I don't think MRK had anything to do with SVNT and the decline. SVNT sold off in the last 2-3 minutes ... was trading at $4.95 - $4.99 and then the bottom fell out. Traded over 300K shares in the last few minutes I think. Interestingly after the close a number of trades went off, one at $4.98 and a bunch in the $4.80's. I suspect some (negative) rumor near the close brought it down.
I doubt it. Imo it was probably some who bought SVNT earlier in the week on margin expecting a bounce from SVNT being added to the index. Perhaps they were worried about getting a margin call over the weekend since they then became pretty sure that SVNT would close under $5. Imo SVNT might have a nice rally next week.
Re those 300,000 shares in the last few minutes were more likely an institution that wanted out this week and simply arranged their trade to execute at that time so as not to disrupt any later trading since its common practice to shove bad news into the weekend when people aren't paying attention to details.
I'd guess it will trade around 4.75 at Monday's opening which gives something to the late trade and yet recognizes it singularity, not generality.