• paracetamol
• poisoning
• N-acetylcysteine

Neonatal paracetamol poisoning is rare and usually the result of maternal poisoning before birth.¹ We report the case of a neonate who received a high dose of propacetamol chlorhydrate by intramuscular injection.

The baby was born at 41 weeks gestation, weighing 3780 g, after a 12 hour labour marked by maternal fever. He was treated for infection with intramuscular injections of ampicillin and gentamicin. On the first day of life, he was accidentally given an intramuscular injection of 2 ml of a dilution of propacetamol chlorhydrate in 9% NaCl containing 800 mg (211 mg/kg) propacetamol, equivalent to 105.5 mg/kg paracetamol. The infant was then transferred to our unit.

As soon as he arrived, he received an intravenous bolus of 150 mg/kg N-acetylcysteine over 15 minutes, and then a perfusion of 50 mg/kg N-acetylcysteine over the next four hours. The first plasma paracetamol concentration, measured four hours after the injection, was below the toxic level (49 mg/l).² Concentrations measured at eight, 12, 20, and 32 hours after the later injections showed a slow decrease (fig 1). The perfusion of N-acetylcysteine was continued at 100 mg/kg/24 hours for 22 hours until the plasma paracetamol concentration reached 3 mg/l. The liver enzymes and the coagulation profile remained normal during the hospital stay and seven days after discharge. No local complication at the injection site occurred besides induration. No adverse effect of N-acetylcysteine was noted.

There are very few data about intramuscular injection of propacetamol, and no data for the neonate. In our observation, the calculated half life was 3.5 hours, similar to that after intravenous injection.³ Given the very slow decrease in plasma paracetamol concentration during the first eight hours, we suggest that, in neonates, after intramuscular injection of a high dose of propacetamol, N-acetylcysteine should be administered even if the early plasma paracetamol concentration is below toxicity level, and continued until the plasma paracetamol concentration reaches the therapeutic level (3–10 mg/l).³

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Figure 1

Evolution of plasma paracetamol concentration compared with toxicity nomograms.² H4, H8, H12, H20, and H32 indicate the number hours after N-acetylcysteine injection. UK, United Kingdom nomogram; US, United States nomogram.