Transit times for oxprenolol and metoprolol Oros drug delivery systems through the gastrointestinal tract have been measured in 35 individuals in six separate studies. A total of 45 systems were recovered in a median time of 27.4 h; individual transit times varied from 5.1 to 58.3 h. The residual amount of drug in recovered systems was inversely related to transit time and corresponded closely with the amount estimated from in vitro dissolution profiles.