(444) Imatinib-Induced Severe Electrolyte Abnormalities Requiring Critical Care Monitoring

Introduction: Imatinib mesylate , a tyrosine kinase inhibitor, is the first line therapy for chronic myeloid leukemia (CML). It has also proven to be effective in treatment of gastrointestinal stromal tumors (GIST) and idiopathic hypereosinophilic syndrome. We found a case of a patient who developed a very rare side effect of imatinib, severe electrolyte abnormalities including hypophosphatemia, hypocalcemia and hypokalemia requiring critical monitoring.

Description: 78 years old male with past medical history of CML, hypertension, atrial fibrillation, chronic kidney disease presented to the hospital with complaints of numbness and tingling in the face for 1 day. He developed numbness at the tip of his nose that spread to the face including forehead. It was associated with headache and bilateral lower extremity muscle twitching and numbness. He denied fever/chills, visual changes, chest pain, shortness of breath, palpitations, abdominal pain, and bladder/bowel changes. He recently started on imatinib 3 months ago. His vitals showed blood pressure 133/69, pulse 58/min, afebrile. Physical examination showed positive chvostek's sign in the right cheek, numbness in the right facial nerve distribution. Labs showed corrected calcium 5.9mg/dl, potassium 2.4 mmol/l, magnesium 0.5mg/dl, phosphorus 2.4mg/dl. EKG showed sinus bradycardia. He received potassium chloride, magnesium sulfate, and phosphate for electrolytes correction and was admitted to intensive care for close monitoring. Hematology and oncology was consulted, imatinib was discontinued as electrolyte imbalance is a rare adverse effect of imatinib.

Discussion: Imatinib inhibits platelet derived growth factor receptor (PDGFR) BCR-ABL tyrosine kinase gene on Philadelphia chromosome. It has dramatically improved the treatment outcomes for CML. The common side effects include anemia, fatigue, nausea, diarrhea, rash, myalgia, arthralgia, granulocytopenia. However, rare side effects include electrolyte disturbance including hypophosphatemia, hypocalcemia, and hypomagnesemia. The proposed mechanism of electrolyte abnormality is bone remodeling by inhibition of osteoclasts and osteoblastic activity leading to hypophosphatemia and hypocalcemia. It should be taken into account as these imbalances may lead to cardiac arrhythmias.