Event – Watchman data get worse as third panel approaches

Boston Scientific needs some good news right now, and it is far from certain whether an FDA advisory panel will oblige. The third adcom to assess the company’s Watchman cardiac plug is due to meet on October 8, and while analysts are bullish the clinical data are disappointing.

Watchman is designed to block the left atrial appendage, a pouch in the heart in which blood clots can form. Boston needs US approval to help capitalise on its forecast return to growth this year, but St. Jude Medical’s rival device is expected to reach the US by year end, and with the most recent clinical data pointing to a stroke risk with Watchman its market could shrink even more.

The project has had a vexed time at the FDA. The first panel to assess it came up with a mixed but positive verdict, and the FDA turned it down. A second panel vote last December also came out broadly positive, but this time the FDA did not even deign to issue an approval decision, instead ordering this third adcom.


Last time around, Boston submitted data from the 407-patient Prevail trial, which missed one of its two co-primary efficacy endpoints (Watchman approval a toss-up after not-so-near miss in Prevail, March 11, 2013). And when more recent Prevail data are included, it now misses both.

Larry Biegelsen, an analyst at Wells Fargo, wrote that since the last adcom in December eight ischaemic strokes had occurred in the Watchman group, but none in the warfarin comparator group. There were fewer haemorrhagic strokes and cardiovascular deaths in the Watchman group than with warfarin in that same period, but still both Prevail efficacy outcomes are a bust.

Nevertheless, Mr Biegelsen puts the chances of the upcoming panel vote going Boston’s way at 60-70%.

But in order for this to happen Boston will have to argue that the low stroke rate seen with warfarin in Prevail was an anomaly, and lean on other Watchman studies such as Protect-AF, which has yielded rather more positive five-year data than Prevail. In fairness, the warfarin stroke rate in Prevail was low – 1.0% per patient-year compared with 2.2% in Protect-AF.

Second place

It therefore seems probable that the panel will recommend restricting the use of Watchman to warfarin-ineligible patients or those at high risk of bleeding.

But given that two adcoms have already passed Watchman only for the FDA to reject or ignore it, a positive vote this time around would surely be no guarantee of approval, even in a restricted population.

According to consensus forecasts compiled by EvaluateMedTech, Watchman is forecast to bring in $256m in 2020. St. Jude Medical’s Amplatzer occluder, however, is expected to gain approval first and rack up $319m in sales by 2020.

Watchman faces a trifecta of worsening data, potential labelling caveats and a faster competitor. Boston could do with a break after this month’s potentially disastrous legal findings (Mesh lawsuits could derail Boston’s big year, September 10, 2014). Watchman is unlikely to supply it.

To contact the writer of this story email Elizabeth Cairns in London at [email protected] or follow @LizEPVantage on Twitter

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