Magnesium

Mechanism of Action

Like other electrolytes, magnesium's role in the body is diverse and complex. Its action mechanism depends on which organ system is involved and its formulation.Physiology of Magnesium

Magnesium is the fourth most common cation in the body. Most magnesium is intracellular; it is the second most common intracellular cation following potassium. Magnesium plays a vital role in over 300 reactions involving metabolism. It involves hormone receptor binding, muscle contraction, neural activity, neurotransmitter release, vasomotor tone, and cardiac excitability. It is necessary to transport potassium and calcium across the cell membrane actively. ATP is dependent on magnesium for proper functioning.[5]

Effects of Magnesium

Gastrointestinal

Oral magnesium promotes defecation via the osmotic retention of fluids. It is also used in over-the-counter antacids.[5]

Cardiovascular

Magnesium acts as a natural calcium channel blocker, a cofactor of the Na-K-ATP pump. Magnesium helps control atrioventricular node conduction. Therefore, hypomagnesemia can cause myocardial excitability, resulting in arrhythmias such as ventricular tachycardia and torsades de pointes.[5]

Neurological system

Magnesium depresses the central nervous system while producing anticonvulsant effects. At neuromuscular junctions, it inhibits the release of acetylcholine, thus blocking peripheral neuromuscular transmission.[5]

Reproductive system

Magnesium is used as a tocolytic during pre-term labor. Magnesium stimulates calcium reuptake by the sarcoplasmic reticulum, which promotes muscle relaxation and vasodilation. For pre-term labor, magnesium decreases the calcium within the uterine muscle.[5]

Musculoskeletal system

Magnesium is a cofactor of parathyroid hormone synthesis. With hypomagnesemia, concurrent hypoparathyroidism ensues. Hypoparathyroidism can lead to decreased calcium and eventually lead to osteopenia or osteoporosis.[5]

Respiratory system

Magnesium administration can cause bronchial smooth muscle relaxation. The cause of smooth muscle relaxation is unclear. It is thought to be either by inhibiting calcium, histamine, or acetylcholine release. There may also be a synergist effect with the concurrent use of beta-agonists.[5]

Hemostasis of magnesium

Roughly 50% of magnesium is located in bone, 25% in muscle, and the remainder in soft tissue, serum, and red blood cells. Like other electrolytes, magnesium can be classified as ionized, protein-bound, or bound to anions. Ionized magnesium has the most biological activity. The intestine, bone, and kidney maintain magnesium homeostasis. Like calcium, magnesium is absorbed through the intestine, stored in the bone, and excreted through the kidneys. Magnesium absorption is inversely proportional to the concentration within the body; if there are low magnesium levels, more magnesium is absorbed.

Administration

Magnesium can be administered in various ways. Dietary intake is the primary source of magnesium for a healthy individual. The recommended daily intake varies with gender and age. Green leafy vegetables, fish, legumes, and whole grains are good sources of magnesium. Magnesium comes in various salts and forms, including magnesium oxide, magnesium citrate, magnesium sulfate, magnesium hydroxide, and magnesium gluconate. Treatment can be via oral magnesium salts or intravenous or intramuscular magnesium sulfate. Intravenous or intramuscular magnesium sulfate is given for severe hypomagnesemia or those unable to tolerate or adhere to oral therapy. Patients with alcohol use disorder are treated empirically to avoid hypomagnesemia. The clinician must increase the dose for patients with renal insufficiency to adjust for the increase in renal loss.[5] The clinician must also address concurrent hypokalemia or hypocalcemia.

Adverse Effects

Adverse reactions are associated with magnesium’s effect on the neuromuscular and cardiovascular systems and can vary depending on the formulation. Effects can include the following:

Serious Adverse Events:

• Cardiovascular collapse
• Respiratory depression or paralysis
• Hypothermia
• Depressed cardiac function
• Pulmonary edema

Common Adverse Events:

• Flushing
• Hypotension
• Vasodilation
• Impaired reflexes
• Abdominal pain
• Diarrhea
• Flatulence
• Nausea/vomiting
• Respiratory depression
• Electrolyte disorders (hypocalcemia, hyperkalemia)
• Hypermagnesemia [9]

Hypermagnesemia can be a serious adverse event, particularly regarding cardiology effects; see the Toxicity section for more information. 

Contraindications

For contraindications, factors to consider are renal function, pregnancy, and neuromuscular disease. It is crucial to assess renal function before giving magnesium. Renal failure can cause decreased magnesium excretion, which can lead to toxicity. Closely monitor magnesium levels in patients with reduced renal function.[2] Patients with neuromuscular disease, such as myasthenia gravis, must be closely monitored to see if they are being given magnesium. Magnesium inhibits the release of acetylcholine, which can cause deterioration. Magnesium is considered class D for pregnancy. Skeletal demineralization, hypocalcemia, and hypermagnesemia are seen with long-term use, more than 5 to 7 days, of magnesium, which is necessary for pre-term labor treatment. There are no contraindications for magnesium supplements with other prescriptions. However, various drugs increase or decrease the concentration of either magnesium or the prescribed medication. Magnesium may be used in pregnancy and lactation; there is no expected risk of fetal or infant harm based on limited data in humans.

Monitoring

Hypermagnesemia may occur from overdose. While administering magnesium, the level of magnesium must be monitored. Serum magnesium levels and those of other electrolytes such as calcium and potassium can be monitored.

Toxicity

Hypermagnesemia: Serum Magnesium Concentration Greater than 2.6 mg/dL

Hypermagnesemia is a potential effect of administering magnesium. If too much magnesium is administered too quickly, hypermagnesemia may ensue. Symptoms include vasodilation causing flushing, hypotension, hyporeflexia, and respiratory depression. With a magnesium concentration above 6 mg/dL, electrocardiogram changes can consist of PR prolongation, widening of QRS, and peaked T waves. Cardiac arrest occurs whenever levels are above 15 mg/dL.[7][9][5] Hypermagnesemia is less common than hypomagnesemia. The most significant cause of hypermagnesemia is renal failure causing increased retention of magnesium. It can also occur in the overuse of magnesium-containing laxatives and antacids.[2] Treatment for hypermagnesemia includes calcium gluconate, diuresis, or dialysis. Maintaining circulatory and respiratory support for those with severe hypermagnesemia is important. Intravenous furosemide is the diuretic of choice, as it increases magnesium excretion.[10][5]

Enhancing Healthcare Team Outcomes

Magnesium is a vital mineral for many bodily functions. However, unless patients are diagnosed with hypomagnesemia, this mineral should not be empirically recommended by the prescribing clinicians, including MDs, DOs, NPs, and PAs. These days, many people consume magnesium supplements because of a false understanding of how to correct the condition. Excessive magnesium intake is not safe either, as it can lead to hypotension, hyporeflexia, and respiratory depression. With a magnesium concentration above 6 mg/dL, electrocardiogram changes can include PR prolongation, widening of QRS, and peaked T waves. Cardiac arrest occurs whenever levels are above 15 mg/dL. When intravenous magnesium is administered, the nurse should constantly monitor the vital signs, especially blood pressure.[10] 

While magnesium is generally safe, given the potential for severe issues in specific cases, the interprofessional team needs to be aware of the patient's supplemental magnesium intake and record such in the patient's health record. This way, the team can make medical decisions based on complete and accurate data. It is incumbent on each interprofessional team member to provide input based on their area of expertise and counsel the patient on the appropriate use of the drug. Pharmacists need to examine the possibility of drug-drug interactions and report to the prescriber as appropriate. An interprofessional approach involving clinicians, mid-level practitioners, pharmacists, and nursing staff collaborating on the activities and openly sharing case information provides the safest and most successful patient care.