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Asacol, Octasa, Pentasa

There are a number of different brands of mesalazine, some of which work in different ways. This means that your treatment could be affected by switching between some brands. Each time you collect a new supply from your pharmacy, check to see if it is the same brand as before. If it is different, discuss this with your pharmacist who will advise you.

It is important that you keep your regular appointments with your doctor so that your progress can be checked. You may require regular blood tests.

Common side-effects include gastrointestinal symptoms and aches and pains. These tend to be minor. Rarely, mesalazine can cause problems with your blood. You should tell your doctor immediately if you have any unexplained bleeding, bruising, red or purple discolourations of the skin, sore throat, a high temperature (fever), or if you feel generally unwell.

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About mesalazine

Type of medicine

An aminosalicylate

Used for

Ulcerative colitis and Crohn's ileo-colitis

Also called

Mesalamine (in US); Asacol®; Mezavant®; Octasa®; Pentasa®; Salofalk®; Zintasa®

Available as

Tablets, granules (sachets), suppositories, enemas, and foam enemas (rectal foam)

Ulcerative colitis causes inflammation of the intestine which leads to problems such as ulceration and bleeding. This causes symptoms such as abdominal pain and diarrhoea. Crohn's disease is a condition which causes inflammation of any part of the gastrointestinal system. When the inflammation is in the area where the small intestine joins the large intestine, then it is called Crohn's ileo-colitis. Aminosalicylates are a group of medicines commonly used to treat inflammatory bowel diseases such as these. Mesalazine is one of the most commonly used aminosalicylates.

Although it is not clear exactly how mesalazine works, it is thought to act on cells lining the intestine to change the way these cells make and release certain chemicals. These chemicals are thought to be a factor in causing the symptoms of ulcerative colitis. Mesalazine allows the damaged intestine to recover and helps to prevent symptoms from flaring up again.

There are a number of different mesalazine preparations and brands. The way the manufacturers make each of these brands differs slightly; this allows the different brands to release mesalazine in specific areas of the intestine. You will be prescribed the brand that allows mesalazine to be released in the part of your intestine which requires it most.

Mesalazine can be taken by mouth as granules or tablets, or it can be given into the back passage as a suppository, rectal foam or enema.

Before taking mesalazine

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking mesalazine it is important that your doctor knows:

  • If you are pregnant or breastfeeding. (Although mesalazine is unlikely to be harmful to babies, it is still important that you tell your doctor if you are expecting or breastfeeding a baby.)

  • If you have any problems with the way your liver works, or if you have any problems with the way your kidneys work.

  • If you have any problems with your breathing.

  • If you have ever had an allergic reaction to a medicine. It is particularly important that you tell your doctor if you have had an unusual reaction to aspirin or a salicylate.

  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

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How to take mesalazine

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about mesalazine, and it will also provide you with a full list of the side-effects which you could experience.

  • Your dose will depend upon which brand of mesalazine has been prescribed for you. Your doctor will tell you how much to take and when to take it, and these directions will also be printed on the label of the pack to remind you about what the doctor said to you. Take mesalazine exactly as your doctor tells you to.

  • Some mesalazine tablets and granules are specially coated to pass through your stomach before they are absorbed. These must be swallowed whole and not broken, chewed or crushed. Check the label on your pack carefully and follow any advice it gives. Also, do not take any indigestion remedies within two hours of taking your doses (either before or after), as this will interfere with the special coating.

  • If you have been given the Mezavant® XL brand of tablets, you should take these after a meal. If you have been given any other brand of tablet, it is unimportant whether you take them before or after a meal.

  • If you have been given granules, place the correct amount on to your tongue and wash them down with a drink of water. Do not chew the granules. You can take them either before or after meals. Alternatively the entire contents of the sachet can be poured onto a yoghurt and eaten straightaway.

  • If you forget to take a dose, take it as soon as you remember (unless it is nearly time for your next dose, in which case leave out the missed dose and take the next dose as normal). Do not take two doses together to make up for a forgotten dose.

How to use mesalazine enema

  1. Shake the enema and release the seal on the nozzle.

  2. Lie down on one side and draw your top knee up towards your chest. Insert the enema nozzle into your back passage.

  3. Squeeze the bottle gently to completely empty the contents. This will take around 30-40 seconds. Remove the nozzle from your back passage. Remain where you are for about 5-10 minutes until the urge to pass the enema has eased.

  4. Throw away the empty enema bottle in a plastic bag (these are provided with some brands of enema).

  5. Wash your hands.

How to use mesalazine foam enema

  1. Shake the can well to mix the contents.

  2. Before you use the can for the first time, remove the plastic safety lock.

  3. Push the plastic applicator on to the nozzle of the can.

  4. Stand up and place one foot on a firm surface, such as a chair.

  5. Hold the canister upside down (with the dome facing down) in the palm of your hand.

  6. Insert the applicator into your back passage as far as is comfortable.

  7. Push the dome once and release it. This will release one dose of the foam. Repeat if you need two doses.

  8. Remove the applicator and place it in one of the plastic bags provided and dispose of it in a bin.

  9. Wash your hands.

How to use mesalazine suppositories

  1. Remove the suppository from the packaging.

  2. Using your finger, gently push the suppository into your back passage (rectum). Some people find it helps to squat, or to lie down on one side and draw their knees up towards their chest to do this.

  3. Push the suppository in as far as is comfortable. You may have the urge to pass the suppository out again but this should ease after a few minutes.

  4. Wash your hands.

Getting the most from your treatment

  • Each time you collect a new supply from your pharmacy, check to see if it is the same brand as before. If it is different, discuss this with your pharmacist who will advise you.

  • Try to keep your regular appointments with your doctor and clinic. This is so your doctor can check on your progress. Your doctor will want you to have regular blood tests during the treatment.

  • Treatment with mesalazine may be long-term to prevent symptom flare-ups. Continue to take/use it unless you are advised otherwise.

  • Your doctor may advise you make some changes to your diet as part of your treatment. This can include a special diet or a nutritional supplement.

  • It is important to stay hydrated whilst being treated with mesalazine, ensure you drink the recommended amount of fluids each day.

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Can mesalazine cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains the most common ones associated with mesalazine. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Common mesalazine side-effects (these affect fewer than 1 in 10 people)

What can I do if I experience this?

Indigestion, feeling sick (nausea) or being sick (vomiting), tummy (abdominal) pain

Stick to simple foods - avoid rich or spicy meals


Drink plenty of water to replace lost fluids

Headache, muscle aches and pains

Drink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the aches continue, let your doctor know

Important: rarely, mesalazine can cause problems with your blood. You should contact your doctor immediately if you have any unexplained bleeding, bruising, red or purple discolourations of your skin, an unexplained sore throat or high temperature (fever), or if you feel generally unwell during the treatment.

In rare cases mesalazine can cause serious allergic skin reactions. Contact your doctor if you develop any signs of an allergic reaction including skin rashes and mouth ulcers.

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

How to store mesalazine

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

If you buy any medicines, check with a pharmacist that they are safe to take with your other medicines.

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine go to the accident and emergency department of you local hospital at once. Take the container with you, even if it is empty.

If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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