Stereoselective features of (R)- and (S)-atenolol: clinical pharmacological, pharmacokinetic, and radioligand binding studies.
In a randomized, double-blind, cross-over study in 12 healthy volunteers, the effects of single oral doses of 100 mg rac-atenolol were compared during exercise to those of equal amounts of the optically pure enantiomers, i.e., 50 mg (R)- and 50 mg (S)-atenolol. The mean rate pressure product decreased with rac-atenolol (-37%; P < 0.01) and half-dosed (S)-atenolol (-35%; P < 0.01) to the same extent, whereas (R)-atenolol caused no effect. Radioligand binding studies in beta-adrenergic receptors of the guinea pig heart yielded a eudismic ratio of 46 for (S)- to (R)-atenolol. The mean AUCs, maximal plasma concentrations, and plasma half-lives of the enantiomers were similar regardless of whether they were administered as optically pure enantiomers or as racemic mixture. On the other hand, the AUC of (R)-atenolol was 1.08-fold greater (P < 0.01) than that of the (S)-enantiomer. The reason for this finding remains unclear. We conclude that only (S)-atenolol, but not (R)-atenolol, contributes to the beta-blocking effect of currently used rac-atenolol since the same effect can be elicited with the (S)-enantiomer alone.
Department of Medicine, Karl Franzens University, Graz, Austria.
K
K
Stoschitzky
G
G
Egginger
G
G
Zernig
W
W
Klein
W
W
Lindner
D000328:Adult; D000818:Animals; D001262:Atenolol / Q000493:pharmacokinetics* / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D003971:Diastole / Q000187:drug effects; D004311:Double-Blind Method; D005260:Female; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007457:Iodine Radioisotopes; D020120:Iodocyanopindolol; D008297:Male; D009206:Myocardium / Q000378:metabolism; D005082:Physical Exertion; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011869:Radioligand Assay; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism; D012016:Reference Values; D013237:Stereoisomerism; D013599:Systole / Q000187:drug effects
D007457:Iodine Radioisotopes; D011943:Receptors, Adrenergic, beta; D001262:Atenolol; D020120:Iodocyanopindolol; D010869:Pindolol