Effect of concomitant opiate ingestion on paracetamol levels in acute overdose

To assess whether the co-ingestion of opiates in acute paracetamol overdose has an effect on the paracetamol level 4 h after ingestion.

A prospective observational study was performed in the emergency department of a teaching hospital. The paracetamol levels at 4 h of consecutive patients who had taken an overdose of either paracetamol alone or in conjunction with an opiate were collected over a 4-month period. The data were then analysed.

After exclusions, the results of 21 patients who took paracetamol alone and 20 who took paracetamol and an opiate showed that paracetamol levels were significantly lower at 4 h if there was co-ingestion of an opiate. Analysis shows that opiate ingestion is a predictor for paracetamol levels at 4 h.

Co-ingestion of opiate decreases the serum paracetamol level at 4 h. If opiate and paracetamol are taken together, there is a case for a repeat measurement of the paracetamol level if the level at 4 h is lower than would be expected in selected patients.