The TGA has issued a safety alert regarding the possibility of eltrombopag (Revolade) interfering with laboratory tests such as total bilirubin and creatinine.

The thrombopoietin receptor (TPO-R) agonist can be hepatotoxic and the manufacturer advises monitoring of ALT, AST and bilirubin. Creatinine monitoring is also advised in patients with renal disease.

However the highly coloured drug can result in discoloration of serum in some patients and therefore interfere with total bilirubin and creatinine testing.

While already documented in the drug’s Product Information (PI), the TGA has followed the example of the UK’s Medicines and Healthcare Products Regulatory Agency to highlight the issue.

The UK warning in July 2018 said the interference could result in falsely low/normal bilirubin and falsely high/normal creatinine levels.

Clinicians are warned that laboratory tests might therefore be inconsistent with clinical observations.

“The false-positive interference with creatinine may result in a misleading clinical picture of apparent renal deterioration,” the UK alert said.

“The interference with bilirubin is less likely to have clinically significant consequences since the stopping criteria for hepatic disorders are based on rises in ALT levels and clinical symptoms/evidence of hepatic decompensation, rather than bilirubin values alone.

The PI advises ‘evaluation of contemporaneous aminotransferase values may help in determining the validity of low total bilirubin levels in the presence of clinical jaundice and blood urea should be evaluated in the event of an unexpectedly high serum creatinine. Re-testing using another method may also help in determining the validity of the result’.

In a EU review of nine case reports of serum discolouration and interference with test results, six were of suspected interactions with bilirubin tests and three reports with creatinine.

At least four cases resulted in either eltrombopag dose reductions or discontinuation.