A first order stochastic semi-empirical model for pharmacokinetics is presented and the real response of drug concentration to vital pharmacokinetics parameters studied. By invoking Gaussian kinetics and the residual drug concentration eliminated, the probability densities and the response of concentration profiles are theoretically simulated, using empirical data based on our experience. The drug is administered for 3 days at regular time intervals of 3hr and 6hr, respectively, by refreshing the drug halflife. Results show that the amount of drug residue decreases with increasing dose, but increases with increase in ingestion time interval for corresponding dose. It is also shown that the real drug concentration increases to a threshold and decreases marginally for subsequent dose. However it is difficult to predict the response of drug concentration with changes in ingestion time interval. We recommend that for higher drug concentration the half-life be increased. Our simulation results qualitatively agree with those documented in the literatures.