MRK was selling at a PE over ten - not just seven as in Pfizer's case.
MRK also had just miserable results on Gardasil which had been so highly publicized just a few years ago. It suffered a pretty amazing 18% decline from a year ago.
I can't imagine a big Pfizer drug doing that with there being a patent expiration involved.
MRK also had to lower full-year estimates whereas PFE's numbers are always conservative enough where they don't have to do that. They already have that seven-cent beat from last quarter under their belt.