Written by Chloe Doris
Last Reviewed: September 2019
Review Due: September 2020
mechanism of action2,3,4
The mechanism of action of paracetamol is not completely understood. It is considered to be a weak inhibitor of prostaglandin synthesis with some selectivity for brain COX2.
Prostaglandins act to sensitise nociceptors to inflammatory mediators such as bradykinin. Paracetamol decreases the production of prostaglandins by inhibiting the enzyme cyclo-oxygenase (COX) and thus decreasing the sensitisation of nociceptors.
Paracetamol is similar to NSAIDs in that it has analgesic and antipyretic actions, but it has very weak anti-inflammatory properties – likely due to its selectively acting within the brain.
Mild to moderate pain
Side effects from paracetamol are rare but can include:
Allergic reaction (rash/swelling)
Flushing, hypotension and tachycardia (associated with IV administration)
Liver and kidney disease in the case of overdose
Patients should not take paracetamol if:
they have had an allergic reaction to paracetamol in the past
they have liver or kidney problems
they regularly drink more than 14 units of alcohol a week
they take medicine for epilepsy or tuberculosis
Hepatic impairment: dose-related toxicity – avoid large doses
Renal impairment: increase IV infusion dose interval to every 6 hours if eGFR <30mL/minute/1.73 m2.5
Paracetamol can increase the anticoagulant effect of the following drugs: Acenocoumarol, Warfarin, Phenindione
Heavy alcohol consumption can cause severe liver damage
Many other drugs can increase the risk of hepatotoxicity when given with paracetamol
Don’t take paracetamol with other paracetamol-containing medications, including co-codamol.
NHS. Paracetamol for Adults. 2019.
Rang H.P, Ritter J.M, Flower R.J, Henderson G. Rang & Dale’s Pharmacology. 8th Ed. Elsevier Churchill Livingstone; 2016. Page 526-527.
NICE. NSAIDs. 2019.
Rang H.P, Ritter J.M, Flower R.J, Henderson G. Rang & Dale’s Pharmacology. 8th Ed. Elsevier Churchill Livingstone; 2016. Page 332.
British National Formulary. Paracetamol.
British National Formulary. Interactions: Paracetamol.