Eisai has released results of a trial in which good old phentermine was added to the company's obesity treatment, Belviq (lorcaserin). The primary endpoint for the trial was to discover if the combination increased the risk of patients having serotonergic adverse events (bad) after 12 weeks. It didn't (good). However, twice as many patients (10.1%) on the combo dropped out due adverse events compared with Belviq alone.

Tantalizingly, we also get a first glimpse at the bodyweight loss associated with this combination: 8.7% for Bel-phen versus 3.8% for Belviq alone. Because there was no placebo arm we cannot tell what component of this weight loss was caused by the drug intervention as opposed to the background diet and exercise program that all patients received.

What we can say is the addition of phentermine resulted in an additional 4.9% weight loss after 12 weeks. That's actually pretty good. Like its combination competitor Qsymia (phentermine/topiramate), the addition of phentermine increases total weight loss, but with the cost of additional adverse events. Side effects leading to discontinuation are most likely going to be mild CNS side-effects such as sleeplessness, headaches, anxiety.

My problem is that this does not paint a particularly strong picture of Belviq when you consider the relative costs of the two drugs. Let us assume that the two drugs in combination do not have a synergistic effect (we can't tell because there was no phentermine-only arm in the trial). Belviq costs patients somewhere in the region of $200 a month for 3.8% weight loss, while generic phentermine will be more like $10-20 a month for 4.9%. If you cannot afford both, phentermine looks to have the strongest cost effectiveness.

If you can afford both then great, but that is a lot of ongoing expenditure for a chronic disease. Why stop at Bel-phen. With new treatments such as Takeda's Contrave (naltrexone/bupropion) reaching the market a whole host of new combination regimens are becoming possible, if unproven: Q-viq  Beltrave Con-phen. This type of combination use will certainly be going on somewhere out there, possibly with interesting results, but I doubt there will ever be the financial will to study them in a randomized controlled trial. In fact, considering the size and cost of trials required to demonstrate Bel-phen is not associated with valvulopathy (the issue that killed off the phen-fen era), Eisai and Arena may not choose to progress Bel-phen studies any further.

Gideon Heap, M.Sc., is an analyst with the Pharmaview team at Decision Resources Group.

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