Biology of Disease

Stage Duration / h Clinical features

I 0.5–24 loss of appetite and anorexia (Chapter 10),

nausea and vomiting,

general malaise,

patient appears normal

II 24–48 less severe symptoms,

abnormal blood chemistry with increases in liver enzymes and bilirubin,

deterioration in renal functions but blood urea concentration remains low

given the decrease in liver function

III 72–96 signs of hepatic necrosis,

coagulation defects, jaundice and renal failure,

reappearance of nausea and vomiting,

death due to hepatic failure

IV 4–14 days hepatic and renal functions return to normal if patient survives stage III

Table 12.2Stages of paracetamol poisoning

Laboratory investigations of paracetamol poisoning

Estimating the concentration of paracetamol in plasma is useful for assessing

the probability of patients developing hepatotoxicity. A nomogram (Figure

12.8) is available for paracetamol poisoning but should only be used when

the size of the overdose and the approximate time of ingestion are known.

Blood samples for paracetamol determination should be drawn at least 4 h

postdose to allow for its complete absorption and the serum concentration

to peak. The concentration of paracetamol in plasma can be used as a guide

to patient management. Other tests that may be useful are determining the

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Figure 12.8 A nomogram to assess paracetamol

toxicity.

500

300

200

100

50

25

10

4 5 6 7 8 9 10 11 12 13 14 15

Time after ingestion / h

Plasma [paracetamol] / mg dm

-3

Toxicity unlikely

Mild toxicity

Moderate toxicity

Severe toxicity

that may be fatal

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