Merck & Company has agreed to buy Cubist Pharmaceuticals for about $8.4 billion and assume $1.1 billion in Cubist’s debt. The success of this deal will give Merck, which is the second-largest American drug maker after Pfizer, control of Cubist Pharmaceuticals and strengthen its ties with hospitals.

The deal fits into Merck’s strategy of purchasing midsize drug makers that complement its existing product portfolio.

Merck will pay $102 per share in cash for Cubist. This represents a 35 percent premium above Cubist’s average share price for the five most recent trading days.

Lexington-based Cubist makes drugs to treat superbugs and dangerous bacteria, including diseases that can cause pandemics. Cubist’s biggest seller Cubicin fits well into Merck’s hospital division. Merck’s sales in hospital acute care division were 10 percent higher in the first three quarters of this year than in the same period in 2013.

Merck said that the deal with Cubist was about expanding revenue, rather than looking for cost savings.

Chief executive of Merck, Kenneth C. Frazier said that the rationale for this deal is revenue growth. He said that their ability to take these products and take them, for example, globally where they have strength around the world is a great opportunity to grow.

Cubist has promising drugs in the pipeline, which includes those it had obtained through two corporate acquisitions of its own. Last year, Cubist purchased Trius and Optimer paying approximately $800 million for each.

For Merck, acquiring Cubist allows it to instantly boost its presence in antibiotics. Cubist is the only company of its size which has a robust and dynamic portfolio of antibiotics.

By selling itself to Merck, Cubist will be able to expand internationally at a faster rate. Cubist antibiotics are sold only in Canada and the United States, though the company was working on expanding to Western Europe.

Chief executive of Cubist, Michael Bonney said that with Merck taking over, they have access to Class A infrastructure around the world.

Merck added that it saw opportunity in expanding sales of Cubist’s products worldwide. Cubist’s products’ international sales made up just 6 percent of the company’s revenues in the first nine months of this year.

Shares of Merck closed 0.6 percent higher, at $61.88. Cubist shares increased 35 percent on Monday, to approximately $100.60.

Merck makes prescription products, oncology treatments and vaccines. Merck posted revenue of around $10.6 billion in the third quarter. Merck said that Cubist would add over $1 billion to its expected 2015 revenues.