Importance of Sex-Dependent Differences for Dosing Selection and Optimization of Chemotherapeutic Drugs

Background: Despite major advances in cancer treatment in the past years, there is a need to optimize chemotherapeutic drug dosing strategies to reduce toxicities, suboptimal responses, and the risk of relapse. Most cancer drugs have a narrow therapeutic index with substantial pharmacokinetics variability. Yet, current dosing approaches do not fully account for the complex pathophysiological characteristics of the patients. In this regard, the effect of sex on anticancer chemotherapeutic drugs' disposition is still underexplored. In this article, we review sex differences in chemotherapeutic drug pharmacokinetics; we suggest a novel approach that integrates sex into the traditional a priori body surface area (BSA) dosing selection model, and finally, we provide an overview of the potential benefits of a broader use of therapeutic drug monitoring (TDM) in oncology. Summary: To date, anticancer chemotherapeutic drug dosing is most often determined by BSA, a method widely used for its ease of practice, despite criticism for not accounting for individual factors, notably sex. Anatomical, physiological, and biological differences between males and females can affect pharmacokinetics, including drug metabolism and clearance. At equivalent doses, females tend to display higher circulating exposure and more organ toxicities, which has been formally demonstrated at present for about 20% of chemotherapeutic drugs. An alternative could be the sex-adjusted BSA (SABSA), incorporating a 10% increase in dosing for males and a 10% decrease for females, though this approach still lacks formal clinical validation. Another strategy to reduce treatment-related toxicity and potentially enhance clinical outcomes could be a more widespread use of TDM, for which a benefit has been demonstrated for 5-fluorouracil, busulfan, methotrexate, or thiopurines. Key Messages: The inclusion of sex besides BSA in an easy-to-implement formula such as SABSA could improve a priori chemotherapy dosing selection, even though it still requires clinical validation. The a posteriori use of TDM could further enhance treatment efficacy and safety in oncology.