New positive top-line results from a second Phase III clinical trial of sodium oxybate in fibromyalgia show that the drug is on track for FDA approval. As such, the treatment is set to enter the market as the fourth drug to be approved for fibromyalgia in the US. Despite impressive efficacy data, however, prescriptions are likely to be limited by accessibility, price and convenience.

According to data released by Jazz Pharmaceuticals, in a second 14-week Phase III trial, assessment of sodium oxybate (4.5g/night and 6g/night) compared to placebo in 573 adult patients with fibromyalgia met its primary endpoint of 30% superior pain relief over placebo based on the pain visual analogue scale (VAS). In addition, sodium oxybate significantly improved patients’ physical functioning and ability to perform tasks. Sodium oxybate is the oral liquid form of gamma-hydroxybutyrate (GHB), an endogenous neurotransmitter and metabolite of GABA. Given its success in this second Phase III trial, the drug is on track for FDA submission by the end of 2009.

Fibromyalgia is a widespread chronic musculoskeletal pain and fatigue disorder for which the cause is still unknown. The latest research suggests that fibromyalgia pain does not originate from trauma, inflammation or nerve damage, but seems to be due to a disturbance in pain processing that originates in the brain. At present, the leading drugs used in the treatment of fibromyalgia are the anticonvulsant Lyrica (gabapentin; Pfizer) and the antidepressant Cymbalta (duloxetine; Eli Lilly).

Sodium oxybate is currently marketed for narcolepsy, where it is branded as Xyrem. Despite superior efficacy on some endpoints compared to the market leading drug, sales have only totaled $42.3m, less than 20% of the total market. Xyrem is a Schedule III drug under the Controlled Substances Act, and as such is only available through a controlled distribution system. This has led to restricted availability and a high price point. In addition, the drug possesses an inconvenient formulation and dosing regime compared to the current therapeutic options, which will further limit penetration of the fibromyalgia market.

With a value of around $1 billion in 2008 across the seven major markets, Datamonitor forecasts the fibromyalgia market to grow to over $2.4 billion by 2018. Furthermore, the European regulatory authorities’ recent rejection of Cymbalta for this indication has created a commercial opportunity which Jazz may exploit, having signed a European marketing agreement for the drug with UCB. Ultimately, however, Datamonitor does not expect sodium oxybate to make a significant impact on the current market players, and forecasts fibromyalgia-specific sales of approximately $220m by 2018 across the seven major markets.

Datamonitor: Stakeholder Opinions: Narcolepsy - Entry-point to a lucrative fatigue-associated market