Health Canada is warning adults using the anti-viral agent telbivudine, sold as SEBIVO, not to take the drug in combination with the immune-boosting drug interferon, as it could result in weakness or burning sensations in the limbs.

In a warning issued Wednesday, Health Canada and SEBIVO manufacturer Novartis Pharmaceuticals Canada Inc. say that mixing the drugs can lead to peripheral neuropathy, that is, weakness, numbness, tingling and/or burning sensations in a patient's arms and legs.

SEBIVO is used to treat adults with chronic hepatitis B, a liver disease

The company says in a small clinical trial testing the use of SEBIVO and interferon Pegasys, roughly 10 per cent of patients suffered serious peripheral neuropathy. The statement says it was occasionally disabling, and usually started about three months after treatment began.

Novartis said it is not known whether the numbness is reversible once treatment stops or whether it may occur when using interferon products other than Pegasys.

Interferon alfa and interferon beta — which help the immune system target viruses, bacteria and other foreign substances — are marketed under brand names including Pegasys, Pegatron, Intron, Unitron Peg, Rebetron, Roferon A, Infergen, Rebif, Betaseron and Avonex.

Peripheral neuropathy is a common adverse reaction of Pegasys, at roughly one to five per cent, the warning said, while it has been reported in less than 0.3 per cent of patients using telbivudine alone.

Patients mixing the drugs should speak with their doctors, the warning said.