Flucloxacillin: uses, side effects and cautions

Flucloxacillin is one of the penicillin antibiotics, but it is chosen for a narrower set of jobs than amoxicillin. The NHS describes it as a treatment for skin and wound infections, ear infections and bone infections including osteomyelitis; chest infection and pneumonia also appear among the conditions linked to it.

Skin infections such as cellulitis and infected wounds are the situations in which most people meet it. The injectable version is normally given in hospital.

As with every antibiotic, it does nothing for viruses, and the decision to prescribe belongs to the clinician examining you.

The instruction that surprises most people is the timing. Food reduces how much flucloxacillin gets into the bloodstream, so the NHS advises taking each dose at least 60 minutes before a meal or at least 2 hours after. In practice many people link doses to the start of the day, mid-morning, mid-afternoon and bedtime rather than to mealtimes.

Leave at least 4 hours between doses. The NHS example spreads four doses across morning, midday, afternoon and bedtime. Children may be prescribed smaller amounts, and pharmacists make up the liquid with a syringe or spoon that you should use instead of a kitchen teaspoon.

• Missed a dose: take it when you remember unless the next one is nearly due, then skip it. Never double up.

• An extra dose once is unlikely to cause harm. Call NHS 111 if you develop stomach pain, vomiting, blood in the urine or passing less urine, or if a child under 5 has taken too much.

• Keep going for the full course. Speak to your doctor if there has been no improvement after 3 to 5 days, or sooner if things worsen.

Most adults and children can take flucloxacillin. Tell the prescriber about any earlier allergic reaction to flucloxacillin, another penicillin or any other medicine.

Liver and kidney problems matter here. The NHS asks you to disclose liver disease, and pale stools, dark urine or yellow skin or eyes during or after treatment should prompt you to seek help quickly. Also mention recent or upcoming vaccinations.

The NHS lists feeling or being sick, diarrhoea, and bloating or indigestion as the common ones, affecting more than 1 in 100 people. Simple meals, regular sips of fluid and smaller portions eaten slowly are the suggested comforts; avoid gas-producing foods such as beans and onions if you are bloated.

Sickness or diarrhoea that goes on can interfere with the contraceptive pill, so keep that in mind if you rely on it.

• Stop and seek advice from NHS 111 or a doctor for bloody or mucus-filled diarrhoea, pale stools with dark urine and yellowing of the skin or eyes, blisters, ulcers or a severe peeling rash, or bruising and skin colour changes.

• Joint or muscle pain beginning around two days in is also a reason to speak up. The NHS notes serious effects can start up to two months after finishing.

• Swollen lips or throat, severe breathing trouble, tight throat, or collapse is anaphylaxis: call 999.

The NHS names methotrexate, warfarin, the gout medicines probenecid and sulfinpyrazone, the antifungal voriconazole and other antibiotics as ones to review with a pharmacist or doctor. If you have recently had, or are due to have, the oral typhoid vaccine, mention it, since flucloxacillin may reduce its effect.

Herbal remedies and supplements have not been tested alongside it to the same standard as licensed medicines, so the NHS cannot say they are safe and advises telling your prescriber about them.

The NHS says flucloxacillin can be used in pregnancy and while breastfeeding; only tiny amounts reach breast milk. Treating the infection is important for the mother, and the baby should be watched for feeding changes, vomiting, diarrhoea, oral thrush or rash. There is no evidence that it affects fertility.

Alcohol is not restricted and the medicine does not impair driving or cycling, according to the NHS common-questions page. Flucloxacillin does not stop contraception working in itself.

The NHS says it is similar to phenoxymethylpenicillin and amoxicillin, and the prescriber chooses between them according to the infection. People with a penicillin allergy are prescribed a different antibiotic instead, chosen by the prescriber.

Suspected side effects can be reported by anyone to the MHRA Yellow Card scheme.