Variability in the pharmacokinetics of atenolol and metoprolol

18 healthy volunteers received conventional atenolol (Tenormin) 50 mg once daily and metoprolol 50 mg twice daily for 6 days in a balanced randomised cross-over fashion. There was a wash-out period of two weeks between each phase. Plasma concentrations of the drugs were measured on the last day of each phase. Comparison of the coefficients of variation showed a lower variability in the pharmacokinetics of atenolol compared to metoprolol. The clinical implications of these findings are discussed.