Objectives: Hypomagnesaemia is a common consequence of treatment with cetuximab. Previous studies have reported an all-grade incidence of hypomagnesaemia of 50% and grade 3/4 incidence of 5-24 %. We undertook an audit to examine clinical monitoring for hypomagnesaemia and to determine clinical practice for magnesium  (Mg) replacement

Methods: A 3-year retrospective audit was performed. Ethics Committee approval was obtained. All patients of the Flinders Medical Centre who received cetuximab between 2010 and 2012 inclusive were identified. Medical records were retrieved and clinical databases were accessed. Patients’ Mg levels and methods of treatment of hypomagnesaemia were recorded and analysed.

Results: 35 patients were identified as eligible and 33 were included (medical records not available for 2 patients). These patients received a total of 578 cetuximab infusions. Mg was measured within 7 days prior to treatment for 397 (70%) of the infusions. 20 patients (60%) had a baseline Mg level measured within 14 days prior to their first infusion. 32 patients (97%) had at least one Mg level measured within 30 days following their first infusion. Mg levels were measured at a mean frequency of every 1.7 weeks. The median time to Mg nadir for those who experienced hypomagnesemia was 12 weeks.  The mean Mg level at the time of treatment for all cetuximab infusions was 0.697 mmol/L. Hypomagnesaemia developed in 17 patients (50%).  11 of these 17 patients (65%) received some sort of Mg replacement therapy, whilst 6 were not treated. On average, 4.3 episodes of hypomagnesaemia were encountered before the patients commenced magnesium replacement. There did not seem to be any consistency in the treatment of hypomagnesaemia, with variable doses of magnesium and both oral and intravenous routesof magnesium administration employed regardless of the Mg level.

Conclusion: The monitoring and management of hypomagnesaemia following cetuximab therapy is variable. Validated management pathways need to be developed.