Carlsbad’s Ionis Pharmaceuticals is entrusting Akcea Therapeutics, a spinout of Ionis, to commercialize the drug inotersen ahead of a showdown.

The deal could be worth up to $1.7 billion to Ionis, plus profit-sharing payments, according to the company.

Ionis' inotersen is up against Alnylam Pharmaceuticals’ drug patisiran. The drugs were both developed for hereditary ATTR amyloidosis with polyneuropathy, in which abnormal protein buildup causes systemic problems that can be fatal.

The U.S. Federal Drug Administration later this year is expected to give each drug the green light.

Ionis has convenience on its side, since inotersen requires an injection once per week at home, while patisiran requires an infusion over four to five hours at a clinic. But analysts say Massachusetts-based Alnylam’s drug may have a better safety profile, which Ionis debates.

Ionis’ partnership — which allows it to keep an eye on commercialization but focus on drug development — includes an ATTR follow-up drug, AKCEA-TTR-LRx.

Under the agreement, Akcea will pay Ionis a $150 million licensing fee upfront, in exchange for Inotersen commercialization rights and 40 percent of profits. The ratio would shift to a 50/50 Ionis-Akcea split following the release of AKCEA-TTR-LRx.

In addition, U.S and Europe Union approval of Inotersen would trigger a $50 million milestone payment, along with $40 million for AKCEA-TTR-LRx. Backing in other areas would spark additional payments.

In support of inotersen’s commercialization, Ionis will buy $200 million in Akcea shares, increasing Ionis’ ownership to 75 percent.