Paracetamol

What it is and why we use it

• Paracetamol (acetaminophen) is a non-opioid analgesic (painkiller) and antipyretic (reduces fever).
• Commonly used as part of multimodal analgesia to reduce opioid requirements and opioid side effects (e.g., nausea, sedation).
• Minimal effect on platelets and gastric mucosa compared with NSAIDs, so often suitable when NSAIDs are avoided (but still check liver risk).

How it works (simple view)

• Acts mainly in the central nervous system to reduce pain and fever (exact mechanism not fully defined).
• Not an anti-inflammatory drug in the same way as NSAIDs (so less useful for strongly inflammatory pain on its own).

Routes and typical adult dosing (safe basics)

• Oral: usually 1 g every 6 hours (max 4 g in 24 hours) in a standard adult.
• IV: commonly 1 g over 15 minutes every 6 hours (max 4 g in 24 hours) in a standard adult; check local policy and product.
• Rectal: slower and more variable absorption; often used in paediatrics or when oral/IV not possible—dose carefully by weight.
• Reduce maximum daily dose in low body weight, frailty, malnutrition, chronic alcohol excess, or liver disease (follow local guideline).
• Always consider total daily intake from all sources (including combination products such as co-codamol).

Paediatric dosing (high-yield principles)

• Dose by weight (mg/kg) and follow your hospital paediatric guideline/formulary for route-specific dosing and maximum daily dose.
• Be extra cautious with neonates/infants: different dosing intervals and maximums; use age-appropriate guidance.
• Avoid duplicate prescribing across routes (e.g., oral plus IV) unless explicitly planned and documented.

When to be cautious / contraindications

• Severe hepatic impairment or acute liver failure: avoid or seek senior advice; risk of hepatotoxicity.
• Chronic liver disease: may still be used but often with reduced maximum daily dose—follow local policy.
• Low body weight (<50 kg), malnutrition, frailty, chronic alcohol excess: higher risk of toxicity—use reduced dosing regimen.
• Severe renal impairment: generally safe but consider longer dosing interval per local guidance.
• Allergy is rare but possible—check history.

Perioperative use: practical tips

• Give early (pre-op or intra-op) to improve baseline analgesia and reduce opioid requirement.
• IV paracetamol is useful when oral intake is not possible; switch to oral as soon as safe.
• Document timing clearly to prevent accidental re-dosing in recovery/ward handover.
• If using regional techniques, paracetamol still adds benefit as part of multimodal analgesia.

Adverse effects and interactions (what to look out for)

• Therapeutic doses: usually well tolerated.
• Overdose: can cause severe liver injury; early symptoms may be mild or non-specific (nausea, vomiting, malaise).
• IV formulation: rare hypotension, especially if given rapidly or in haemodynamically unstable patients—infuse over recommended time.
• Drug interactions: enzyme inducers (e.g., some antiepileptics) and chronic alcohol excess can increase risk of toxicity; warfarin—prolonged regular use may increase INR (monitor if relevant).

Overdose: what new starters should do

• Treat any suspected overdose as urgent—even if the patient looks well.
• Get an accurate history: time(s) of ingestion, total dose, body weight, co-ingestants, and risk factors (malnutrition, alcohol excess).
• Take bloods as per local protocol (including paracetamol level at the correct time point, LFTs, INR, U&Es, glucose, VBG/ABG if unwell).
• Start treatment promptly when indicated (N-acetylcysteine) and involve senior/TOXBASE guidance early.
• In repeated supratherapeutic ingestion or uncertain timing, do not rely on a single level—follow local/toxicology guidance.