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Indications

Metronidazole is indicated in the treatment of following diseases:
  • The prevention of post-operative infections due to anaerobic bacteria (particularly species of bacteroides and anaerobic streptococci).
  • The treatment of septicaemia, bacteraemia, peritonitis, brain abscess, pelvic abscess, pelvic cellulitis and post-operative wound infections caused by anaerobes.
  • In the treatment of urogenital trichomoniasis.
  • Bacterial vaginosis (also known as non-specific vaginitis).
  • All forms of amoebiasis (intestinal, extra-intestinal disease and that of symptomless cyst passers).
  • Giardiasis.
  • Acute ulcerative gingivitis.
  • Anaerobically infected leg ulcers and pressure sores.
  • Acute dental infections due to anaerobic organisms.
  • Antibiotic associated pseudomembranus colitis.

Pharmacology

Metronidazole is a member of the imidazole class of antibacterial drug and is classified therapeutically as an antiprotozoal agent. The 5-nitro group of Metronidazole is reduced by anaerobes metabolically. Studies have demonstrated that the reduced form of this drug interacts with DNA and gives bactericidal action of Metronidazole.

Dosage & Administration

Tablet and Suspension:

Trichomoniasis (Adults & Children over 10 yrs)-
  • 200 mg tid or 400 mg bid for 7 days
  • 800 mg in the morning and 1-2 gm at night for 2 days
  • 2 gm as a single dose for 1 days
Trichomoniasis (Children)-
  • Children 7-10 yrs: 100 mg tid
  • Children 3-7 yrs: 100 mg bid
  • Children 1-3 yrs: 50 mg tid
Intestinal amoebiasis (Adults & Children over 10 yrs)- 
  • 800 mg tid for 5 days
Intestinal amoebiasis (Children)-
  • Children 7-10 yrs: 400 mg tid
  • Children 3-7 yrs: 200 mg qid
  • Children 1-3 yrs: 200 mg tid
Extra-intestinal & Asymptomatic amoebiasis (Adults & Children over 10 yrs)-
  • 400-800 mg tid for 5-10 days
Extra-intestinal & Asymptomatic amoebiasis (Children)-
  • Children 7-10 yrs: 200-400 mg tid
  • Children 3-7 yrs: 100-200 mg qid
  • Children 1-3 yrs: 100-200 mg tid
Giardiasis (Adults & Children over 10 yrs)-
  • 2 gm once daily for 3 days
Giardiasis (Children)-
  • Children 7-10 yrs: 1 gm once daily
  • Children 3-7 yrs: 600-800 mg once daily
  • Children 1-3 yrs: 500 mg once daily
Acute ulcerative  gingivitis (Adults & Children over 10 yrs)-
  • 200 mg tid for 3 days
Acute ulcerative  gingivitis (Children)-
  • Children 7-10 yrs: 100 mg tid
  • Children 3-7 yrs: 100 mg bid
  • Children 1-3 yrs: 50 mg tid
Acute dental infections (Adults & Children over 10 yrs)-
  • 200 mg tid for 3-7 days
Bacterial Vaginosis (Adults & Children over 10 yrs)-
  • 400 mg bid for 7 days
  • 2 gm as a single dose for 1 days
Leg ulcers and pressure sores (Adults & Children over 10 yrs)-
  • 400 mg tid for 7 days
Anaerobic infections (Adults & Children over 10 yrs)-
  • 800 mg initially and then 400 mg tid for 7 days
Anaerobic infections (Children)-
  • Children 1-10 yrs: 7.5 mg/kg tid
Surgical prophylaxis (Adults & Children over 10 yrs)-
  • 400 mg tid started 24  hours before  surgery for 1 days
Surgical prophylaxis (Children)-
  • Children 1-10 yrs: 7.5 mg/kg tid

Vaginal Gel:

The recommended dose is one applicator full of Metronidazole gel (approximately 5 grams containing approximately 37.5 mg of Metronidazole) intravaginally once or twice a day for 5 days. For once a day dosing, Metronidazole gel should be administered at bedtime.


Suppository:

Anaerobic Infections-
  • Adults: 1 g every 8 hours for 3 days, then 1 g every 12 hours.
  • Children: 5-10 years: 500 mg every 8 hours for 3 days, then every 12 hours, Over 10 years adult dose.
Surgical Prophylaxis-
  • Adults: 1 g 2 hours before surgery; up to 3 further doses of 1 g may be given every 8 hours for high risk procedures.
  • Children: 5-10 years: 500 mg 2 hours before surgery; up to 3 further doses of 500 mg may be given every 8 hours for high risk procedures.


IV Infusion:

Metronidazole intravenous infusion requires no dilution and should not be mixed with any other drugs prior to administration.
  • Adults and children over 12 years: Infuse 500 mg 8 hourly at a rate of 5 ml/minute and a maximum of 4 g should not be exceeded during a 24-hour period. Treatment for 7 days is sufficient for most patients, but treatment can be extended, especially for cases where reinfection is likely. For surgical prophylaxis, administration shortly before surgery should be followed by 8-hourly doses for the next 24 hours.
  • Children under 12 years: 7.5 mg/kg body weight/day every 8 hours at a rate of 5 ml/minute.

Interaction

  • Disulfiram: Psychotic reactions have been reported in patients who were using metronidazole and disulfiram concurrently.
  • Alcohol: Alcoholic beverages and drugs containing alcohol should not be consumed during therapy and for at least one day afterwards because of the possibility of a disulfiram-like (antabuse effect) reaction (flushing, vomiting, tachycardia). Oral anticoagulant therapy (warfarin type): Potentiation of the anticoagulant effect and increased hemorrhagic risk caused by decreased hepatic catabolism. In case of co-administration, prothrombin time should be more frequently monitored and anticoagulant therapy adjusted during treatment with metronidazole.
  • Lithium: Plasma levels of lithium may be increased by metronidazole.
  • Cyclosporin: Serum cyclosporin and serum creatinine should be closely monitored when co-administration is necessary.
  • Phenytoin or phenobarbital: increased elimination of metronidazole resulting in reduced plasma levels.
  • 5-Fluorouracil: Reduced clearance of 5-fluorouracil resulting in increased toxicity of 5-fluorouracil.
  • Busulfan: Plasma levels of busulfan may be increased by metronidazole, which may lead to severe busulfan toxicity.

Contraindications

Metronidazole is contraindicated in patients with a history of hypersensitivity to Metronidazole or other Nitroimidazole derivatives.

Side Effects

Metallic taste, nausea, vomiting, diarrhoea, drowsiness, rashes may be observed during treatment.

Pregnancy & Lactation

US FDA Pregnancy Category of Metronidazole is B. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed. Metronidazole have been shown to be excreted in human milk. So, caution should be exercised when Metronidazole is administered to a nursing woman.

Precautions & Warnings

  • If for compelling reasons, metronidazole must be administered longer than the usually recommended duration, it is recommended that hematological tests, especially leucocyte count should be carried out regularly and that patients should be monitored for adverse reactions such as peripheral or central neuropathy (such as paresthesia, ataxia, dizziness, convulsive seizures).
  • Metronidazole should be administered with caution to patients with hepatic encephalopathy.
  • Patients should be warned that metronidazole may darken urine.

Use in Special Populations

Hepatic impairment: Metronidazole is mainly metabolised by hepatic oxidation. Substantial impairment of metronidazole clearance may occur in the presence of advanced hepatic insufficiency. Significant cumulation may occur in patients with hepatic encephalopathy and the resulting high plasma concentrations of metronidazole may contribute to the symptoms of the encephalopathy. Metronidazole should therefore, be administered with caution to patients with hepatic encephalopathy. The daily dosage should be reduced to one third and may be administered once daily. Patients should be warned that metronidazole may darken urine.

Renal impairment: The elimination half-life of metronidazole remains unchanged in the presence of renal failure. The dosage of metronidazole therefore needs no reduction. Such patients however retain the metabolites of metronidazole. The clinical significance of this is not known at present. In patients undergoing haemodialysis metronidazole and metabolites are efficiently removed during an eight hour period of dialysis. Metronidazole should therefore be re-administered immediately after haemodialysis. No routine adjustment in the dosage of Metronidazole need be made in patients with renal failure undergoing intermittent peritoneal dialysis (IDP) or continuous ambulatory peritoneal dialysis (CAPD).

Overdose Effects

Single oral doses of metronidazole, up to 12 g have been reported in suicide attempts and accidental overdoses. Symptoms were limited to vomiting, ataxia and slight disorientation. There is no specific antidote for metronidazole overdosages. In case of suspected massive overdosages, a symptomatic and supportive treatment should be instituted.

Therapeutic Class

Amoebicides, Anti-diarrhoeal Antiprotozoal

Storage Conditions

Store below 30°C. Keep protected from light. Keep medicines out of the reach of children. Do not use later than the date of expiry.