- The effects of the human MDR1 genotype on the expression of duodenal P-glycoprotein and disposition of the probe drug talinolol. Siegmund, W., Ludwig, K., Giessmann, T., Dazert, P., Schroeder, E., Sperker, B., Warzok, R., Kroemer, H.K., Cascorbi, I. Clin. Pharmacol. Ther. (2002)