Nov. 24 (Bloomberg) -- Sanofi-Aventis SA, France’s largest drugmaker, increased the most in 19 years in Paris trading after Morgan Stanley analysts raised the rating on the stock to “overweight” from “equal weight.”

The shares rose 5.69 euros, or 15 percent, to 44.50 euros, the biggest gain since October 1989. The stock was the best performer today in the 18-member Bloomberg Europe Pharmaceutical Index, which rose 6.5 percent. Sanofi has lost 29 percent this year.

New Chief Executive Officer Chris Viehbacher, who starts Dec. 1, is likely to cut research expenses, Morgan Stanley analysts led by Andrew Baum wrote in a note dated today. Generic copies of the blood-thinning drugs Lovenox and Plavix probably will be delayed, they wrote.

Morgan Stanley raised its price estimate on the stock to 50 euros from 49 euros.

To contact the reporter on this story: Kristen Hallam at khallam@bloomberg.net; Jonathan Browning in London jbrowning9@bloomberg.net.

Last Updated: November 24, 2008 11:49 EST