Antibiotics can sometimes interact with other medicines or substances. This means it can have an effect that is different to what you expected.
Some of the more common interactions are listed below, but this isn't a complete list.
If you want to check that your medicines are safe to take with your antibiotics, ask your GP or local pharmacist.
Some antibiotics need to be taken with food, while others need to be taken on an empty stomach. You should always read the patient information leaflet that comes with your medicine.
You should completely avoid alcohol while taking the antibiotics metronidazole or tinidazole, and for 48 hours afterwards, as this combination can cause very unpleasant side effects, such as:
- feeling and being sick
- stomach pain
- hot flushes
It's recommended that you don't drink alcohol while taking antibiotics. However, as long as you drink in moderation, alcohol is unlikely to interact significantly with your medication.
Read more information about drinking alcohol while taking antibiotics.
Combined oral contraceptives
Some antibiotics, such as rifampicin and rifabutin, can reduce the effectiveness of the combined oral contraceptive pill.
If you're prescribed rifampicin or rifabutin, you may need to use additional contraception, such as condoms, while taking antibiotics. Speak to your GP, nurse or pharmacist for advice.
Some of the medications you may need to avoid, or seek advice on, while taking a specific class of antibiotic are outlined below.
It's usually recommended that you avoid taking penicillin at the same time as methotrexate, which is used to treat psoriasis, rheumatoid arthritis and some forms of cancer. This is because combining the two medications can cause a range of unpleasant and sometimes serious side effects.
However, some forms of penicillin, such as amoxicillin, can be used in combination with methotrexate.
You may experience a skin rash if you take penicillin and allopurinol, which is used to treat gout.
Cephalosporins may increase the chance of bleeding if you're taking blood-thinning medications (anticoagulants) such as heparin and warfarin.
If you need treatment with cephalosporins, you may need to have your dose of anticoagulants changed or additional blood monitoring.
The risk of damage to your kidneys and hearing is increased if you're taking one or more of the following medications:
- antifungals – used to treat fungal infections
- cyclosporin – used to treat autoimmune conditions such as Crohn's disease and given to people who have had an organ transplant
- diuretics – used to remove water from the body
- muscle relaxants
The risk of kidney and hearing damage has to be balanced against the benefits of using aminoglycosides to treat life-threatening conditions such as septicaemia.
In hospital, blood levels are carefully monitored to ensure the antibiotic is only present in the blood in safe amounts. If aminoglycosides are used properly in topical preparations, such as ear drops, these side effects don't occur.
You should check with your GP or pharmacist before taking a tetracycline if you're currently taking any of the following:
- vitamin A supplements
- retinoids – such as acitretin, isotretinoin and tretinoin, which are used to treat severe acne
- blood-thinning medication
- kaolin-pectin and bismuth subsalicylate – used to treat diarrhoea
- medicines to treat diabetes – such as insulin
- atovaquone – used to treat pneumonia
- antacids – used to treat indigestion and heartburn
- sucralfate – used to treat ulcers
- lithium – used to treat bipolar disorder and severe depression
- digoxin – used to treat heart rhythm disorders
- strontium ranelate – used to treat osteoporosis
- colestipol or colestyramine – used to treat high cholesterol
- ergotamine and methysergide – used to treat migraines
It's highly recommended that you don't combine a macrolide with any of the following medications unless directly instructed to by your GP, as the combination could cause heart problems:
You should check with your GP or pharmacist before taking a fluoroquinolone if you're currently taking any of the following:
- theophylline – used to treat asthma; also found in some cough and cold medicines
- non-steroidal anti-inflammatory drug (NSAID) painkillers – such as ibuprofen
- probenecid – used to treat gout
- clozapine – used to treat schizophrenia
- ropinirole – used to treat Parkinson's disease
- tizanadine – used to treat muscle spasms
- glibenclamide – used to treat diabetes
- cisapride – used to treat indigestion, heartburn, vomiting or nausea
- tricyclic antidepressants – such as amitriptyline
- steroid medications (corticosteroids)
Some fluoroquinolones can intensify the effects of caffeine (a stimulant found in coffee, tea and cola), which could make you feel irritable, restless and cause problems falling asleep (insomnia).
You may need to avoid taking medication that contains high levels of minerals or iron, as this can block the beneficial effects of fluoroquinolones. This includes:
- zinc supplements
- some types of multivitamin supplements