WASHINGTON (Reuters) – Generic drug maker Hikma Pharmaceuticals has won U.S. antitrust approval to buy Custopharm, Inc on condition that it divest an injectable steroid, the U.S. Federal Trade Commission said on Tuesday. Hikma, which makes anesthetics, pain medications, sedatives, neuromuscular agents and other drugs, announced the deal in September as a way for it to strengthen its injectable treatments unit in the United States. It was valued at $425 million at that time. Under a deal struck with the FTC, Custopharm’s parent company will retain assets related to the corticosteroid drug triam…