Marathon Pharmaceuticals LLC said it was "pausing" the launch of its Duchenne muscular dystrophy drug after U.S. lawmakers questioned why the company priced it at $89,000 a year when patients had been able to import it for as little as $1,000.

In a statement posted on the patient advocacy website Cure Duchenne, Marathon's chief executive, Jeffrey Aronin, said the company was pausing the launch amid "concerns about how the pricing and reimbursement details will affect individual patients and caregivers."

The company said it would maintain its "expanded access program" under which 800 patients currently receive the drug for nothing. It said patients currently importing the drug from overseas would continue to be able to do so.

The furore is the latest in a series related to U.S. drug prices, including Mylan NV's emergency EpiPen allergy treatment, that have drawn the ire of patients and lawmakers of all political stripes.

Marathon's drug, Emflaza, known generically as deflazacort, is a steroid, one of a class of drugs commonly used to treat Duchenne's that patients could import for personal use because it was not available in the United States. Last week it won U.S. approval, in theory closing off that option.

Earlier on Monday independent Senator Bernie Sanders of Vermont and Democratic congressman Elijah Cummings of Maryland, called on privately held Marathon to justify the price of the drug by documenting the cost involved in bringing it to market.

Marathon, the lawmakers wrote in a letter to Aronin, did not after all develop the product, which has been around for decades. The company acquired rights to two clinical trials that had already been completed. And it conducted further toxicology and other tests to bring it through the U.S. regulatory process.

Marathon argues that the studies it conducted had value in determining proper dosing, potential side effects and drug-to-drug interactions, allowing physicians to prescribe "with confidence."

In a separate statement, Marathon said it appreciated the opportunity to discuss "the value of an FDA approval of a medicine" with Sanders and Cummings "and futhering our shared goal that every patient who needs this drug receives it."

U.S. President Donald Trump has said he wants to lower drug prices and increase competition though he has not spelled out how.

The Food and Drug Administration approved Emflaza under its "orphan" drug program that provides incentives to drug makers to develop treatments for diseases with small patient populations. The incentives include seven years of market exclusivity. Duchenne's, a devastating muscle-wasting disease, affects some 15,000 patients in the United States, mostly young boys.

"Marathon will have a monopoly on deflazacort for years to come, preventing less expensive generic competitors from entering the market, despite the fact that this drug is already available in generic form in other countries," Sanders and Cummings wrote.