The TGA has released a safety warning on inadvertent overdose of oral methotrexate in the wake of inquest into man’s death from methotrexate toxicity
Two weeks ago, Coroner Rosemary Carlin found that 77-year-old Melbourne man Ian Gilbert’s death due to methotrexate toxicity was “needless and entirely preventable” following a lengthy inquest.
The pharmacist who had dispensed the medicine told the inquest she became worried that the dose could be lethal, and telephoned the doctor with “extreme concerns” over the twice daily 2.5mg dose of methotrexate – as the medication was usually taken weekly, not twice daily.
But when she called the prescribing GP, he insisted the dosage he had given Mr Gilbert was correct, so she dispensed it anyway, the court heard.
Following this disclosure, pharmacist indemnity organisations were quick to urge pharmacists to raise concerns and remember that they have the right to refuse supply.
The TGA has now released a medicines safety alert reminding pharmacists about the importance of reiterating the once-weekly dosing regimen.
“Inadvertent overdose of oral methotrexate – usually from accidental daily administration of a weekly dose – can lead to serious and potentially fatal toxicity,” says the TGA.
“When used for the treatment of rheumatoid arthritis and psoriasis, methotrexate is typically prescribed in a once weekly dosage regimen.
“Taken correctly, methotrexate is usually a safe and effective medicine, but it has the potential for serious toxicity.
“Dosing errors are a known and avoidable risk associated with methotrexate tablets, but a TGA investigation has found that the factors leading to such errors are complex.”
In Australia, methotrexate tablets are marketed as Methoblastin.
To address the risk of adverse events, the TGA has worked with the sponsor of Methoblastin to undertake the following regulatory actions:
- The carton and container label artwork have been updated to include a new warning – ‘Caution: Usual dose is once weekly. Check dose and frequency with your doctor or pharmacist.’
- The Product Information has been updated to more prominently warn of the risk of accidental dosing errors, highlight that for rheumatoid arthritis and psoriasis methotrexate is most often prescribed as a once-weekly dose.
For pharmacists and other health professionals that are treating patients with methotrexate tablets, the TGA recommends reiterating the once-weekly dosing regimen and specifying which day of the week the dose is to be taken.
“You are also encouraged to educate those patients about the signs and symptoms of toxicity and advise them of the circumstances in which they should seek medical advice,” says the TGA.
“If you’re a pharmacist dispensing methotrexate tablets, highlight to patients the importance of only taking the dose once weekly and reinforce the day of the week to be taken.
“Good dispensing practices can also help to avoid dosing errors, including:
- Labelling the medicine container and not just the external packaging; and
- Ensuring that the label specifies the number of tablets to be taken and the specific day of the week they should be taken.”