Advantages of everolimus therapeutic drug monitoring in oncology when drug–drug interaction is suspected: A case report

Introduction Drug interactions involving everolimus are fairly well known because of its common use, primarily as an immunosuppressant. Several recommendations regarding therapeutic drug monitoring are also available for the use of everolimus-based immunosuppression regimens. However, everolimus use in oncology differs substantially, particularly because of the high doses involved. Therapeutic drug monitoring, although sometimes necessary, is not recommended as a routine in oncology. Thus, it was deemed inapplicable due to the lack of clear recommendations. Case report Here, we present a case where a patient was prescribed everolimus for renal cell carcinoma. The patient benefitted from a pharmaceutical consultation prior to treatment initiation, and a drug interaction with verapamil was suspected. Management and outcome: Therapeutic drug monitoring of everolimus was proposed. Based on the everolimus values reported in the literature, trough plasma concentration in the patient was greatly increased. The patient was then diagnosed with grade 4 oral mucositis, thereby requiring temporary suspension of everolimus treatment. Management of adverse effects was performed through multiple medicated mouthwashes. Discussion Therapeutic drug monitoring for everolimus is important for potential drug interactions or the occurrence of severe adverse events. In such cases, dose adjustments should be managed according to everolimus plasma concentrations. Clear oncological recommendations regarding plasma everolimus thresholds are required for a successful follow-up of the patient’s condition and to ensure adequate response to treatment.