Update on Xenoport's Horizant - Analyst Blog

The US Food and Drug Administration (FDA) has asked for additional pre-clinical data on XP13512 (known as Horizant (gabapentin enacarbil) in the US), co-developed by XenoPort (XNPT) and GlaxoSmithKline (GSK) for the treatment of primary restless legs syndrome (RLS).

Although a New Drug Application (NDA) for Horizant extended release tablets was submitted in January 2009, the companies received a complete response letter (CRL) in February 2010. The FDA was convinced about Horizant’s effectiveness to treat RLS and there weren’t any safety issues related to the drug.  However, the agency was concerned about the occurrence of pancreatic acinar cell tumors in the preclinical stage in rats. As a result, the FDA decided against approving Horizant in its current form.
 
The decision for additional data was taken at a meeting conducted recently with the FDA. We are pleased to note that no new clinical trial is needed at present. XenoPort expects to file a response to the CRL in the second half of 2010.
 
GlaxoSmithKline will be responsible for commercializing the drug globally except the Asia Pacific regions of Japan, Korea, Philippines, Indonesia, Thailand and Taiwan. Astellas Pharma has the drug rights for these areas. An NDA for XP13512 was submitted to the Pharmaceuticals and Medical Device Agency (PMDA) in Japan in November 2009.
 
Horizant is being studied for other indications as well including neuropathic pain associated with post-herpetic neuralgia (PHN) and migraine prophylaxis. Data released from a mid-stage study in September 2009 demonstrated statistically significant improvements in baseline pain score vs. placebo for all doses tested (1200mg, 2400mg and 3600mg).
 
The neuropathic pain market is significantly larger than the RLS market, but competition is also stronger. Pfizer’s (PFE) Lyrica and Eli Lilly’s (LLY) Cymbalta have gained sizable market share in this category.
 
Successful commercialization of Horizant for any of the indications will be a major boost for the company.