Shares of Merck (MRK) - Get Report are lower in early afternoon trading on Monday, after the stock was downgraded to "underperform" from "hold" at Jefferies this morning. The firm has a price target of $48 on the health care company.

"I didn't buy this call," TheStreet's Jim Cramer said in an appearance on CNBC's "Fast Money Halftime Report" today. "I think Keytruda is going to be a big winner. I think that they have a lot in the pipe. I think they beat Bristol (Myers) (BMY) - Get Report head to head. I also think that there could be some levitation here."

Keytruda is a drug the company produces to treat a type of lung cancer and melanoma.

"Merck is not a bad actor in terms of pricing," Cramer continued. Some of the drug maker's competitors have been dealing with backlash over the rising cost of medications. Recently, Mylan (MYL) - Get Report came under fire for a large increase in the price of its EpiPen allergy medication.

"Merck has been very, very circumspect over this kind of, you know, it's not a Teva, (TEVA) - Get Report it's not a Mylan. It's the old Saint Merck, I think that they're being very responsible. I think that Keytruda is a gigantic drug. I would go the other way on this," Cramer explained.