Arrowhead Pharmaceuticals Inc. said it voluntarily paused a phase I/II study of its RNAi candidate for treating cystic fibrosis (CF) out of an “abundance of caution” while considering its next steps. “This may delay our pulmonary program a bit, but it’s just part of drug development,” said Christopher Anzalone, Arrowhead’s CEO. The halt was prompted by signals of local lung inflammation found in an ongoing chronic toxicology study in rats.