Fitch Ratings has affirmed Merck & Co.'s (Merck) ratings, and revised the Rating Outlook to Negative from Stable. The ratings affirmed are: --Long-term Issuer Default Rating (IDR) at 'AA-'; --Senior unsecured debt rating at 'AA-'; --Bank loan rating at 'AA-'; --Short-term IDR at 'F1+'. The ratings apply to approximately $6.93 billion of outstanding debt. The Rating Outlook is Negative.