Apheresis has a wider scope in terms of target molecules. The production rate can vary among patients because some patients will have acute illness, while others will have chronic illnesses. Individualized therapy should be considered because the dynamics of target molecules within the circulation in patients with critical illnesses can differ from steady state conditions. Therefore, the dosage or frequency of therapy should be determined according to the dynamics of the targeted pathogenic substance [1, 2]. In this chapter, therapy variables affecting dosage and frequency are discussed.