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Abstract: TH-PO379

Too Much of a Good Thing Can Be Deadly

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical


  • Brooker, David Michael, Allegheny Health Network, Pittsburgh, Pennsylvania, United States
  • Soundranayagam, Sheahahn V., Allegheny Health Network, Pittsburgh, Pennsylvania, United States
  • Dunmyre, Brandon T., Allegheny Health Network, Pittsburgh, Pennsylvania, United States
  • Khalil, Patricia, Allegheny Health Network, Pittsburgh, Pennsylvania, United States

The treatment of megaloblastic anemia from vitamin B12 deficiency results in an increase in hematopoietic cell production leading to potassium uptake into the cells. This has been reported to cause hypokalemia. It is rare for this to cause arrhythmias leading to cardiac arrest. We present a case of hypokalemia following vitamin B12 administration which resulted in cardiac arrest.

Case Description

A 29 y/o G1P0 female was found to have anemia with workup revealing low vitamin B12 level. She was started on oral B12 which was escalated to IM injections at 33 weeks gestation. She received weekly doses of IM B12 1,000mcg x 4 doses. Serum potassium 4 months prior was 3.9 mmol/L and was not repeated. Ten days after her final dose, at 37 weeks gestation she suffered a cardiac arrest with achievement of ROSC. Workup at the hospital revealed a serum potassium of 2.1 mmol/L which required intensive IV potassium repletion. Along with that she had features of pre-eclampsia. Blood pressure ranged from systolic readings of 110 to 150 mmHg, with serum creatinine ranging from 0.3-0.7 mg/dL, and spot UPCR of 350mg/g. She had spontaneous vaginal birth at 37 weeks gestation. Cardiac workup showed no coronary disease and no evident etiology for the cardiac arrest. Workup for hypokalemia was initiated and no other cause was identified including no endocrinology or genetic conditions. Discharged in stable condition on potassium supplementation with external defibrillator. She was taken off potassium supplementation as outpatient with stable potassium levels and no other cardiac event.


In normal pregnancy, vitamin B12 levels can decline by as much as 30% by the third trimester. Typically recommendations are to replete if symptomatic or with macrocytic anemia. Dangerously low levels of potassium leading to cardiac arrest are possible following vitamin B12 replacement therapy. This is mentioned by the manufacturer. No cases were described in pregnancy. However in a more recent experience, this was found not to be clinically significant. Potassium levels are not routinely checked during parenteral vitamin B12 administration. This raises the question if we should check potassium levels in certain circumstances. Ordering providers should be aware of hypokalemia after vitamin B12 supplementation with consideration of following potassium level after administration especially in pregnancy.