Interactions with other medicines
Antibiotics can sometimes interact with other medicines or other substances. This means the effects of one of the medicines can be altered by the other.
Some of the more common interactions are listed below. However, this is not a complete list.
If you want to check that your medicines are safe to take with your antibiotics, ask your GP or local pharmacist.
You should also always read the patient information leaflet that comes with your medicine carefully.
Combined oral contraceptives
Some antibiotics, such as rifampicin and rifabutin, can reduce the effectiveness of the combined oral contraceptive pill. Other antibiotics do not have this effect.
If you are prescribed rifampicin or rifabutin, you may need to use additional contraception, such as condoms, while taking antibiotics. Speak to your GP or nurse 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 is usually recommended you avoid taking penicillin at the same time as a medication called methotrexate, which is used to treat some types of cancers and severe autoimmune conditions such as the skin condition psoriasis.
This is because combining the two medications can cause a range of unpleasant and sometimes serious side effects.
You may experience a skin rash if you take penicillin and a medication called allopurinol, which is used to treat gout.
Cephalosporins may not be suitable to take if you are also taking blood-thinning medications (anticoagulants) such as heparin and warfarin.
If you need treatment with cephalosporins, you may temporarily have to stop taking the blood-thinning medication.
The risk of damage to your kidneys and hearing is increased if you are 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 do not occur.
You should check with your GP or pharmacist before taking a tetracycline if you are currently taking any of the following medications:
- vitamin A supplements
- retinoids – such as acitretin, isotretinoin and tretinoin; 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 is highly recommended you do not 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 are currently taking any of the following medications:
- 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
Interactions with food
Some antibiotics need to be taken with food, while others need to be taken on an empty stomach.
Make sure you read the information leaflet that comes with your medication carefully to find out whether this is the case.
Can I drink alcohol if I'm on antibiotics?
You should completely avoid alcohol if you're taking the antibiotics metronidazole or tinidazole as this can cause very unpleasant side effects, such as:
- feeling and being sick
- stomach pain
- hot flushes
It's recommended you avoid alcohol with all antibiotics as drinking could make your infection last longer. But provided you drink in moderation, alcohol is unlikely to interact significantly with your medication.
Read more information about drinking alcohol while taking antibiotics.
Page last reviewed: 05/06/2014
Next review due: 05/06/2016