Idenix/Novartis have filed for FDA approval of their antiviral telbivudine. If approved, the drug candidate would become the fourth nucleoside reverse transcriptase inhibitor available to treat hepatitis B in the US. A strong efficacy and safety profile should ensure robust sales for the product, although it is set to face stiff competition in various markets.
The new drug application (NDA) submission is based primarily on one-year data from a phase III study named GLOBE. The GLOBE study is the largest registration hepatitis B study to date and the first to involve hepatitis B patients and clinical sites in mainland China. This could be significant as China is home to one third of the world's chronic heptatitis B patients.
Data from GLOBE indicate that telbivudine had a greater impact on lowering hepatitis B virus (HBV) DNA and ALT levels after 18 months, while at the same time demonstrating lower viral breakthrough, compared to lamivudine (marketed by GlaxoSmithKline as Zeffix).
While these results are encouraging, there is concern that 12-18 month data may not be sufficient to determine the long-term side-effect profile of nucleoside reverse transcriptase inhibitors (NRTIs) such as telbivudine. Late-stage clinical trial data shows that more patients on telbivudine had transient creatine elevations compared to those on lamivudine, although these adverse events were not strong enough to warrant dose reduction or treatment cessation. Nevertheless, this may be a point of concern, given that hepatitis B antivirals are often taken on a long-term basis.
Furthermore, while a telbivudine approval would broaden treatment options for hepatitis B patients, and provide them with a more efficacious drug than lamivudine, other challengers could prove aggressive rivals to telbivudine.
Indeed, with a viral breakthrough rate of 3% observed at week 76, telbivudine's viral resistance profile is unlikely to beat Gilead's Hepsera (adefovir). Furthermore, strong competition from Bristol-Myers Squibb's Baraclude (entecavir) in terms of efficacy and safety may restrict telbivudine's revenue-generating capabilities. To make matters worse, the entry of generic entecavir is also likely to be a significant threat to telbivudine.
Nevertheless, sales could be bolstered if Idenix and Novartis can capitalize on their investment in carrying out clinical trials in China with effective marketing in this region. However, China is a highly cost-conscious market, meaning Idenix and Novartis have a fight on their hands to maximize sales here as well.