Therapeutic Drug Monitoring of 5-Fluorouracil in Head and Neck Cancer Patients: An Interventional Pilot Study

Abstract Introduction 5-fluorouracil (5-FU) is a crucial agent in treating various types of cancer, particularly recurrent head and neck cancers (HNCs). According to prior studies, individuals who underwent therapeutic drug monitoring (TDM) based 5-FU dosage adjustments showed significantly higher response rates and experienced fewer adverse events compared with those who received the standard 5-FU administration. This study aims to enhance our understanding of the overall clinical outcomes in patients with recurrent HNCs who received 500 mg of 5-FU through a pharmacokinetic (PK) analysis. Objectives Our objectives are to conduct TDM in selected HNC patients and observe individual PK responses, efficacy, tolerability, and drug toxicity. Materials and Methods We enrolled a total of 12 patients with recurrent metastatic HNC, and all of them received a fixed dose of 500 mg with cisplatin in a 21-day cycle. During cycle II or III, we analyzed the blood concentrations and PK parameters of 5-FU using the liquid chromatography and mass spectrometry (LC–MS) technique. Notably, we calculated the Concentration maximum (Cmax), time at which the concentration reaches maxiumum (Tmax), Half life of the drug (T1/2), and area under the curve (AUC) for the 500-mg dose of 5-FU, as the PK data for this particular dose were unavailable, making our study uniquely valuable for assessing efficacy and toxicity. Results Within the study group, 83.33% obtained an average AUC range of 1,000 to 3,000 h/µg/mL. Out of this group, 41.66% showed a partial response, 33.33% experienced disease progression, and 25% remained stable during the therapy. One patient had an AUC below the expected value (832.21 h/µg/mL), while another had an overexposed AUC value (5726.87 h/µg/mL), resulting in a poor clinical outcome. After interpreting the results, suggestions for dosage adjustments were made to the clinician. Conclusion From our interventional study, it is evident that at a flat dose of 500 mg, PK-based individual dosage regimens play a superior role in managing advanced cancer patients with minimal toxicities. This PK analysis showed us clarity on the outcomes of 5-FU at a 500-mg dose.