Metronidazole is a member of the Nitroimidazole class of antibiotic, antimicrobial, and antiprotozoal medicines. The nitroimidazole drug metronidazole is used to treat bacterial infections, rosacea inflammation, amebiasis, trichomoniasis, and to prevent postoperative infections.

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December 12, 2022
Metronidazole
medicaldialogues.in/generics/metronidazole-2722630
Indications, Uses, Dosage, Drugs Interactions, Side effects
Metronidazole
Medicine Type :
Allopathy
Prescription Type:
Prescription Required
Approval :
DCGI (Drugs Controller General of India)
Schedule
Schedule H
Pharmacological Class:
Nitroimidazole class,
Therapy Class:
Antibiotic, Antimicrobial, Antiprotozoal agents,
Metronidazole is a Nitroimidazole class belonging to
antibiotic/antimicrobial/antiprotozoal agents.
Metronidazole is a nitroimidazole used to treat trichomoniasis, amebiasis, inflammatory
lesions of rosacea, and bacterial infections, as well as prevent postoperative infections.

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Metronidazole rapidly and almost completely absorbed from the gastrointestinal tract.
Food may delay absorption. The time to peak plasma concentration is approximately 1-2
hours (oral); 20 minutes (IV); 5-12 hours (rectal); 8 hours (intravaginal gel). The
Bioavailability found to be 60-80% (rectal); 20-25% (vag pessaries); 56% (intravaginal
gel). Metronidazole is the major component appearing in the plasma, with lesser
quantities of metabolites also being present. Less than 20% of the circulating
metronidazole is bound to plasma proteins. Metronidazole appears in cerebrospinal fluid,
saliva, and breast milk in concentrations like those found in plasma. The metabolites of
metronidazole result primarily from side-chain oxidation [1-(βhydroxyethyl)-2-
hydroxymethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole-1-ylacetic acid] and
glucuronide conjugation. Both the parent compound and the hydroxyl metabolite possess
in vitro antimicrobial activity. The major route of elimination of metronidazole and its
metabolites is via the urine (60 to 80% of the dose), with approximately 20% of the
amount excreted appearing as unchanged metronidazole. Renal clearance of
metronidazole is approximately 10 mL/min/1.73 m . Fecal excretion accounts for 6 to
15% of the dose.
Metronidazole shows common side effects like Vomiting, nausea, Diarrhoea, constipation,
upset stomach, stomach cramps, loss of appetite, headache, dry mouth, sharp, unpleasant
metallic taste, furry tongue, mouth, or tongue irritation.
Metronidazole is available in the form of Oral Tablet, Oral Capsule, Injectable Solution,
Topical Cream, Lotion, and Gel.
Metronidazole is available in India, US, China, Japan, Singapore, France, Spain, Italy,
Malaysia, Russia, and Australia.
Metronidazole belongs to the antibiotic/antimicrobial/antiprotozoal agents acts as a
Nitroimidazole class.
Metronidazole, a nitroimidazole, exerts antibacterial effects in an anaerobic environment
against most obligate anaerobes. Once metronidazole enters the organism by passive
diffusion and activated in the cytoplasm of susceptible anaerobic bacteria, it is reduced;
this process includes intra-cellular electron transport proteins such as ferredoxin, transfer
of an electron to the nitro group of the metronidazole, and formation of a short-lived
nitroso free radical. Because of this alteration of the metronidazole molecule, a
concentration gradient is created and maintained which promotes the drug’s intracellular
transport. The reduced form of metronidazole and free radicals can interact with DNA
leading to inhibition of DNA synthesis and DNA degradation leading to death of bacteria.
The precise mechanism of action of metronidazole is unclear.
The onset of action of Metronidazole is not clinically established.
The duration of action for Metronidazole is around 12 hours.
The Tmax of Metronidazole is approximately 1-2 hours (via Oral).
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Metronidazole is available in the form of Oral Tablet, Oral Capsule, Injectable Solution,
Topical Cream, Lotion, and Gel.
Metronidazole is an antibiotic medicine. It is used in the treatment of infections of the
stomach, intestines, liver, lungs, heart, vagina, and skin. It is also used in the combination
with other antibiotics in surgical prophylaxis. This medicine acts by killing the bacteria
and preventing the spread of infection.
Metronidazole is a Nitroimidazole class belonging to
antibiotic/antimicrobial/antiprotozoal agents.
Metronidazole interacts with the microbial DNA to break its strand and helical structure
leading to inhibition of protein synthesis, degradation, and cell death.
Metronidazole is approved for use in the following clinical indications
Adult Dose
Oral
Amebiasis, intestinal or extraintestinal
Skin and soft tissue infection
Surgical prophylaxis
Intra-abdominal infection
Intracranial abscess
Pneumonia, aspiration
Topical
Bacterial vaginosis
Rosacea
Trichomoniasis
Although not approved, there have been certain off-label indications. These include
Balantidiasis
Bite wound infection, prophylaxis or treatment, animal or human bite
Clostridioides difficile infection, treatment
Crohn disease
Dientamoeba fragilis infection
Giardiasis
Helicobacter pylori eradication
Odontogenic infection
Pouchitis, acute
Sexually transmitted infections
Tetanus
Pediatric Dose

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Oral
Amebiasis
Appendicitis, perforated
Balantidiasis
Catheter; exit-site or tunnel infection
Clostridioides difficile infection
Dientamoeba fragilis
Giardiasis
Helicobacter pylori eradication
Inflammatory bowel disease
Intra-abdominal infection
Pelvic inflammatory disease
Peritonitis
Prophylaxis against sexually transmitted diseases following sexual assault
Surgical prophylaxis
Tetanus
Trichomoniasis; treatment
Vaginosis, bacterial
Topical
Bacterial vaginosis
Periorificial dermatitis
Adult Dose
Oral
Amebiasis, intestinal or extraintestinal
Oral: 500 to 750 mg every 8 hours for 7 to 10 days followed by an intraluminal agent (eg,
paromomycin).
Skin and soft tissue infection
Necrotizing infection
IV: 500 mg every 6 hours. Continue until further debridement is not necessary, patient
has clinically improved, and patient is afebrile for 48 to 72 hours.
Surgical site infection, incisional
IV: 500 mg every 8 hours in combination with other appropriate agents. Duration
depends on severity, need for debridement, and clinical response.
Surgical prophylaxis

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IV: 500 mg within 60 minutes prior to surgical incision in combination with other
antibiotics. Considered a recommended agent for select procedures involving the GI tract,
urologic tract, or head and neck.
Oral
Colorectal surgical prophylaxis (off-label use): 1 g every 3 to 4 hours for 3 doses with
additional oral antibiotics, starting after mechanical bowel preparation the evening before
a morning surgery and followed by an appropriate IV antibiotic prophylaxis regimen.
Uterine evacuation (induced abortion or pregnancy loss) (alternative agent) (off-label
use): 500 mg as a single dose 1 hour prior to uterine aspiration; may be administered up
to 12 hours before the procedure.
Intra-abdominal infection
Oral, IV: 500 mg every 8 hours as part of an appropriate combination regimen. Duration
of therapy is 4 to 5 days following adequate source control; for diverticulitis or
uncomplicated appendicitis managed without intervention, duration is 10 to 14 days.
Intracranial abscess
IV: 7.5 mg/kg (usually 500 mg) every 6 to 8 hours (maximum dose: 4 g/day) for 6 to 8
weeks in combination with other appropriate antimicrobial therapy.
Pneumonia, aspiration
Oral, IV: 500 mg 3 times daily in combination with an appropriate beta-lactam (eg, oral
amoxicillin, IV penicillin, or an IV third-generation cephalosporin) for 7 days.
Topical
Bacterial vaginosis
0.75% gel:
Intravaginal: One applicatorful (5 g containing ~37.5 mg metronidazole) once daily at
bedtime for 5 days. For suppressive therapy following retreatment in patients with
multiple disease recurrences, give twice weekly for 3 to 6 months.
1.3% gel (alternative agent):
Intravaginal: One applicatorful (5 g containing ~65 mg metronidazole) as a single dose;
administer at bedtime.
Rosacea
0.75%: Topical: Apply and rub a thin film twice daily, morning and evening, to entire
affected areas after washing.

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1%: Topical: Apply thin film to affected area once daily.
Trichomoniasis
10%: Intravaginal: Insert one applicatorful (equal to metronidazole 500 mg)
intravaginally once or twice daily for 10 or 20 consecutive days (even during menses).
Although not approved, there have been certain off-label indications. These include
Balantidiasis
Oral: 750 mg 3 times daily for 5 days.
Bite wound infection, prophylaxis or treatment, animal or human bite
Oral, IV: 500 mg every 8 hours. Duration is 3 to 5 days for prophylaxis; duration of
treatment for established infection is typically 5 to 14 days and varies based on clinical
response and patient-specific factors.
Clostridioides difficile infection, treatment
Nonsevere (ie, WBC ≤15,000 cells/mm and serum creatinine <1.5 mg/dL),
initial episode
Oral: 500 mg 3 times daily for 10 to 14 days.
Fulminant infection (ie, ileus, megacolon, and/or hypotension/shock)
IV: 500 mg every 8 hours in combination with oral and/or rectal vancomycin for 10 days;
may be extended up to 14 days if patient has improved but has not had symptom
resolution.
Crohn disease
Management after surgical resection
Monotherapy: Oral: 20 mg/kg/day (in 3 divided doses) or 1 to 2 g/day in divided doses
for 3 months; begin as soon as oral intake is resumed after surgery.
Combination therapy: Oral: 250 mg 3 times daily or 1 to 2 g/day in divided doses for 3
months; begin as soon as oral intake is resumed after surgery and administer in
combination with a thiopurine (azathioprine or mercaptopurine) or a TNF-alpha inhibitor
(eg, adalimumab).
Treatment of simple perianal fistulas
Adjunctive agent: Oral: 500 mg twice daily for 4 weeks initially; if clinical response
(ie, cessation of drainage and closure of fistula), continue at 250 mg 3 times daily for an
additional 4 weeks or 10 to 20 mg/kg/day in divided doses for 4 to 8 weeks with or
without ciprofloxacin.
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Dientamoeba fragilis infection
Oral: 500 to 750 mg 3 times daily for 10 days.
Giardiasis
Oral: 250 mg 3 times daily or 500 mg 2 times daily for 5 to 7 days.
Helicobacter pylori eradication
Clarithromycin triple regimen
Oral: Metronidazole 500 mg 3 times daily in combination with clarithromycin 500 mg
twice daily and a standard-dose or double-dose proton pump inhibitor (PPI) twice daily;
continue regimen for 14 days.
Bismuth quadruple regimen
Oral: Metronidazole 250 mg 4 times daily or 500 mg 3 or 4 times daily in combination
with either bismuth subsalicylate 300 to 524 mg or bismuth subcitrate 120 to 300 mg 4
times daily, tetracycline 500 mg 4 times daily, and a standard-dose PPI twice daily;
continue regimen for 10 to 14 days.
Concomitant regimen
Oral: Metronidazole 500 mg twice daily in combination with clarithromycin 500 mg
twice daily, amoxicillin 1 g twice daily, and a standard-dose PPI twice daily; continue
regimen for 10 to 14 days.
Sequential regimen (alternative regimen)
Oral: Amoxicillin 1 g twice daily plus a standard-dose PPI twice daily for 5 to 7 days; then
follow with clarithromycin 500 mg twice daily, metronidazole 500 mg twice daily, and a
standard-dose PPI twice daily for 5 to 7 days; some experts prefer the 10-day sequential
regimen (amoxicillin for 5 days, followed by metronidazole and clarithromycin for 5 days)
over the 14-day sequential regimen (amoxicillin for 7 days, followed by metronidazole and
clarithromycin for 7 days) due to the lack of data showing superiority of the 14-day
regimen over the 10-day regimen in North America.
Hybrid regimen (alternative regimen)
Oral: Amoxicillin 1 g twice daily plus a standard-dose PPI twice daily for 7 days; then
follow with amoxicillin 1 g twice daily, clarithromycin 500 mg twice daily, metronidazole
500 mg twice daily, and a standard-dose PPI twice daily for 7 days.
Odontogenic infection
Acute simple gingivitis, plaque-associated

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Oral: 500 mg every 8 hours in combination with penicillin V for 5 to 7 days.
Periodontitis, severe, plaque-associated
Oral: 500 mg every 8 hours in combination with amoxicillin for 14 days or until clinical
resolution; use in addition to periodontal debridement.
Pyogenic odontogenic soft tissue infection (alternative agent)
IV, Oral: 500 mg every 8 hours as part of an appropriate combination regimen until
resolution, typically for 7 to 14 days. Use in addition to appropriate surgical management
(eg, drainage and/or extraction).
Pouchitis, acute
Initial therapy (alternative agent)
Oral: 500 mg every 12 hours for 14 days.
Refractory disease
Oral: 500 mg every 12 hours in combination with ciprofloxacin for 28 days.
Sexually transmitted infections
Bacterial vaginosis
Oral: 500 mg twice daily for 7 days. For multiple disease recurrences, 500 mg twice daily
for 7 days in combination with or prior to a multi-week course of boric acid, followed by
suppressive topical therapy.
Empiric treatment following sexual assault in females
Oral: 500 mg twice daily for 7 days, as part of an appropriate combination regimen.
Pelvic inflammatory disease
Oral, IV: 500 mg every 12 hours for 14 days as part of an appropriate combination
regimen.
Trichomoniasis (index case and sex partner)
Initial treatment:
Females: Oral: 500 mg twice daily for 7 days.
Males: Oral: 2 g as a single dose.
Refractory infection:

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Oral: 2 g once daily for 7 days. Alternatively, 500 mg twice daily for 7 days may be
sufficient for patients with refractory infection following a single-dose regimen.
Tetanus
Oral, IV: 500 mg every 6 to 8 hours for 7 to 10 days in combination with supportive
therapy.
Pediatric Dose
Oral
Amebiasis
Infants, Children, and Adolescents: Oral: 35 to 50 mg/kg/day in divided doses every 8
hours for 7 to 10 days; maximum dose: 750 mg/dose; for severe infection or
extraintestinal disease, IV may be necessary.
Appendicitis, perforated
Divided dosing: Children and Adolescents: IV: 10 mg/kg/dose every 8 hours.
Once-daily dosing: Children and Adolescents: IV: 30 mg/kg/dose once daily in
combination with ceftriaxone; maximum reported daily dose: 1,500 mg/day; however,
other pediatric trials did not report a maximum; in adult patients, a maximum daily dose
of 1,500 mg/day for once-daily dosing is suggested; in pediatric patients, once-daily
metronidazole in combination with ceftriaxone has been shown to have similar efficacy as
triple-combination therapy with ampicillin, clindamycin, and gentamicin.
Balantidiasis
Infants, Children, and Adolescents: Oral: 35 to 50 mg/kg/day in divided doses every 8
hours for 5 days; maximum dose: 750 mg/dose.
Catheter; exit-site or tunnel infection
Infants, Children, and Adolescents: Oral: 10 mg/kg/dose 3 times daily. Maximum dose:
500 mg/dose.
Clostridioides difficile infection
Infants: Mild to moderate infection: Oral, IV: 7.5 mg/kg/dose every 6 hours for 10 days.
Children and Adolescents
Non-severe infection, initial or first recurrence: Oral: 7.5 mg/kg/dose 3 to 4 times daily
for 10 days; maximum dose: 500 mg/dose.
Severe/fulminant infection, initial: IV: 10 mg/kg/dose every 8 hours for 10 days;
maximum dose: 500 mg/dose; use concomitantly with oral or rectal vancomycin.

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Dientamoeba fragilis
Infants, Children, and Adolescents: Oral: 35 to 50 mg/kg/day in divided doses every 8
hours for 10 days; maximum dose: 750 mg/dose.
Giardiasis
Infants, Children, and Adolescents: Oral: 5 to 10 mg/kg/dose every 8 hours for 5 to 7
days; maximum dose: 250 mg/dose.
Helicobacter pylori eradication
Weight-directed dosing: Children and Adolescents: Oral: 10 to 15 mg/kg/dose twice
daily; maximum dose: 500 mg/dose.
Fixed dosing: Children and Adolescents:
25 to <25 kg: Oral: 250 mg twice daily.
25 to <35 kg: Oral: 500 mg in the morning and 250 mg in the evening or 375 mg twice
daily (if using liquid preparation).
≥35 kg: Oral: 500 mg twice daily.
Inflammatory bowel disease
Crohn disease, perianal disease; induction: Children and Adolescents: Oral: 7.5
mg/kg/dose 3 times daily for 6 weeks with or without ciprofloxacin; maximum dose: 500
mg/dose.
Ulcerative colitis, pouchitis, persistent: Children and Adolescents: Oral: 20 to 30
mg/kg/day in divided doses 3 times daily for 14 days with or without ciprofloxacin or oral
budesonide; maximum dose: 500 mg/dose.
Intra-abdominal infection
Infants, Children, and Adolescents: IV: 30 to 40 mg/kg/day in divided doses 3 times
daily as part of combination therapy; maximum dose: 500 mg/dose.
Pelvic inflammatory disease
Adolescents: Oral: 500 mg twice daily for 14 days; give with doxycycline plus a
cephalosporin.
Peritonitis
Prophylaxis: Gastrointestinal or genitourinary procedures: Infants, Children, and
Adolescents: IV: 10 mg/kg once prior to procedure in combination with cefazolin;
Maximum dose: 1,000 mg/dose.

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Treatment: Infants, Children, and Adolescents: Oral: 10 mg/kg/dose 3 times daily.
Maximum daily dose: 1,200 mg/day.
Prophylaxis against sexually transmitted diseases following sexual
assault
Adolescents: Oral: 2,000 mg as a single dose in combination with azithromycin and
ceftriaxone.
Surgical prophylaxis
Children and Adolescents: IV: 15 mg/kg as a single dose 30 to 60 minutes prior to
procedure; maximum single dose: 500 mg.
Tetanus
Infants, Children, and Adolescents: IV, Oral: 30 mg/kg/day in divided doses 4 times daily
for 7 to 10 days; maximum daily dose: 4,000 mg/day.
Trichomoniasis; treatment
Children <45 kg: 45 mg/kg/day in divided doses 3 times daily for 7 days; maximum daily
dose: 2,000 mg/day.
Children ≥45 kg and Adolescents: 500 mg twice daily for 7 days or 2,000 mg as a single
dose once.
Vaginosis, bacterial
Children >45 kg and Adolescents: 500 mg twice daily for 7 days.
Topical
Bacterial vaginosis
Vaginal gel 0.75%: Adolescents: Intravaginal: One applicatorful (~37.5 mg metronidazole)
intravaginally once daily at bedtime for 5 days.
Vaginal gel 1.3%: Children ≥12 years and Adolescents: Intravaginal: One applicatorful
(~65 mg metronidazole) intravaginally once at bedtime as a single dose.
Periorificial dermatitis
Infants ≥6 months, Children, and Adolescents: Topical: 0.75% gel: Apply thin film once or
twice daily.
Metronidazole is available in various strengths as 250mg, 500mg, 375mg, 500 mg (100
mL), 5 mg/mL (100 mL [DSC]), and 500 mg/100 mL (100 mL), 1%(45g), 10%(60g),
0.75% (3 g, 60 g, 70g); 1% (3 g, 60 g).

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Metronidazole is available in the form of Oral Tablet, Oral Capsule, Injectable Solution,
Topical Cream, Lotion, and Gel.
Dosage Adjustment in Kidney Patient
IV, Oral
CrCl ≥10 mL/minute: No dosage adjustment necessary; however, monitor closely for
adverse effects due to accumulation of metabolites in patients with more severe
impairment (CrCl <30 mL/minute), particularly with prolonged courses of therapy.
CrCl <10 mL/minute: No dosage adjustment necessary; however, monitor closely for
adverse effects due to accumulation of metabolites, particularly with prolonged courses of
therapy. A dose of 500 mg every 12 hours may be adequate to achieve therapeutic plasma
levels for nonsevere non-Clostridioides difficile infections.
Metronidazole is contraindicated in patients with
Hypersensitivity
Metronidazole Tablets is contraindicated in patients with a prior history of
hypersensitivity to metronidazole or other nitroimidazole derivatives. In patients with
trichomoniasis, Metronidazole Tablets is contraindicated during the first trimester of
pregnancy.
Psychotic Reaction with Disulfiram
Use of oral metronidazole is associated with psychotic reactions in alcoholic patients who
were using disulfiram concurrently. Do not administer metronidazole to patients who
have taken disulfiram within the last two weeks.
Interaction With Alcohol
Use of oral metronidazole is associated with a disulfiram-like reaction to alcohol,
including abdominal cramps, nausea, vomiting, headaches, and flushing. Discontinue
consumption of alcohol or products containing propylene glycol during and for at least
three days after therapy with metronidazole.
Cockayne Syndrome
Metronidazole Tablets are contraindicated in patients with Cockayne syndrome. Severe
irreversible hepatotoxicity/acute liver failure with fatal outcomes have been reported after
initiation of metronidazole in patients with Cockayne syndrome.
Superinfection
Prolonged use may result in fungal or bacterial superinfection, including C. difficile-
associated diarrhea (CDAD) and pseudomembranous colitis; CDAD has been observed >2
months postantibiotic treatment.

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Carcinogenic
Possibly carcinogenic based on animal data. Unnecessary use should be avoided.
CNS effects
Aseptic meningitis, encephalopathy, seizures, and neuropathies (peripheral and optic)
have been reported with systemic metronidazole, especially with increased doses and
chronic treatment; peripheral neuropathy has also been reported with topical products;
monitor and consider discontinuation of therapy if signs/symptoms occur. Use with
caution in patients with CNS diseases. Discontinue immediately if abnormal neurologic
signs develop.
Eye irritation
May cause tearing of the eye; avoid contact with the eyes. In the event of accidental
contact, wash out immediately.
Hepatic impairment
Use with caution in patients with severe liver impairment due to potential accumulation.
Alcohol Warning
Avoid consuming alcohol while taking Metronidazole as it may enhance the adverse/toxic
effect of Alcohol (Ethyl). A disulfiram-like reaction may occur which leads to symptoms
like fast heartbeat, warmth, headache, and breathing difficulty.
Breast Feeding Warning
Metronidazole is present in human milk at concentrations like maternal serum levels, and
infant serum levels can be close to or comparable to infant therapeutic levels. Because of
the potential for tumorigenicity shown for metronidazole in mouse and rat. studies, a
decision should be made whether to discontinue nursing or to discontinue the drug,
considering the importance of the drug to the mother. Alternatively, a nursing mother
may choose to pump and discard human milk for the duration of metronidazole therapy,
and for 24 hours after therapy ends and feed her infant stored human milk or formula.
Pregnancy Warning
Metronidazole crosses the placenta and rapidly distributes into the fetal circulation
following oral administration. The amount of metronidazole available systemically
following topical application is less in comparison to oral doses. Most studies have not
shown an increased risk of adverse events to the fetus following maternal use during
pregnancy.
Common

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Nausea, Vaginitis, Headache, Genital pruritus, Abdominal pain, diarrhea, xerostomia,
Dysmenorrhea, urinary tract infection, urine abnormality, Bacterial infection, candidiasis,
Dizziness, metallic taste, Flu-like symptoms, pharyngitis, rhinitis, sinusitis, upper
respiratory tract infection.
Rare
Chest pain, facial edema, flattened T-wave on ECG, flushing, palpitations, peripheral
edema, syncope, tachycardia, Erythematous rash, hyperhidrosis, pruritus, urticaria,
Decreased libido, Abdominal cramps, anorexia, constipation, decreased appetite,
dysgeusia, epigastric discomfort, glossitis, hairy tongue, proctitis, stomatitis, vomiting,
Cystitis, dark urine, dyspareunia, dysuria, urinary incontinence, urine discoloration,
vaginal dryness, vulvovaginal candidiasis, Agranulocytosis, eosinophilia, Drug reaction
with eosinophilia and systemic symptoms, Inflammation at injection site, injection site
reaction, Chills, depression, drowsiness, epilepsy, hypoesthesia, insomnia, irritability,
malaise, numbness, psychosis, Arthralgia, asthenia, muscle spasm, myalgia, Abnormal
eye movements (saccadic), nystagmus disorder, Polyuria, Dyspnea, nasal congestion,
Fever.
Disulfiram
Psychotic reactions have been reported in alcoholic patients who are using metronidazole
and disulfiram concurrently. Metronidazole should not be given to patients who have
taken disulfiram within the last two weeks.
Alcoholic Beverages
Abdominal cramps, nausea, vomiting, headaches, and flushing may occur if alcoholic
beverages or products containing propylene glycol are consumed during or following
metronidazole therapy.
Warfarin And Other Oral Anticoagulants
Metronidazole has been reported to potentiate the anticoagulant effect of warfarin and
other oral coumarin anticoagulants, resulting in a prolongation of prothrombin time.
When METRONIDAZOLE is prescribed for patients on this type of anticoagulant therapy,
prothrombin time and INR should be carefully monitored.
Lithium
In patients stabilized on relatively high doses of lithium, short-term metronidazole
therapy has been associated with elevation of serum lithium and, in a few cases, signs of
lithium toxicity. Serum lithium and serum creatinine levels should be obtained several
days after beginning metronidazole to detect any increase that may precede clinical
symptoms of lithium intoxication.
Busulfan

15. 15/18
Metronidazole has been reported to increase plasma concentrations of busulfan, which
can result in an increased risk for serious busulfan toxicity. Metronidazole should not be
administered concomitantly with busulfan unless the benefit outweighs the risk. If no
therapeutic alternatives to metronidazole are available, and concomitant administration
with busulfan is medically needed, frequent monitoring of busulfan plasma concentration
should be performed and the busulfan dose should be adjusted accordingly.
Drugs That Inhibit CYP450 Enzymes
The simultaneous administration of drugs that decrease microsomal liver enzyme activity,
such as cimetidine, may prolong the half-life and decrease plasma clearance of
metronidazole.
Drugs That Induce CYP450 Enzymes
The simultaneous administration of drugs that induce microsomal liver enzymes, such as
phenytoin or phenobarbital, may accelerate the elimination of metronidazole, resulting in
reduced plasma levels; impaired clearance of phenytoin has also been reported.
Drugs That Prolong the QT interval
QT prolongation has been reported, particularly when metronidazole was administered
with drugs with the potential for prolonging the QT interval.
The common side effects of Metronidazole include the following
Common side effects
Vomiting, nausea, Diarrhea, constipation, upset stomach, stomach cramps, loss of
appetite, headache, dry mouth, sharp, unpleasant metallic taste, furry tongue, mouth, or
tongue irritation.
Rare side effects
Numbness, pain, burning, or tingling in your hands or feet, seizures, Rash, itching, Hives,
peeling or blistering skin, flushing, stuffy nose, fever, sore throat, or other signs of
infection, joint pain, dizziness, difficulty speaking, problems with coordination,
Confusion, agitation.
Pregnancy Category B
Teratogenic Effects: There are no adequate and well controlled studies of Metronidazole
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 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 ten randomized placebo-controlled clinical trials enrolled more than 5000 pregnant

16. 16/18
women to assess the use of antibiotic treatment (including metronidazole) for bacterial
vaginosis on the incidence of preterm delivery. Most studies did not show an increased
risk for congenital anomalies or other adverse fetal outcomes following metronidazole
exposure during pregnancy. Three studies conducted to assess the risk of infant cancer
following metronidazole exposure during pregnancy did not show an increased risk;
however, the ability of these studies to detect such a signal was limited. Metronidazole
crosses the placental barrier and its effects on the human fetal organogenesis are not
known. Reproduction studies have been performed in rats, rabbits, and mice at doses
similar to the maximum recommended human dose based on body surface area
comparisons. There was no evidence of harm to the fetus due to metronidazole.
Nursing Mothers
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 the potential for tumorigenicity shown for metronidazole in mouse and rat.
studies, a decision should be made whether to discontinue nursing or to discontinue the
drug, considering the importance of the drug to the mother. Alternatively, a nursing
mother may choose to pump and discard human milk for the duration of metronidazole
therapy, and for 24 hours after therapy ends and feed her infant stored human milk or
formula.
Pediatric Use
In one study newborn infants appeared to demonstrate diminished capacity to eliminate
metronidazole. The elimination half-life, measured during the first three days of life, was
inversely related to gestational age. In infants whose gestational ages were between 28
and 40 weeks, the corresponding elimination half-lives ranged from 109 to 22.5 hours.
Geriatric Use
Following a single 500 mg oral or IV dose of metronidazole, subjects >70 years old with
no apparent renal or hepatic dysfunction had a 40% to 80% higher mean AUC of hydroxy
metronidazole (active metabolite), with no apparent increase in the mean AUC of
metronidazole (parent compound), compared to young healthy controls < 40 years old. In
geriatric patients, monitoring for metronidazole associated adverse events is
recommended.
Use of dosages of intravenous metronidazole hydrochloride higher than those
recommended has been reported. These include the use of 27 mg/kg three times a day for
20 days, and the use of 75 mg/kg as a single loading dose followed by 7.5 mg/kg
maintenance doses. No adverse reactions were reported in either of the two cases. Single
oral doses of metronidazole, up to 15 g, have been reported in suicide attempts and
accidental overdoses. Symptoms reported included nausea, vomiting, and ataxia. Oral
metronidazole has been studied as a radiation sensitizer in the treatment of malignant
tumors. Neurotoxic effects, including seizures and peripheral neuropathy, have been
reported after 5 to 7 days of doses of 6 to 10.4 g every other day.

17. 17/18
Pharmacodynamic
Metronidazole treats amebiasis, trichomoniasis, and giardiasis, exerting both
antibacterial and antiprotozoal activities. Metronidazole is an effective treatment for some
anaerobic bacterial infections. Metronidazole has shown antibacterial activity against the
majority of obligate anaerobes, however, during in vitro studies, it does not demonstrate
significant action against facultative anaerobes or obligate aerobes. The nitro group
reduction of metronidazole by anaerobic organisms is likely responsible for the drug's
antimicrobial cytotoxic effects, causing DNA strand damage to microbes. A note on
convulsions and neuropathy and carcinogenesis. It is important to be aware of the risk of
peripheral neuropathy and convulsions associated with metronidazole, especially at
higher doses. If convulsions or numbness of an extremity occur, discontinue the drug
immediately. Metronidazole has been found to be carcinogenic in mice and rats. The
relevance to this effect in humans is unknown. It is advisable to only administer
metronidazole when clinically necessary and only for its approved indications.
Pharmacokinetics
Absorption
Metronidazole rapidly and almost completely absorbed from the gastrointestinal tract.
Food may delay absorption. The time to peak plasma concentration is approximately 1-2
hours (oral); 20 minutes (IV); 5-12 hours (rectal); 8 hours (intravaginal gel). The
Bioavailability found to be 60-80% (rectal); 20-25% (vag pessaries); 56% (intravaginal
gel).
Distribution
Metronidazole is the major component appearing in the plasma, with lesser quantities of
metabolites also being present. Less than 20% of the circulating metronidazole is bound
to plasma proteins. Metronidazole appears in cerebrospinal fluid, saliva and breast milk
in concentrations similar to those found in plasma. Bactericidal concentrations of
metronidazole have also been detected in pus from hepatic abscesses. Following a single
intravenous dose of metronidazole 500 mg, 4 healthy subjects who underwent
gastrointestinal endoscopy had peak gastric juice metronidazole concentrations of 5 to 6
mcg/mL at one-hour post-dose. In patients receiving intravenous metronidazole in whom
gastric secretions are continuously removed by nasogastric aspiration, sufficient
metronidazole may be removed in the aspirate to cause a reduction in serum levels.
Metabolism and Excretion
The metabolites of metronidazole result primarily from side-chain oxidation [1-
(βhydroxyethyl)-2- hydroxymethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole-1-
ylacetic acid] and glucuronide conjugation. Both the parent compound and the hydroxyl
metabolite possess in vitro antimicrobial activity. The major route of elimination of
metronidazole and its metabolites is via the urine (60 to 80% of the dose), with

18. 18/18
approximately 20% of the amount excreted appearing as unchanged metronidazole. Renal
clearance of metronidazole is approximately 10 mL/min/1.73 m . Fecal excretion
accounts for 6 to 15% of the dose.
There are some clinical studies of the drug Metronidazole mentioned below:
1. Loesche WJ, Syed SA, Morrison EC, Kerry GA, Higgins T, Stoll J. Metronidazole in
periodontitis: I. clinical and bacteriological results after 15 to 30 Weeks. Journal of
periodontology. 1984 Jun;55(6):325-35.
2. Zandbergen D, Slot DE, Cobb CM, Van der Weijden FA. The clinical effect of scaling
and root planing and the concomitant administration of systemic amoxicillin and
metronidazole: a systematic review. Journal of periodontology. 2013
Mar;84(3):332-51.
3. Schmadel LK, McEvoy GK. Topical metronidazole: a new therapy for rosacea.
Clinical pharmacy. 1990 Feb 1;9(2):94-101.
https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/018890s052lbl.pdf
https://medlineplus.gov/druginfo/meds/a689011.html#side-effects
https://www.mims.com/india/drug/info/metronidazole?type=full&mtype=generic
https://www.practo.com/medicine-info/metronidazole-182-api
https://www.rxlist.com/flagyl-drug.htm#overdosage
https://go.drugbank.com/drugs/DB00916
https://www.uptodate.com/contents/metronidazole-systemic-drug-
information#F8771184
https://www.uptodate.com/contents/metronidazole-topical-drug-
information#F51776142
Dr JUHI SINGLA
Dr JUHI SINGLA has completed her MBBS from Era’s Lucknow
Medical college and done MD pharmacology from SGT UNIVERSITY
Gurgaon. She can be contacted at editorial@medicaldialogues.in.
Contact no. 011-43720751
Jyoti Suthar
Jyoti is a Post graduate in Pharmaceutics ( M Pharm) She did her
graduation ( B Pharm) From SSR COLLEGE OF PHARMACY And
thereafter did her M Pharm specialized in Pharmaceutics from SSR
COLLEGE OF PHARMACY
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