‘Osteo’ formulations of modified-release paracetamol should be restricted or even banned because of their disproportionate role in overdose harms, toxicologists say.
The modified release (665mg) formulations of paracetamol marketed for arthritis pain are difficult to manage in overdose and associated with higher average doses of paracetamol in overdose, according to articles published in the MJA.
In a review, researchers from the NSW Poisons Information Centre found there had been a significant increase in paracetamol overdose-related hospital admissions since 2004, and greater numbers of liver injury diagnoses.
The annual number of overdose cases increased by 44.3% from 2007–08 to 2016–17 (3.8% per year) while the annual number of toxic liver disease cases increased by 108% during the study period (7.7% per year).
The increase in paracetamol overdose harm was driven by increases in the average number of tablets taken (up from 15 in 2004 to 20 in 2017). Modified release paracetamol ingestion numbers increased 38% between 2004 and 2017, and they were now implicated in 33% of overdoses, the report authors said.
They noted that overdoses with modified release paracetamol involved significantly more tablets than those with standard paracetamol and – since the tablets are higher strength – the total amount of paracetamol taken was also higher (12.6 g v 8g).
The researchers said overdoses with modified-release paracetamol overdoses were more difficult to treat because of delayed and erratic absorption of drug and prolonged elevation of serum paracetamol concentrations. This meant liver injury could develop after a prolonged period, despite use of the recommended antidote acetylcysteine.
Lead author Dr Rose Cairns, Director of Research at the NSW Poisons Information Centre and the University of Sydney, suggested that Australia might follow the lead of the European Medicines Authority (EMA), which banned the sale of modified-release paracetamol in 2018 due to concerns about its role in overdose.
In Australia, modified release paracetamol is available over the counter in packs of 96 caplets, so that a lethal dose of 63.8 grams can be ingested from one box, she noted.
The Therapeutic Goods Administration recently announced plans to up-schedule Modified release paracetamol from Schedule 2 to Schedule 3 (pharmacist only) from 2020.
“Access restrictions, including reduced pack sizes, could reduce the harm caused by paracetamol overdoses in Australia, and should be considered, together with other policy changes for curbing this growing problem,” the researchers concluded.