MSACL 2023 Abstract

Feasibility of Routine Therapeutic Drug Monitoring for 5-Fluorouracil. Why Aren’t We Doing It?

Peter Galettis (1,2), Mirjana Radovanovic (1,2), Sarah Glewis (3,4), Michael Michael (4,5) & Jennifer H Martin (1,2).
(1) Centre for Drug Repurposing and Medicines Research, University of Newcastle, Newcastle, Australia; (2) Hunter Medical Research Institute, Newcastle, Australia; (3) Department of Pharmacy, Peter MacCallum Cancer Centre, Melbourne, Australia; (4) Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia; (5) Lower & Upper GI Oncology Service, Peter MacCallum Cancer Centre, Melbourne, Australia.

Peter Galettis, PhD (Presenter) University of Newcastle

Presenter Bio: Dr Galettis currently holds the position of Head of the Clinical Pharmacology Laboratory at the University of Newcastle. He has previously held senior laboratory roles in academia, pathology and hospital settings where he was responsible for the development and implementation of new assays. Dr Galettis's research interests are entirely within the field of clinical pharmacology and toxicology, specialising in assay development for use in drug monitoring for the last 30 years, focussing on anticancer agents and drugs of abuse.

Relevant Financial Disclosures (within past 24 months) No relevant financial relationship(s) to disclose. Discussing Products? NO, presenter will NOT present educational content related to products/services of the ineligible company(ies) listed above. Conflict mitigation NOT REQUIRED.

Introduction:
In 2019 the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT) produced recommendations for the monitoring of 5-Fluorouracil with a target AUC range of 20-30 mg/L*h. However, the monitoring of 5-Fluorouracil is not practiced routinely in Australia, even though approximately two thirds of patients are dosed incorrectly.

Aims:
We set out to determine the feasibility of providing a routine TDM service for 5-Fluorouracil.

Methods:
We conducted a feasibility study of patients receiving infusions of 5-Fluorouracil greater than 24 hours. Plasma samples were sent to the Clinical Pharmacology Laboratory at the University of Newcastle where they were analysed for 5-Fluorouracil using a validated LC-MSMS. The results of the 5-Fluorouracil analysis were returned to the referring oncologist who then decided whether to adjust the dose of 5-Fluorouracil given to the patient.

Results:
The study recruited 38 patients receiving 5-Fluorouracil infusions, which ranged in age from 33 to 77 years. There were 23 males and 15 females. Of the 38 patients 36 received a 46 hour infusion while 2 received a 96 hour infusion. Only 36% (13/36) of patients were within the 5-Fluorouracil therapeutic range consistent with previous studies. Only 1 patient had an AUC greater than 30, while 61% (22/36) of patients had an AUC less than 20. On a second round of monitoring 4/12 achieved an AUC between 20-30, a further 2/4 achieved the target after 3 rounds of TDM and 2 reached the target after 4 and 5 rounds of TDM. Median time to provide results of the clinician was 5 days from collection of the sample with a range of 2 to 9 days.

Discussion:
Only 36% of patients achieved the therapeutic 5-Fluorouracil AUC of 20-30 with standard treatment, this was increased to 58% after clinicians decided to increase the dose of 5-Fluorouracil after performing TDM. We have shown that routine TDM of 5-Fluorouracil is feasible with a sample turnaround time of under a week providing oncologist with sufficient time to adjust 5-Fluorouracil dose if desired.