It’s more than just a headache pill. In fact, acetaminophen and compounds containing it are the pain relievers that doctors most commonly prescribe, accounting for three per cent of all prescriptions in North
America. It’s also the most common ingredient for aches and pains in non-prescription analgesics. As an analgesic, it is used in cough, cold, fever, and flu remedies, and it is also used to treat muscle and back ache, menstrual pain and arthritis.
The acetaminophen family of compounds was first discovered and used in 1886, but the original compound, acetanilid, while an effective pain reliever was extremely toxic. It caused a blood problem which resulted in reduced oxygen levels, leading to cyanosis and death. With more research, acetaminophen was discovered in 1893, and by 1949 it was established as a safe and effective analgesic.
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The drug was first used in Europe where even today it is called paracetamol rather than acetaminophen. There it was used initially for headaches with early formulations combining ingredients like acetaminophen, acetylsalicylic acid (ASA), caffeine, and a barbiturate. The earliest sources of acetaminophen were coal tar compounds. Yes, the same coal tar that is used in paving roads, dandruff shampoos, paints, and dyes! As acetaminophen, it has been available without a prescription in North America since 1955.
Acetaminophen, an aniline analgesic, is thought to act by interfering with prostaglandins which are chemical messengers needed for pain impulse transmission. It follows that if these messengers can be stopped, then pain can be stopped. Cyclo-oxgenase or COX enzymes manufacture prostaglandins and when these enzymes are inhibited, prostaglandin levels drop, and so does pain. There are different types of COX enzymes, that is COX-1, COX-2, and COX-3. Nonsteroidal anti-inflammatory drugs act on COX-1 and COX-2, which acetaminophen only weakly inhibits. However, recent evidence points to acetaminophen inhibiting COX-3 to reduce pain.
Acetaminophen is an analgesic and antipyretic, that is it reduces pain and fever. It has no anti-inflammatory action and is not a good choice for pain where inflammation is a factor. It can however be taken along with an anti-inflammatory drug for added pain relief.
Acetaminophen does not interfere with blood clotting or gout treatment. It acts quickly with peak blood levels within 30 to 60 minutes, which means that “quick-acting” formulations act no faster than regular formulations.
For children’s aches, pains and fever, acetaminophen is the most common recommendation, but it is also the most common drug involved in childhood accidental poisoning. The maximum dose for children is considered to be 91 milligrams per pound of body weight in a 24-hour period. For a child weighing 20 pounds, this is just three to four adult extra strength tablets!
When you administer acetaminophen to a child, take extra care. Calculate the dose based on the child’s weight, measure the dose correctly and avoid teaspoonfuls. Be aware that children’s drops and liquids have different acetaminophen concentrations, and don’t forget that acetaminophen is a common ingredient in cough, cold, and flu remedies.
The signs of acetaminophen overdose are nausea, vomiting, lethargy and abdominal pain, but if you think there may an overdose, contact your local poison centre immediately.
In general the maximum recommended dose of acetaminophen for adults is four grams daily, that is eight extra strength or 500-milligram tablets. Recently, because of the drug’s ability to cause liver damage even in lower doses, there has been some controversy with lower recommendations being considered by the FDA in the United States.
Individuals with existing liver disease, who are prone to liver damage, or drink alcohol even moderately, have an increased risk, and unfortunately, liver damage has few symptoms. The FDA has considered limiting package sizes and maximum tablet strengths, along with reducing dosing recommendations to a maximum single dose of 650 milligrams or two regular 325-milligram tablets, and maximum daily dose to 2.6 grams or eight regular strength tablets.
If you take acetaminophen for chronic pain, try taking the lowest effective dose, but take it regularly to prevent pain, and don’t drink alcohol!
Acetaminophen just shows you that no drug is absolutely safe. You need to use all drugs, even non-prescription ones, with care.
Marie Berry is a lawyer/pharmacist interested in health care and education.
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