Oncology Medication-Related Problems
Chemotherapy holds, dose adjustments, and stopping harmful medicines — a systematic clinical approach
Medication-related problems are among the highest-risk issues in oncology practice. Cytotoxic and targeted therapies have narrow therapeutic indices and interact significantly with commonly prescribed medicines. Systematic evaluation of chemotherapy holds, dose adjustments for organ impairment, and stopping harmful concomitant medicines is essential at every point of care in oncology.
Why Medication-Related Problems Matter in Oncology
Patients with cancer are typically prescribed multiple medicines — for the cancer itself, for supportive care, and for pre-existing conditions. The interaction between these medicines and cytotoxic or targeted therapies creates a uniquely high-risk environment. Physiological changes caused by cancer (renal impairment, hepatic infiltration, altered protein binding, electrolyte disturbances) further alter drug handling. Medication errors in oncology are disproportionately associated with serious harm, and many are preventable through systematic medicines reconciliation, pre-cycle blood monitoring, and application of protocol-specific dose modification guidelines.
Chemotherapy Holds — Recognising When to Stop
Every chemotherapy protocol defines specific thresholds at which treatment must be held or permanently discontinued. Common reasons to hold include Grade 3 or 4 toxicity (using CTCAE v5 grading), haematological parameters below protocol minimums (neutrophils, platelets), significant organ dysfunction, and immune-related adverse events in patients receiving checkpoint inhibitors. Capecitabine is held for severe hand-foot syndrome or diarrhoea. Trastuzumab is held if cardiac ejection fraction drops significantly. Checkpoint inhibitors such as pembrolizumab or nivolumab must be stopped for Grade 3 or higher immune-related events. Holding chemotherapy is a clinical decision that must be documented, communicated to the oncology team, and followed up with a clear plan for restart or discontinuation.
Dose Adjustments for Renal and Hepatic Impairment
Many cytotoxic agents are renally excreted or hepatically metabolised, and organ impairment directly affects drug clearance and toxicity. Carboplatin dosing relies on the Calvert formula, which incorporates eGFR — any change in renal function between cycles must trigger dose recalculation. Capecitabine is dose-reduced at eGFR 30 to 50 mL/min and is contraindicated below 30 mL/min. Methotrexate requires dose reduction in renal impairment and carries risk of life-threatening accumulation. Irinotecan toxicity is increased in hepatic dysfunction and in patients with UGT1A1*28 polymorphism. Pre-cycle renal and hepatic function is not merely routine monitoring — it is a clinical evaluation that directly informs whether treatment can proceed and at what dose.
Stopping Harmful Concomitant Medicines
A structured medication review at every oncology contact must actively identify medicines that become harmful in the context of cancer treatment. ACE inhibitors and ARBs should be held in renal impairment or where nephrotoxic chemotherapy is prescribed. Metformin must be stopped during AKI or when IV contrast is required. Calcium and vitamin D supplements are contraindicated in malignancy-associated hypercalcaemia. NSAIDs increase bleeding risk in thrombocytopenic patients. Warfarin interacts unpredictably with fluoropyrimidines (5-FU, capecitabine) via CYP2C9 inhibition, and LMWH or a DOAC is generally preferred in cancer-associated thrombosis. Herbal medicines including St John's Wort induce CYP3A4 and can dramatically reduce plasma levels of targeted therapies. These are not edge-case concerns — they appear in almost every oncology patient's medicines list.