In this paper, the effects of administration strategies on the design of multi-drug chemotherapy treatments were studied. Two separate approaches were suggested, such that in the first one, drugs are administered sequentially, and on the second approach, simultaneous injection of drugs was suggested. A multi-drug two-compartment pharmacokinetic model and a multi-drug cell- cycle nonspecific tumor growth model are expanded to investigate how the tumor behaves when applying the simultaneous strategy. The chemotherapy design is structured as a nonlinear optimization problem, aiming to maximize the treatment’s effectiveness and minimize the quantity of cancerous cells remaining after the completion of the therapy. By developing an optimal control problem and employing a genetic algorithm to solve it, the most appropriate drug regimens are determined. This study seeks to determine whether or not the way of drugs administration may affect the treatment outcome. The simulation results are reported for several scenar
