Pfizer is spending $6.7 billion to buy a drugmaker with no products on the market and a focus on developing treatments for inflammatory conditions like Chrohn’s disease. The pharmaceutical giant said Monday it will pay $100 in cash for each share of Arena Pharmaceuticals in a deal already approved by the boards of both companies. Pfizer says the deal will help bolster its expertise in inflammation and immunology. It plans to pay for the acquisition with cash on hand. Arena has a potential treatment for ulcerative colitis in late-stage clinical testing that it also is testing to treat Chrohn’s disease.