Why Are Clinical Trials in MS so Difficult?
There are a number of reasons why it is difficult to conduct clinical trials of new MS medications. First of all, clinical trials of almost any medication are difficult. It takes many years to properly study a new medication, hundreds of volunteer patients, and almost 1 billion dollars before a drug can be approved by the FDA. Compounding these general challenges, there are several features of MS that pose additional challenges to conducting clinical trials.
In other illness, like many cancers, it is relatively easy to define and measure the desired outcome: survival. If people receiving a trial medication survive longer than patients receiving placebo, then the medication is considered a success. Because many cancers are fatal in a relatively short period of time, trials need only last several years. By comparison, MS is a disease that usually takes its toll over many decades. Most patients live 30 to 40 years after diagnosis.
How then, do you measure the success of a drug in MS, where it can take decades for disability to develop? Clearly, it would not be possible to run a clinical trial lasting 10 or 20 years, and most trials in MS last no longer than 2 years. The most commonly used technique in MS trials is to measure the effect of the medication on relapse rates. And indeed all of the medications approved to date have shown a decreased number of relapses compared to placebo. Another common technique is to measure accumulation of new brain and spinal cord lesions that appear on MRIs. And indeed the medications have demonstrated a reduced rate of accumulation of new lesions on MRIs.
Certainly, these outcomes are not trivial. While relapses are rarely (and quite fortunately) permanently disabling, they can be psychologically devastating and expensive. Moreover, it is hard to imagine that having fewer MRI lesions is not better than having more. But the long-term impact of preventing relapses and MRI lesions is surprisingly unclear.
Fundamentally, the more important and difficult question regarding the medications is to what extent they prevent permanent disability. Thus far, it seems that the medications are effective in doing so, at least to some degree. Finally, disability is surprisingly difficult to measure as well. Intuitively, it might not seem so difficult a task. Certainly some things, like whether a patient needs a cane to walk a certain distance, are relatively straightforward. But other aspects of the illness, such as cognitive ability, pain, fatigue, and psychiatric symptoms are not so easy to measure. Certainly, doctors and drug companies face significant hurdles in studying medications for MS. I hope that this provides an indication as to why development of new MS medications is often slower than anyone would like.
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