AdvertisementsOverdose of this essential mineral rarely occurs among healthy people by way of consuming rich food sources. Magnesium overdose or toxicity with several symptoms occurs when too much of the mineral is ingested in the form of supplements, antacids and laxatives in a short span of time. It occurs because, the intake through the oral or intravenous route exceeds the renal excretory threshold, thereby building up Mg2+ ions in the serum.
Causes of magnesium overdoseMagnesium overdose with several symptoms, sometimes fatal, occurs when there is renal insufficiency. In such patients, even foods containing high levels of the mineral can lead to its elevated serum levels. In the event of acute renal failure, unmonitored intake of Mg can sometimes be fatal.
Patients suffering from intestinal hypomotility (constipation) take laxatives containing magnesium. In such patients, persisting intestinal hypomotility without evacuation can cause accumulation of laxatives in the gastrointestinal tract as well as its increased absorption into the body causing several overdose symptoms. Certain systemic diseases and syndromes can also cause elevated Mg levels.
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Kutsal E et al reported a case of magnesium overdose caused in a constipated child. The child had normal renal function. To relieve constipation, she was given magnesium hydroxide cathartic tablets for seven days. The serum Mg levels reached 14.9 mg/dL and the child had symptoms of lethargy and hypotension when referred to a hospital. Immediate hemodialysis provided relief from the hypermagnesemia related symptoms. Eclamptic mother who has undergone magnesium sulfate infusion may cause hypermagnesemia symptoms in the newborn.
Magnesium overdose symptomsIn mild overdose, there may not be any immediate observable clinical symptoms and the condition may stay undetected. Depending upon the elevation of serum magnesium, the symptoms may progress in severity. The first symptoms are gastrointestinal. Elevated serum magnesium, functioning as physiologic calcium channel blocker, leads to abnormalities in electrical conduction and nerve-to-muscle transmission, affecting almost all organ systems. Any impairment to the electrical pathways will have neuromuscular, renal, cardiovascular and respiratory manifestations.
Gastrointestinal manifestationsA mild magnesium overdose causes diarrhea which is due to its laxative effects. The laxative effects are due to osmotic activity of unabsorbed Mg salts in the intestine. The patient may also have symptoms like nausea, lack of appetite and vomiting. The affected patient may have abdominal pain, cramps, distension, stomach pain, increased thirst and bloating.
Neuromuscular dysfunctionsThe calcium channel blocking effects cause the malfunction of excitation-contraction coupling of skeletal, smooth, and cardiac muscles. As an effect of magnesium overdose, deep tendon reflexes will appear diminished at serum concentrations of over 2.5 mmol/L and will vanish when levels exceed 5 mmol/L. The impairment of the electrical pathways in skeletal muscles cause neuromuscular symptoms including muscle pain, weakness, fatigue, lethargy, cutaneous flushing, tiredness, joint pain, loss of muscle tone (hypotonia) and hyporeflexia.
Cardiovascular manifestationsThe impairment of the electrical pathways in the smooth and cardiac muscles has several manifestations. Vasodilation, a condition of relaxation of smooth muscles within the blood vessel walls, leads to drop in arterial pressure, cardiac output, and peripheral resistance to blood flow. The immediate effect is the drop in blood pressure (hypotension) and bradycardia (low resting heart rate or pulse rate).
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Another effect of impaired electrical conduction and pacemaker signals is cardiac dysrhythmia (arrhythmia or irregular heartbeat). In severe magnesium overdose, heart block, an impairment of electrical system of the heart, may occur with symptoms like lightheadedness, fainting and palpitations. In extreme conditions, the cardiac electrical activity in patient ceases and asystolic death occurs.
Respiratory and cerebral manifestationsThe hypotonia causes hypoventilation (respiratory depression) and impaired breathing, which in turn cause cerebral hypoxia (reduced oxygen) or hypoxic encephalopathy. Poor oxygen supply to brain and impaired electrical pathways can cause symptoms such as dizziness, fainting, lightheadedness, drowsiness, confusion, sleepiness, visual disturbances, restlessness, anxiety syndromes, loss of consciousness and brain death. In case of extreme magnesium overdose the patient may even develop coma, respiratory arrest and cardiac arrest.
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Chronic magnesium overdose can place a great deal of stress on the kidneys and cause their malfunction. Elevated serum levels of the mineral interfere with the effects of parathyroid hormone, resulting in hypocalcemia. There are several contraindications with certain medications, which is dealt in the topic on magnesium side effects.
Magnesium overdose treatment
- Stopping intake of supplements, antacids and laxatives containing magnesium may resolve conditions connected with mild to moderate overdose.
- In case of magnesium poisoning stomach evacuation (stomach pumping, gastric irrigation, gastric suction or gastric lavage) can stop further absorption of the mineral from the GI tract.
- Administering intravenous fluids increases the serum volume and brings down the relative level of magnesium immediately and also helps in faster excretory clearance of the element by the kidney.
- In patients with renal insufficiency, immediate haemodialysis is the solution.
- Intravenous calcium gluconate is administered to negate the effect of magnesium on the neuromuscular and cardiac functions and reduce the severity of symptoms.
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