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Hypo-K+ Equals Hypo-Mg++…Right??

October 31, 2022

Written by Amanda Mathews

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This retrospective single-center study found that hypokalemic patients who received magnesium within 4 hours of their potassium supplementation had no significant difference in time to serum potassium normalization.

Why does this matter?
Hypokalemia is a common electrolyte abnormality that can cause cardiac dysrhythmias, weakness, paralysis, ileus, and other problems if not corrected appropriately. It is frequently recommended to co-administer magnesium with potassium when treating hypokalemia, but there is a dearth of clinical evidence to support this practice.

Don’t want to be in this type of K+ hole…
This retrospective, single-center cohort study was conducted at an academic teaching hospital and Level 1 trauma center Emergency Department. It included adult patients who presented with serum potassium level <3.3 mMol/L and received IV potassium. Outcomes were compared between patients who received either oral or IV magnesium within 4 hours of potassium administration (100 patients in control and intervention group each). The primary outcome was time to normalization of serum potassium level ( ≥3.5 mMol/L).

Patients in the magnesium administration group (MG+) were more likely to have been symptomatic from their hypokalemia and more likely to have had severe hypokalemia (< 2.5 mMol/L). The study found that time to serum potassium normalization, frequency of potassium normalization within 24 hours of treatment, and changes in serum potassium after treatment were all similar between the MG+ and MG- groups. Hypermagnesemia more often occurred in the intervention group (7% vs. 1%, p=0.03); 2g was the median magnesium dose given to these patients.

I’ve been taught that “hypo-K+ = hypo-Mg++.” The patients who got magnesium in this study had lower serum potassium values to start with, potentially contributing to their prolonged time to serum normalization, despite magnesium co-administration. Although the intervention group had more cases of hypermagnesemia, this was not associated with an increase in any negative outcomes. I will continue to give both potassium and magnesium to patients with symptomatic hypokalemia or hypokalemia with EKG changes, although I will likely supplement potassium-only (without magnesium) in asymptomatic patients with mild potassium deficiency (>3.0 mMol/L).

The Effects of Magnesium Coadminstration During Treatment of Hypokalemia in the Emergency Department. J Emerg Med. 2022 Oct 11:S0736-4679(22)00347-X. doi: 10.1016/j.jemermed.2022.06.007. Epub ahead of print.

What are your thoughts?