versus metronidazole in giardiasis. Indian Pediatr. 1995 Mar;32(3):291-4. PubMed
  • 5. Zar FA, Bakkanagari SR, Moorthi KM, Davis MB. A comparison of vancomycin and metronidazole for the treatment of Clostridium difficile-associated diarrhea, stratified by disease severity. Clin Infect Dis. 2007 Aug 1;45(3):302-7. PubMed
  • 6. Cañete R, Rodríguez P, Mesa L, Brito K, Prior A, Guilhem D, Novaes MR. Albendazole versus metronidazole in the treatment of adult giardiasis: a randomized, double-blind, clinical trial. Curr Med Res Opin. 2012 Jan;28(1):149-54. PubMed
  • 7. Johnson S, Louie TJ, Gerding DN, et al. Vancomycin, metronidazole, or tolevamer for Clostridium difficile infection: results from two multinational, randomized, controlled trials. Clin Infect Dis. 2014 Aug 1;59(3):345-54. PubMed
  • 8. Stevens VW, Nelson RE, Schwab-Daugherty EM, et al. Comparative Effectiveness of Vancomycin and Metronidazole for the Prevention of Recurrence and Death in Patients With Clostridium difficile Infection. JAMA Intern Med. 2017 Feb 6. PubMed
  • 9. Li R, Lu L, Lin Y, et al. Efficacy and Safety of Metronidazole Monotherapy versus Vancomycin Monotherapy or Combination Therapy in Patients with Clostridium difficile Infection: A Systematic Review and Meta-Analysis. PLoS One. 2015 Oct 7;10(10):e0137252 PubMed

Published: March 31, 2008
Last updated: February 21, 2017


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