** Shares of drug developer Certara CERT.O up 29.3% at $13.59 in extended trading

** U.S. FDA says it plans to replace animal testing with "human-relevant methods", including AI-based models, to improve drug safety and lower costs, and will start implementing this new approach immediately

** Analysts at brokerage Leerink Partners say FDA's announcement is a "clear incremental positive" for CERT, as its biosimulation capabilities may see higher demand, although "ultimate upside is unclear"

** Leerink Partners adds that CERT's biosimulation platform "takes on incremental value", as it could be a replacement or add-on to animal testing

** Brokerage also sees Labcorp's LH.N 5% decline, at market close, as an "overreaction" to FDA's announcement, since early development $(ED)$ business is "not entirely animal-based" and animal testing isn't ending immediately

** ED business's contribution to LH's overall revenue is relatively small, at around 6.5%, and the stock's decline exceeds its ED EBIT contribution - brokerage

** As of last close, CERT down 1.3%, and LH down 4.7%, YTD

(Reporting by Kamal Choudhury in Bengaluru)

((Kamal.Choudhury@thomsonreuters.com;))