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Metronomic chemotherapy describes the close, regular administration of chemotherapy drugs at less-toxic doses over prolonged periods of time. In 2015, the results of randomized phase III clinical trials demonstrated encouraging, albeit limited, efficacy benefits of metronomic chemotherapy regimens administered as adjuvant maintenance therapy for the treatment of breast cancer, or as maintenance therapy in combination with an antiangiogenic agent for metastatic colorectal cancer. Owing to the investigational nature of this approach, metronomic chemotherapy regimens are highly empirical in terms of the optimal dose and schedule for the drugs administered; therefore, greater knowledge of the pharmacokinetics of metronomic chemotherapy is critical to the future success of this treatment strategy. Unfortunately, such preclinical and clinical pharmacokinetic studies are rare. Herein, we present situations in which active drug concentrations have been achieved with metronomic schedules, and discuss their associated pharmacokinetic parameters. We summarize examples from the limited number of clinical studies in order to illustrate the importance of assessing such pharmacokinetic parameters, and discuss the influence this information can have on improving efficacy and reducing toxicity.

Background: A randomized, double-blind trial is reported of the clinical efficacy of red blood cells (RBCs) treated for pathogen inactivation with S-303, a synthetic labile alkylating agent., Study Design and Methods: Patients undergoing complex cardiac surgeries were randomly assigned to receive either S-303-treated (test) or conventional (control) RBC transfusion during surgery and for 6 days thereafter. Efficacy was evaluated by comparing the occurrence of a composite primary endpoint of treatment-related morbidity (myocardial infarction and renal failure) and mortality., Results: Two-hundred twenty-three patients were randomly assigned and 148 patients who received transfusions (74 with S-303-treated RBCs and 74 with control RBCs) were evaluable. The incidence of the primary endpoint was equivalent between the two groups (22 and 21% in the S-303-treated and control RBC groups, respectively). Secondary endpoints, including hemoglobin increment (mean, 1.4 vs. 1.5 g/dL), number of RBC transfusions (mean, 4.4 vs. 3.8 units), and other blood product support, were also comparable. The adverse event profile was similar between groups; however, patients who received S-303 RBCs were significantly more likely to develop constipation and less likely to suffer supraventricular extrasystoles. Four patients (2 test and 2 control) demonstrated positive indirect antiglobulin tests with reactivity for S-303 RBCs at one or more time points before or after transfusion, without evidence of hemolysis., Conclusion: S-303-treated and conventional RBCs were equivalent with respect to clinical efficacy and safety in supporting the transfusion needs of cardiac surgery patients. Investigations are under way to ascertain the significance of S-303 RBC antibodies and to prevent their occurrence.

The immunodepressant action of cyclophosphamide, thiophosphamide and sarcolysine was examined in experimental primary immune response in mice of different lines immunized with sheep red blood cells. DBA/2 and C3H/Sn mice were marked by the highest sensitivity to the immunodepressant action of the alkylating agents. BALB/c mice were relatively resistant to the immunodepressant action. Possible reasons for the interspecific differences found are discussed.