What is aspirin? How does it work (mechanism of action)?
Aspirin is a nonsteroidal antiinflammatory drug (NSAID) effective in treating fever, pain, and inflammation in the body. It also prevents blood clots (i.e., is antithrombotic). As a group, NSAIDs are non-narcotic relievers of mild to moderate pain of many causes, including
- menstrual cramps,
- arthritis, and
- other musculoskeletal conditions.
Other members of this class include ibuprofen (Motrin), indomethacin (Indocin), nabumetone (Relafen) and several others. They all work by reducing the levels of prostaglandins, chemicals that are released when there is inflammation and that cause pain and fever. NSAIDs block the enzyme that makes prostaglandins (cyclooxygenase), resulting in lower concentrations of prostaglandins. As a consequence, inflammation, pain, and fever are reduced. Inhibition of prostaglandins also reduces the function of platelets and the ability of blood to clot. Aspirin, inhibits the function of platelets in a manner that is different from other NSAIDs, and its antithrombotic effects last longer than other NSAIDs. This is why aspirin is used for preventing heart attacks and strokes. The FDA approved Bayer aspirin in June 1965.
What are the uses for aspirin?
Aspirin is used for the treatment of inflammation, fever, and pain that results from many forms of arthritis, including:
- Rheumatoid arthritis
- Juvenile rheumatoid arthritis
- Systemic lupus erythematosus
- Ankylosing spondylitis
- Reiter's syndrome
- Soft tissue injuries, such as tendinitis and bursitis
Aspirin also is used for rapid relief of mild to moderate pain and fever in other inflammatory conditions. Because aspirin inhibits the function of platelets for prolonged periods of time, it is used for reducing the risk of another stroke or heart attack in people who have already had a stroke or heart attack.
What are the side effects of aspirin?
Most patients benefit from aspirin and other NSAIDs with few side effects. However, serious side effects can occur and generally tend to be dose-related. Therefore, it is advisable to use the lowest effective dose to minimize side effects.
The most common side effects of aspirin involve the gastrointestinal system and ringing in the ears.
Gastrointestinal side effects are
- abdominal burning,
- gastritis, and
- even serious gastrointestinal bleeding and
- liver toxicity.
Sometimes, ulceration and bleeding can occur without any abdominal pain. Black tarry stools, weakness, and dizziness upon standing may be the only signs of internal bleeding.
Ringing in the ears
- Should ringing in the ears occur, the daily dose should be reduced.
Other side effects include:
Other side effects and adverse reactions
- Aspirin should be avoided by patients with peptic ulcer disease or poor kidney function, since this medication can aggravate both conditions.
- Aspirin may exacerbate asthma.
- Aspirin can raise the blood uric acid level and is avoided in patients with hyperuricemia and gout.
- Children and teenagers should avoid aspirin for symptoms of the flu or chickenpox because of the associated risk of Reye's Syndrome, a serious disease of the liver and nervous system that can lead to coma and death.
- Aspirin can increase the effect of medicines used to treat diabetes mellitus, resulting in abnormally low blood sugars if blood sugar levels are not monitored.
- NSAIDs should be discontinued prior to elective surgery because of a mild tendency to interfere with blood clotting. Aspirin, because of its prolonged effect on platelets, is best discontinued at least ten to fourteen days in advance of the procedure.
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What is the dosage for aspirin?
Aspirin should be taken with food. Doses range from 50 mg to 6000 mg daily depending on the use.
- Usual doses for mild to moderate pain are 350 or 650 mg every 4 hours or 500 mg every 6 hours.
- Doses for rheumatoid arthritis include 500 mg every 4-6 hours; 650 mg every 4 hours; 1000 mg every 4-6 hours; 1950 mg twice daily.
- Heart attacks are prevented with 75, 81, 162 or 325 mg daily.
- 160 to 325 mg of non-enteric coated aspirin should be chewed immediately when experiencing symptoms of a heart attack.
- The dose for preventing another stroke is 75 to 100 mg daily.
Which drugs or supplements interact with aspirin?
Aspirin is associated with several suspected or probable interactions that affect the action of other drugs. The following examples are the most common of the suspected interactions.
NSAIDs may increase the blood levels of lithium (Eskalith, Lithobid) by reducing the excretion of lithium by the kidneys. Increased levels of lithium may lead to lithium toxicity.
Aspirin may reduce the blood pressure lowering effects of blood pressure medications. This may occur because prostaglandins have a role in the regulation of blood pressure.
When aspirin is used in combination with methotrexate (Rheumatrex, Trexall) or aminoglycoside antibiotics (for example, gentamicin) the blood levels of the methotrexate or aminoglycoside may increase, presumably because their elimination from the body is reduced. This may lead to more methotrexate or aminoglycoside-related side effects.
Individuals taking oral blood thinners or anticoagulants, for example, warfarin, (Coumadin) should avoid aspirin because aspirin also thins the blood, and excessive blood thinning may lead to serious bleeding.
Who suffers more frequently from migraine headaches?
Is aspirin safe to take if I’m pregnant or breastfeeding?
Aspirin is generally avoided during pregnancy because it may adversely effect the fetus. However, low aspirin doses have been safely used for the prevention of complications of pregnancy.
Aspirin is excreted into breast milk and may cause adverse effects in the infant.
What else should I know about aspirin?
What preparations of acetylsalicylic acid are available?
Chewable tablets: 81mg; caplets and tablets: 325mg, 500mg; enteric coated (safety coated) caplets and tablets: 325mg, 500mg.
How should I keep acetylsalicylic acid stored?
Aspirin should be stored at room temperature, 20 C to 25 C (68 F to 77 F), in a sealed container, avoiding moisture.
Aspirin is available is available in generic form without a prescription from your doctor or other healthcare professional.