Magnesium Dosing Based On Levels - Treatments Based On Severity (2024)

Magnesium Dosing

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Magnesium
(RDA) of magnesium is 4.5mg/kg which is a total daily allowance of 350-400 mg foradult men and 280-300 mg for adult women. During pregnancythe RDA is 300 mg and during lactation the RDA is 355 mg.Dave's tip: Generally donot exceed ~40meq (490mg elemental Mg++)/day with oralsupplements to reduce incidence of diarrhea.
ProductAmount needed toobtain ~40 meq of Mg++/day
MgOxide 400 mg2 tablets
MagGluconate 500 mg~17 tablets
MgChloride (Slow-Mag®), 535 mg7.5 tablets
MgHydroxide (MOM) (1200 mg / 15 mL)(500mg Mg2+/15ml)15 ml
[Oral absorption isvariable - 20 - 50% of an oral dose isabsorbed] [aggressive oralsupplementation can lead to diarrhea]
Cathartic dose: 80-160 meq Mg/day.
INTRAVENOUS MAGNESIUMREPLACEMENT:
For Mg levels < 1.2 mg/L or symptomatic orpatient unable to take oral.
(~1 gram IV/hour)

SYMPTOMATIC/ASYMPTOMATIC
WEIGHT OR Mg < 1.2 mg/dl AND Mg > 1.2 mg/dl
< 50 kg 2-3 gm Mg Sulfate1-2 gm Mg Sulfate
>50 kg 3-4 gm Mg Sulfate2-3 gm Mg Sulfate

Additional doses of 1-2 gms/dayof Mg sulfate may be required for several days if thepatient has not previously been receiving magnesium.Renal insufficiency (CLcr <20ml/min) may require lower doses of magnesium. Cautionshould be used when replacing magnesium in any patient withrenal insufficiency.

MAXIMUM CONCENTRATION: 1 gmin 10 ml D5W or NS
MAXIMUM INFUSION RATE: 1 gm over 7 minutes (150mg/min)
(Requires ECG monitoring; cases involving potentially lethalventricular arrhythmias may require higher doses under closemedical supervision.)

Magnesium
Serum magnesium: 1.5-2.5 mg/dL
(MW: 24.3)Overview Dietary Sources: Average diet provides a daily Mg intake rangingform ~17 to ~ 50 mEq ( 200 - 600 mg). Mg is ubiquitous in food, but itis particularly abundant in dairy products, bread and cereals,vegetables (specially the leafy types), meat, and nuts (speciallyalmonds).Mg++is an important ion that is required by the human body in relativelylarge amounts. It is essential for the optimal function of over 300 keyenzymes involved in energy transformation, protein synthesis and nucleicacid metabolism. It is also essential for the stability and normalfunction of the cell membranes of excitable tissues. Thus, Mgabnormalities can have profound effects on neuromuscular transmissionand cardiac conduction. Also, a normal body Mg content is necessary forthe maintenance of electrolyte balance particularly for Ca++andK+.
Transplant patients are particularly prone to the development of Mgdeficiency due to a direct effect of tacrolimus and cyclosporine on therenal tubules which results in enhanced urinary Mg loss.

Distribution and Balance
Average body Mg content is about 1000 mmoles (14 mmoles / kg of bodywt), of which ~50% resides in soft tissues and the remainder in bones.The extracellular space contains <1% of total body Mg. The plasma Mglevel normally varies within a relatively wide range (1.5 - 2.5 mEq/L).Clinical laboratories typically measure total plasma Mg, of which ~30%is bound to plasma proteins, ~ 20% is complexed with such ions asphosphate and citrate, and ~50% exists in the ionized (physiologicallyactive) state. Due to the relatively low protein binding, variations inthe plasma protein level have little influence on the total plasma Mgconcentration. This is unlike the case plasma calcium of which ~45% isprotein-bound. To correct for low plasma protein levels:

Corrected Calevel = Actual Ca level + 0.8 (4 - Alb).
Corrected Mg level = Actual Mg level + 0.08 (4 - Alb)

Although serum Mg may not accuratelyreflect the overall body Mg balance, clinical symptoms of Mg deficiencycorrelate well with serum Mg. Levels < 1.0 mEq/L usually indicatesignificant total body Mg depletion. However, the severity of thesymptoms among patients with similar degrees of hypomagnesemia varywidely. The so-called Mg retention test should not be used in patientswith renal impairment or in transplant patients receiving cyclosporineor tacrolimus which cause urinary Mg wasting.
Mg balance is primarily a renal function (Mg intake does not appear tobe regulated). The average diet provides 20 - 30 mEq daily, but the netabsorption is only about 7 mEq. The kidneys normally excrete an equalamount in order to maintain Mg balance. However, in the presence of Mgdeficiency urinary Mg excretion can be reduced to a minimum of about 2mEq/day. Renal Mg reabsorption takes place primarily in the proximaltubule (30% of the filtered load) and the thick ascending limb ofHenle's loop (65%). Overall renal reabsorption appears to be saturable,so that a higher Mg intake results in a proportional increase urinaryexcretion. For this reason, it is difficult for patients with normalrenal function to develop hypermagnesemia.

Causes of hypomagnesemia
  1. GI problems
    • Diarrhea, NG suction, fistulas,etc
    • Poor intake (as in alcoholics)
    • Poor absorption (malabsorption,ileal bypass, etc]
  2. Renal Losses
    • Acute alcohol consumption.
    • Osmotic or saline diuresis
    • Primary hyperaldosteronism
    • Hypercalciuric disorders
    • Tubulo-interstitialnephropathies
    • Drugs: diuretics,aminoglycosides,
      cyclosporine A, tacrolimus, cis-platinum, etc.
    • Primary Renal Mg Wasting
  3. Internal Redistribution (fromECF to ICF)
    • IV administration of glucose oraminoacids (TPN)
    • Treatment of diabeticketoacidosis (DKA)
    • Pancreatitis
Symptoms of hypomagnesemia
  1. Neural and Neuromuscular:
    Neural and neuromuscular abnormalities are the most common clinicalsigns of hypomagnesemia. Lowered excitability threshold may bemanifested as irritability, psychosis, esophageal spasms (leading todysphagia), and convulsions. Neuromuscular manifestations includetremor, fasciculations, and tetany. The latter occurs almostexclusively in presence of hypocalcemia.
    Chronic, whole-body Mg depletion may be associated with lethargy,poor appetite, nausea, muscle cramps, paresthesias, and mentalabnormalities (irritability, confusion, disorientation, etc.).
  2. Cardiovascular
    • ECG changes: Prolonged PR & QTintervals and flattening of the T waves.
    • Ventricular dysrhythmias:Premature contractions, tachycardia, and fibrillation. Theseoccur almost exclusively in patients receiving digoxin therapybecause both digoxin and hypomagnesemia promote the loss of Kfrom myocardial cells. Thus, hypomagnesemia, like hypokalemia,predisposes patients to digitalis toxicity.
  3. Metabolic
    Although an acute fall in plasma Mg tends to stimulate the releaseof parathormone (PTH), chronic hypomagnesemia has the oppositeeffect, resulting in hypoparathyroidism and hypocalcemia. Also,hypomagnesemia is associated with target-tissue resistance to theactions of PTH. Correction of the hypocalcemia induced by Mgdeficiency requires the repletion of Mg stores as an essential firststep.

    Because Mg++ is necessaryfor the activation of the Na-K-ATPase, Mg deficiency is almostalways associated with intracellular K+ depletion.Also, Mg depletion induces renal K + loss possibly byinhibiting K + reabsorption in the proximal tubules. Thehypokalemia associated with Mg deficiency can be correctedonly through the administration of both ions.

Magnesium Products
Products
Note: Oral magnesiumis not generally adequate for repletion in patients withserum magnesium concentrations <1.5 mEq/L (1.2 meq/L)?
Magnesium hydroxide (Milk of Magnesia): Dosing (Adults): Laxative ( Onsetof action: Laxative: 4-8 hours): Oral:> 12 years: 30-60 mL/dayor in divided doses. Antacid: Oral: 5-15 mL up to 4times/day as needed. RenalInsufficiency: Patients in severe renal failureshould not receive magnesium due to toxicity fromaccumulation.
Magnesium oxide: Mag-Ox ®400, Uro-Mag®. Dosing (Adults): Dietary supplement: Oral:20-40 mEq (1-2 tablets) 2-3 times/day. Product labeling:Mag-Ox 400®: 1-2 tablets daily with food ( Do nottake more than 2 tablets in a 24-hr period, except under theadvice and supervision of a physician.) Uro-Mag®:1-2 tablets 3 times/day with food.
Magnesium gluconate:Magonate® : Dietary supplement: Oral: 54-483 mg/day individed doses. Absorption: Oral: 15% to 30%.
Slow-Mag: enteric-coatedtablet - 64 mg elemental magnesium and 106 mg elementalcalcium. Magnesium chloride formulation that isenteric-coated to help prevent the stomach upset commonlyassociated with oral magnesium supplements. Tablets providemagnesium chloride for increased absorption versus magnesiumoxide. Dosing: dietary supplement: take 2 tabletsdaily or as directed by a physician.

Magnesium Tables (formulations)
Oral Supplementation
[Oral absorption is variable - 20 - 50% of an oral dose isabsorbed]
[aggressive oral supplementation can lead todiarrhea]
Mag Oxide, 400mg (Mag-Ox®)241.3 mg (20.1mEq)
Uro-Mag® cap140 mg(84.5 mg) 6.93mEq
Mag Gluconate,500 mg27 mg (2.25mEq)
Mag Gluconate,liquid (Magonate)54 mg (4.5mEq) per 5mL
Mg Chloride(Slow-Mag®), 535 mg64 mg (5.33mEq)
Mg Hydroxide(MOM) (1200 mg / 15 mL)
(500mg Mg2+/15 ml)
166.7 mg (13.7mEq) per 5 mL.
(start with 5 mL tid = 41 meq)
MgL-Aspartate HCl (Maginex)615 mg (5 mEq)/ tablet
1230 mg (10mEq) / packet
Mg lactate (Mag-TabSR) 84 mg (7 mEq)
(start with 14 mEq bid)
IV
Exists as magnesium sulfate heptahydrate - MgSO4.7H2OMW=246.47Calculations:(1gram MgSO4 (2ml of 50% soln)/246.47) x 1000= 4.057 or ~4.06 mmol x valence (2) = 8.12 meq.(contains 10% elemental magnesium)
Magnesium SaltM.Wt.% MgmEq/g
Sulfate [MgSO4.7H2O]246.5108.1
Chloride [MgCl2.6H2O]203.2129.8
Oxide [MgO]40.36049.6
Hydroxide [Mg(OH)2]58.34234
Citrate4511613
Gluconate [.2H2O]4505.44.5
Lactate202.5129.8
L-Aspartate HCl245.99.98.1
(1) Flink EB. Magnesium deficiency. Etiology and clinical spectrum.Acta Med Scand Suppl 1981;647:125-37

"The documentation of normal renal function is absolutely necessaryfor maximum doses. The order of magnitude of dose is 1.0 meq Mg/kg onday 1, and 0.3 to 0.5 mEq/kg per day for 3 to 5 days. In emergenciessuch as convulsions or ventricular arrhythmias, a bolus injection of1.0 gm (8.1 meq) of MgSO4 is indicated. Therapy of Mg deficiency inthe presence of renal insufficiency requires smaller doses andfrequent monitoring. Complete repletion occurs slowly."
(2) Abbott LG, Rude RK. Department of Endocrinology, LAC+USC MedicalCenter, Los Angeles 90033. Clinical manifestations of magnesiumdeficiency. Miner Electrolyte Metab 1993;19(4-5):314-22.

(3) Berkelhammer C, Bear RA. A clinical approach to commonelectrolyte problems: 4. Hypomagnesemia. Can Med Assoc J 1985 Feb15;132(4):360-8.

(4) DiPalma JR. Magnesium replacement therapy. Am Fam Physician 1990Jul;42(1):173-6

(5) al-Ghamdi SM, Cameron EC, Sutton RA. Magnesium deficiency:pathophysiologic and clinical overview. Am J Kidney Dis. 1995Jun;25(6):973. //
Am J Kidney Dis 1994 Nov;24(5):737-52.

(6) Tso EL, Barish RA. Magnesium: clinical considerations. J EmergMed 1992 Nov-Dec; 10(6):735-45.

(7) Kingston ME, Al-Siba'i MB, Skooge WC. Clinical manifestations ofhypomagnesemia.
Crit Care Med 1986 Nov;14(11):950-4 .

(8) Whang R, Hampton EM, Whang DD. Magnesium homeostasis and clinicaldisorders of magnesium deficiency. Ann Pharmacother 1994Feb;28(2):220-6.

Magnesium Dosing Based On Levels - Treatments Based On Severity (2024)

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