Orphan Drug Designation Granted to Pediatric Hepatitis B Therapy

This morning, ContraVir Pharmaceuticals, Inc. announced that the U.S. Food and Drug Administration (FDA) has granted orphan drug designation to tenofovir exalidex (TXL), an investigational drug candidate for the potential treatment of chronic hepatitis B infection in a pediatric patient population.

The pediatric population indication is important because it pertains to children from ages 0 years to 11, in whom infection rates related to chronic hepatitis B virus (HBV) are especially prevalent. Currently available treatment options for those infected with HBV at birth or in early childhood have had limited success.

HBV is a rare liver disease that can become chronic and lead to more severe diseases, including cirrhosis, hepatocellular carcinoma and early death. According to the Centers for Disease Control and Prevention (CDC), in the United States there are approximately 20,000 HBV infections that are diagnosed annually — most of which, however, occur in adults.

As of the announcement, TXL is the only investigational or approved HBV treatment that has been granted orphan drug designation for the pediatric patient population.

“This designation underscores the significant unmet need in this highly vulnerable patient population and provides a critical development path for TXL to bring to market a new treatment option for this under-served patient population,” said James Sapirstein, Chief Executive Officer at ContraVir in a press release. “We look forward to continued collaboration with the FDA addressing the urgency of successfully developing treatments for hepatitis B in the pediatric and adult populations.”

TXL is being developed as a highly potent prodrug of the antiviral tenofovir (TFV), which is an active component of both tenofovir alafenamide (Vemlidy) and tenofovir disoproxil fumarate (Viread). The drug’s unique liver-targeting prodrug structure is intended to decrease systemic circulating levels of TFV, thus reducing the potential for renal and skeletal side effects.

A Phase 2 randomized, open-label, ascending, sequential dose group, multiple dose study was recently completed of TXL in HBV-infected subjects. Primary objectives included safety and tolerability of multiple oral doses of TXL at multiple ascending dose levels, and a comparison of TXL versus TFV disproxil fumarate. The study’s secondary objective was to evaluate the pharmacokinetics of multiple doses of TXL at multiple dose levels in a fasted state.

In the study, HBV-infected subjects were administered doses up to 100 mg for 28 days and ContraVir is now augmenting its formulation to further enhance delivery of the drug. To date, TXL has achieved clinical proof of concept for antiviral activity and displayed an exceptional safety, tolerability, and pharmacokinetic profile.

In September, the FDA approved an Investigational New Drug Application (IND) for TXL as a potential treatment for HBV.

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