Sounds like 'kla-RITH-roe-MYE-sin'

Clarithromycin is an antibiotic used to treat different infections caused by bacteria. Find out how to take it safely and possible side effects.

Type of medicine Also called
  • Antibiotic (to treat infections)
  • Macrolide antibiotic
  • Apo-Clarithromycin®
  • Klacid®

What is clarithromycin?

Clarithromycin is an antibiotic that is used to treat infections such as chest infections. It works by killing or stopping the growth of bacteria (bugs) that cause infection. Like all antibiotics, clarithromycin is not effective against infections caused by viruses. Clarithromycin is also used with other medicines to get rid of Helicobacter pylori, a bacteria that can cause stomach and duodenal ulcers. Read more about Helicobacter pylori

In New Zealand clarithromycin is available as tablets (250 mg and 500 mg) and liquid and can be given as an injection in the hospital. 


  • Adults: the usual dose is 250 mg or 500 mg  two times a day.
  • Children: the dose for children will depend on their body weight. It is usually given 2 times a day.
  • Your doctor will advise you on how long to take clarithromycin for (usually 7 to 14 days).
  • Always take your clarithromycin exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it, and any special instructions. 

How to take clarithromycin

  • You can take clarithromycin with or without food.
  • Tablets: swallow the tablets with a glass of water.
  • Liquid: shake the medicine well. Measure the right amount using an oral syringe or medicine spoon. You can get these from your pharmacy. Do not use a kitchen spoon as it will not give you the right amount. Read more: Tips on how to give medicines to babies and children.
  • Take your doses at the same times each day. 
  • Try to space your doses evenly throughout the day - this should be in the morning and in the evening.
  • If you forget to take your dose at the correct time, take one as soon as you remember. Try to take the correct number of doses each day. Do not take two doses at the same time to make up for a forgotten dose.
  • If you are sick (vomit) less than 30 minutes after having a dose of clarithromycin, take the same dose again. But, if you are sick (vomit) and it is more than 30 minutes after having a dose of clarithromycin, you do not need to take another dose. Wait until the next normal dose.
  • If you are vomiting and are worried, contact your doctor or Healthline (0800 611 116) for advice.

Other tips

  • Store your tablets in a cool, dry place, away from direct heat and light. If you have been given liquid medicine, this will have been made up by the pharmacy and you may need to keep it in the fridge - check the instructions on the bottle. Make sure the medicine does not freeze.
  • It is best to take the whole course of antibiotics for the number of days your doctor has told you to. Do not stop taking it, even if you feel your infection has cleared up.

Precautions – before starting clarithromycin

  • Do you have problems with your kidneys or liver?
  • Do you have problems with your heart, especially changes in your heart rate?
  • Do you have myasthenia gravis (causes tired and weak muscles)?
  • Are taking any other medicines? This includes any medicines you are taking which you can buy without a prescription, as well as herbal and complementary medicines.

If so, it’s important that you tell your doctor or pharmacist before you start clarithromycin. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Possible side effects

Abnormal heart rhythms

Clarithromycin can increase your risk of abnormal heart rhythms. It can cause fast, irregular heartbeats (known as arrhythmia), which may trigger a sudden fainting spell, or in some cases, if the heart does not regain its normal rhythm it may cause sudden death. You are at higher risk if you already have 'long QT syndrome', or if other members of your family have 'long QT syndrome'. You are also at increased risk if you have heart problems or are taking other medicines that cause 'long QT syndrome'. Read more about long QT syndrome

Other side effects

Like all medicines, clarithromycin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Nausea (feeling sick) or vomiting
  • Take clarithromycin with or after food.
  • Diarrhoea (runny poos)
  • Headache
  • These may go away with time.
  • Tell your doctor if troublesome.
  • Vaginal itching, soreness or discharge (thrush)
  • Tell your doctor or pharmacist.
  • Changes in your taste, sore mouth or dry mouth
  • Tell your doctor if troublesome.
  • Signs of problems with your liver such as yellowing of the skin or eyes, dark urine, pain in the abdomen. 
  • Tell your doctor immediately or ring HealthLine 0800 611 116 


Clarithromycin interacts with many other medicines and herbal supplements, so check with your doctor or pharmacist before starting clarithromycin. Also, check with a pharmacist before taking over-the-counter medicines. If you are taking the contraceptive 'pill', the effectiveness of the 'pill' can be reduced if you have a bout of being sick (vomiting) or diarrhoea which lasts for more than 24 hours. If this happens, ask your doctor or pharmacist for advice about contraception over the following few days.

Learn more

The following links has more information about clarithromycin. 

New Zealand Formulary Patient Information: clarithromycin


  1. Clarithromycin New Zealand Formulary
  2. Apo-clarithromycin Medsafe Datasheet, April 2015
  3. Macrolides - Don't Upset the Rhythm Medsafe Prescriber Update,  June 2015
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 05 Apr 2019