Medically reviewed by Bandela Mgoqi (B.Pharm, M.Pharm, MPS). Last updated on September 17, 2026.
Klacid XL is an antibiotic belonging to a group called macrolides. Antibiotics stop the growth of bacteria (bugs) which cause infections. Its use is described below.
Klacid XL is used to treat infections such as:
Do not take Klacid XL tablets:
Klacid XL must be taken with food and must be swallowed whole and not chewed.
If you are pregnant or breast feeding a baby, do not take Klacid XL tablets without consulting your doctor, pharmacist or other health care professional for advice first, as the safety of Klacid XL tablets in pregnancy and breastfeeding is not known.
Klacid XL must be taken with food and must be swallowed whole and not chewed. The usual dose of Klacid XL for adults and children over 12 years of age is 500 mg once daily for seven to fourteen days. Your doctor may increase the dose to two 500 mg tablets daily in severe infections. These tablets are not suitable for children under 12 years of age as liquid medicines are generally preferable – your doctor will prescribe another suitable medicine for your child.
Do not stop taking Klacid XL tablets because you feel better. It is important to take the tablets for as long as the doctor has told you to, otherwise the problem might come back.
If you forget to take Klacid XL:
If you forget to take a Klacid XL tablet, take one as soon as you remember and then continue dosing as normal. Do not take more tablets in one day than your doctor has told you to. If you are concerned about having missed one or more doses of medicine, consult your doctor or pharmacist.
If you take more Klacid XL than you should:
If you accidentally take more than two Klacid XL tablets in one day, or if a child accidentally swallows some tablets, seek medical advice urgently - in the event of overdosage, consult your doctor or pharmacist. If neither is available, contact the nearest hospital or poison control centre. An overdose of Klacid XL tablets is likely to cause vomiting and stomach pains, and there is a possibility of allergic reactions.
Not all side-effects reported for this medicine are included in this leaflet. Should your general health worsen while taking this medicine, please consult your doctor, pharmacist or other health care professional for advice.
Klacid XL can sometimes cause stomach problems such as feeling sick, vomiting, stomach pain or diarrhoea. You may also experience numbness or a feeling of ‘pins and needles’. Headache, joint pain or muscle pain, or loss of muscle tissue have also been reported. If you develop severe or prolonged diarrhoea, which may have blood or mucous in it, during or after taking Klacid XL tablets, consult your doctor immediately.
If you have a blood test while taking Klacid XL it may show raised liver enzymes. These levels usually return to normal, and it is unlikely that you will show any symptoms. However, Klacid XL can rarely cause jaundice and other liver or gall bladder disorders, which can be severe or even fatal in extremely rare circumstances. If you feel generally unwell or develop yellow skin and/or eyes, or pale stools with dark urine, consult you doctor immediately. Kidney problems, including raised levels of protein normally excreted by the kidneys, and rarely kidney failure, have also been reported. Occasionally, a blood test may also show low levels of white blood cells.
Allergic reactions, including rashes, have been reported with Klacid XL. In very rare cases, difficulty in breathing, fainting and swelling of the face and throat can occur, which may need emergency treatment. Allergic rashes may range in severity from mild, itchy skin eruptions to a rarer, more serious condition called Stevens-Johnson syndrome (which causes severe illness with ulceration of the mouth, lips and skin) or toxic epidermal necrolysis (which causes severe illness and sloughing of the skin).
Some people taking Klacid XL notice a funny taste in their mouth, or a change in their sense of taste and smell. However, these are only temporary effects and you should not stop taking the tablets because of them. Very rarely, the teeth become discoloured, but in most cases this can be removed by professional dental cleaning.
There have also been reports of Klacid XL causing the tongue to swell or darken, sore mouth or tongue and ‘thrush’ in the mouth. There have also been some reports of dizziness, loss of bearings, ‘ringing’ in the ears, difficulty in sleeping, depression, hallucinations (seeing things), bad dreams, confusion, change in sense of reality and panicking. These effects are usually short-lived and soon disappear. Very rarely, fainting due to low blood sugar, and mood and behavioural disorders have been reported, which in severe cases have required hospitalisation. Very rarely, some patients may experience unexpected bruising and their blood may take longer to clot after a cut to the skin. Changes in heart rhythm, inflammation of the pancreas and convulsions have also been reported rarely. There have been rare reports of loss of sense of smell and of hearing with Klacid XL, which is a temporary effect and is usually reversible on stopping treatment. Consult your doctor immediately if you develop any of these problems or have any other unexpected or unusual symptoms.
Do not use these tablets after their ‘use - by’ (expiry) date, which is printed on the box and indented on the blister strip. If the tablets are out of date, return them to your pharmacist and, if necessary, get a new prescription from your doctor.
Store at room temperature (below 30°C) in a dry place, protected from light. Store in the original package.
Store all medicines out of reach of children – keep this medicine in a safe place where children cannot reach it. If your doctor decides to stop your treatment with Klacid XL, return any remaining tablets to a pharmacist.
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