Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

What started out as a cataclysmic day for investors has turned into a boring one, as the Dow Jones Industrial Average (^DJI 1.05%) has bounced all the way back from triple-digit losses earlier in the trading session. As of 2:45 p.m. EST, the Dow Jones has clawed its way back to breakeven. Although most blue-chip stocks on the index are still in the red, a few tech stocks have turned around the Dow's fortunes -- particularly Cisco, which is having a big day with gains of more than 2%.

Merck (MRK 1.70%) has swung lower in the health care sector, while rival Pfizer (PFE 1.04%) has hung flat so far. Let's catch up on the latest with these two big pharma giants.

Merck's Januvia problem
Little news has emerged from either company, but both Merck and Pfizer are still dealing with the aftermath of the patent cliff that has hammered sales. Pfizer has recovered more strongly, with a positive earnings report for the third quarter that lifted shareholders' spirits. Merck, on the other hand, didn't impress Wall Street with its own third-quarter results.

Part of the problem is Merck's reliance on diabetes powerhouse duo Januvia and Janumet for its future. With the diabetes market exploding, the two drugs seemed like surefire bets to continue the rise that made them blockbuster drugs, picking up a combined $2.8 billion in sales over the first half of the year. However, the growth of the two drugs -- particularly Januvia -- is stalling out, and Merck's own growth projections have failed to materialize.

That's not to say there isn't still hope for Merck. While the company's pipeline isn't as impressive as those of certain industry peers, including Pfizer, the company does have a few potential blockbusters in its pocket, such as bone treatment drug odanacatib and hepatitis C therapies MK-5172 and MK-8742. Growth of a few other, less prominent drugs on the market already, such as the HPV vaccine Gardasil, has been acceptable.

Further, it's not over for Januvia and Janumet. The diabetes market isn't slowing down at all, particularly given the rising incidence of the disease in major up-and-coming markets like China and India. The former could have as many as 114 million adults suffering from the disease, according to a recent study.

However, the troubles with Januvia and Janumet emphasize why pharmaceutical companies -- like portfolios -- shouldn't rely too much on one good thing. Pfizer, by comparison, has broadened its drug portfolio to weather patent expirations on drugs like Lipitor. While new blockbuster hopefuls like rheumatoid arthritis drug Xeljanz and blood thinner Eliquis have had slow starts, they're both expected to hit blockbuster status one day. Meanwhile, Pfizer has kept its pipeline in tip-top shape, and the company's future looks bright.

Both Merck and Pfizer are diverse drugmakers -- it's part of being among big pharma's best. However, Pfizer's been one of the strongest in the industry at overcoming the patent cliff and moving on with strong drug development. Investors would gladly welcome a little more of the same from Merck.