AstraZeneca, Shire shares drop as U.S. tightens tax rules
LONDON, Sept 23 (Reuters) - Shares in drugmakers AstraZeneca and Shire both fell more than 5 percent on Tuesday after the U.S. Treasury took steps to curb "inversion" deals that allow companies to escape high U.S. taxes by reincorporating abroad. The move appears to jeopardise an agreed de
