Sanofi, GSK and Haleon lead $40-billion rout on heartburn drug

Sanofi fell 13% on Thursday, taking its 2-day decline to 20%; GSK slid 6.9%

Sanofi, GSK Plc and Haleon Plc have lost a combined $40 billion in market value since Tuesday’s close amid mounting concerns about litigation around the recalled heartburn drug Zantac.

Sanofi fell as much as 13% on Thursday in trading volumes nearly 10 times the average, taking its two-day decline to 20%, the steepest drop ever over that timeframe. GSK slid as much as 12% in London, while its recent spinoff Haleon slumped 13%. GSK shares were at one point showing their worst one-day retreat since February 1998, before paring losses.

Zantac was a once-popular antacid that has drawn a flurry of US