Skip to main content


On this page

  1. About clarithromycin
  2. Key facts
  3. Who can and cannot take clarithromycin
  4. How and when to take it
  5. Side effects
  6. How to cope with side effects
  7. Pregnancy and breastfeeding
  8. Cautions with other medicines
  9. Common questions

1. About clarithromycin

Clarithromycin is an antibiotic.

It's used to treat chest infections, such as pneumonia, skin problems such as cellulitis, and ear infections.

It's also used to get rid of Helicobacter pylori, a bacteria that can cause stomach ulcers.

Clarithromycin is sometimes used by people who have an allergy to penicillin and antibiotics similar to penicillin, like amoxicillin.

Clarithromycin is only available on prescription.

It comes as tablets, granules, or a liquid that you drink.

It can also be given by injection, but this is usually only done in hospital.

2. Key facts

  • It's usual to take clarithromycin twice a day: once in the morning and once in the evening.
  • Some people take slow-release clarithromycin tablets. These are taken once a day.
  • For most infections, you should feel better within a few days.
  • The most common side effects of clarithromycin are feeling or being sick, stomach cramps, and diarrhoea.
  • You can drink alcohol while taking clarithromycin.
  • Clarithromcyin is also called by the brand names Clarie XL, Klaricid, Klaricid XL and Xetinin XL.

3. Who can and cannot take clarithromycin

Clarithromycin can be taken by adults and children.

Clarithromycin isn't suitable for some people.

To make sure clarithromycin is safe for you, tell your doctor if you have:

  • had an allergic reaction to clarithromycin or any other medicines in the past
  • had diarrhoea when you have taken antibiotics before
  • fast, pounding or irregular heartbeats
  • abnormally low levels of potassium in your blood
  • liver or kidney problems
  • porphyria (a rare, inherited blood disorder)
  • myasthenia gravis - clarithromycin can make the symptoms of this muscle-weakening illness worse
  • an illness called phenylketonuria - people with phenylketonuria have to avoid the sweetener aspartame and some brands of liquid clarithromycin contain aspartame

Also tell your doctor if you're pregnant, trying to get pregnant, or breastfeeding.

Clarithromycin isn't generally recommended during pregnancy and while breastfeeding.

4. How and when to take it

The usual dose of clarithromycin is 250mg to 500mg twice a day.

The dose may be lower for children and if you have kidney problems.

If your doctor prescribes slow release or modified release tablets, the dose is 500mg once a day. These tablets release the medicine slowly, which means that 1 dose a day is enough.

Try to take your medicine at the same time every day.


Carry on taking this medicine until the course is completed, even if you feel better. If you stop your treatment early, your infection could come back.

How to take it

Clarithromycin tablets come in 250mg or 500mg strengths.

Swallow clarithromycin tablets or capsules whole with a drink of water, with or without food.

Do not chew or break them.

Clarithromycin granules come in 250mg sachets. Open the pack - or packets - and mix the granules with a small amount of water to drink.

There's also a liquid clarithromycin for children and people who find it difficult to swallow tablets.

If you or your child are taking clarithromycin as a liquid, your pharmacist will usually make it up for you.

The medicine will come with a plastic syringe or spoon to help you take the right amount.

If you don't have a syringe or spoon, ask your pharmacist for one.

Do not use a kitchen teaspoon as it will not give the right amount.

What if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it's nearly time for your next dose.

In this case, just leave out the missed dose and take your next dose as normal.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you often forget doses, it may help to set an alarm to remind you.

You could also ask your pharmacist for other ways to remember your medicine.

What if I take too much?

Taking an extra dose of clarithromycin by accident is unlikely to harm you or your child.

It may give you temporary side effects, like stomach pain, feeling and being sick, and diarrhoea.

Talk to your pharmacist or doctor if you're worried or get severe side effects, or if you or your child accidentally take more than 1 extra dose.

5. Side effects

Like all medicines, clarithromycin can cause side effects, although not everyone gets them.

Common side effects

These common side effects of clarithromycin happen in more than 1 in 100 people.

Keep taking the medicine, but tell your doctor if these side effects bother you or don't go away:

  • feeling sick (nausea)
  • diarrhoea and being sick (vomiting)
  • losing your appetite
  • bloating and indigestion
  • headaches
  • difficulty sleeping (insomnia)

Serious side effects

Serious side effects are rare and happen in less than 1 in 1,000 people.

Call a doctor straight away if you get:

  • a faster or irregular heartbeat
  • pale poo together with dark pee, yellow skin or the whites of your eyes turn yellow - this can be a sign of liver problems
  • severe pain in your stomach or back - these can be warning signs of inflammation of the pancreas (pancreatitis)
  • paleness, feeling tired, faint or dizzy, purple spots, blotching on the skin, any sign of bleeding (like bleeding from your gums, bleeding for a long time and bruising more easily), a sore throat, a fever (a temperature of 38C or more) and getting infections more easily - these can be signs of a blood or bone marrow disorder
  • diarrhoea (perhaps with muscle cramps) that contains blood or mucus - if you have severe diarrhoea without blood or mucus for more than 4 days, you should also speak to a doctor
  • hallucinations (seeing or hearing things that aren't there)
  • ringing in your ears or hearing loss, or feeling unsteady on your feet

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to clarithromycin.

Immediate action required: Call 999 or go to A&E now if:
  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

You could be having a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of clarithromycin. For a full list, see the leaflet inside your medicine packet.


You can report any suspected side effect using the Yellow Card safety scheme.

Visit Yellow Card for further information.

6. How to cope with side effects

What to do about:

  • feeling sick (nausea) - stick to simple meals and do not eat rich or spicy food while you're taking this medicine. It might help to take your clarithromycin after you have had a meal or snack.
  • diarrhoea and being sick (vomiting) - drink lots of fluids, such as water or squash, to avoid dehydration. Take small, frequent sips if you're being sick. Signs of dehydration include peeing less than usual or having strong-smelling pee. Do not take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.
  • losing your appetite - eat when you'd usually expect to be hungry. If it helps, eat smaller meals more often than usual. Snack when you're hungry. Have nutritious snacks that are high in calories and protein, such as dried fruit and nuts.
  • bloating and indigestion - try not to eat foods that cause wind (like lentils, beans and onions). Eat smaller meals, eat and drink slowly, and exercise. There are pharmacy medicines that can also help, such as charcoal tablets or simethicone. Ask a pharmacist for advice.
  • headaches - rest and drink plenty of fluids. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller if you need one. Talk to your doctor if the headaches last longer than a week or are severe.
  • difficulty sleeping (insomnia) - avoid having a big meal, smoking, and drinking alcohol, tea or coffee in the evening. Try not to watch television or use your mobile phone before going to bed. Instead, try to relax for an hour before bedtime.

7. Pregnancy and breastfeeding

Clarithromycin isn't normally recommended during pregnancy and while breastfeeding.

But your doctor may prescribe it if the benefits of you taking it are greater than the risks.

Erythromycin is the antibiotic most often used in pregnancy.

For more information about how clarithromycin can affect you and your baby during pregnancy, read this leaflet on the Best Use of Medicines in Pregnancy (BUMPS) website.

Non-urgent advice: Tell your doctor if you're:

  • trying to get pregnant
  • pregnant
  • breastfeeding

8. Cautions with other medicines

There are some medicines that don't mix well with clarithromycin.

Tell your doctor if you're taking these medicines before you start clarithromycin:

Mixing clarithromycin with herbal remedies and supplements

There are no known problems with taking herbal remedies or supplements alongside clarithromycin.

Important: Medicine safety

Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.

9. Common questions

How does clarithromycin work?

Clarithromycin is from a group of medicines called macrolide antibiotics.

Macrolide antibiotics work by killing the bacteria causing the infection.

When will I feel better?

For most infections, you should feel better within a few days.

For skin problems such as cellulitis, you may have to take the medicine for about 7 days before you see any improvement.

If you have a Helicobacter pylori infection, even if the bacteria are no longer in your stomach, it can take some time before you feel better.

Your doctor will usually give you a medicine to reduce stomach acid, such as omeprazole or lansoprazole, while the ulcer heals.

You should start feeling better when you finish treatment to reduce your stomach acid.

It's very important that you keep taking clarithromycin until your course is finished.

Do this even if you feel better. It'll help to stop the infection coming back.

What if I don't get better?

Tell your doctor if you don't start feeling better after taking clarithromycin for:

Also tell them if, at any time, you start to feel worse.

If you have a Helicobacter pylori infection, your doctor will arrange a follow-up test 6 to 8 weeks after you started clarithromycin.

They'll also usually give you a medicine to reduce stomach acid, such as omeprazole or lansoprazole.

If your symptoms don't get better in that time or you notice any new problems, like losing weight, contact your doctor as soon as possible.

How does clarithromycin compare with other antibiotics?

There are other macrolide antibiotics that work in the same way as clarithromycin.

They include azithromycin and erythromycin.

It's usual to take clarithromycin twice a day. For azithromycin it's once a day, and for erythromycin it's usually 4 times a day.

Clarithromycin and azithromycin are less likely to cause diarrhoea than erythromycin.

All macrolides can be used to treat chest and skin infections.

Azithromycin and erythromycin can also be used to treat sexually transmitted infections.

Clarithromycin can also be used to treat Helicobacter pylori, a bacteria that can cause stomach ulcers.

Clarithromycin and other macrolide antibiotics kill similar types of bacteria to penicillin antibiotics, such as amoxicillin.

Some people are allergic to penicillin antibiotics - they can take clarithromycin instead.

Can I drink alcohol with it?

Yes, you can drink alcohol with clarithromycin.

Will it give me thrush?

Some people get a fungal infection called thrush after taking a course of antibiotics like clarithromycin.

It happens because antibiotics kill the normal harmless bacteria that help to protect you against thrush.

Ask your pharmacist or doctor for advice if this happens to you.

Will it stop my contraception working?

Clarithromycin doesn't stop contraception from working, including the combined pill or emergency conraception.

But if clarithromycin makes you vomit or have severe diarrhoea (6 to 8 watery poos in 24 hours) for more than 24 hours, your contraceptive pills may not protect you from pregnancy.

Look on the pill packet to find out what to do.

Read more about what to do if you're on the pill and you're being sick or have diarrhoea.

Will it reduce my fertility?

There's no firm evidence to suggest that taking clarithromycin will reduce fertility in either men or women.

But speak to a pharmacist or your doctor before taking it if you're trying to get pregnant.

Is there any food or drink I need to avoid?

You can eat and drink normally while taking clarithromycin.

Page last reviewed: 6 December 2018
Next review due: 6 December 2021