Dosing & Uses
Dosage Forms & Strengths
capsule
- 375mg
tablet
- 250mg
- 500mg
tablet, extended-release
- 750mg
infusion solution
- 500mg/100mL
Anaerobic Bacterial Infections
Loading dose: 15 mg/kg IV; not to exceed 4 g/day
Maintenance dose: 7.5 mg/kg PO/IV (over 1 h) q6hr x 7-10 days (or 2-3 weeks if severe)
Sexually Transmitted Disease
Prevention following sexual assault
2 g PO as a single dose; 3-drug regimen that also includes ceftriaxone or cefixime, PLUS azithromycin or doxycycline (CDC STD guidelines, 2010)
Bacterial Vaginosis
Nonpregnant women
- 500 mg PO BID x 7 days, OR
- 2 g PO qDay single dose, OR
- Extended-release: 750 mg PO qDay x 7 days
Pregnant women
- 500 mg PO BID x 7 days, OR
- 250 mg PO TID x 7 days
Colorectal Surgical Infection
Prophylaxis; start after mechanical bowel preparation the afternoon and evening before surgery
1 g PO q6-8hr for 3 doses
15 mg/kg IV over 30-60 min; complete approximately 1 hr before surgery; may administer 7.5 mg/kg IV over 30-60 min at 6 and 12 hr after initial dose for maintenance; discontinue within 12 hr after surgery
Trichomoniasis
250 mg PO q8hr for 7 days; alternatively, 375 mg PO q12hr for 7 days
2 g PO qDay single dose; alternatively, 1g PO q12hr for 2 doses
Amebiasis
500-750 mg PO q8hr for 5-10 days
Giardiasis (Off-label)
500 mg PO q12hr for 5-7 days
Gardnerella Infection
Immediate release: 500 mg PO q12hr
Extended-release: 750 mg PO qDay for 7 days; take on empty stomach
Helicobacter Pylori Infection (Off-label)
250-500 mg PO QID in combination with tetracycline (500 mg) and bismuth subsalicylate (525 mg) x 14 days
Nongonococcal Urethritis (Off-label)
2 g PO qDay single dose with erythromycin (500 mg QID) or erythromycin ethylsuccinate (800 mg QID) x 7 days
Pelvic Inflammatory Disease (Off-label)
500 mg PO q12hr for 14 days in conjunction with ofloxacin or levofloxacin
Dosing Considerations
Hepatic failure
- Mild to moderate hapatic impairment (Child-Pugh A or B): No dosage adjustment needed but patients should be monitored for metronidazole associated adverse events
- Severe hepatic impairment: Reduce dose of by 50%
Renal failure
- Mild to moderate renal impairment: Dose adjustment not considered necessary as elimination half-life not significantly altered
- Severe renal impairment or end stage of renal disease: Metronidazole and metronidazole metabolites may accumulate significantly because of reduced urinary excretion; monitor in severe renal impairment or end stage of renal disease, not undergoing hemodialysis
- Hemodialysis removes significant amounts of metronidazole and its metabolites from systemic circulation; supplementation may be necessary
- Peritoneal dialysis: Monitor for signs of toxicity due to potential accumulation of metronidazole metabolites
Pouchitis (Orphan)
Orphan indication sponsor
- Formac Pharmaceuticals, NV; Gaston Geenslaan 1; Belgium
Crohn Disease (Orphan)
Topical treatment of active perianal Crohn disease
Orphan indication sponsor
- Braintree Laboratories, Inc; 60 Columbian Street West; PO Box 850929; Braintree, MA 02185-0929
Perioral Dermatitis (Orphan)
Orphan indication sponsor
- Galderma Laboratories, Inc; P.O. Box 331329; Fort Worth, TX 76163
Dosage Forms & Strengths
capsule
- 375mg
tablet
- 250mg
- 500mg
tablet, extended-release
- 750mg
infusion solution
- 500mg/100mL
Neonatal (<28 Days) Anaerobic Infection
<1.2 kg
<7 days
- 1.2-2 kg: 7.5 mg/kg IV/PO qDay
- >2 kg: 15 mg/kg/day IV/PO divided q12hr
>7 days
- 1.2-2 kg: 15 mg/kg/day IV/PO divided q12hr
- >2 kg: 30 mg/kg/day IV/PO divided q12hr
Infants and Children
- 30 mg/kg/day PO/IV divided q6hr; not to exceed 4 g/day
Clostridium Difficile Colitis
30 mg/kg/day IV/PO divided q6hr IV/PO for 7-10 days (American Academy of Pediatrics)
Amebiasis
35-50 mg/kg PO divided q8hr for 10 days
Giardiasis
15 mg/kg/day IV/PO divided q8hr for 5 days
Trichomoniasis
< 45 kg body weight: 15 mg/kg/day IV/PO divided q8hr for 7 days; not to exceed 2 g/day
Helicobacter Pylori-Associated Peptic Ulcer Disease (Off-label)
With amoxicillin and bismuth subsalicylate: 15-20 mg/kg/day PO divided q12hr for 4 weeks
Interactions
Interaction Checker
No Results

Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor

Adverse Effects
Frequency Not Defined
Appetite loss
Candidiasis
Diarrhea
Dizziness
Headache
Nausea
Vomiting
Ataxia
Dark urine
Disulfiram-type reaction with ethanol
Furry tongue
Hypersensitivity
Neutropenia
Metallic taste
Neuropathy
Pancreatitis
Seizures
Thrombophlebitis
Xerostomia
Encephalopathy
Aseptic meningitis
Optic neuropathy
Stevens-Johnson syndrome
Toxic epidermal necrolysis
Decreased libido
Postmarketing Reports
Dyspareunia, proctitis, fleeting joint pains that may resemble serum sickness, Crohn’s disease, hiccup, psychosis
Warnings
Black Box Warnings
Animal data have shown possible carcinogenic effect
Contraindications
Hypersensitivity to metronidazole or other nitroimidazoles (although cautious desensitization has been applied)
Pregnancy, 1st trimester in patients with trichomoniasis
Use of disulfiram within past 2 weeks; use of alcohol during therapy or within 3 days of discontinuing therapy
Cautions
Seizures and aseptic meningitis reported with increase in dose and chronic therapy
Cases of encephalopathy and peripheral neuropathy (including optic neuropathy) reported with metronidazole
Encephalopathy reported in association with cerebellar toxicity characterized by ataxia, dizziness, and dysarthria; CNS lesions seen on MRI described in reports of encephalopathy; CNS symptoms are generally reversible within days to weeks upon discontinuation of therapy; lesions seen on MRI have also been described as reversible
Peripheral neuropathy, mainly of sensory type reported and characterized by numbness or paresthesia of an extremity
Prescribing metronidazole tablets in absence of a proven or strongly suspected bacterial or parasitic infection or a prophylactic indication is unlikely to provide benefit to patient and increases risk of development of drug-resistant bacteria and parasites
Superinfection may occur with prolonged use
Severe hepatic impairment; administer lower doses with caution
Use with caution; potential accumulation in end stage renal disease; supplemental doses may be needed in patients receiving hemodialysis
Use with caution in history of heart failure, hepatic failure, H. pylori infection, renal impairment
Use with care in patients with evidence of or history of blood dyscrasia; agranulocytosis, leukopenia and neutropenia have been associated with metronidazole administration; monitor complete blood count; monitor complete blood count (CBC) for leukopenia before, during, and after prolonged repeated therapy
Avoid alcohol while taking medication and for at least three days after discontinuation
Antiandrogen: May cause gynecomastia
Known or previously unrecognized candidiasis may present more prominent symptoms during therapy and requires treatment with a candicidal agent
Metronidazole injection, USP contains 790 mg of sodium per 100 mL; use care when administering injection to patients receiving a controlled sodium diet or corticosteroids or to patients predisposed to edema
Severe neurological disturbances, including encephalopathy, cerebellar symptoms, convulsive seizures, and aseptic meningitis, reported in patients treated with metronidazole; advise patients to report neurologic symptoms that occur during metronidazole administration; discontinue metronidazole treatment if any abnormal neurologic symptoms occur such as ataxia, dizziness, confusion or any other CNS adverse reaction
Cases of severe hepatotoxicity/acute hepatic failure, including cases with a fatal outcome with very rapid onset after treatment initiation in patients with Cockayne syndrome reported with products containing metronidazole for systemic use; in this population, metronidazole should therefore be used after careful benefit-risk assessment and only if no alternative treatment available; obtain liver function tests prior to start of therapy, within first 2-3 days after initiation of therapy, frequently during therapy and after end of treatment; discontinue metronidazole if elevation of liver function occurs, and monitor liver function tests until baseline values are reached; advise patients with Cockayne syndrome to stop taking metronidazole immediately if they experience any symptoms of potential liver injury, such as abdominal pain, nausea, change in stool color or jaundice, and to contact their healthcare provider
When metronidazole tablets are prescribed to treat a bacterial infection, patients should be told that the medication should be taken exactly as directed; skipping doses or not completing full course of therapy may decrease effectiveness of immediate treatment and increase likelihood that bacteria will develop resistance and will not be treatable by metronidazole tablets in the future
Drug interaction overview
- Metronidazole reported to potentiate anticoagulant effect of warfarin and other oral coumarin anticoagulants, resulting in a prolongation of prothrombin time and increased risk of hemorrhages; prothrombin time and international normalized ratio (INR) should be carefully monitored and anticoagulant dose adjusted accordingly; monitor patients for signs and symptoms of bleeding
- Metronidazole reported to increase plasma concentrations of busulfan, which can result in an increased risk for serious busulfan toxicity such as sinusoidal obstruction syndrome, gastrointestinal mucositis, and hepatic veno-occlusive disease; metronidazole should not be administered concomitantly with busulfan unless benefit outweighs risk
- Simultaneous administration of drugs that decrease microsomal liver enzyme activity, such as cimetidine, may decrease metabolism and reduce plasma clearance of metronidazole which may result in metronidazole toxicity
- Simultaneous administration of drugs that induce microsomal liver enzyme activity, such as phenytoin or phenobarbital, may accelerate elimination of metronidazole and therefore decrease its efficacy
- Concomitant use of metronidazole and CYP3A4 substrates (e.g., amiodarone, tacrolimus, cyclosporine, carbamazepine, phenytoin, and quinidine) may increase respective CYP3A4-substrate plasma levels; monitoring of plasma concentrations of CYP3A4 substrates may be necessary
- Metronidazole decreases clearance of 5-fluorouracil and may therefore cause 5-fluorouracil toxicity
- Metronidazole may potentiate effects of vecuronium
Pregnancy & Lactation
Pregnancy
There are no adequate and well-controlled studies of in pregnant women; there are published data from case-control studies, cohort studies, and 2 meta-analyses that include more than 5000 pregnant women who used metronidazole during pregnancy; many studies included first trimester exposures; one study showed increased risk of cleft lip, with or without cleft palate, in infants exposed to metronidazole in utero; however, these findings were not confirmed
Metronidazole crosses placental barrier and its effects on human fetal organogenesis are not known; reproduction studies have been performed in rats, rabbits and mice at doses similar to maximum recommended daily dose based on body surface area comparisons; there was no evidence of harm to fetus due to metronidazole; healthcare provider should carefully consider potential risks and benefits for each specific patient before prescribing therapy
Lactation
Metronidazole is present in human milk at concentrations similar to maternal serum levels, and infant serum levels can be close to or comparable to infant therapeutic levels
Because of potential for tumorigenicity shown for metronidazole in mouse and rat studies, a decision should be made whether to discontinue nursing or to discontinue drug, taking into account importance of drug to mother; alternatively, a nursing mother may choose to pump and discard human milk for duration of metronidazole therapy, and for 24 hours after therapy ends and feed her infant stored human milk or formula
Study Data
There are published data from case-control studies, cohort studies, and 2 meta-analyses that included more than 5000 pregnant women who used metronidazole systemically during pregnancy
Many studies included first trimester exposures
One study showed an increased risk of cleft lip, with or without cleft palate, in infants exposed to metronidazole in utero; however, these findings were not confirmed
In addition, more than 10 randomized, placebo-controlled clinical trials that together enrolled over 5000 pregnant women assessed the possible effect of systemic antibiotic treatment (including with metronidazole) for bacterial vaginosis on the incidence of preterm delivery; most studies did not show an increased risk of congenital anomalies or other adverse fetal outcomes following metronidazole exposure during pregnancy
Three studies conducted to assess the risk of infant cancer following systemic metronidazole exposure during pregnancy did not show an increased risk; however, the ability of these studies to detect such a signal was limited
Pregnancy Categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk. C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done. D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk. X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist. NA: Information not available.Pharmacology
Mechanism of Action
Inhibits nucleic acid synthesis by disrupting DNA and causing strand breakage; amebicidal, bactericidal, trichomonacidal
Absorption
Bioavailability: 80% absorption from GI tract (PO)
Protein binding (<20%)
Peak serum time: 1-2 hr
Distribution
Widely distributed; similar pattern for PO and IV
Metabolism
Liver
Enzymes inhibited: Hepatic CYP2C9
Elimination
Half-life: 25-75 hr (neonates); 8 hr (others); prolonged in patients with hepatic impairment
Excretion: Urine (77%); feces (14%)
Administration
IV Incompatibilities
Some drugs may be incompatible with reconstituted solution from powder (which contains metronidazole HCl) but compatible with RTU IV solution (which contains metronidazole), and vice versa
Additive: Aztreonam, cefepime(?), ciprofloxacin (may be compatible with RTU solution), dopamine, meropenem
Y-site: Amphotericin B cholesteryl sulfate, aztreonam, filgrastim, meropenem, warfarin
IV Preparation
Reconstitute powder with 4.4 mL sterile water for injection, bacteriostatic water for injection, NS, or bacteriostatic NS to a final concentration of 100 mg/mL (pH 0.5-2)
Further dilute in glass or plastic container to no more than 8 mg/mL with NS, D5W, or LR
Neutralize with approximately 5 mEq NaHCO3 per 500 mg metronidazole; final pH 6-7
No dilution or buffering necessary for ready-to-use IV solution
IV Administration
Infusion only
Avoid contact between drug and aluminum in infusion set (less critical for RTU infusion solution containing metronidazole rather than metronidazole HCl)
Storage
Store at 15-30°C
Protect from light
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Formulary
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