Analysis of the necessity of serum electrolyte monitoring for up to eight weeks after the completion of anti-epidermal growth factor receptor antibody administration.

Electrolyte disturbances are a known side effect of cetuximab (cmab) and panitumumab (pmab) administration and monitoring is recommended during and for at least 8 weeks after pmab administration. However, the recommended duration of electrolyte monitoring is not stated on the cmab package insert in the EU or Japan and no previous studies have investigated the appropriate monitoring period for cmab and pmab. We retrospectively investigated electrolyte levels in 16 cmab-treated patients and 7 pmab-treated patients between 1 June 2009 and 31 December 2014. The mean minimum levels of serum magnesium, potassium, and calcium were analyzed in these patients before administration (baseline) and in period A (during administration), period B (time of the last administration), period C (from the completion of administration to 4 weeks after), and period D (from 4-8 weeks after administration). Hypokalemia persisted until period D in 1 cmab-treated patient. Hypomagnesemia persisted until period D in two pmab-treated patients and hypokalemia persisted until period D in 1 pmab-treated patient. In addition, the serum magnesium levels in periods A, B, and C in the cmab-treated patients were significantly lower than the baseline level (P < 0.05). In pmabtreated patients, the serum magnesium levels in periods A, C, and D, and the serum calcium levels in periods A, B, and C were lower than the baseline levels (P < 0.05). These findings indicate that it is necessary to monitor electrolyte levels for at least 8 weeks after the completion of administration of cmab or pmab.