Thursday, June 14, 2007

Aspirin

After a surgical patient of mine told me that she was taking Excedrin (2 days after her surgery) I wanted to review which "common" products that contain aspirin (listed here). [I may need to list them all rather than just saying "no aspirin".] Excedrin, for me, is an easy one. I have to remind myself that Pepto Bismol contains aspirin. I also thought I would share a brief review of aspirin. Folks my age (I’ll hit 50 yr later this year) grew up with aspirin. It’s what we used for fever and headaches. My nieces and nephews have never had aspirin.

Aspirin will be 100 years old this October! Aspirin was developed in Germany by a chemical process described by research chemist Felix Hoffman on October 10, 1897. The active ingredient in aspirin, acetyl salicylic acid, is a synthetic derivative of a compound, salicin, which occurs naturally in plants, notably the willow tree. Extracts of willow were traditionally used in folk medicine and as early as 400 BC the Greek physician Hippocrates recommended a brew made from willow leaves to treat labour pains. Later in 1763 an English clergyman, Reverend Edward Stone carried out the first proper scientific study of the herbal medicine when he described the benefits he observed after giving ground up willow bark to 50 parishioners suffering from rheumatic fever.

How aspirin works was a mystery until relatively recently. During the 1970s the British scientist Professor John Vane discovered that it blocked an enzyme needed for the production of natural hormones called prostaglandins involved in many body processes including pain and tissue injury. In 1982 Professor Vane, now Sir John Vane, won the Nobel Prize for Medicine for this work.

The liver appears to be the principal site for salicylate metabolism, although other tissues may also be involved.. The half-life of aspirin in the circulation is from 13 to 19 minutes so that the blood level drops quickly after absorption is complete. However, the half-life of the salicylate ranges between 3.5 and 4.5 hours, which means that 50% of the ingested dose leaves the circulation within that time. [The affect on platelets can be "felt" up to 10 days, which is why patients are asked not to take aspirin for 2 weeks prior to surgery.] Excretion of salicylates occurs principally via the kidneys. Salicylate can be detected in the urine shortly after its ingestion but the full dose requires up to 48 hours for complete elimination.


ASA is one of the most frequent causes of accidental poisonings in toddlers and infants. The adult aspirin is 5 grains (325 mg), the "baby" aspirin is 1.25 grains (81 mg). A toxic dose of aspirin is equivalent to 1 gr per pound of body weight (150 mg / kg). A minimal lethal dose is equal to 3-4 grains / lb (450 mg / kg). Symptoms of an overdose: In mild overdosage these may include rapid and deep breathing, nausea, vomiting, vertigo, tinnitus, flushing, sweating, thirst and tachycardia. In more severe cases, acid-base disturbances including respiratory alkalosis and metabolic acidosis can occur. Severe cases may show fever, hemorrhage, excitement, confusion, convulsions or coma and respiratory failure.

Treatment of an overdose: Activated charcoal can be given as soon as possible and, if bowel sounds are present, may be repeated q 4 h until charcoal appears in the stool. Treatment then consists of prevention and management of acid-base and fluid and electrolyte disturbances. More in depth treatment information can be found at Merck Medicus

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