Download magnesium supplements

DECEMBER 2011
MAGNESIUM SUPPLEMENTS
M
agnesium is an essential mineral present in every magnesium deficiency, including:
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diarrhoea
cell type in the body. Magnesium acts as a necessary
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vomiting
activator of around 300 different enzymes and plays
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steatorrhoea
a central role in metabolism and muscle function.
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alcoholism
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sprue
Magnesium (Mg) salts are available in various supplements
as orotate, amino acid chelate, citrate, oxide, phosphate;
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vomiting
all with differing amounts of elemental magnesium and
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short bowel syndrome
differing absorption and bioavailability.
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inflammatory bowel disease
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chronic pancreatitis
Magnesium aspartate (MagMin) is available on the PBS for
patients with documented hypomagnesaemia. It is available Causes of Magnesium Excess
as a 500mg tablet containing 37.4mg of Mg.
Raised serum magnesium levels can occur with excessive
use of vitamin products, antacids and laxatives in patients
Role in the Body
with chronic kidney disease.
Magnesium is responsible for a large number of processes in
the body, including the following:
Hypermagnesaemia may also occur with dehydration and
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energy metabolism
diabetic ketoacidosis. Other causes include hypothyroidism,
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glucose utilisation
hypoparathyroidism and Addison’s disease.
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protein synthesis
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fatty acid synthesis and breakdown
Signs and Symptoms
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muscle contraction
Hypomagnesaemia
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almost all hormonal reactions
Many people with low serum magnesium have no symptoms,
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maintenance of cellular ionic balance
whilst some may complain of non-specific symptoms like
nausea, tiredness, lethargy or mental confusion.
Magnesium is often suggested to be taken with calcium
supplements and many products contain amounts of Patients with severe hypomagnesaemia often have coexistent
both minerals. Magnesium affects calcium homeostasis. hypokalaemia and hypocalcaemia, which can contribute to
Impaired parathyroid hormone secretion associated with potentially life-threatening events such as tetany, seizures
hypomagnesaemia may also cause hypocalcaemia.
and cardiac arrhythmias, and may not be easily corrected
without magnesium supplementation. Low magnesium
People with low magnesium levels may have low plasma levels are associated with prolongation of the QT interval
calcium that remains refractory to calcium supplementation and associated risk of ventricular arrhythmias.
until the magnesium deficiency is corrected.
Muscular symptoms of magnesium deficiency include
The normal range for serum magnesium is 0.7-1.0mmol/L. muscle tremor, ataxia, tetany, and cramps.
Magnesium is not included in routine electrolyte testing.
When magnesium concentrations are altered, serum calcium Other symptoms include anorexia, insomnia, depression,
and potassium should also be checked.
hyperirritability and excitability.
Dietary Sources
Hypermagnesaemia
Dietary sources of magnesium include whole grain cereals, Mild hypermagnesaemia (serum Mg 1-2mmol/L) is
green leafy vegetables, legumes, soybeans, nuts, dried fruit, associated with bradycardia, flushing sweating, sensation of
warmth, nausea and vomiting.
animal protein and seafood.
The minimum recommended daily intake of magnesium for At levels around 2mmol/L deep tendon reflexes disappear
and muscle weakness occurs.
adults is 0.25 mmol (6 mg)/kg body weight.
As levels increase, respiratory distress and asystole (absence
A number of gastrointestinal conditions may lead to of heartbeat or cardiac arrest) may occur.
Causes of Magnesium Deficiency
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Shingles, continued
Drug-Induced Hypomagnesaemia
Hypomagnaesemia may occur with use of the following
medications:
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loop diuretics (frusemide, bumetanide, ethacrynic acid)
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thiazide diuretics (chlorothiazide, indapamide, hydrochlorothiazide)
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digoxin
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cyclosporin
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tacrolimus (Prograf)
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foscarnet (Foscavir)
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cisplatin
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alcohol
PPI Use
Recently, it has been suggested that use of protonpump inhibitors (PPIs) (e.g. omeprazole, esomeprazole,
pantoprazole, lansoprazole, rabeprazole) are associated
with magnesium depletion.
There have been case reports of magnesium deficiency with
PPI therapy, usually after long-term use and not associated
with the dose of the PPI.
No studies have investigated the use of a magnesium
supplement to prevent magnesium deficiency during PPI
therapy.
Magnesium supplementation with continued PPI use will
not always resolve the deficiency, even after months of
use. Stopping the PPI usually restores magnesium levels
rapidly (generally within 1 to 2 weeks) without the need for
magnesium supplementation.
The US FDA recommends that serum magnesium levels
should be checked before initiating patients with PPIs for
long-term therapy (generally 1 year or longer) and when the
drugs will be administered with other agents that can cause
low magnesium levels, such as diuretics or digoxin.
The Australian Medicines Safety Update cautions prescribers
should be vigilant to the potential risk of hypomagnesaemia
in patients requiring long-term PPI treatment, and suggests
that patients developing hypomagnesaemia may require PPI
discontinuation.
Leg Cramps
Magnesium supplements, often in combination with
calcium, have been suggested for treatment of leg cramps,
but there is poor evidence to support its use.
Magnesium appears to be ineffective in non-pregnant
people with leg cramps. Trials have shown no significant
difference between placebo and magnesium in doses of
900mg magnesium citrate twice daily or 1830mg at night.
There is better evidence for the effectiveness of magnesium
for women with pregnancy-associated cramps and in people
who have an actual deficiency of serum magnesium (e.g.
long term diuretic therapy, often associated with low serum
potassium as well).
© Manrex Pty Ltd (ABN: 63 074 388 088) t/as Webstercare - 2011
Treatment
Treatment of low serum magnesium levels should start with
identifying possible underlying causes.
Recommended doses of various magnesium salts vary.
Magnesium aspartate 500mg (MagMin) contains 1.65mmol
Mg ion per tablet and is prescribed at 2 to 4 tablets per day.
At higher doses it is likely to cause diarrhoea.
Side Effects
The most common side effect of magnesium is diarrhoea,
which is not surprising as magnesium sulphate (Epsom
Salts) is a saline laxative used to manage constipation.
Hypermagnesaemia can occur with excessive or unnecessary
intake or with renal insufficiency.
Magnesium supplementation is contraindicated in renal
failure and heart block.
Drug Interactions
Magnesium supplements can also affect the absorption
of certain medicines (including tetracycline and
fluoroquinolone antibiotics and bisphosphonates used for
osteoporosis) so they need to be taken at least 2 hours apart
from these other medicines.
Summary
Magnesium is an essential mineral with a wide range of
biological functions. The need for magnesium supplements
should be assessed carefully in older residents with renal
insufficiency. The recent suggestion that people taking
PPIs should routinely take magnesium supplements is not
supported by the current best available evidence.
Numerous drug interactions occur with magnesium
supplements, so a Residential Medication Management
Review (RMMR) is suggested to identify and manage
drug interactions and to determine the appropriateness and
ongoing need for supplementation.
References
Medicines Safety Update Volume 2, Number 3, June 2011
Australian Prescriber 2007;30:102-5.