Ornidazole: Uses, adverse effects & interactions!

Ornidazole is a drug belonging to the nitroimidazole class of antibiotics. It serves its purpose as an antibiotic, anti-protozoal & anti-parasitic drug.



  • Bacterial vaginosis
  • Endometriosis
  • Pelvic inflammatory disease (PID)
  • Colitis
  • Aspiration pneumonia
  • Meningitis
  • Topical rosacea
  • Topical fungal wounds
  • Intra-abdominal infections
  • Lung abscess
  • Periodontits/Gum disease
  • Amebiasis like amebic dysentery & amebic liver abscess
  • Oral infections
  • Symptomatic & Asymptomatic trichomoniasis
  • Giardiasis
  • Eradication of H.Pyroli.


Dosage forms available:

  • Film coated immediate release tablet: 250 mg, 500 mg
  • Extended release (XR) tablet: 750 mg
  • Capsule: 375 mg, 500 mg
  • Topical cream/gel: 7.5 mg/g
  • IV injection: 500 mg/100 mL
  • Various combination doses & preparation with adjunct drugs.

Dosage intake:

  • For vaginal infections, 250 mg/day for 7 days
  • For various amoebic infections: 500 mg – 750 mg XR or capsule depending on the infection for 5-10 days.
  • In Trichomoniasis: Metronidazole capsules are given (375 mg/ 2 times a day) for 7 days, or metronidazole tablets (250 mg/ 3 times a day) for 7 days.
  • For various other infections doses are adjusted according to age, sex, weight, immune health, duration of infection, etc.

Missed dose: Other doses depend on factors like the type & location of infection, bacteria, age, sex, presence of underlying diseases, immunity & doctor’s guidance.

a) Doses above 4-5 mg per day can present with overdose.
b) Management with administration of gastric lavage & induction of vomiting to remove metronidazole from the stomach.



  • Diarrhea,
  • Painful or difficulty urinating,
  • Trouble sleeping,
  • Depression,
  • Irritability,
  • Headache,
  • Dizziness
  • Weakness,
  • Lightheadedness,
  • Blisters or ulcers in your mouth,
  • Red or swollen gums, and
  • Trouble swallowing
  • Numbness


  • Seizures/Convulsions
  • Encephalopathy
  • Optic nerve damage
  • Paresthesia
  • Damage to the nerves of the periphery
  • Vertigo
  • Confusion & ataxia
  • Muscle weakness
  • Severe abdominal pain accompanied with vomiting or diarrhea
  • Metallic taste
  • Furry tongue
  • Pruritis
  • Reduced WBC count
  • Stevens-Johnson Syndrome
  • Severe hypersensitivity reaction & signs
  • Inflammation of the mouth
  • Flattening of the T-wave in heart readings.


Ornidazole is contraindicated in patients & precaution is advised with following conditions:

  • Cockayne Syndrome
  • Patients with hepatic impairment metabolize metronidazole slowly
  • ESRD
  • Candidiasis
  • Blood dyscrasia
  • Patients with prior history of hypersensitivity
  • In pregnant patients with trichomoniasis, metronidazole is contraindicated in the first trimester.
  • Crohn’s Disease
  • Anemia
  • Drug allergy
  • Metronidazole is contraindicated in patients that have alcohol addiction.


  • The drug should not be given in presence of disulfiram.
  • Beverages or medicines containing Propylene Glycol, can lead to abdominal cramping, flushing, rashes, etc.
  • Ornidazole increases the anti-coagulant activity of warfarin.
  • Ornidazole is given with ofloxacin for treatment of giardiasis & fungal infections.
  • Increase plasma concentration of busulfan & subsequent toxicity.
  • Drugs that inhibit CYP450 enzyme activity such as cimetidine can decrease plasma clearance time of ornidazole.
  • Drugs like phenytoin that induce CYP540 enzyme activity can in turn increase its excretion.
  • Can interfere with certain type of serum lab tests, blood tests & determinations of markers & enzymes.
  • Ornidazole in presence with alcohol can lead to a severe unpleasant reaction called disulfiram reactions that leads to vomiting, abdominal cramping, headache, dizziness, weakness, heart problems, etc.


  • Pregnancy: No sufficient data is available for the effect that ornidazole may produce on pregnant women.
  • Breast Feeding: The drug is present in breast milk, and due to its tumor causing factors is not recommended in breast feeding mothers.
  • Children: Safety and effectiveness in pediatric patients have not been established, except for the treatment of amebiasis.