A San Diego compounding pharmacy says it plans to come to patients' rescue by offering a cheaper version of the antiparasite drug Daraprim (pyrimethamine), whose price skyrocketed overnight this summer, but the pharmacy may be skating on thin ice with the FDA.

Since Turing Pharmaceuticals bought Daraprim in August and immediately raised its price from $13.50 to $750 per pill, the story has become a symbol of what's wrong with drug pricing in America. The move prompted national outrage, and presidential candidates Hillary Clinton and Bernie Sanders weighed in with plans to fix the problem.

But last week, Imprimis Pharmaceuticals, a compounding pharmacy in San Diego, announced that it would be able to sell a Daraprim alternative for $1 a pill as part of Imprimis Cares, a new program to compound cheaper alternatives to pricey commercial drugs. Other drugs to be sold under the program have yet to be announced.

"Today, some drug prices are simply out of control and we believe we may be able to help control costs by offering compounded alternatives to several sole source legacy generic drugs," Imprimis President and CEO Mark Baum said in a statement last week. "Imprimis Cares and its team of compounding pharmacists will work with physicians and their patients to ensure they have affordable access to the medicines they need from the over 7,800 generic FDA-approved drugs."

However, as a compounding pharmacy, Imprimis is beholden to section 503A of the federal Food, Drug, and Cosmetic Act, which states that it can't compound drugs "that are essentially copies of a commercially available drug product." The only legal exception to 503A would be if a company altered an existing drug for an individual patient to make a "significant difference" for that patient, according to the law.

A classic example of this is if a patient is allergic to a component in a commercially available pill he or she needs, said Gabrielle Cosel, manager of drug safety for The Pew Charitable Trusts. In that case, a doctor could write a prescription for a pill without that component, and a compounding pharmacist could make it.

"Another example often used is children," Cosel said. "If their doctor wants to give them medicine only available in pill form and the child can't swallow pills, the pharmacy compounder could put that into syrup form."

When MedPage Today asked the FDA about how Imprimis' Daraprim announcement fit into this law, the agency said that it is looking into the issue and could provide no further comment.

But even if it determines the product would violate the law, the agency can use its "enforcement discretion" to, in effect, look the other way when it believes it's in the public interest to do so.

In 2011, the FDA did exactly that after it approved the preterm birth drug Makena (hydroxyprogesterone caproate), which the manufacturer, KV Therapeutics, decided to price at $1,500 per injection. Previous compounded versions of the drug had cost from $10 to $20 per injection. But the program under which Makena was approved was supposed to give KV exclusivity under the Orphan Drug Act for 7 years.

In the end, the FDA continued to allow compounding pharmacies to produce hydroxyprogesterone caproate because, it said, the compounded version predated the Makena brand name and an FDA analysis of compounded samples didn't yield major safety concerns.

Imprimis told MedPage Today that its alternative to Daraprim won't violate the law because it won't be an exact copy. Instead, their pharmacists are adding leucovorin to pyrimethamine.

Leucovorin is usually prescribed with Daraprim to mitigate bone marrow side effects because pyrimethamine blocks the production of folic acid, which can lead to bone marrow suppression, according to Dennis Saadeh, Imprimis' senior vice president of corporate development.

Allan Coukell, Pew's senior director for health programs, said he couldn't comment on Imprimis, but stressed key terms in the federal law.

"Congress's intent was that compounders should not copy marketed drugs," he said. "Congress didn't say 'exact copy.' They said 'essentially a copy.'"

Boston University School of Law professor Kevin Outterson, JD, LLM, told MedPage Today that he doesn't expect the FDA to take action against Imprimis unless the agency somehow learns that Imprimis isn't following safety protocols. Furthermore, he said it's rare for anyone to verify whether a patient really needs a compounded drug and isn't being given the prescription simply because the compounded version is cheaper.

"This is a unique situation that plays into the politics of the high-priced pill," he said. "The FDA has a lot of enforcement discretion. So long as what's being sold is safe, so long as it's slightly different... I think they're in business."