Phenoxymethylpenicillin (penicillin V): uses and cautions

Penicillin V is the tablet or liquid penicillin traditionally used when the likely bacteria are sensitive to it. The NHS lists ear, throat, chest and skin infections as treated conditions. Its second job is different in kind: for people with sickle cell disease, or who have had the spleen removed, a daily low-intensity course helps prevent serious infections, because the body is less able to defend itself.

That prevention use is why some readers will have taken it for many years. The NHS states that prophylaxis can continue for a long time, sometimes for life, so it is something you take daily and do not stop because you feel well.

Penicillin V tablets should be swallowed whole with a glass of water. Liquid is measured with the syringe or spoon in the pack. Doses are spaced evenly during the day, and the stomach matters: the NHS asks you to take it at least 30 minutes before eating or at least 2 to 3 hours after.

For a short infection, keep going to the end of the prescription even when symptoms fade. For long-term prevention the instruction is simply to continue as prescribed.

• Missed a dose: take it when you remember, unless the next one is nearly due; do not double up.

• Overdose: speak to a pharmacist, call NHS 111 if one is not available or the overdose was deliberate, and use 999 if you feel seriously unwell.

Most adults and children can take penicillin V. It is unsuitable if you have ever had an allergic reaction or serious side effect to it, to another penicillin or to another antibiotic. The NHS also asks about a stomach condition that regularly makes you sick, since vomiting stops the tablet being absorbed, and about kidney problems, allergies or asthma.

Pregnancy and breastfeeding are generally acceptable according to the NHS, but you should still tell your doctor or pharmacist first.

Common effects are mostly digestive: nausea, vomiting, diarrhoea, stomach pain or cramps, loss of appetite and wind. Taking it as directed and keeping drinking fluids usually helps, and the NHS says it does not normally affect driving or using machines.

Serious reactions are uncommon but need action.

• Anaphylaxis, with a swollen mouth, throat or tongue, breathing difficulty or severe dizziness: call 999.

• Angioedema, swelling of the lips, tongue or face, which the NHS says is more of a risk with black skin: call 999.

• An itchy or painful rash with blisters or sores in the mouth, eyes or genitals, a sign of Stevens-Johnson syndrome: call 999.

• Severe diarrhoea containing blood or mucus: seek urgent medical advice.

The NHS names methotrexate, tetracycline antibiotics, erythromycin, neomycin, warfarin and probenecid as medicines that can interact. Tell the prescriber about all of your medicines, including supplements and herbal remedies.

Alcohol is not forbidden, but the NHS suggests limiting how much you drink while on it because alcohol can add to side effects such as nausea.

The prescriber chooses between antibiotics according to the infection. People with penicillin allergy are offered a different antibiotic family, and those prescribed it for prevention are reviewed to make sure the plan still suits them.

You can report suspected side effects to the MHRA Yellow Card scheme, and the pharmacist can answer questions about timing with meals.