When is 5 years not 5 years? When it's the FDA counting, Eisai claims

What makes a 5-year exclusivity period? Under U.S. law, it's the 5 years after FDA starts the clock ticking. Eisai has no qualms about that. But the Japanese drugmaker says the agency started that clock much too soon for two of its products--and it's suing the FDA to change that.

Eisai markets the weight loss drug Belviq, developed by Arena Pharmaceuticals ($ARNA), and the seizure remedy Fycompa. Both drugs were deemed new chemical entities (NCEs), which means they automatically win that 5 years of exclusive access to the market. But both drugs had to clear another hurdle before they could actually hit drugstore shelves. They had to make it through the Drug Enforcement Administration's controlled substance scheduling process.

For both drugs, that process turned out to be a lengthy one. The DEA took almost a full year after Belviq's FDA approval to send the drug on its way with proper scheduling. For Fycompa, the process took even longer. But as Eisai alleges in its lawsuit, the FDA started the exclusivity period for each drug on the date of agency approval--not on the day the drugs could legally be marketed.

Eisai claims that the FDA doesn't have to set the exclusivity period in motion with approval. The agency has the authority to hold off till a drug can actually go on sale. In fact, the lawsuit claims, the FDA has done just that in at least one case. Razadyne ER, an Alzheimer's disease drug sold by Johnson & Johnson's ($JNJ) Janssen unit, had its exclusivity trigger moved from the FDA approval date to the date when it could be marketed.

Eisai, of course, wants the FDA to do the same thing for Belviq and Fycompa. Both drugs could definitely use the extra time. While Belviq waited for DEA scheduling, a rival drug from Vivus ($VVUS), Qsymia, hit the market. That drug has its own problems, but in any case, Eisai's hands were tied. And when Belviq finally did hit the market, the drug faced challenges in gaining reimbursement from payers and getting a toehold with patients reluctant to take a drug to lose weight.

The Japanese company has since doubled the size of its Belviq sales force and is starting to see some results. But if its 5 years of exclusivity does expire on the fifth anniversary of its approval date--June 27, 2012--then Belviq has less than three years left before generic competition hits. That's just about when the drug might hit its stride.

Meanwhile, Fycompa won its FDA approval in October 2012, and by August of last year, Eisai was fed up enough to sue the DEA for dragging its feet. The all-clear finally came January 2, 2014.

When the drug was first approved, analysts had predicted $500 million to $1 billion in sales within three years. Now almost two years in--and with a bit more than three left to go before the exclusivity period expires--the first-in-class treatment naturally isn't anywhere near that level.

Eisai has already petitioned the FDA to switch the exclusivity dates on both drugs. Obviously, the agency hasn't cooperated. Whether the lawsuit approach will be any more successful remains to be seen. If it isn't? Yet another argument for steering clear of central nervous system drug development. It's CNS drugs, after all, that might need DEA scheduling. Developing them to begin with is crapshoot enough.