GlaxoSmithKline has followed the example of rival Roche and added warnings of possible psychiatric problems to the US label for its influenza treatment Relenza.

The company has informed healthcare professionals of changes to the prescribing information for Relenza (zanamivir) as a result of postmarketing reports, mostly from Japan, of delirium and abnormal behaviour leading to injury in patients with influenza who are receiving neuraminidase inhibitors, such as GSK's drug. The new warning notes that influenza can be associated with symptoms which can include seizures, hallucinations and delirium, and in some cases it can result in fatal outcomes. It also calls for closer monitoring of patients for signs of abnormal behaviour.

However, GSK stresses that "the contribution of Relenza to these events has not been established", and the company had originally said that it did not feel an updating of the warning was necessary. The move comes a month after Roche added a similar warning to its influenza treatment Tamiflu (oseltamivir) which "reflect observations from a growing body of data”, though the Swiss firm also noted that the data “shows no evidence of a causal relationship between Tamiflu and the reported events".

The revised labels reflected recommendations from the US Food and Drug Administration’s Paediatric Advisory Committee made in November last year. Those recommendations followed a review of around 700 cases of psychiatric adverse events for both drugs, and 25 incidences of paediatric deaths in patients taking Tamiflu reported to the FDA up until May last year. No fatalities were reported for Relenza.