** Shares of life science firm Avantor AVTR.N down 16.1% at $13 in early trading
** Stock trading at its lowest since April 2020
** Co announces Michael Stubblefield to step down as CEO as soon as successor is found
** Posts Q1 net sales of $1.58 bln, slightly below estimate of $1.60 bln - data compiled by LSEG
** AVTR reports adj. EPS of 23 cents, matching analysts' expectations
** Fourteen of 24 brokerages rate the stock "buy" or higher, 10 "hold"; median PT is $21.50 - data compiled by LSEG
** Including day's move, AVTR down 26.4% YTD
(Reporting by Twesha Dikshit)
((Twesha.Dikshit@thomsonreuters.com))