Aspirin (Caprin 300mg)

How does it work?

Caprin enteric-coated tablets contain the active ingredient acetylsalicylic acid, otherwise known as aspirin. (NB. Aspirin is also available without a brand name, ie as the generic medicine.)

Aspirin belongs to a group of medicines called non-steroidal anti-inflammatory drugs (NSAIDs). It works by blocking the action of a substance in the body called cyclo-oxygenase.

Cyclo-oxygenase is involved in the production of various chemicals in the body. These are known as prostaglandins, prostacyclins and thromboxane. By blocking the action of cylo-oxygenase, aspirin prevents the production of these chemicals.

Prostaglandins are produced in response to injury or certain diseases and go on to cause pain, swelling and inflammation. High doses of aspirin (300mg and over) reduce the production of prostaglandins and a 300mg dose of aspirin is seen as a pain-relieving dose. Caprin 300mg tablets are used to relieve pain and inflammation. The tablets have a special enteric coating that is designed to stop the aspirin from irritating the stomach. However, because this coating doesn't dissolve until the tablet reaches the small intestine, the absorption of the aspirin into the bloodstream is delayed. This means that Caprin tablets don't act quickly enough for the short-term relief of pain with a single dose, for example to relieve a headache or toothache. Instead they are used for people who need to take aspirin regularly, for example to relieve the ongoing pain and inflammation of arthritis.

Aspirin in low doses (75mg to 150mg daily) does not have an anti-inflammatory effect and is used instead as an anti-clotting or blood-thinning agent for people who have heart disease, or who have already had a heart attack, heart bypass or stroke. Low doses of aspirin prevent the production of thromboxane by blood cells called platelets. Thromboxane is one of the chemicals that causes platelets to clump together and start off the clotting process. Stopping its production reduces the chance of a clot forming in the blood that could cause a heart attack or stroke. In some situations a higher 300mg daily dose of aspirin may also be prescribed to prevent blood clots. It is important to follow the instructions given by your doctor.

Aspirin is also used in the emergency situation of a heart attack. Anyone who has the symptoms of a heart attack (chest pain, possibly radiating towards the arm or neck, shortness of breath) should chew one 300mg aspirin tablet as soon as possible (unless they are allergic to aspirin), as this has been shown to increase the chances of surviving a heart attack. This is because the aspirin prevents the blood clot that is blocking the supply of blood to the heart from growing any bigger. If using Caprin tablets for this purpose it is especially important to chew the tablet, because the enteric coating of these tablets would otherwise delay the absorption of the aspirin. In the emergency situation of a heart attack the aspirin needs to be absorbed as quickly as possible.

What is it used for?

  • Relieving ongoing pain, inflammation and fever, for example in rheumatic conditions such as arthritis. Caprin aspirin is not suitable for relieving short-term pain such as headaches.
  • Preventing blood clots in the blood vessels and thus reducing the risk of heart attack and stroke, for example in people with angina, or people who have already had a heart attack, heart bypass, stroke or mini-stroke (TIA).
  • To improve survival in emergency situation of a heart attack.

How do I take it?

  • To relieve pain, inflammation and fever: adults over 16 years of age can take up to three Caprin 300mg tablets every six to eight hours as necessary. People with rheumatic problems such as arthritis may need higher doses than this - ask your doctor for advice. The tablets should be swallowed whole with a drink of water and not broken, crushed or chewed.
  • To prevent blood clots, heart attacks and strokes: aspirin is taken once a day. However, you should only take this medicine for this purpose after getting advice from your doctor first. Your doctor may ask you to take one Caprin 300mg tablet every day, or may ask you to use a product that contains a lower dose of aspirin. The tablets should be swallowed whole with a drink of water and not broken, crushed or chewed.
  • In an emergency situation of a suspected heart attack: call for an ambulance. If the casualty is not allergic to aspirin, get them to slowly chew one Caprin 300mg tablet as a single dose. Keep the packet to show the paramedics.


  • You should get advice from your doctor or pharmacist if you are considering taking aspirin to reduce the risk of suffering a stroke or heart attack, to make sure it would be a suitable thing for you to do. Aspirin can actually increase the risk of a particular type of stroke in certain people, and it may also have side effects that outweigh its potential benefits for some people.
  • Children under 16 years of age must not take aspirin, unless prescribed by a doctor. This is because aspirin use in children has been associated with a rare condition called Reye's syndrome. This condition affects the brain and liver and though extremely rare, can be fatal. The causes of Reye's syndrome are not fully understood, but use of aspirin to treat fever in children with a virus has been implicated. There are many paracetamol and ibuprofen products not associated with Reye's syndrome available to treat pain and fever in this age group. For more advice talk to your pharmacist.
  • Do not exceed the dose recommended in the leaflet supplied with this medicine.
  • Aspirin is generally well-tolerated and most people do not experience any side effects. The most common side effects are related to stomach irritation and include abdominal pain, indigestion and nausea. Rarely, serious side effects such as ulceration or bleeding in the stomach or intestines may occur. These are more likely with high doses and in elderly people. If you experience any sign of bleeding from the stomach or bowels after taking this medicine, for example vomiting blood and/or passing black/tarry/bloodstained stools, you should stop taking this medicine and consult your doctor immediately. You should also stop taking this medicine and consult your doctor if you experience any any other unusual bleeding, for example nosebleeds, purple spots or bruising under your skin, blood in your urine or coughing up blood.

Use with caution in

  • Elderly people.
  • Decreased kidney function.
  • Decreased liver function.
  • People with uncontrolled high blood pressure (hypertension).
  • People who are dehydrated.
  • People who suffer from asthma.
  • People with a history of allergies.
  • People with a deficiency of an enzyme called glucose-6-phosphate dehydrogenase (G6PD) in their blood.

Not to be used in

  • Children and adolescents under 16 years of age, unless prescribed by a doctor (see warning above).
  • People in whom aspirin or other NSAIDs, eg ibuprofen, cause allergic reactions such as asthma attacks, itchy rash (urticaria), nasal inflammation (rhinitis) or swelling of the lips, tongue and throat (angioedema).
  • People with an active peptic ulcer or a history of this.
  • People with bleeding disorders such as haemophilia.
  • Severely decreased liver function.
  • Severely decreased kidney function.
  • Severe heart failure.
  • Treatment of acute attacks of gout.
  • Third trimester of pregnancy.
  • Breastfeeding.

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.

  • Aspirin should not be taken during pregnancy unless on the advice of a doctor. High, painkilling doses of aspirin should be avoided wherever possible in the last three months of pregnancy, because it may increase the risk of bleeding, delay labour, increase the length of labour and cause complications in the newborn baby. Get medical advice from your doctor or midwife before using this medicine during any other stage of pregnancy.
  • This medicine passes into breast milk. It should not be taken by breastfeeding mothers as it may be harmful to a nursing infant. Seek further medical advice from your doctor, pharmacist or midwife.

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 does not mean that all people using this medicine will experience that or any side effect.

  • Indigestion.
  • Feeling sick or vomiting.
  • Stomach or intestinal discomfort.
  • Inflammation of the stomach (gastritis).
  • Ulceration or bleeding in the stomach or intestines (see warning section above).
  • Sensation of ringing, or other noise in the ears (tinnitus).
  • Worsening of asthma.
  • Allergic reactions such as skin rash, swelling of the lips, tongue and throat (angioedema) or narrowing of the airways (bronchospasm).
  • Increased bleeding time.
  • Bleeding disorders (see warning section above).

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 taking this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.

Caprin tablets have a special 'enteric coating' that is designed to stop the aspirin from irritating the stomach. Antacids (indigestion remedies) should not be taken two hours before or after Caprin tablets because they allow this special coat to dissolve too early.

There is an increased risk of side effects, particularly on on the gut, if aspirin is taken in combination with other non-steroidal anti-inflammatory drugs (NSAIDs), eg ibuprofen, diclofenac, naproxen, indometacin, or with selective inhibitors of COX-2 such as celecoxib or etoricoxib. If you are taking one of these types of medicine you should not take painkilling doses of aspirin (300mg or more per day) as well.

There may be an increased risk of bleeding if aspirin is taken with any of the following medicines:

  • anticoagulant medicines used to prevent the blood clotting, eg warfarin (if you are taking warfarin you should only take aspirin on the advice of a doctor)
  • other 'blood-thinning' (antiplatelet) medicines such as clopidogrel or dipyridamole
  • heparins
  • iloprost
  • SSRI antidepressants, eg fluoxetine, paroxetine, citalopram
  • venlafaxine.

There may be an increased risk of bleeding or ulceration in the stomach or intestines if aspirin is taken with corticosteroids, eg prednisolone, dexamethasone.

Aspirin reduces the rate at which the body can remove the medicine methotrexate and so could increase the risk of its side effects. If you are taking methotrexate you should not take aspirin unless you have been advised to by your doctor.

There may be an increased risk of side effects if high doses of aspirin are taken with acetazolamide.

Regular use of aspirin as a painkiller may increase the amount of the following medicines in the blood:

  • valproate
  • zafirlukast.

Aspirin may oppose the effects of the following medicines:

  • probenecid
  • sulfinpyrazone.

Other medicines containing the same active ingredient

Angettes 75 Aspro clear Caprin (75mg)
Disprin Disprin direct Maximum strength aspro clear
Micropirin Nu-seals (300mg) Nu-seals (75mg)

Aspirin tablets, dispersible tablets, enteric-coated tablets and suppositories are also available without a brand name, ie as the generic medicine.