It’s been a busy week in biotech, and despite it now drawing to a close, there’s still plenty of volatility out there. Here are two of the week’s biggest movers, and what drove the action. One winner, one loser.

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Mylan N.V. (NASDAQ:MYL)

First then, the loser. Mylan Kicked off Thursday’s session at just shy of $51 a share – a level around which it has traded pretty consistently for the last three months. The company closed out Thursday for $41 a share – an 18% decline. So what drove the selloff? Pre-session, Mylan announced a deal that sees it acquire Swedish pharma, Meda AB, for $7.2 billion. Meda is strong in developing nations, with a number of hit-selling drugs in its portfolio that outperform in China, Brazil and Russia – all markets that Mylan has struggled to break into. The deal gives the company instant access into these potentially lucrative spaces, and to Meda’s promising pipeline of over the counter clinical candidates. This is the upside to the deal.

The downside, is the price the company paid. $7.2 billion represented a more than 90% premium on Meda’s pre-buyout close (markets valued Meda at a little over $3.7 billion pre-deal), and market sentiment is leaning towards an overpay. Biotech buyouts will always have an associated premium, but it is rarely above 50%, and pretty much never as high as 90%. Making things worse, there’s also the potential for dilution in Mylan stock, as a result of the way the two companies are structuring the deal.

Longer term, markets will probably ease up on Mylan – it’s just an initial response to what seems like a high price to pay at times of wider market uncertainty. Near term, however, we could easily see further downside as the week draws to a close and fringe investors shut out their exposure ahead of the long weekend in the US.

FibroGen, Inc. (NASDAQ:FGEN)

FibroGen gained 14% throughout Thursday’s session, to see its market capitalization breach the $1 billion mark. The company has had a tough start to the year, having opened at just ahead of $31 a share and – even with the latest boost – closing out at $17, a 45% decline year to date. The recent upside, however, could be a sign that market sentiment is reversing, and in turn, that there is some upside ahead for FibroGen.

It’s a development stage biotech, with no revenues to speak of and only two candidates in its pipeline, but to pick up a $1 billion plus valuation at this stage is quite an achievement, and so it shouldn’t be overlooked. The company just got an upgrade from Credit Suisse, and we got some promising (albeit early stage) data from a phase II in one of its two lead pipeline candidates – FG-3019 in a pancreatic cancer indication. It’s what’s called a CGTF inhibitor. Certiain types of cancer are classed as fibrotic (pancreatic being one of them) and in these types, CGTF promotes the survival and evasion of cancerous cells. Through inhibition, FibroGen believes it can halt the spreading of these sorts of cancers. The recently released data (in which the company is trialling the drug in combination with SOC chemotherapy) the drug looks well tolerated, and showed some initial signs of efficacy. It’s early days, but positive data is positive data.

FibroGen’s other drug is called Roxadustat, and is the more advanced of the two from a development perspective. It’s an an oral small molecule HIF prolyl hydroxylase (HIF-PH) inhibitor with a primary target indication of anemia in chronic kidney disease. The drug is in a host of phase III trials, some of which target anemia in patients on dialysis, and some of which target patients that aren’t. Alongside the phase IIs already discussed, these are the likely primary valuation drivers throughout the remainder of 2016 and beyond. Primary completions are slated throughout the first half of 2017, and we’ll likely get interim analysis throughout the second and third quarters of this year. In other words, plenty of potential upside catalysts If the company can show efficacy.

Again, we may see a small correction before the market closes today, in anticipation of a reduced over-the-weekend exposure ahead of President’s Day on Monday in the US.