Here's Why Ionis Pharmaceuticals and Akcea Therapeutics Plummeted Today

What happened

Shares of Akcea Therapeutics (NASDAQ: AKCA) are down 26% at 11:41 a.m. EDT while Ionis Pharmaceuticals (NASDAQ: IONS) is down 16% after the FDA issued a complete response letter -- the agency's euphemism for a rejection -- for their triglyceride-lowering drug Waylivra that was up for approval for a rare genetic disease called familial chylomicronemia syndrome (FCS).

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So what

Akcea Therapeutics and Ionis Pharmaceuticals squeaked though the FDA's Metabolism and Endocrinology Products Advisory Committee with a 12-8 recommendation to approve the drug, with a majority of the outside experts voting that the efficacy justified the risk of thrombocytopenia, or low blood platelet levels, which is associated with taking the drug. As I wrote after the vote, given the large number of dissenting votes, an approval wasn't a slam-dunk since the FDA doesn't have to follow the advice of its outside advisors.

There was also the issue of Akcea and Ionis changing the proposed dosing of the drug and how patients should be monitored for thrombocytopenia compared to what was done in the clinical trial that supported the approval.

Now what

Unfortunately investors are in the dark about exactly what Akcea and Ionis have to do to eventually get Waylivra approved. The lack of disclosure isn't atypical as companies often want clarity from the FDA about a path forward before making a public announcement, but it seems likely this won't be a quick fix; it may involve running another clinical trial.

Waylivra is also being tested in a phase 3 trial for patients with familial partial lipodystrophy that is due to read out next year, which might help supplement the application for FCS if the FDA simply wants more data on the risk of thrombocytopenia.

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Brian Orelli has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Ionis Pharmaceuticals. The Motley Fool has a disclosure policy.