RESUMEN
In this article, we present four cases of renal failure secondary to hypercalcaemia which were brought to the attention of our hospital's nephrology team. These happened in the setting of simple medication changes for hypoparathyroidism post-thyroid surgery. These cases have in common minor changes in preparations leading to significant adverse events. In two cases, excipient changes were the only changes identified in the patients' regimen. In all cases, cessation of the offending calcium preparation and treatment with IV rehydration led to a return to baseline creatinine levels. Communicating to patients the importance of consistency in how calcium and vitamin D supplements are taken is crucial in preventing adverse effects. Prescribers should be aware of excipient changes and that these are not always clinically insignificant.