Quick answer: Antibiotics treat bacterial infections only. They do not work against viruses such as colds, flu, most sore throats and coughs, dengue or most diarrhoea. Take an antibiotic only when a doctor prescribes it, exactly as directed, for the duration the doctor sets. Misuse helps bacteria become resistant, which makes infections longer, costlier and more dangerous.

When do antibiotics work, and when do they not?

Antibiotics kill bacteria or stop them multiplying. They have no effect on viruses. So they do not help with colds, flu, most sore throats, most coughs, dengue, or most cases of diarrhoea, which usually settle with fluids and rest (see our guide to treating diarrhoea at home with ORS and zinc). Taking an antibiotic for a viral illness will not make you better faster, and it can still cause side effects.

Only a doctor can judge whether an illness is bacterial, sometimes after an examination or a lab test. A fever alone does not mean you need an antibiotic; our fever guide explains what to do first. Infections that may need an antibiotic include some throat, ear, urinary, skin and chest infections, and typhoid.

How should I take an antibiotic?

  • Follow the prescription exactly: the right dose, at the right times, with or without food as instructed.
  • Follow the duration your doctor sets. Guidance on how long to treat differs from infection to infection, and some courses are now shorter than they used to be. Do not stop early or carry on longer by yourself. If you feel better, or feel worse, call the doctor and ask.
  • Never share, save or reuse leftovers. A medicine chosen for one person's infection may be wrong for yours.
  • Do not buy antibiotics without a prescription. In Bangladesh antibiotics are often sold over the counter without one, and this is a major driver of resistance. A prescription is the safe route, and our prescription medicine page is for orders with a valid prescription.
  • Missed dose: take it when you remember, unless it is nearly time for the next one. Then skip the missed dose. Never take a double dose.

Take tablets or capsules with a full glass of water unless told otherwise, and keep the pack where you will see it so doses are not missed. Syrups should be measured with the supplied cup or syringe, and powders that are mixed with water must be made up exactly as the label says. When the course is finished, ask your pharmacist how to dispose of any leftover medicine instead of saving it for later.

If the prescription abbreviations are unclear, our guide on how to read a prescription and take medicines safely explains BD, TDS and 1+0+1.

What is antibiotic resistance and why does it matter?

Resistance happens when bacteria change so that antibiotics no longer kill them. Every unnecessary or incomplete use gives bacteria more chances to adapt. Resistant infections last longer, need stronger and costlier medicines, can mean hospital stays, and are more likely to be fatal. WHO describes antimicrobial resistance as one of the top global public-health threats.

This is why doctors now prescribe antibiotics more carefully: they are kept for infections where they are likely to help, and the shortest effective course is chosen. If your doctor decides you do not need one, that is good care, not neglect.

Resistance affects everyone, not only the person who misused the medicine, because resistant bacteria spread between people, through food and water, and in hospitals.

What are the side effects and interactions?

Common side effects are nausea, loose stools, stomach upset, rash and thrush (a white coating in the mouth or genital itching). Mild ones often settle, but tell your doctor if they bother you rather than stopping on your own.

  • Alcohol: avoid it with metronidazole and tinidazole.
  • Calcium, iron, antacids and dairy: these can reduce absorption of doxycycline and ciprofloxacin-type antibiotics. Keep about 2 hours between them, and check the leaflet.
  • Pregnancy and allergies: tell the doctor and pharmacist if you are pregnant, breastfeeding or have ever reacted to a medicine.
  • Other medicines: mention everything you take, including supplements and herbal products.

How can I reduce the need for antibiotics?

  • Wash hands with soap before eating and after the toilet.
  • Keep vaccinations up to date, for you and your children.
  • Use safe drinking water and properly cooked, hygienically handled food.
  • Do not ask a doctor for an antibiotic for a cold, flu or other viral illness, and accept it when they say you do not need one.

When an antibiotic is prescribed, ask: What infection do I have? Why do I need an antibiotic? How long should I take it? What side effects should I watch for?

A "gastric tablet" is not automatically needed with every antibiotic course; see acidity, GERD and safe use of acid-reducing medicines.

When should I see a doctor or get emergency help?

  • Emergency (call 999 or go to hospital): rash with swelling of the lips, face or tongue, wheezing or difficulty breathing, or fainting after a dose. These are signs of a serious allergy.
  • See a doctor promptly: severe watery or bloody diarrhoea during or after antibiotics, a spreading rash, or vomiting that stops you keeping the medicine down.
  • Call your doctor: no improvement within the time your doctor expected, symptoms getting worse, or questions about stopping.

You can talk to a qualified doctor through online doctor consultation.

References

This article is for general awareness only and is not a substitute for advice from a qualified doctor. Always follow your own doctor's instructions.