Antibiotics Penicillins

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.

Alcohol

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
• headaches

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.

Combined oral contraceptives

Some antibiotics, such asrifampicin 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 yourGP, nurse or pharmacist for advice.

Medications

Some of the medications you may need to avoid, or seek advice on, while taking a specific class of antibiotic are outlined below.

Penicillins

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

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.

Aminoglycosides

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.

Tetracyclines

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 areused to treat severe acne
• blood-thinning medication
• diuretics
• 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
• methotrexate
• strontium ranelate used to treat osteoporosis
• colestipol or colestyramine used to treat high cholesterol
• ergotamine and methysergide used to treat migraines

Macrolides

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:

• terfenadine, astemizole and mizolastine these are all antihistamines used to treat allergic conditions such as hay fever
• amisulpride used to treat episodes of psychosis
• tolterodine used to treat urinary incontinence
• statins used to treat high cholesterol

Fluoroquinolones

You should check with your GP or pharmacist before taking a fluoroquinolone if you're currently taking any of the following:

• theophyllineused to treat asthma; also found in some cough and cold medicines
• non-steroidal anti-inflammatory drug (NSAID) painkillerssuch as ibuprofen
• ciclosporin
• probenecidused to treat gout
• clozapineused to treat schizophrenia
• ropiniroleused to treat Parkinson's disease
• tizanadineused to treat muscle spasms
• glibenclamideused to treat diabetes
• cisaprideused to treat indigestion, heartburn, vomiting or nausea
• tricyclic antidepressantssuch 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 toavoid taking medication that contains high levels of minerals or iron, as this can block the beneficial effects of fluoroquinolones. This includes:

• antacids
• zinc supplements
• some types of multivitamin supplements