Recently, a model for drug interactions considering also side effects has been proposed. According to this model, the effect compartment concentration range maximizing the global well-being of the patient can be identified. This optimal range represents the set which should be targeted by drug infusion. In this work, we apply this novel model to the clinically relevant combination of intravenous morphine and ketamine. The optimal range is identified and its center used as the reference value for controller design. The control problem can be formulated as consisting of mixed continuous and discrete parts. By solving the optimal control problem, the optimal infusion policy is identified minimizing the drug consumption.