Doxycycline: uses, side effects and how to take it safely

Doxycycline treats or prevents several kinds of bacterial problem. The NHS names urinary tract infections, sexually transmitted infections, chest infections and gum infections, and it also lists acne, rosacea and malaria prevention for people travelling.

It comes as tablets, capsules and dispersible tablets that dissolve in water. The NHS lists the brand names Vibramycin-D, Efracea and Periostat. Low-dose and acne regimens are prescribed differently from infection courses, so follow your own label.

The key instruction is posture. Swallow tablets or capsules whole with a full glass of water while sitting or standing, and do not lie down for at least 30 minutes afterwards, to avoid irritation of the gullet. Take doses at the same time each day.

Whether to take it with food depends on the dose prescribed, so check the packet. Indigestion remedies and iron or zinc supplements interfere with it, so ask a pharmacist how far apart to take them.

• Missed dose: take it as soon as you remember unless the next is due soon; never double up.

• Overdose: an extra dose is unlikely to cause problems, but can sometimes be dangerous, so ask NHS 111 if you took more than prescribed.

• Finish the course even if you feel better.

The NHS says doxycycline is not usually given to younger children because it can affect how their teeth develop, and lists children under 12 as people who should avoid it. It is also unsuitable if you are allergic to it, have liver or kidney conditions, lupus, myasthenia gravis or alcohol dependence.

Pregnancy and breastfeeding are generally avoided, although a doctor may still recommend it if the benefits outweigh the risks.

Common effects are headaches, nausea, vomiting and a rash; they often settle, and the NHS says they do not normally affect driving. Speak to a pharmacist or doctor if they continue.

• Allergic reactions (anaphylaxis) need 999.

• Increased sensitivity to sunlight can cause rash and redness; take care in strong sun.

• Bowel inflammation can cause stomach pain and bloody diarrhoea; call NHS 111.

• Blood changes can cause tiredness or easy bruising; call NHS 111.

The NHS lists anticoagulants such as warfarin, antacids and indigestion treatments, some acne medicines and iron or zinc supplements as medicines that interact. Tell the prescriber about everything you take, including vitamins.

Alcohol is the other big one: the NHS says it is best not to drink, because it can stop doxycycline working properly. This is stricter advice than for most antibiotics.

Several of these rules aim at the same thing: keeping the amount of doxycycline absorbed steady. Taking it at the same time each day, keeping it apart from minerals and indigestion remedies, and avoiding alcohol all protect that. If a rule is hard to fit into your routine, ask the pharmacist to help you plan the day around the doses.

If doxycycline is unsuitable, for instance in pregnancy or for a child, the prescriber will choose another antibiotic or treatment.

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