Drug overdose

Question 1

Hx: young woman presents with non-specific abdo pain, N + V, and altered clotting (raised PT), with a history of depression?

Ex: a few days later - jaundice, RUQ pain, encephalopathy and ALF?

Answer 1

paracetamol OD

Question 2

how is paracetamol poisonous?

Answer 2

• metabolism is saturated
• the alternative pathway (CYP P450 enzymes) generates a toxin
• this is NAPQI

Question 3

Ix suspected paracetamol OD?

Answer 3

BEDSIDE:
• ECG

BLOODS:
• FBC, LFTs, U+E, coag -PT/INR, albumin, glucose, HCO3
• serum paracetamol >4 after ingestion
• ABG (lactic acidosis if severe)

Question 4

Tx paracetamol OD?

Answer 4

Medical:
• NAC IV (*give within 8 hours)
• activated charcoal if < 1 hr from ingestion
• (methionine PO 2nd line)
• correct hypoglycaemia

Surgical:
• transplant

Question 5

within what timeframe to
• check paracetamol levels?
• give NAC IV?

Answer 5

• > 4 hours
• within 8 hours = most effective and completely prevents ALF
(NAC is given over 24 hours)

Question 6

indications for liver transplant in paracetamol OD?

Answer 6

• pH <7.3 after 24 hours
OR
• INR>6.5/PT>100 + creatinine >300 + grade 3 or above encephalopathy

Question 7

prognosis/complications of paracetamol OD?

poor prognostic indications?

Answer 7

• ALF (50 percent of these die)
• AKI (3-7 days)
• death (3-6 days post ingestion)

• ↑ PT, lactate, bilirubin, encephalopathy, creatinine or ↓ pH

Question 8

if > 24 hrs since paracetamol ingested - how to Tx?

Answer 8

if ANY paracetamol detected or abnormal liver function - give NAC IV

Question 9

S/E of IV NAC?

Answer 9

• V (give ondansetron)
• anaphylactoid reaction
• coagulopathy

Question 10

Hx patient develops urticaria, V., wheeze and ↓BP twenty minutes after receiving a NAC infusion for paracetamol OD.

What has happened?

How do you Tx him?

Answer 10

• anaphylactoid reaction
• in <10 percent
• a dose-related histamine release
• causes urticaria, wheeze and ↓BP, V, shock

Tx
• stop NAC
• chlorphenamine +/- steroids, Adr
• THEN RE-START NAC
(if just a rash/mild skin reaction reduce infusion, give chlorphen., but don't stop)

Question 11

what is a potentially fatal amount of paracetamol?

Answer 11

12g (or 150mg/kg)

• unless malnutrition or enzyme induction (drugs, alcohol) - can be 7.5g