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.

Stocks are stumbling on Tuesday, as the Dow Jones Industrial Average (DJINDICES:^DJI) has lost more than 37 points as of 2:40 p.m. EST to drop below 16,000 again on a wobbly day when most blue-chip stocks are in the red. Health care's big names are running into a wall today, as Pfizer has shed 0.7% to rank among the Dow's leading laggards, with Merck (NYSE:MRK) and Johnson & Johnson (NYSE:JNJ) not far behind. Let's catch up on what you need to know.

Merck moves ahead with trials
Merck's stock has fallen around 0.4% on the day so far, but the company's looking into the future as it steps up clinical trials for one of its developmental drugs. The company's BACE inhibitor MK-8931, a therapy for Alzheimer's disease, won the go-ahead to move into late-stage trials from a data monitoring committee reviewing its safety. Merck's pushing into phase 3 studies now with thousands of patients for the experimental therapy.

Alzheimer's drugs have been a tricky proposition among Big Pharma. BACE inhibitors, in particular, have garnered a lot of heat lately: Eli Lilly, one of Merck's top rivals, racked up safety concerns for its own phase 2 trials of its version earlier this year, forcing the company to shelve the testing. However, Merck's push into late-stage studies is a good sign so far for MK-8931, and this company needs all the help it can get from its pipeline to counteract falling sales caused by the patent cliff. Keep an eye on MK-8931's progress moving ahead, although this drug still has some way to go before it can be called a real success.

Johnson & Johnson's down slightly today after receiving a minor 11 million euro fine from the European Commission over accusations of collusion. Despite the stock's slip, you shouldn't worry: Johnson & Johnson's been a big riser on the Dow Jones this year, especially for such a diverse and broad-reaching company with its fingers in many niches of the health-care sector.

As far as Europe goes, it's been one of Johnson & Johnson's top markets. The company's European sales jumped by a whopping 12% in the third quarter alone, and through the first nine months of the year Johnson & Johnson's European revenue soared by 10.4%, nearly 4 percentage points above its American sales growth. Today's hiccup might sting, but Johnson & Johnson's still performing exceptionally across the Atlantic. No need for fear, investors.

Fool contributor Dan Carroll has no position in any stocks mentioned. The Motley Fool recommends Johnson & Johnson. The Motley Fool owns shares of Johnson & Johnson. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.