healthmedicinet

Reluctant to say it aloud, Natalie Stack wrote her 12th birthday wish on a restaurant napkin: “To have my disease go away forever.”

A decade later, her wish is a step closer to being realized.

On Tuesday, the Food and Drug Administration approved a new drug developed with early financing from a foundation that Natalie’s parents established in response to that plea. The drug, which will be sold by the Raptor Pharmaceutical Corporation under the name Procysbi, is for nephropathic cystinosis, an extremely rare inherited disease that, if untreated, typically destroys the kidneys by age 10 and even with a kidney transplant can lead to death by early adulthood.

The story behind Procysbi’s development is yet another example of the important role that determined parents and disease foundations can play in supporting drug development, particularly for rare diseases.

But Procysbi’s approval could also raise troubling questions about whether society can afford to pay extremely high prices for drugs that treat rare diseases. That is because Procysbi is not a new chemical entity, but rather a more convenient and more tolerable version of an existing drug. The existing drug costs about $8,000 a year, whereas Procysbi will cost $250,000 on average.

High prices are typical for drugs to treat so-called orphan diseases. The health care system has tolerated that because, given the small numbers of patients, the overall cost is not that high. But as the orphan drug business model becomes increasingly popular among pharmaceutical companies, the collective cost of the drugs is beginning to mount.

The market research firm EvaluatePharma recently predicted that orphan drugs will constitute 15.9 percent of spending on prescription drugs by 2018, up from 5.1 percent in 1998. And a survey of 50 insurers and pharmacy benefit managers by J. P. Morgan found that drugs for rare diseases would be one of the areas increasingly subject to scrutiny and possible restrictions on use.

While many medicines are unpleasant to take, the existing drug for cystinosis — Cystagon, from Mylan Inc. — literally stinks. It has a strong rotten-egg smell that causes bad breath and body odor. It also causes nausea, vomiting and other abdominal problems. Moreover, it must be taken every six hours, which means patients have to get up in the middle of the night, or their parents must wake them.

Procysbi has the same ingredient as Cystagon but consists of enteric-coated spheres for delayed release. It can be taken every 12 hours instead of every six. The gastrointestinal side effect, halitosis and body odor, are reduced, though not eliminated, according to the parents of children with the disease.

Christopher M. Starr, co-founder and chief executive of Raptor, said he expected it would take time to persuade insurers to bear the extra cost.

“I get it,” he said. “It seems trivial when you first look at this.” He said doubters would think: “You’re dying of a disease. Take it every six hours if that is what you need to do.”

But Dr. Starr argued that the “subtle advantages” of Procysbi “add up to a significant benefit.” He said as many as 80 percent of patients skip doses of Cystagon, which studies have shown can lead to more rapid deterioration of the kidneys, eyes and other organs. The more tolerable Procysbi should allow people to better take their medicines.

Dr. Starr said the price reflected the value of the drug and the need to recoup Raptor’s development costs. The company’s regulatory filings show it has spent $37.4 million on research and development of the cystinosis drug from the company’s inception in 2005 through the end of 2012. Total corporate expenses in that period were $110 million.

Procysbi is the first drug approved for Raptor, which is based in Novato, Calif. Analysts expect sales could exceed $100 million annually. s of Raptor closed at $6.90 Tuesday, up 5 percent.

Procysbi treats a very rare disease. Only about 500 people in the United States, and 3,000 worldwide, are estimated to have cystinosis, according to the F.D.A. The disease is characterized by a buildup in cells of the amino acid cystine. The buildup damages the kidneys and eyes and eventually the thyroid gland, muscles and other organs.

Procysbi works by breaking down cystine. Its active ingredient is cysteamine, the same as in Cystagon. Cysteamine was first shown to work in the 1970s by a team led by Dr. Jerry A. Schneider at the University of California, San Diego. The F.D.A. approved Cystagon in 1994.