Tetracycline antibiotics with iron, calcium, magnesium and zinc

Tetracyclines are a family of antibiotics. Doxycycline is the one most often prescribed in the UK, and the NHS says it is mainly used for bacterial infections including some urinary tract infections, sexually transmitted infections, chest infections and gum infections, and, as the NHS also notes, is sometimes used for skin conditions like acne and rosacea and to prevent malaria. Lymecycline, oxytetracycline and tetracycline itself are others in the group.

Most people take doxycycline once or twice a day for a few days or weeks, as the NHS says. Because courses can be long, there is more chance of overlapping with everyday supplements and remedies, which is where this interaction comes in.

Iron, zinc, calcium and magnesium are minerals found in many supplements, and the NHS says antacids and other indigestion treatments may also interact. The BNF describes the effect as these minerals decreasing the absorption of oral doxycycline, so check the label of any remedy or supplement you use.

The BNF presents the practical result for doxycycline. Iron decreases absorption and the manufacturer advises taking doxycycline 2 to 3 hours after iron. Magnesium decreases absorption with separation of at least 2 to 3 hours. Calcium acetate and zinc are predicted to reduce absorption, again with separation of 2 to 3 hours. Sucralfate might decrease absorption and the BNF advises separating administration.

A pharmacist can tailor timing, but the BNF numbers give a good starting point. Where a supplement or remedy contains one of these minerals, aim for a gap of at least 2 to 3 hours with doxycycline.

• Iron tablets: take doxycycline 2 to 3 hours after iron, as the BNF advises.

• Magnesium supplements and magnesium-containing indigestion remedies: separate by at least 2 to 3 hours.

• Calcium and zinc supplements, and multivitamin tablets that contain them: separate by 2 to 3 hours.

• Sucralfate: separate administration, as the BNF advises.

• Check the label of any antacid or multivitamin, because the minerals listed decide whether spacing is needed.

Interaction timing is one part of taking a tetracycline correctly. The NHS says to take it at the same time each day, swallow capsules or tablets whole with a glass of water while sitting or standing, and avoid lying down for at least 30 minutes afterwards, which helps stop the medicine irritating your throat. It also says to check the packet or leaflet about taking it with food.

The NHS also lists possible serious side effects including skin that is more sensitive to the sun, inflammation in the bowel with stomach ache and bloody diarrhoea, and changes in blood cells, and says to call NHS 111 if you think you are having serious side effects.

Alcohol is the other practical point. The NHS says you can eat as normal but it is best not to drink alcohol because it can stop the medicine working properly.

The NHS also lists anticoagulants such as warfarin and acne medicines as things that may not mix well with doxycycline. The BNF says doxycycline increases the anticoagulant effect of warfarin and advises monitoring INR, and that rifampicin modestly decreases exposure to doxycycline with advice to adjust the dose.

The take-home message is not to avoid supplements, but to tell the prescriber and pharmacist about everything you use so that a timetable can be set.

Doxycycline can be prescribed by many different clinicians, and many people are given only a short label. If anything on your own list contains iron, zinc, calcium or magnesium, say so, and ask whether you should pause the supplement for the length of the course or just shift the time. Pharmacists can usually answer this at the counter.