Stocks were poised for a lower open on Wednesday after the S&P 500 notched its biggest gain in a month as investors digested another round of corporate earnings.

The benchmark S&P on Tuesday climbed 1.55 percent, its biggest percentage gain since March 13, after Coca-Cola Co led a round of solid earnings reports and on concerns eased over the euro zone debt crisis.

Investors don't like volatility but large run-ups can be equally unsettling too because investors question if that is going to hold, said Tim Speiss, a partner at Eisner Amper in New York.

According to Thomson Reuters data, 22 companies in the S&P 500 were expected to report on Wednesday, including American Express Co , Qualcomm Inc and eBay Inc .

Of the 39 S&P 500 companies posting earnings before Tuesday's opening bell, 74.4 percent beat estimates.

International Business Machines Corp shed 2.2 percent to $203 in premarket trade after reporting quarterly profit late Tuesday that beat expectations but revenue missed estimates.

Investors should not overreact to positive news nor should they be overreacting to really what could be viewed as isolated earnings reports. One report does not make a trend, unfortunately, said Speiss.

Intel Corp dropped 2.7 percent to $27.69 premarket after the chipmaker said late Tuesday sales would accelerate in the second half of the year, but the costs of upgrading its chip making factories were temporarily hurting margins.

S&P 500 futures fell 3.2 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 35 points, and Nasdaq 100 futures declined 2 points.

BlackRock Inc , the world's largest asset manager, said first-quarter profits were steady, bolstered by strong inflows into its popular iShares exchange-traded funds.

Halliburton Co advanced 1.9 percent to $33.29 in premarket after the world's No. 2 oilfield services company reported higher quarterly profit as North American revenue reached a record high.

Earnings at diversified manufacturer Textron Inc quadrupled, helped by a strong recovery in demand for business aircraft and helicopters. Textron gained 1.3 percent to $28 premarket.

Nestle SA , the world's biggest food group, is near a deal to buy Pfizer Inc's
infant nutrition business for up to $10 billion to boost its China business and extend its lead in the baby formula milk sector, sources said. Pfizer slipped 0.4 percent to $22.23 premarket.

SXC Health Solutions Corp will buy pharmacy benefit manager Catalyst Health Solutions Inc for about $4.4 billion. Catalyst jumped 32 percent to $83.87 and U.S.-listed shares of SXC Health climbed 9 percent to $87.50.

Berkshire Hathaway Inc Chief Executive Warren Buffett said he has stage 1 prostate cancer but it is not remotely life-threatening or even debilitating in any meaningful way. Berkshire Class B shares lost 1.1 percent to $79.91 premarket.

(Reporting By Chuck Mikolajczak; editing by Jeffrey Benkoe)