Pfizer (NYSE:PFE) has completed its $6.7 billion acquisition of Arena Pharmaceuticals, a developer of immuno-inflammatory drugs. The acquisition of San Diego-based Arena will bolster Pfizer’s pipeline of therapeutic candidates in gastroenterology, dermatology and cardiology. Among Arena Pharmaceuticals’ assets is etrasimod, an oral, selective sphingosine 1-phosphate (S1P) receptor modulator with the potential to treat ulcerative colitis…