August 15, 2012

Q&A: Mechanism of Action of Metronidazole

Metronidazole is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat several conditions. Metronidazole is available by mouth, as a cream, and by injection into a vein. Common side effects include nausea, a metallic taste, loss of appetite, and headaches. Occasionally seizures or allergies to the medication may occur. Metronidazole began to be commercially used in 1960 in France. It is on the World Health Organization's List of Essential Medicines. It is available in most areas of the world.

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This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find more useful one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.
In this article:
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

MCQ exam: clinical scenario

A patient suffering from suspected Pseudomembranous colitis is treated with metronidazole. The role of metronidazole in eradicating the causative organism is to:

a) Cleave bacterial DNA
b) Dissolve the pseudomembranes
c) Disrupt bacterial mitochondrial function
d) Compete with broad spectrum antibiotics
e) This statement is false, metronidazole is contraindicated in suspected Pseudomembranous colitis

MCQ questions & answers on

MCQ exam: answer

The correct answer is A.

MCQ exam: explanation

Pseudomembranous colitis or antibiotic-induced colitis is acute diarrheal disease caused by Clostridium difficle. It is associated with the use of broad spectrum antibiotics especially ampicillin, lincomycin, clindamycin, cephalosporins etc. The broad spectrum antibiotics cause the destruction of the normal bacterial flora in the gut which results in the overgrowth of Clostridium difficle which is resistant to most of these antibiotics. Clostridium difficle is an anaerobic bacteria. Due to its anaerobic character it is resistant to all the usual antibiotics.

The drug of choice is Metronidazole which is the most effective antibiotic for all anaerobic infections. Reduced metronidazole, which is cytotoxic but short-lived, interacts with DNA to cause a loss of helical structure, strand breakage, and resultant inhibition of nucleic acid synthesis and cell death in the anaerobic bacteria.

1). "Metronidazole". The American Society of Health-System Pharmacists. Archived from the original on 6 September 2015. Retrieved 31 July 2015.
2). McDonald LC, Gerding DN, Johnson S, Bakken JS, Carroll KC, Coffin SE, et al. (March 2018). "Clinical Practice Guidelines for Clostridium difficile Infection in Adults and Children: 2017 Update by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA)". Clinical Infectious Diseases. 66 (7): e1–e48. doi:10.1093/cid/cix1085. PMC 6018983. PMID 29462280.
3). Rossi S, ed. (2013). Australian Medicines Handbook (2013 ed.). Adelaide: The Australian Medicines Handbook Unit Trust. ISBN 978-0-9805790-9-3.

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