Acetylsalicylic acid

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Acetylsalicylic acid

Acetylsalicylic acid, commonly known as aspirin, is the most popular therapeutic drug in the world. It is an analgesic (pain-killing), antipyretic (fever-reducing), and anti-inflammatory sold without a prescription as tablets, capsules, powders, or suppositories. The drug reduces pain and fever, is believed to decrease the risk of heart attacks and strokes, and may deter colon cancer and help prevent premature birth. However, aspirin can have serious side effects, and its use results in more accidental poisoning deaths in children under five years of age than any other drug.

History

In the mid- to late-1700s, English clergyman Edward Stone chewed on a piece of willow bark and discovered its analgesic property after hearing a story that declared a brew from the bark was “good for pain and whatever else ails you.” The bark’s active ingredient was isolated in 1827 and named salicin for the Greek word salix, meaning willow. Salicylic acid, first produced from salicin in 1838 and synthetically from phenol in 1860, was effective in treating rheumatic fever and gout but caused severe nausea and intestinal discomfort.

Acetylsalicylic acid was first synthesized in 1898 by a chemist working at Bayer Laboratories in Germany. Soon thereafter, the process for making large quantities of acetylsalicylic acid was patented, and aspirin—named for its ingredients acetyl and spiralic (salicylic) acid—became available by prescription. Its popularity was immediate and worldwide. Huge demand in the United States brought the manufacture of aspirin to that country in 1915 when it also became available without a prescription.

Acetylsalicylic acid has a number of actions. One of these is as an analgesic. Acetylsalicylic acid blocks the production of hormones (chemical substances formed by the body) called prostaglandins that may be released by an injured cell, triggering release of two other hormones that sensitize nerves to pain. The blocking action prevents this response and is believed to work in a similar way to prevent tissue inflammation. Acetylsalicylic acid is only effective on cells producing prostaglandins—for instance, injured cells. The recommended maximum therapeutic dosages for children (2,000 mg daily, spread over four-500 mg doses separated by at least four hours) and adults of (4,000 mg daily) works best against “tolerable” pain; extreme pain is virtually unaffected, as is pain in internal organs. Its effect lasts for about four hours.

Antipyretic action

Acetylsalicylic acid also reduces fever (antipyresis). This action is believed to occur at the anterior (frontal) hypothalamus, a portion of the brain that regulates such functions as heart rate and body temperature. The body naturally reduces its heat through perspiration and the dilation (expansion) of blood vessels. Prostaglandins released in the hypothalamus inhibit the body’s natural heat-reducing mechanism. As acetylsalicylic acid blocks these prostaglandins, the hypothalamus is free to regulate body temperature. Acetylsalicylic acid lowers abnormally high body temperatures while normal body temperature remains unaffected.

Finally, acetylsalicylic acid reduces the formation of blood clots due to platelet aggregation. It accomplishes this by inhibiting the production of a prostaglandin called thromboxane A₂, which is instrumental in platelet aggregation. This “thinning the blood” can reduce the risk of heart attack and stroke, and so acetylsalicyclic acid is frequently prescribed in low doses (such as 75–80 mg daily) over long periods for at-risk patients.

Despite these benefits, use of acetylsalicylic acid formulations such as aspirin has risks. Aspirin’s availability and presence in many prescription and non-prescription medications makes the risk of accidental overdose relatively high. Children and the elderly are

KEY TERMS

Analgesic —A compound that relieves pain without loss of consciousness.

Antipyretic —Anything that reduces fever.

Hypothalamus —A small area near the base of the brain where release of hormones influence such involuntary bodily functions as temperature, sexual behavior, sweating, heart rate, and moods.

Placenta —An organ that develops in the uterus during pregnancy to which the fetus is connected by the umbilical cord and through which the fetus receives nourishment and eliminates waste.

Platelets —Irregularly shaped disks found in the blood of mammals that aid in clotting the blood.

Prostaglandins —Groups of hormones and active substances produced by body tissues that regulate important bodily functions, such as blood pressure.

Suppository —Medication placed in a body cavity, usually the vagina or rectum, that melts and is absorbed by the body.

particularly susceptible, as their toxicity thresholds are much lower than adults. About 10% of all accidental or suicidal episodes reported by hospitals are related to aspirin.

As aspirin slows down platelet aggregation, its use increases risk of bleeding, a particular concern during surgery and childbirth. Aspirin’s irritant effect on the stomach lining may cause internal bleeding, sometimes resulting in anemia.

Reye syndrome is an extremely rare disease, primarily striking children between the ages of three and 15 years after they have been treated with aspirin for a viral infection. Reye syndrome manifests as severe vomiting, seizures, disorientation, and sometimes coma, which can result in permanent brain damage or death. The cause of Reye syndrome is unknown, but the onset strongly correlates to the treatment of viral infections with aspirin. Incidents of Reye syndrome in children on aspirin therapy for chronic arthritis are significant. In 1985, these observations were widely publicized and warning labels placed on all aspirin medications, resulting in a decline in the number of children with viruses being treated with aspirin and a corresponding decline in cases of Reye syndrome.

Aspirin can adversely affect breathing in people with sinusitis or asthma, and long-term use may cause kidney cancer or liver disease. There is some evidence that it delays the onset of labor in full-term pregnancies and, as it crosses the placenta, may be harmful to the fetus.