Alnylam set out nearly two decades ago to deliver novel RNAi medicines against diseases with inadequate treatment options, and with a new approval for Oxlumo, it’s gearing up for its third launch that fits that bill.

The med won approval Monday as the first medicine for primary hyperoxaluria type 1, or PH1, a severe rare disease that causes patients to suffer from recurrent kidney stones and often forces patients into organ transplants. The FDA move follows a European nod for the drug on Nov. 19.

Alnylam is pricing the medicine at $493,000 per patient per year on average, and it expects the net price will come in at about $380,000 per patient per year, CEO John Maraganore, Ph.D., said in an interview. At the same time, Alnylam is inking three-pronged value-based agreements with payers so that it only collects payments if the drug works.

Under those accords, the biotech will agree on “success criteria” with payers and collect payments after one year if patients respond to the treatment, Maraganore said. Further, if diagnoses increase over time as disease awareness grows, the company is prepared to lower the list price.

[huge_it_slider id=”15″]Finally, since the drug is dosed by weight and patients grow over the course of their lives, Alnylam will agree to cap the total number of vials that payers would need to cover for each patient to provide “budget reliability,” Maraganore said.

The company expects a “steady” launch rather than a huge initial uptake, as right now there’s “inadequate patient diagnosis and disease awareness,” Maraganore said. As physicians become more aware, the CEO says Oxlumo will become a “very attractive ultra-rare orphan product” that the biotech expects will generate $500 million in annual sales at peak.

The company expects a “steady” launch rather than a huge initial uptake, as right now there’s “inadequate patient diagnosis and disease awareness,” Maraganore said. As word gets out to doctors, the CEO says Oxlumo will become a “very attractive ultra-rare orphan product” that the biotech expects will generate $500 million in annual sales at peak.

Between 1,000 and 1,700 patients are diagnosed with the disease in the U.S. and Europe each year.

Oxlumo works by targeting a mutation that leads to an excess production of a compound called oxalate, which causes recurrent kidney stones and leads to end-stage kidney disease, studies have shown. It’s an “absolutely terrible” disease that causes serious complications and increased mortality, Maraganore said.

Patients with PH1 experience a progressive decline of their kidney function over time, and many end up needing a dual liver-kidney transplant. Before the approval, an approach called “hyperhydration,” which uses excess fluid to dilute oxalate, was the only treatment option. Oxlumo is given subcutaneously every three months.

Oxlumo is Alnylam’s third marketed RNAi drug after FDA approvals in August 2018 for Onpattro and November 2019 for Givlaari. Those meds turned in “solid” third-quarter performances, Evercore ISI analysts Maneka Mirchandaney and Josh Schimmer wrote to clients at the time, posting sales of $82.5 million and $16.7 million, respectively. Onpattro is approved in polyneuropathy caused by hereditary transthyretin-mediated amyloidosis, while Givlaari treats acute hepatic porphyria.

The analysts wrote that they don’t expect an early “bolus” of patients for Givlaari—or Oxlumo—but they added that the meds “could both grow to be meaningful opportunities over time.”