Pharmacokinetic-pharmacodynamic model of magnesium sulfate in treatment of pregnancy-induced hypertension

Ten pregnancy-induced hypertension gravidas aged 24-36 (28.1 +/- 3.31) yr were infused iv with fast (7.5 g in 1 h) and slow (7.5 g in 5 h) rates consecutively. Blood pressure were measured and blood samples were collected at 0, 1, 6, 7, 9, 11, 15 h. The drug concentration of each sample in the serum was determined by colorimetric method. The integrated pharmacokinetic and pharmacodynamic model was used to analyze the data. The serum data were fitted to a biexponential equation and the effect data were fitted to a sigmoid Emax model. Their pharmacodynamic parameters were: Kco = 0.52.h-1, T1/2(kco) = 1.33 h, Emax = 20.5% Cc (50) = 6.15 micrograms.ml-1), y = 3.64. kco was not equal to k21 of the mammillary model. It shows that the site of action is situated in the effect compartment. The predicted effect could last 24 h.