CVS has struggled since its 2007 merger with Caremark Rx to getthe PBM side of its business running smoothly, to the point wherecritics began calling for the company to undo the merger. Earlierthis month, Moody's Investors Service gave CVS a vote ofconfidence, assigning it the highest credit rating among the threelargest PBMs - CVS, Express Scripts and Medco Health Solutions.