Magnesium Supplementation & Diarrhea

Question: What is the maximum amount of magnesium supplementation one can take before causing diarrhea?

Background Information:

Hypomagnesemia in alcoholism --

• multifactorial -- reduced intake, pancreatic insufficiency, chronic vomiting and diarrhea, urinary wasting
• hospitalized --> often receive IV dextrose --> greater reductions in magnesium concentration

Symptomatic hypomagnesemia -- use IV

Asymptomatic hypomagnesemia -- use oral 

Typical oral repletion dose in patient with normal renal function = 240-1000 mg (20-80 mEq) of elemental magnesium in divided doses

Serum levels rise quickly, intracellular stores take longer to replete --> continue repletion for at least 1-2 days after serum levels normalize

Supplementation: 

Recommended Daily Intake --

320 mg/day = women

420 mg/day = men

Sustained-release formulations minimize renal excretion and therefore allow for the use of lower doses --> minimizes diarrhea

• magnesium chloride
• magnesium L-lactate

Immediate-release 

• magnesium oxide
• magnesium hydroxide (milk of magnesia)

chloride: 143 mg tablet

oxide: 242 mg in 400 mg tablet

hydroxide: 167 mg in 400 mg tablet or 5 mL oral suspension

citrate: 48 mg in 290 mg/5 mL oral solution

gluconate: 27 mg in 500 mg tablet

lactate: 84 mg tablet

*Bold = most likely to cause diarrhea (faster-acting)

• absorption decreases as dietary intake increases
• elderly and CKD reduce absorption
• accumulates with renal insufficiency
• choice of therapy should be determined by severity of symptoms (if present), degree of hypomagnesemia, and renal function

Clinical Answer:

Although there are no specific dosage maximum recommendations relating to a threshold for causing diarrhea, it is well-documented in the literature that sustained-release formulations reduce the risk of causing diarrhea in comparison to an immediate-release formulation. Recommend products like magnesium gluconate, chloride, or lactate vs. citrate, oxide, or hydroxide. Due to cost, it is plausible to try supplementation with magensium oxide first. If not tolerated due to diarrhea, then switch to a more sustained-release formulated product.

References: 

DiPiro J. Pharmacotherapy: A Pathophysiologic Approach, 6th Edition. Chapter 36. 

Yu A. Evaluation and treatment of hypomagnesemia. UpToDate. Goldfarb S (Ed). Accessed on: 10 November 2016.