The inhibition effect of blood pressure control drug particles, metoprolol (C34H56N2O12), and atenolol (C14H22N2O3), on the enzyme catalyzed decomposition of hydrogen peroxide reaction has been investigated by ultraviolet spectrophotometry. The results obtained when hydrogen peroxide was spectrophotometrically monitored were compared with those previously obtained from electrochemical measurements. As expected, the two series of measurements were shown to be consistent with the reaction stoichiometry. The Lineweaver-Burk linear equation was used to determine the Michaelis-Menten constant (K-M) and the maximum reaction rate (r(max)). Based on the variation of the Michaelis-Menten constant, respectively, the maximum reaction rate with inhibitor concentration, it was determined the inhibition parameters that characterize the enzyme-inhibitor (EI) and the enzyme-inhibitor-substrate (EIS) complexes. A mixed inhibition mechanism has been established for both drugs. Due to its selectivity and sensitivity, the development of a kinetic method for trace analysis of drugs, based on their inhibition effect on the enzyme-catalyzed reaction rate appears to be promising.