(Reuters) - The U.S. Food and Drug Administration approved on Friday Alexion Pharmaceuticals Inc’s rare blood disorder drug Ultomiris, an early backing that also solidifies the company’s dominant market position.

The company’s flagship drug, Soliris, was the lone FDA-approved treatment for the blood disorder, paroxysmal nocturnal hemoglobinuria (PNH), and raked in $3.13 billion last year, accounting for nearly 89 percent of total revenue.

Ultomiris sales are expected to reach $1.66 billion by 2022, according to IBES data from Refinitiv, and the trial showed that the drug had results similar to Soliris.

Also, patients on Ultomiris need medication only every eight weeks, compared every two weeks for those on Soliris.

“With its strong profile, including a longer half-life and less frequent dosing and what we see as a superior clinical data package, we think this early approval will hasten Alexion’s market conversion from Soliris to Ultomiris,” said Christopher Raymond, an analyst with Piper Jaffray.

Ultomiris will have a wholesale acquisition cost of $6,404 per vial, the company said in a filing. This compares with $6,543 per vial for Soliris.

Alexion’s shares were down 2.2 percent at $98.97 in noon trading, with analysts pointing to Ultomiris’ boxed warning, FDA’s harshest, which flagged the risk of life-threatening meningococcal infections and sepsis.

“I think people are not paying attention to the fact that Soliris’ black box is exactly the same,” Raymond said.

PNH is a rare acquired life-threatening disorder in which red blood cells are prematurely destroyed by the patient’s immune system and is caused by the absence of a certain protein.

Alexion, one of the stars of the biotech sector in the first half of this decade, is rebuilding from a series of setbacks, including an exodus at the top and a sales practices scandal related to Soliris.

The company this year bought two drug developers working in the rare disorders field. In April, Alexion acquired Sweden’s Wilson Therapeutics for $855 million, and followed that up with the purchase of Syntimmune for a total value of up to $1.2 billion in September.

The FDA had set Feb. 18 as the date for a decision on Ultomiris.

The drug regulator on Friday also approved a treatment from Stemline Therapeutics for another rare blood disorder.