What: Shares of Molson Coors Brewing Company (NYSE:TAP) had bubbled up 10% as of 12:15 p.m. Tuesday after Anheuser-Busch InBev reached an agreement to acquire London-based SABMiller, both of which were also up as of this writing, though not as much as Molson Coors.

So what: After turning down multiple offers since SABMiller revealed AB Inbev's intentions almost a month ago, SABMiller's board agreed to unanimously recommend that shareholders approve AB InBev's latest proposal to acquire SABMiller in a deal worth $104.2 million, or £44 per share. That's a 50% premium to its closing price on Sept. 14, which marked the last business day prior to renewed speculation of AB InBev's approach.

As I noted last month, Molson Coors currently holds a 42% stake in its MillerCoors joint venture with SABMiller. If this acquisition goes through, it will almost certainly be subject to antitrust concerns and result in the breakup of the joint venture, giving Molson Coors the chance to acquire at an attractive price the remaining 58% of MillerCoors it doesn't already own. Given the healthy margins of that joint venture and potential operating synergies Molson Coors could enjoy, it seems safe to expect Molson Coors will jump at the opportunity.

Now what: Again, however, AB InBev and SABMiller need to navigate an impending onslaught of regulatory scrutiny. And though I'm certain both companies are ready to do so given both industry consolidation that has already taken place in recent years, as well as the fact AB InBev reportedly began to secure financing for the deal over a year ago, there are no guarantees an international merger of this size will happen. 

With shares of Molson Coors now up 25% over the past month, that's why I think investors would be wise to take at least some of today's quick gains off the table.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.