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Chapter: Clinical Pharmacology: Drugs for fluid and electrolyte balance


Magnesium is the most abundant cation in ICF after potassium.



Magnesium is the most abundant cation in ICF after potassium.It’s essential in transmitting nerve impulses to muscle and activat-ing enzymes necessary for carbohydrate and protein metabolism. About 65% of all magnesium is in bone, and 20% is in muscle.


Officiating in the ICF


Magnesium stimulates parathyroid hormone secretion, thus regu-lating ICF calcium levels.


Traffic control


Magnesium also aids in cell metabolism and the movement of sodium and potassium across cell membranes.


A run on magnesium


Magnesium stores may be depleted by:


·                 malabsorption


·                 chronic diarrhea


·                 prolonged treatment with diuretics

·                 nasogastric suctioning


·                 prolonged therapy with parenteral fluids not containing magne-sium


·                 hyperaldosteronism


·                 hypoparathyroidism or hyperparathyroidism


·                 excessive release of adrenocortical hormones


·                 acute and chronic alcohol consumption


·                 drugs, such as cisplatin, aminoglycosides, cyclosporine, and am-photericin B.


Restocking the mineral stores


Magnesium is typically replaced in the form of magnesium sulfate when administered I.V. or in the form of magnesium oxide if given orally.



Magnesium sulfate is distributed widely throughout the body. I.V. magnesium sulfate acts immediately, whereas the drug acts within 30 minutes after I.M. administration. However, I.M. injec-tions can be painful, can induce sclerosis, and need to be repeated frequently.

Metabolism and excretion


Magnesium sulfate isn’t metabolized and is excreted unchanged in urine and stool; some appears in breast milk.



Magnesium sulfate replenishes and prevents magnesium deficien-cies. It also prevents or controls seizures by blocking neuromus-cular transmission.



I.V. magnesium sulfate is the drug of choice for replacement thera-py in symptomatic magnesium deficiency (hypomagnesemia). It’s widely used to treat or prevent preeclamptic and eclamptic sei-zure activity and is used to treat ventricular arrhythmias such as torsades de pointes. It’s also used to treat seizures, severe toxe-mia, and acute nephritis in children.

Drug interactions


Magnesium has few significant interactions with other drugs.


·                 Magnesium used with digoxin may lead to heart block.

·                 Magnesium sulfate combined with alcohol, narcotics, antianxi-ety drugs, barbiturates, antidepressants, hypnotics, antipsychoticdrugs, or general anesthetics may increase central nervous system depressant effects.

·                 Magnesium sulfate combined with succinylcholine or tubocu-rarine potentiates and prolongs the neuromuscular blocking ac-tion of these drugs. (See Adverse reactions to magnesium.)


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