Overdose with modified-release paracetamol results in delayed and prolonged absorption of paracetamol

A modified-release formulation of paracetamol is currently available in Australasia and marketed under a number of different trade names. These include: Panadol Osteo, Panadol Extend Tablets, and Duatrol SR. We report four cases of intentional overdose with this formulation resulting in delay to peak plasma paracetamol concentrations and prolonged paracetamol absorption. Physicians must be aware that a single plasma paracetamol estimation four or more hours post-ingestion may not be adequate in the risk assessment of patients requiring treatment with N-acetylcysteine (NAC). Current Australasian guidelines for the management of modified-release paracetamol overdose advise empiric commencement of NAC if the suspected ingested dose is greater than 10 grams or 200 mg/kg (whichever is the least), an initial plasma paracetamol concentration should be assayed four or more hours post-ingestion and a second assay should be estimated four hours after the first. Treatment with NAC should continue if either concentration falls above the paracetamol treatment nomogram line. With massive ingestions of this paracetamol formulation (>50 grams) plasma concentrations may be elevated for several days and prolonged treatment with NAC is recommended. When modified-release paracetamol overdose is suspected a clinical toxicologist or Poisons Information Centre should be consulted to help guide management decisions.