Clarithromycin (Klaricid)

How does it work?

Klaricid tablets, paediatric suspension, adult sachets and injection all contain the active ingredient clarithromycin, which is a type of medicine known as a macrolide antibiotic. It is used to treat infections caused by bacteria. (NB. Clarithromycin is also available without a brand name, ie as the generic medicine.)

Clarithromycin works by preventing bacteria from producing proteins that are essential to them. Without these proteins the bacteria cannot grow, replicate and increase in numbers. Clarithromycin doesn'’t directly kill the bacteria, but leaves them unable to increase in numbers. The remaining bacteria eventually die or are destroyed by the immune system. This treats the infection.

Clarithromycin is a broad-spectrum antibiotic that is active against a wide variety of bacteria that cause a wide variety of infections. Clarithromycin may be used to treat infections of the upper or lower airways, skin or soft tissue, or ears.

Clarithromycin is also used to eradicate a type of bacteria called Helicobacter pylori (H pylori) from the gut. The presence of these bacteria in the gut is associated with ulcers of the stomach and duodenum (an area of the intestine directly after the stomach). Eradicating H pylori from the gut allows ulcers to heal and also helps prevent them recurring. Clarithromycin is used in combination with a proton pump inhibitor such as lansoprazole or omeprazole and the antibiotics metronidazole or amoxicillin for this purpose (triple therapy). Proton pump inhibitors reduce the production of acid in the stomach and help create an environment in the stomach in which the antibiotic can work more effectively against the bacteria. They also help the ulcer to heal.

To make sure the bacteria causing an infection are susceptible to clarithromycin your doctor may take a tissue sample, for example a swab from the throat or skin, or a sputum sample.

What is it used for?

  • Bacterial infections of the lungs (chest or lower respiratory tract infections), eg bronchitis, pneumonia.
  • Bacterial infections of the nasal passages, sinuses or throat (upper respiratory tract infections) eg sinusitis, pharyngitis.
  • Bacterial infections of the skin or soft tissue, eg cellulitis, folliculitis or erysipelas.
  • Bacterial infections of the middle ear (otitis media).
  • Lyme disease.
  • Eradicating Helicobacter pylori bacteria from the gut in people with peptic ulcers.

How do I take it?

  • The dose of this medicine and how long it needs to be taken for depends on the type of infection you have and your age. Follow the instructions given by your doctor. These will be printed on the dispensing label that your pharmacist has put on the packet of medicine.
  • Clarithromycin is usually taken twice a day (every 12 hours). It can be taken either with or without food.
  • Klaricid adult sachets contain granules that should be mixed with a small amount of water before taking.
  • Bottles of Klaricid paediatric suspension should be shaken before measuring out a dose. Only use the measuring spoon provided with the suspension. You should not use a regular teaspoon or tablespoon to take the medicine, as this will not give an accurate dose.
  • Unless your doctor tells you otherwise, it is important that you finish the prescribed course of this antibiotic medicine, even if you feel better or it seems the infection has cleared up. Stopping the course early increases the chance that the infection will come back and that the bacteria will grow resistant to the antibiotic.


  • Broad-spectrum antibiotics can sometimes cause inflammation of the bowel (colitis). For this reason, if you get diarrhoea that becomes severe or persistent or contains blood or mucus, either during or after taking this medicine, you should consult your doctor immediately.
  • All antibiotics can sometimes result in overgrowth of organisms that are not susceptible to the antibiotic, in particular fungi. You should let your doctor know if you think you have developed any other infections while you are taking this medicine, so that they can be treated appropriately.
  • Klaricid paediatric suspension can be stored at room temperature (below 30°C). Any suspension remaining after 14 days should be disposed of, preferably by returning it to your pharmacist.

Use with caution in

  • Decreased kidney function.
  • Decreased liver function.
  • People with an abnormal heart rhythm seen on a heart monitoring trace (ECG) as a 'prolonged QT interval', or people at risk of this (your doctor will know).

Not to be used in

  • People allergic to other macrolide-type antibiotics, eg erythromycin, azithromycin.
  • People taking astemizole, cisapride, pimozide, terfenadine or ergot derivatives, eg ergotamine, dihydroergotamine.
  • Klaricid tablets and adult sachets are not suitable for children under 12 years of age.
  • Klaricid adult sachets and Klaricid paediatric suspensions contain sucrose and are not suitable for people with rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • The safety of this medicine during pregnancy has not been established. It should not be used in pregnant women unless the expected benefit to the mother is greater than any possible risk to the developing baby. Seek medical advice from your doctor.
  • This medicine passes into breast milk, but the effect on the nursing infant is unknown. It should not be used in breastfeeding women unless the expected benefit to the mother is greater than any possible risk to the nursing infant. Seek medical advice from your doctor.

Label warnings

  • Take at regular intervals. Complete the prescribed course unless otherwise directed.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Disturbances of the gut such as diarrhoea, nausea, vomiting, indigestion, abdominal pain.
  • Sore mouth or tongue.
  • Tongue or tooth discolouration.
  • Oral thrush (see warning section above).
  • Pins and needles sensations.
  • Headache.
  • Pain in the muscles or joints.
  • Disturbance of taste or smell.
  • Allergic skin reactions.
  • Dizziness.
  • Spinning sensation (vertigo).
  • Difficulty sleeping or bad dreams.
  • Confusion.
  • Reversible loss of hearing.
  • Inflammation of the large intestine (colitis) - see warning section above.
  • Low blood sugar (hypoglycaemia).
  • Liver or kidney disorders.
  • Abnormal heart beats (arrhythmias).

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

Clarithromycin should not be taken by people who are taking any of the following medicines, because clarithromycin can raise the blood levels of these medicines, resulting in an increased risk of serious side effects:

  • astemizole
  • cisapride
  • dronedarone
  • eletriptan
  • eplerenone
  • ergot derivatives, eg ergotamine, dihydroergotamine or methysergide (used to treat migraine)
  • everolimus
  • ivabradine
  • mizolastine
  • pimozide
  • ranolazine
  • saquinavir
  • simvastatin
  • terfenadine.

Clarithromycin may reduce the breakdown of the medicines listed below. If the blood levels of these medicines are raised as a result, it may lead to an increased risk of their side effects. If you are taking one of these medicines and are prescribed clarithromycin you should let your doctor or pharmacist know if you experience any new or increased side effects:

  • alprazolam
  • aprepitant
  • bromocriptine
  • cabergoline
  • carbamazepine
  • ciclosporin
  • cilostazol
  • colchicine
  • digoxin
  • disopyramide
  • droperidol
  • etravirine
  • fesoterodine
  • itraconazole
  • maraviroc
  • methylprednisolone and possibly other corticosteroids
  • midazolam
  • nilotinib
  • pazopanib
  • phenytoin
  • quetiapine
  • reboxetine
  • repaglinide
  • rifabutin (increased risk of uveitis)
  • sildenafil
  • sirolimus
  • tacrolimus
  • tadalafil
  • theophylline
  • tolterodine
  • triazolam
  • vardenafil
  • verapamil
  • zopiclone.

Clarithromycin may also increase the blood levels and hence anti-blood-clotting effects of the anticoagulants nicoumalone and warfarin. As this may increase the risk of bleeding, people taking these combinations, particularly elderly people, may need more frequent monitoring of their blood clotting time (INR) so the dose of anticoagulant can be adjusted if necessary.

Clarithromycin may also increase the blood levels of cholesterol-lowering medicines called statins, eg atorvastatin and simvastatin. This may increase the risk of side effects on the muscles (myopathy) from these medicines. Combined use of simvastatin and clarithromycin should be avoided.

Clarithromycin may decrease the absorption of zidovudine from the gut. If you are taking both these medicines the clarithromycin should be taken at least two hours before or after the zidovudine to avoid the interaction. Ask your pharmacist for further advice.

There may be an increased risk of abnormal heart beats if clarithromycin is taken in combination with any of the following medicines:

  • anti-arrhythmic medicines (for an irregular heartbeat), eg amiodarone, disopyramide, quinidine
  • certain antimalarials, eg chloroquine, quinine, mefloquine, halofantrine
  • certain antipsychotics, eg chlorpromazine, thioridazine, fluphenazine, haloperidol.

Oral typhoid vaccine (Vivotif) should not be taken until at least three days after you have finished a course of this antibiotic, because the antibiotic could make this vaccine less effective.

In the past, women using hormonal contraception such as the pill or patch would be advised to use an extra method of contraception (eg condoms) while taking an antibiotic like this one and for seven days after finishing the course. However, this advice has now changed. You no longer need to use an extra method of contraception with the pill, patch or vaginal ring while you take a course of antibiotics. This change in advice comes because to date there is no evidence to prove that antibiotics (other than rifampicin or rifabutin) affect these contraceptives. This is the latest guidance from the Faculty of Sexual & Reproductive Healthcare.

However, if you are taking the contraceptive pill and experience vomiting or diarrhoea as a result of taking this antibiotic, you should follow the instructions for vomiting and diarrhoea described in the leaflet provided with your pills.

Ritonavir may increase the blood level of clarithromycin. This is not normally a problem, but if you have kidney problems and are taking ritonavir your doctor may prescribe you a lower than normal dose of clarithromycin.

Other medicines containing the same active ingredient

Klaricid XL

Clarithromycin tablets, suspension and injection also available without a brand name, ie as the generic medicine.