Calixa Therapeutics is a privately-held biopharmaceutical company that is dedicated to addressing the growing problem of multi-drug resistant organisms. Their lead product, CXA-101, is an intravenous formulation of a unique cephalosporin that has shown promising potency against multi-drug resistant Pseudomonas aeruginosa. Calixa plans to combine this product with a beta-lactamase inhibitor to create CXA-201, which has the potential to become the preferred treatment for serious infections caused by gram-negative organisms. In 2009, Calixa Therapeutics was acquired by Cubist Pharmaceuticals, which was later acquired by Merck.