Paracetamol
A pain and fever reliever with little anti-inflammatory effect, safe at normal doses but able to cause liver failure in overdose.
Also called acetaminophen (US name) or APAP (abbreviation).
Drug card
- How it works
- Reducing pain and fever by central actions that are not fully understood
- Used for
- Mild to moderate pain, such as headache
- Fever
- Moderate to severe pain, alongside an opioid
- Period pain
- Known for
- Liver failure after overdose
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does paracetamol work?
Paracetamol's exact mechanism is not established. It seems to act centrally, perhaps by blocking prostaglandin synthesis in the brain and acting on the hypothalamic heat-regulating center. The liver conjugates most of a dose; a small part, made mainly by CYP2E1, becomes NAPQI, which glutathione normally neutralizes.
Uses
What is paracetamol used for?
- Mild to moderate pain, such as headache
- Fever
- Moderate to severe pain, alongside an opioid
- Period pain
Side effects
Side effects of paracetamol
- Liver failure after overdoseKnown forSerious
- Kidney damage after overdoseSerious
- Nausea and vomiting
- Headache
- Trouble sleeping
- Itching
- Constipation
- Severe skin reactions (SJS, TEN, AGEP)Serious
- Allergic reactions, including anaphylaxisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Overdose can look harmless for 2 to 3 days while the liver is damaged; give acetylcysteine as early as possible.
- Many cold and combination products contain it, so taking two at once can lead to accidental overdose.
- Liver risk is higher with heavy drinking, liver disease, malnutrition or dehydration; avoid in severe liver disease.
- Regular use can raise the INR in people taking warfarin.
Good to know: It has no meaningful effect on platelets or bleeding time, and the NHS calls it the usual painkiller of choice in pregnancy and breastfeeding.
Remember it
A way to remember it
Two Ps but no I: paracetamol treats Pain and Pyrexia, not Inflammation.
Unlike NSAIDs it has little anti-inflammatory action and does not touch platelets; its one big danger is liver failure after an overdose.
Written for biofideX
Its class
Paracetamol
How paracetamol works is not fully known; it is thought to act mainly in the central nervous system. It may block prostaglandin production in the brain and act on the hypothalamus, which sets body temperature, so fever falls. It has little anti-inflammatory effect and does not affect platelets. In overdose its reactive metabolite NAPQI overwhelms the liver's glutathione and kills liver cells.
Easily mixed up with non-steroidal anti-inflammatory drugs and selective COX-2 inhibitors.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Acetaminophen injection: label (DailyMed)
- Acetaminophen 500 mg: OTC label (DailyMed)
- Acetaminophen (NCI Thesaurus)
- Paracetamol for adults (NHS)
- Acetylcysteine injection: label (DailyMed)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Pain, fever and inflammation
Paracetamol is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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