Stereoselective differences in propranolol disposition in female Sprague-Dawley and Dark Agouti rats

Although genetic constitution is recognized as an important factor in drug elimination, there is still only a modest amount of information about its impact on stereoselective drug disposition. To examine how strain differences in cytochrome P-450 expression may affect stereoselective drug elimination, the disposition of R- and S-propranolol was examined in female Sprague-Dawley (SD) and Dark Agouti (DA) rats. The half-life of R-propranolol was increased and its apparent oral clearance decreased significantly in DA rats relative to the SD strain [85 +/- 41 min (DA) vs. 26 +/- 10 min (SD) and 0.020 +/- 0.014 liter/min/kg (DA) vs. 0.31 +/- 0.14 liter/min/kg (SD)], respectively. Strain differences in S-propranolol half-life and apparent oral clearance also were observed, but were not as marked [97 +/- 36 min (DA) vs. 52 +/- 35 min (SD) and 0.20 +/- 0.13 liter/min/kg (DA) vs. 0.70 +/- 0.68 liter/min/kg (SD)], respectively. Due to a more pronounced effect of rat strain on the disposition of R-propranolol, the stereoselective S-/R- oral clearance ratio for propranolol was also strain-dependent [10 +/- 3 (DA) vs. 2.1 +/- 0.9 (SD)]. These differences could not be accounted for by propranolol stereoselective plasma protein binding or by a difference in the blood/plasma ratio for R- or S-propranolol in these separate strains. This represents one of the few examples where an increase in stereoselective drug disposition has been observed due to strain differences that diminish drug elimination.