O2
O2 is a tablet that contains Ofloxacin 200 mg + Ornidazole 500 mg. It combines Ofloxacin: antibiotic (fluoroquinolone) and Ornidazole: anti-amoebic and antibacterial.
| Ingredient (salt) | Amount |
|---|---|
| Ofloxacin | 200 mg |
| Ornidazole | 500 mg |
Ofloxacin
What it is used for
Treats urine, gut, chest and some ear and eye infections.
How it works
A fluoroquinolone antibiotic, also used as ear and eye drops, often combined with ornidazole for gut infections.
How to take it
Tablets usually 200 to 400 mg twice a day. Take at evenly spaced times and finish the full course even when you feel better, unless your doctor says otherwise.
Common side effects
- Nausea
- Diarrhoea
- Dizziness
- Trouble sleeping
Get medical help straight away if
- Tendon pain or swelling, especially the heel (stop and rest)
- Tingling, numbness or burning in the hands or feet
- Mood changes or confusion
- Severe diarrhoea
- Palpitations
Be careful
Can rarely damage tendons and nerves; avoid antacids at the same time.
Other medicines and interactions
Antacids, iron, zinc, calcium and milk taken at the same time block absorption; separate by at least 2 hours before or 6 hours after. Raises tendon risk with steroids. Can affect warfarin, diabetes medicines (blood sugar swings) and heart rhythm medicines.
Pregnancy and breastfeeding
Usually avoided in pregnancy and while breastfeeding unless no other antibiotic will work.
Ornidazole
What it is used for
Treats amoebic dysentery, giardia and some gut infections.
How it works
A nitroimidazole that kills amoebas, giardia and anaerobic bacteria; often combined with ofloxacin for diarrhoea.
How to take it
Usually 500 mg twice a day after food for 5 to 10 days.
Common side effects
- Metallic taste
- Nausea
- Dizziness
- Headache
Get medical help straight away if
- Numbness or tingling in hands or feet
- Fits
- Severe diarrhoea
- Dark urine with yellow skin
Be careful
Avoid alcohol during and for 2 days after the course.
Other medicines and interactions
Do not drink alcohol during the course and for 3 days after (severe flushing, vomiting and palpitations). Strengthens warfarin; can raise lithium levels.
Pregnancy and breastfeeding
Avoid in the first three months of pregnancy; ask a doctor about breastfeeding.
Same composition, other brands (14)
Ask your doctor or pharmacist before switching brands.
Common questions
What is O2?
O2 is a tablet containing Ofloxacin 200 mg + Ornidazole 500 mg.
What is O2 used for?
Treats urine, gut, chest and some ear and eye infections. Treats amoebic dysentery, giardia and some gut infections.
How should I take O2?
Tablets usually 200 to 400 mg twice a day. Take at evenly spaced times and finish the full course even when you feel better, unless your doctor says otherwise. Usually 500 mg twice a day after food for 5 to 10 days. Always follow the dose your doctor or the pack gives.
What are the side effects of O2?
Common side effects include: Nausea, diarrhoea, dizziness, trouble sleeping, Metallic taste, nausea, dizziness, headache. Get medical help straight away for: Tendon pain or swelling, especially the heel (stop and rest), tingling, numbness or burning in the hands or feet, mood changes or confusion, severe diarrhoea, palpitations, Numbness or tingling in hands or feet, fits, severe diarrhoea, dark urine with yellow skin.
Does O2 need a prescription?
Yes. In India it is a prescription (Schedule H) medicine, so a pharmacist should sell it only with a doctor's prescription.
Can I take O2 in pregnancy or while breastfeeding?
Usually avoided in pregnancy and while breastfeeding unless no other antibiotic will work. Avoid in the first three months of pregnancy; ask a doctor about breastfeeding.
What are the substitutes for O2?
Brands with the same composition: Oflox-OZ, Zenflox-OZ, Oflotas OZ, Nor Metrogyl Plus, Nicoflox-O, Olox OZ, Normet, Orni-O, Oflomac OZ, Ornof, Saril, Brakke. Ask your doctor or pharmacist before switching.
Sources and further reading
- Ofloxacin: NHS · MedlinePlus
- Ornidazole: NHS · MedlinePlus
NHS (UK National Health Service) and MedlinePlus (US National Library of Medicine) are free, reviewed medicine guides. Brand names and doses there may differ from India.
Composition checked against pack details from large Indian online pharmacies. Last reviewed 31 October 2026. Written by Satya Babu.
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