Bacterial Infections

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Bacterial Infections

This section lists Doxycycline 100 mg from Omega Pharma, a prescription antibiotic for certain bacterial infections such as some chest infections, chlamydia and Lyme disease. Because antibiotics don't work on viruses and each one covers different bacteria, the right choice depends on an accurate diagnosis, and sometimes a test, from a doctor, pharmacist or sexual health clinic.

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Bacterial Infections: Knowing When You Need Treatment

Bacteria and viruses can cause very similar symptoms, such as fever, a sore throat, cough or diarrhea, yet they are treated in completely different ways. Antibiotics act only on bacteria, and no single antibiotic suits every bacterial infection. Working out the likely cause is the first step towards the right treatment.

Bacterial or Viral?

Usually viralOften bacterial
Colds and fluUrinary tract infections (UTIs)
Most sore throats and coughsCellulitis and impetigo (skin infections)
Most sinus infectionsSome pneumonias
Most stomach bugsChlamydia, gonorrhoea and syphilis

Green or yellow mucus does not by itself mean you need an antibiotic. When it matters, tests such as a urine sample, throat or genital swab, or blood test can confirm the cause.

When to See a Doctor

  • Urinary symptoms: burning when passing urine, needing to go often, or cloudy or bloody urine. Seek advice promptly if you are a man, are pregnant, or have a fever or pain in your back or side, which can signal a kidney infection.
  • Skin: redness, warmth or swelling that is spreading, red streaks, or a wound that is leaking pus.
  • Fever: a temperature of 102°F (39°C) or higher, a fever lasting more than three days, or symptoms that improve and then get worse.
  • Sexual health: unusual discharge, pain when urinating, genital sores, or a partner diagnosed with an STI. Get tested before treatment so the right antibiotic is used and partners can be treated too.
  • Tick bites: an expanding red rash, sometimes shaped like a bull's-eye, appearing days to weeks later.

Sepsis: Call Emergency Services

Sepsis is a life-threatening reaction to an infection. Call emergency services if someone with an infection has:

  • Slurred speech, confusion or unusual drowsiness
  • Extreme shivering or severe muscle pain
  • Passed no urine in a day
  • Severe breathlessness
  • Mottled, bluish or very pale skin, or a rash that doesn't fade when a glass is pressed against it
  • A strong sense that something is seriously wrong

Why the Right Antibiotic Matters

Each antibiotic works against a particular range of bacteria and reaches some parts of the body better than others. The choice also depends on local resistance patterns, allergies, pregnancy and other medicines. Doxycycline 100 mg, for instance, suits chlamydia, Lyme disease and some chest infections, but is not a usual choice for a typical bladder infection or for gonorrhoea. The wrong antibiotic can delay recovery and encourage resistance. For dosing, side effects and responsible use, see our antibiotic guide.

Frequently Asked Questions

Should I start antibiotics before seeing a doctor?

No. Starting without a diagnosis can hide symptoms and make tests less reliable, especially for UTIs and STIs.

How soon should I feel better?

Many people improve within two to three days of starting the right antibiotic. If you are no better by then, or are getting worse, contact your doctor.

The information on this page is general guidance only and does not replace a medical assessment. Antibiotics are prescription medicines and should only be taken for an infection diagnosed by a qualified healthcare professional.

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