Metronidazole, Indications, Dosage, Side Effects, Interactions

Metronidazole
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Metronidazole is a synthetic nitroimidazole derivative with antiprotozoal and antibacterial activities. Although its mechanism of action is not fully elucidated, un-ionized metronidazole is readily taken up by obligate anaerobic organisms and is subsequently reduced by low-redox potential electron-transport proteins to an active, intermediate product. Reduced metronidazole causes DNA strand breaks, thereby inhibiting DNA synthesis and bacterial cell growth.

A metroimidazole is an antibiotic and antiprotozoal medication used to treat amebiasis; vaginitis; trichomonas infections; giardiasis; anaerobic bacteria; and treponemal infections. It has also been proposed as a radiation sensitizer for hypoxic cells.

Machanism of Action of Metronidazole

Metronidazole, a synthetic antibacterial and antiprotozoal agent of the nitroimidazole class, is used against protozoa such as Trichomonas vaginalis, amebiasis, and giardiasis. Metronidazole is extremely effective against anaerobic bacterial infections and is also used to treat Crohn’s disease, antibiotic-associated diarrhea, and rosacea.Metronidazole is a prodrug. Unionized metronidazole is selective for anaerobic bacteria due to their ability to intracellularly reduce metronidazole to its active form. This reduced metronidazole then covalently binds to DNA, disrupt its helical structure, inhibiting bacterial nucleic acid synthesis and resulting in bacterial cell death.

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Metronidazole is bactericidal, amebicidal, and trichomonacidal in action. The exact mechanism of action of the drug has not been fully elucidated. Metronidazole is un-ionized at physiologic pH and is readily taken up by anaerobic organisms or cells. In susceptible organisms or cells, metronidazoleis reduced by low-redox-potential electron transport proteins (e.g., nitroreductases such as ferredoxin) to unidentified polar product(s) which lack the nitro group. The reduction product(s) appears to be responsible for the cytotoxic and antimicrobial effects of the drug which include disruption of DNA and inhibition of nucleic acid synthesis. Metronidazole is equally effective against dividing and nondividing cells.
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In in vivo studies in rats given metronidazole in dosages of 2-4 mg/100 g of body weight, the drug reportedly inhibited the development of formalin-induced edema in the rat paw. In vitro in neutrophils, metronidazole has a dose-dependent inhibitory effect on generation of hydrogen peroxide and hydroxyl radicals, oxidants that may cause tissue injury at the site of inflammation. This antioxidant effect appears to be caused by a direct effect on neutrophil function and may contribute to the drug’s anti-inflammatory effect in vivo.

Indications of Metronidazole

  • Bacterial Vaginitis
  • Bacterial Infection
  • Amebiasis
  • Aspiration Pneumonia
  • Dental Abscess
  • Clostridium difficile-associated diarrhea and colitis,
  • Helicobacter pylori infection and duodenal ulcer disease, bacterial vaginosis,
  • Giardia lamblia gastro-enteritis, amebiasis
  • STD Prophylaxis
  • Bacteremia
  • Balantidium coli
  • Bone infection
  • Clostridial Infection
  • Crohn’s Disease, 
  • Deep Neck Infection
  • Dientamoeba fragilis
  • Diverticulitis
  • Dracunculiasis
  • Endocarditis
  • Giardiasis
  • Helicobacter Pylori Infection
  • Intraabdominal Infection
  • Joint Infection
  • Lemierre’s Syndrome
  • Meningitis
  • Nongonococcal Urethritis
  • Pelvic Inflammatory Disease
  • Peritonitis
  • Pneumonia
  • Pouchitis
  • Pseudomembranous Colitis
  • Skin or Soft Tissue Infection
  • Surgical Prophylaxis
  • Trichomoniasis
  • For the treatment of anaerobic infections and mixed infections, surgical prophylaxis requiring anaerobic coverage, Clostridium difficile-associated diarrhea and colitis, Helicobacter pylori infection and duodenal ulcer disease, bacterial vaginosis, Giardia lamblia gastro-enteritis, amebiasis caused by Entamoeba histolytica, acne rosacea (topical treatment), and Trichomonas infections.

Therapeutic Indications of Metronidazole

  • Oral metronidazole (extended release formulation) is used in the treatment of bacterial vaginosis caused by Gardnerella vaginalis, Mobiluncus spp, mycoplasma hominis and anaerobes (peptostreptococcus spp and Bacteroides spp).
  • Metronidazole is used in the treatment of periodontal infections caused by Bacteroides species.
  • Oral metronidazole is used in the treatment of giardiasis caused by Giardia lamblia.
  • Some studies indicate that metronidazole may be effective, in combination with bismuth subsalicylate or colloidal bismuth subcitrate, and other oral antibiotic therapy, such as ampicillin or amoxicillin, in the treatment of Helicobacter pylori-associated gastritis and duodenal ulcer. However, metronidazole resistance may occur, especially in patients who have been previously exposed to metronidazole.
  • Metronidazole is used in the treatment of dracunculiasis (guinea worm infection) caused by Dracunculus medinensis. It decreases the inflammation around the ulcer, increasing the ease of removing the worm.
  • Metronidazole is used in the treatment of antibiotic-associated diarrhea and colitis caused by Clostridium difficile.
  • Metronidazole is used in the treatment of inflammatory bowel disease.
  • Metronidazole is used in the treatment of Balantidium coli infection.
  • Oral metronidazole is indicated in the treatment of symptomatic and asymptomatic trichomoniasis, in males and females, caused by Trichomonas vaginalis.
  • Metronidazole is indicated in the treatment of skin and soft tissue infections caused by Bacteroides species, including the Bacteroides fragilis group. Clostridium species, Fusobacterium species, Peptococcus species, and Peptostreptococcus species.
  • Metronidazole is indicated in the treatment of bacterial septicemia caused by Bacteroides species, including the Bacteroides fragilis group, and Clostridium species.
  • Metronidazole is indicated in the treatment of lower respiratory tract infections, including pneumonia, emphysema, and lung abscess, caused by Bacteroides species, including the Bacteroides fragilis group.
  • Intravenous metronidazole is indicated for the prophylaxis of perioperative infections during colorectal surgery.
  • Metronidazole is indicated in the treatment of female pelvic infections, including endometritis, endomyometritis, tubo-ovarian abscess, and postsurgical vaginal cuff infections, caused by Bacteroides species, including the Bacteroides fragilis group, Clostridium species, Peptoccus species, and Peptostreptococcus species.
  • Metronidazole is indicated in the treatment of intra-abdominal infections, including peritonitis, intra-abdominal abscess, and liver abscess, caused by Bacteroides species, including the Bacteroides fragilis group, Clostridium species, Eubacterium species, Peptococcus species, and Peptostreptococcus species
  • Metronidazole is indicated in the treatment of endocarditis caused by Bacteroides species, including the Bacteroides fragilis group.
  • Metronidazole is indicated in the treatment of CNS infections, including meningitis, caused by Bacteroides species, including the Bacteroides fragilis group.
  • Metronidazole is indicated in the treatment of brain abscess caused by Bacteroides species, including the Bacteroides fragilis group.
  • Metronidazole is indicated in the treatment of bone and joint infections caused by Bacteroides species, including the Bacteroides fragilis group (Bacteroides fragilis, Bacteroides distasonis, Bacteroides ovatus, Bacteroides thetaiotaomicron, Bacteroides vulgatus).
  • Oral metronidazole is indicated in the treatment of acute intestinal amebiasis caused by Entamoeba histolytica. Metronidazole may not eradicate intestinal amebic infections, requiring treatment with a luminal amebicide.
  • Metronidazole is indicated in the treatment of extraintestinal amebiases, including amebic liver abscess, caused by Entamoeba histolytica. When used in the treatment of invasive amebiasis, metronidazole should be administered concurrently or sequentially with a luminal amebicide (eg, iodoquinol, paromomycin, tetracycline, diloxanide furoate). When used in the treatment of amebic liver abscesses, metronidazole therapy does not obviate the need for aspiration of the abscess.
  • Metronidazole is not effective against facultative anaerobes, obligate aerobes, Propionibacterium acnes, Actinomyces species, or Candida albicans.
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Contra Indications of Metronidazole

Dosage of Metronidazole

Strengths:  250 mg;400 mg 375 mg; 500 mg; 750 mg; 500 mg/100 mL;

Bacterial Infection

IV

  • Loading dose: 15 mg/kg IV once infused over 1 hour
  • Maintenance dose: 7.5 mg/kg IV infused over 1 hour every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Oral ,Immediate-release Capsules and Tablets

  • 7.5 mg/kg orally every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Amebiasis

Acute Intestinal Amebiasis (Acute Amebic Dysentery)

  • Immediate-release capsules and tablets: 750 mg orally 3 times a day for 5 to 10 days

Amebic Liver Abscess

  • Immediate-release capsules and tablets: 500 to 750 mg orally 3 times a day for 5 to 10 days

Trichomoniasis

  • Immediate-release Capsules: 375 mg orally twice a day for 7 consecutive days

Immediate-release Tablets

  • One-day regimen: 2 g orally as a single dose or 1 g twice given in the same da
  • Seven-day regimen: 250 mg orally 3 times a day for 7 consecutive days

US CDC recommendations ,Immediate-release Tablets

  • Recommended regimen: 2 g orally as a single dose
  • Alternative regimen: 500 mg orally twice a day for 7 days

Trichomoniasis in HIV-infected women

  • Immediate-release tablets: 500 mg orally twice a day for 7 days

Treatment failure with single-dose therapy and reinfection is excluded

  • Immediate-release tablets: 500 mg orally twice a day for 7 days; for patients failing this regimen, 2 g orally once a day for 7 days should be considered

Helicobacter pylori Infection

Some experts recommend

  • Bismuth quadruple therapy: 250 mg orally 4 times a day
  • Clarithromycin-based triple therapy: 500 mg orally twice a day
  • Duration of therapy: 10 to 14 days
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Pelvic Inflammatory Disease

US CDC recommendations
Mild to moderately severe acute pelvic inflammatory disease (PID)

  • Immediate-release tablets: 500 mg orally twice a day for 14 days

Bacterial Vaginosis

  • Extended-release Tablets: 750 mg orally once a day for 7 consecutive days

US CDC recommendations

  • Immediate-release tablets: 500 mg orally twice a day for 7 days

Intraabdominal Infection

IV

  • Loading dose: 15 mg/kg IV once infused over 1 hour
  • Maintenance dose: 7.5 mg/kg IV infused over 1 hour every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Oral

  • Immediate-release capsules and tablets: 7.5 mg/kg orally every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

IDSA and SIS recommendations

  • Immediate-release tablets: 500 mg IV every 8 to 12 hours or 1500 mg IV every 24 hours

Peritonitis

IV

  • Loading dose: 15 mg/kg IV once infused over 1 hour
  • Maintenance dose: 7.5 mg/kg IV infused over 1 hour every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Oral

  • Immediate-release capsules and tablets: 7.5 mg/kg orally every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Liver Abscess

IV

  • Loading dose: 15 mg/kg IV once infused over 1 hour
  • Maintenance dose: 7.5 mg/kg IV infused over 1 hour every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Oral

  • Immediate-release capsules and tablets: 7.5 mg/kg orally every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Joint Infection

IV:
-Loading dose: 15 mg/kg IV once infused over 1 hour
-Maintenance dose: 7.5 mg/kg IV infused over 1 hour every 6 hours
-Maximum dose: 4 g per day
-Duration of therapy: 7 to 10 days

Oral

  • Immediate-release capsules and tablets: 7.5 mg/kg orally every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Osteomyelitis

IV

  • Loading dose: 15 mg/kg IV once infused over 1 hour
  • Maintenance dose: 7.5 mg/kg IV infused over 1 hour every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Oral

  • Immediate-release capsules and tablets: 7.5 mg/kg orally every 6 hours
  • Maximum dose: 4 g per day
  • Duration of therapy: 7 to 10 days

Pediatric Bacterial Infection

American Academy of Pediatrics (AAP) recommendations ,Neonates
7 days or less

  • Up to 2 kg: 7.5 mg/kg IV every 12 hours
  • Greater than 2 kg: 7.5 mg/kg IV every 8 hours

8 to 28 days

  • Up to 2 kg: 7.5 mg/kg IV every 12 hours
  • Greater than 2 kg: 7.5 mg/kg IV every 6 hours
  • Postmenstrual age less than 34 weeks: 7.5 mg/kg IV every 12 hours
  • Postmenstrual age 34 to 40 weeks: 7.5 mg/kg IV every 8 hours
  • Postmenstrual age greater than 40 weeks: 7.5 mg/kg IV every 6 hour

1 month or older

  • IV: 22.5 to 40 mg/kg/day IV in 3 divided doses
  • Maximum dose: 1.5 g/day

Oral

  • 30 to 50 mg/kg/day orally in 3 divided doses
  • Maximum dose: 2.25 g/day

Side Effects of Metronidazole

The most common side effects 

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Common

Rare

Drug Interactions of Metronidazole

Metronidazole may interact with following drugs, supplements, & may change the efficacy of drugs

Pregnancy & Lactation of Metronidazole

FDA Pregnancy Category B 
Pregnancy

According to the manufacturer, oral metronidazole is contraindicated during the first trimester of pregnancy in patients with trichomoniasis. However, the CDC states that metronidazole can be used for trichomoniasis at any stage of pregnancy as studies have not demonstrated an association between metronidazole and teratogenic effects.

Lactation

Metronidazole is excreted into breast milk. Breastfeeding is not recommended during treatment with systemic products. While there is some systemic absorption from topical and vaginal products, plasma concentrations would be lower than demonstrated with systemic formulations; however, caution is still advised. Metronidazole is a mutagen in vitro and has been shown to be carcinogenic in animal studies. In general, increased oral and rectal Candida colonization and loose stools have been reported in infants exposed to metronidazole via breast milk.


  1. References

    1. https://www.webmd.com/drugs/2/drug-6426/metronidazole-oral/details/list-contraindications

 

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