GlaxoSmithKline plc (ADR) (GSK), Gilead Sciences, Inc. (GILD): Did Sarepta Therapeutics Inc (SRPT) Just Knock Out Its DMD Competitor?

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Ignore the bickering between shareholders of Sarepta Therapeutics Inc (NASDAQ:SRPT) and GlaxoSmithKline plc (ADR) (NYSE:GSK) /Prosensa  for a moment, because these are exciting times for the roughly 1 in 4,000 newborns worldwide who are born with Duchenne muscular dystrophy.

Source: Andres Rueda, Wikimedia Commons.

There are two drugmakers currently knocking on the doorstep of the Food and Drug Administration, each with a unique drug — eteplirsen for Sarepta Therapeutics Inc (NASDAQ:SRPT), and drisapersen for GlaxoSmithKline plc (ADR) (NYSE:GSK)/Prosensa — that has the ability to slow or stop the muscle-destroying effects of DMD. With very few treatment options currently available to DMD patients, and an average lifespan of just 25 years, this is very encouraging news.

Sarepta Therapeutics IncUntil recently, the data on the two drugs was similarly positive, but the edge in recent weeks had been sliding back into drisapersen’s favor. This big concern that has plagued Sarepta Therapeutics Inc (NASDAQ:SRPT) shareholders recently is that the FDA has had a difficult time accepting increased dystrophin production as a primary endpoint to improved results in DMD patients. It also hasn’t helped Sarepta Therapeutics Inc (NASDAQ:SRPT)’s case that its study is only mid-stage in nature and based on just 12 patients. This was the primary reason the FDA refused to accept an accelerated new drug application filing from Sarepta.

But, the gloves came off again on Friday, which may have again given the upper hand to Sarepta Therapeutics Inc (NASDAQ:SRPT). New data was released on drisapersen that showed that the drug was effective in spurring dystrophin production in 72% of boys taking the drug and 59% in those that took it intermittently. The results are good, but nowhere near the 100% figure that Sarepta Therapeutics Inc (NASDAQ:SRPT)’s eteplirsen delivered in its mid-stage trial.

Not so fast…
There are, though, a number of questionable factors to contend with here that may not be telling the entire story — the first of which is the size of each drugmaker’s mid-stage trial. Eteplirsen was examined in just 12 patients, whereas drisapersen’s trial involved 53 patients. This reminds me of the mid-stage study in hepatitis C between Gilead Sciences, Inc. (NASDAQ:GILD) sofosbuvir and AbbVie‘s hep-C combo drug, which produced 100% and 97% sustained virologic resposnes, respectively. Gilead Sciences, Inc. (NASDAQ:GILD)’s patient subset consisted of just 25 patients tested with sofosbuvir and ribavirin. AbbVie, however, tested its combo on 79 patients, with 77 of them exhibiting no detectable sign of the disease after 12 weeks. Did this prove conclusively that Gilead Sciences, Inc. (NASDAQ:GILD)’s drug was superior to AbbVie’s because it returned 100% SVR12 compared to AbbVie’s 97%? Not in the least, because it’s more than just about the percentages! In this case, both drugs may prove to be blockbusters, and that could also be the case in DMD with these two drugs.

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