The Future of Tysabri: A Reader’s Perspective (ELN, BIIB, SRA)

I received the following email from a reader criticizing comments I made regarding the multiple sclerosis drug, Tysabri, in the October 17th post on Serono:

You state in your blog, "I find it difficult to believe the FDA will allow a product for a non-fatal disease on the market with the risk profile of Tysabri.

You must be distressed at the prospect of Serano's (sic) Rebif losing market share to Tysabri when it returns to market. Just more bad news for a company that's had a spate of it lately.

As for the "risk profile of Tysabri", as a monotherapy this risk is negligible as no cases of Ty mono have been linked to PML - zero. The two MS patients who contracted it were using Ty in combo with Avonex for between 2 and 3 years. Avonex reduces the rate of clearance of Ty from the body and that effect is cummulative. The Crohn's patient who was rediagnosed as having died from PML was on a cocktail of immunosuppressants including the highly toxic Imuran for five years. That drug is itself linked to cases of PML.

As for Ty's benefits to MSers, they were nothing short of phenomenal (sic) - 67% reduction in relapses for Ty mono, and reversal of disability in a significant number of patients, far superior results compared to currently available therapies.

You really need to do better research to understand the true risk/benefit considerations of Elan/Biogen's wonder-drug Tysabri if your (sic) intend is to help investors.

Or maybe you're just biased in favor of SRA and couldn't care less.

Obviously I touched a nerve.

I realize that I asked for this stinging criticism since I made an assertion without providing supporting evidence. Therefore, I will address the reader’s claims and in the process make a case as to why I believe it will be difficult for Tysbari to get back on the market anytime soon with its original label.

Claim 1: As for the "risk profile of Tysabri", as a monotherapy this risk is negligible as no cases of Ty mono have been linked to PML - zero. This hypothesis is not supported by clinical data. The only evidence to support this claim is the fact that the two MS patients that developed PML were concomitantly treated with Avonex and Tysabri for over two years. This retrospective analysis is informative but far from conclusive. Moreover, a patient on monotherapy did indeed die from PML, which the reader tried to explain away using the next claim.

Claim 2: The Crohn's patient who was rediagnosed as having died from PML was on a cocktail of immunosuppressants including the highly toxic Imuran for five years. That drug is itself linked to cases of PML. Data published in the July 27, 2005, issue of the New England Journal of Medicine suggests otherwise.

The following table is from the article, “Progressive Multifocal Leukoencephalopathy after Natalizumab Therapy for Crohn’s Disease,

Comments

[boswells:]

This is all well an fine that you can quote rates, market share and percentages of who has this and how much of what cocktail they may have taken. What it all boils down to is how much of a personal risk one is willing to take once all the other options you've tried for the last 6 years fail to keep the enemy at bay. I'm a firm believer, if you know all your options and make an informed decision, your future is in your hands. For some of us, Tysabri is the last stand, literally.

2005 Oct 31 09:46 AM

[BioBlogger_:]

Your point is well taken. I would not be surprised if Tysabri comes back on the market, but only as a salvage treatment. However, I believe you are wrong when you say that, "What it all boils down to is how much of a personal risk one is willing to once all the other options you've tried...fail." If you are an MS patient and develop PML and die or are disabled, your loved one are more than likely to sue the doctor and the company; therefore, it is not simply the patients decision. Moreover, the FDA is concerned about the potential fallout of allowing a drug with potentially fatal side effects without defining the risks. At this point, there are a lot of questions that need to be answered: Does monontherapy increase risk or is it only combo therapy? If only combo, how long does a washout period need be before giving Tysabri? What will be the monitoring procedure? There is no effective diagnostic test. Rather than trying to make a prediction about Tysabri's fate, what I am really trying to say is that the risk/reward in playing this from an investment perspective is not there. ELN is trading as though Tysabri has a 100% probably of getting back on the market with blockbuster revenue potential.

2005 Oct 31 11:57 AM

[BioBlogger_:]

Boswells,

One more thing. Thank you very much for your comment.

2005 Oct 31 11:58 AM