Paracetamol overdose accounts for up to 20% of poisonings presenting to Australian and North American emergency departments.
Modified-release paracetamol taken for osteoarthritis has been on the Australian market since 2001, and listed on the PBS since 2008.
A study of people who intentionally take more than the recommended dose warns that the current pack size of the medication may put patients at risk of larger overdose.
The study by, clinical toxicologist and emergency physician Professor Andis Graudins, from the School of Clinical Sciences at Monash Health and Monash University, is published as an Early View article in Emergency Medicine Australasia, the journal of the Australasian College for Emergency Medicine.
This is the first case series to describe poisoning with this formulation of paracetamol in a larger patient group.
Between October 2009 and September 2013, 42 cases of poisoning with modified-release paracetamol were identified in patients attending Monash Health Emergency Departments.
This is about 5% of all the cases of paracetamol seen in that time period.
Twenty-seven were large acute ingestions of modified-release paracetamol who received immediate treatment.
Four patients requiring treatment had an initial blood paracetamol reading that was non-toxic. Treatment was required because the blood paracetamol concentration later increased into the toxic range.
The delay in toxicity is related to the modified-release nature of the formulation.
Professor Graudins said most people with overdose of modified-release paracetamol are easily recognised and treated, but vigilance is required by doctors to ensure poisoning is not missed in the small number who have late rises in their blood paracetamol concentrations that indicate the need for treatment.