UPDATED: Alexion wins FDA OK on Strensiq, but startles analysts on price

Alexion's $1.08 billion deal to buy Enobia has paid off with an FDA approval of the "breakthrough" therapy that it gained in the blockbuster bargain. The FDA announced Friday afternoon that asfotase alfa--to be sold as Strensiq--won marketing clearance as a new therapy for extremely rare cases of a metabolic disease known as hypophosphatasia (HPP).

A pioneer in marketing drugs for rare diseases, Alexion ($ALXN) paid $610 million upfront to buy Enobia and this drug back in 2012.

But Alexion shares slid on Monday after the company startled analysts with an annual average price of $285,000, well below the $400,000 consensus that Barclays' analyst Geoff Meacham had been tracking. A few industry observers on Twitter tied the lower-than-expected price to the current brouhaha over drug pricing that has bedeviled Valeant. But Meacham still sees a solid upside for the biotech.

"While the annual pricing was lower than our model ($400K blended average, in-line with Soliris) and consensus, we expect average pricing to have an upward trajectory as the patient mix ages," Meacham noted on Monday. "Nevertheless, we are modestly lowering our Strensiq forecasts to reflect the pricing disclosure."

The FDA heralded the approval as fresh evidence of the benefits being paid through the agency's breakthrough drug program.

"For the first time, the HPP community will have access to an approved therapy for this rare disease," said Dr. Amy Egan, deputy director of the Office of Drug Evaluation III in the FDA's Center for Drug Evaluation and Research. "Strensiq's approval is an example of how the Breakthrough Therapy Designation program can bring new and needed treatments to people with rare diseases."

Alexion CEO David Hallal

In addition to the FDA approval, Alexion also gained a big bonus prize with the approval. The agency is handing over a rare pediatric disease priority review voucher, a ticket for a regulatory shortcut that was designed to encourage development of new drugs for the prevention and treatment of rare pediatric diseases. The last voucher on the market sold for $350 million.

The enzyme replacement therapy--which has earned peak sales estimates hovering around the $500 million mark--is injected three to six times a week.

Hypophosphatasia is a disorder brought on by a metabolic disaster. Patients with HPP can't produce an enzyme needed to maintain phosphate levels in metabolites required for normal bone formation as well as brain and muscle function. Asfotase alfa is a recombinant protein designed to address the genetic deficiency, according to Alexion, preventing or reversing the impact of dysregulated calcium and phosphate metabolism.

"We are pleased that the label includes a survival benefit in infants, substantial bone healing, and improvements in growth and mobility in patients with HPP who had symptoms prior to the age of 18 and were treated with Strensiq," noted Alexion CEO David Hallal in a statement.

- here's the FDA release
- and Alexion's release