Medicines Q&As
Q&A 111.1
What oral magnesium preparations are available in the UK and
which preparation is preferred for the treatment and prevention of
hypomagnesaemia?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
Date prepared: 3rd August 2010
Background
Oral magnesium preparations may be given for the treatment of chronic or asymptomatic
hypomagnesaemia in doses adjusted according to individual requirements (1). In acute symptomatic
hypomagnesaemia, rapid replacement therapy with intravenous magnesium salts may be necessary
(1). To prevent the recurrence of hypomagnesaemia in adults, magnesium may be given orally in a
dose of up to 24 mmol daily in divided doses (1,2).
There is no medicine licensed in the UK to be given orally for the treatment of hypomagnesaemia.
This Q&A therefore lists some suppliers of various oral magnesium salts in the UK and aims to review
the evidence for the comparative efficacy and safety of these products for the treatment and
prevention of hypomagnesaemia.
Answer
Evidence
At the time of writing no national guidelines or studies comparing oral magnesium salts for the
treatment or prevention of hypomagnesaemia which evaluated clinical outcomes were identified.
The British National Formulary states magnesium glycerophosphate tablets or liquid are suitable
preparations for oral magnesium supplementation (2).
Bioavailability studies
There are several small studies which have compared the bioavailability of various magnesium
preparations. However, these studies did not look at clinical outcomes in patients with
hypomagnesaemia and were conducted in healthy volunteers.
A small study in 16 healthy volunteers compared four oral magnesium salts and concluded there is a
relatively poor bioavailability of magnesium oxide, but greater and equivalent bioavailability of
magnesium chloride, lactate and aspartate (3).
The relative absorbability and bioequivalence of magnesium amino acid chelate, magnesium citrate
and magnesium oxide were compared with placebo in a randomised double-blind study in 51 healthy
volunteers (4). The study concluded that the organic forms of magnesium (citrate and amino-acid
chelate) are more absorbable than magnesium oxide or placebo as assessed by the 24 hour urinary
excretion after 60 days of daily supplementation (4). Magnesium citrate was found to be the most
bioavailable preparation as it resulted in the greatest serum magnesium concentrations following both
acute and daily supplementation (4). Another small study in 17 healthy volunteers also concluded that
magnesium citrate was more soluble and bioavailable than magnesium oxide (5).
A small study in 3 groups of 8 healthy volunteers found that cumulative urinary magnesium excretion
(a marker for magnesium absorption) was lower with magnesium oxide than with magnesium-Laspartate. However plasma magnesium remained the same throughout the treatment periods (6). The
difference in stool frequency between the groups was not statistically significant (6).
From the NHS Evidence website www.evidence.nhs.uk
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Medicines Q&As
Table 1 Examples of Oral Magnesium Preparations Available in the UK (NB other suppliers may be
available)
Magnesium
(Mg2+) salt and
form
Supplier (Brand)
Licensed status in
UK
Magnesium-Laspartate7,8,9,10
KoRa Healthcare
Ltd
(Magnaspartate®)
Not classified as a
medicine.
Classified as a food
for special medical
purposes
Unlicensed
IDIS World
Medicines
Magnesium
carbonate10,11
Magnesium
citrate10
Magnesium
Hydroxide12,13
Magnesium
glycerophosphate
,10,11,14,15,16,17
Magnesium
lactate10
Magnesium
orotate10
Magnesium
oxide10,18
IDIS World
Medicines OR
Martindale
Pharma
IDIS World
Medicines
GlaxoSmithKline
(Phillips Milk of
Magnesia®)
Special Products
Limited
OR Mitovie
Pharma
(Glysmag®)
IDIS World
Medicines OR
Martindale
Pharma
IDIS World
Medicines
IDIS World
Medicines
Martindale
Pharma
IDIS World
Medicines
Magnesium
IDIS World
Pidolate10
Medicines
Key: X=information not available
Unlicensed
medicine
Unlicensed
medicine
Not licensed for
hypomagnesaemia.
Licensed as an
antacid.
Unlicensed
medicine
Form and
strength of salt
(where
available)
6.5g oral
powder
Mg2+ content in
dosage form
mg
mmol
243.12
10
Granules
121.5
5
615mg tablets
60.8
2.5
Tablets
182.3
7.5
Various forms and strengths
available
1830mg
granules
83mg/ml liquid
295.7
12
34.59
mg/ml
1.424
mmol/
ml
Unlicensed
medicine
Tablets- varying 97
4
quantity of salt
to give the
required
quantity of Mg2+
Liquid - varying
24.25
1mmo
quantity of salt
mg/ ml l/ml
to give the
required
quantity of Mg2+
Various forms and strengths
available
Unlicensed
500mg tablets
47.40
X
Unlicensed
medicine
Unlicensed
medicine
500mg tablets
32.8
1.35
Unlicensed
medicine
Unlicensed
medicine
Made to order in strength required
(e.g.
Magnesium oxide 100mg capsules
containing approximately 57mg
magnesium (2.5mmol))
400mg tablets
241.3
9.93
140mg capsules 84.5
3.48
150mg/ml liquid
X
X
From the NHS Evidence website www.evidence.nhs.uk
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Medicines Q&As
Case Reports
One published case report was identified where a 39 year old patient with hypomagnesaemia due to
malabsorption was given increasing doses of magnesium glycerophosphate, to a maximum of
108mmol of magnesium per day (19). This failed to maintain adequate serum magnesium
concentrations and the patient required several intravenous magnesium “top ups” because of
repeated episodes of symptomatic hypomagnesaemia (19). The patient was changed to magnesium
oxide, equivalent to 67.5mmol of magnesium per day, which maintained her magnesium between
0.58mmol and 0.62mmol/litre and she was asymptomatic (19). The authors comment that they do not
know the reason for this improved absorption in this patient, but suggest magnesium oxide may be
better absorbed than magnesium glycerophosphate in patients with a shortened small bowel (19).
However, in another case report a 65 year old patient with short bowel syndrome and
hypomagnesaemia was given an initial trial of magnesium glycerophosphate (20). This was
insufficient to maintain her serum magnesium levels and she required frequent “top ups” with
intravenous magnesium (20). She was therefore switched to magnesium oxide supplementation but
despite this the frequency of intravenous magnesium “top ups” was not reduced (20).
Adverse effects
Adverse effects of oral magnesium salts include gastrointestinal irritation and watery diarrhoea (1).
Chronic diarrhoea from long term use may result in electrolyte imbalance (1). Parenteral therapy may
be preferred in patients with poor gastrointestinal absorption of magnesium or who are unable to
tolerate oral supplements (usually because they cause diarrhoea) (1). No studies comparing the
adverse effects of oral magnesium preparations were identified.
Summary
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Robust evidence of the superiority of one oral magnesium preparation over another does not
exist; therefore it is not possible to recommend one particular preparation over another on the
basis of efficacy and safety
Large scale clinical outcome studies are needed to compare the different oral magnesium
preparations in patients with hypomagnesaemia
Information from the small studies available suggests there are differences in the
bioavailability of some magnesium salts
Factors affecting the choice of oral magnesium preparation for the treatment or prevention of
hypomagnesaemia may include local availability, patient tolerability, and price.
If one oral magnesium preparation is not effective in raising magnesium levels or causes
adverse effects in a patient it is reasonable to try an alternative oral preparation, if the
patient’s condition allows.
Examples of oral magnesium preparations which are available in the UK are given in Table 1
Limitations
This Q&A is not intended as a guideline for the treatment of hypomagnesaemia. The list of oral
magnesium preparations listed in table 1 is not exhaustive and other preparations may be available.
Disclaimer
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Medicines Q&As are intended for healthcare professionals and reflect UK practice.
Each Q&A relates only to the clinical scenario described.
Q&As are believed to accurately reflect the medical literature at the time of writing.
The authors of Medicines Q&As are not responsible for the content of external websites and
links are made available solely to indicate their potential usefulness to users of NeLM. You
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contain.
See www.ukmi.nhs.uk/activities/medicinesQAs/default.asp for full disclaimer.
From the NHS Evidence website www.evidence.nhs.uk
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Medicines Q&As
References
1. Sweetman S. Martindale: The Complete Drug Reference. Accessed online via:
www.medicinescomplete.com on 20.07.2010
2. Martin J (editor). British National Formulary 59. Accessed online via: www.bnf.org on 22.07.2010
3. Firoz M and Graber M. Bioavailability of US commercial magnesium preparations. Magnesium
Research 2001; 14: 257-262.
4. Walker A, Marakis G, Christie S and Byng M. Mg citrate found more bioavailable than other Mg
preparations in a randomised double-blind study. Magnesium Research 2003; 16: 183-191.
5. Lindberg J, Zobitz M, Poindexter J and Pak C. Magnesium bioavailability from magnesium citrate
and magnesium oxide. J Am Coll Nutr 1990; 9: 48-55.
6. Muhlbauer B. Schwenk M, Coran WM et al. Magnesium-L-aspartate-HCL and magnesium-oxide:
bioavailability in healthy volunteers. Eur J Clin Pharmacol 1991; 40: 437-438.
7. Martin J (editor). British National Formulary for Children 2010-2011. Accessed online via
www.bnfc.org on 20.07.2010
8. Personal Communication with Medicines Information. KoRa Healthcare Ltd. 23.07.2010
9. Product Information for Magnaspartate®. August 2007 Supplied by KoRa Healthcare Ltd
23.07.2010
10. Personal Communication with Medicines Information, IDIS World Medicines. 27.07.2010
11. Personal Communication with Medicines Information, Martindale Pharma.28.07.2010
12. Summary of Product Characteristics - Phillips Milk of Magnesia. GlaxoSmithKline Consumer
Healthcare Ltd. Accessed via http://emc.medicines.org.uk/medicine/17293/SPC/Phillips’ Milk of
Magnesia/ on 26.07.2010 [date of revision of the text 20.07.2009]
13. Personal Communication with Medicines Information. GlaxoSmithKline Consumer
Healthcare.23.07.2010 and 26.07.2010
14. March, G.A. Magnesium Glycerophosphate 4mmol Chewable Tablets Data Sheet. 15 August
2006. Supplied by Special Products Limited 20.07.2010
15. Magnesium Glycerophosphate Oral Liquid 1mmol in 1ml sugar-free liquid. Supplied by Special
Products Limited 20.07.2010.
16. Personal Communication Mitovie Pharma. 28.07.2010.
17 Personal Communication Mitovie Pharma. 29.07.2010.
18. Personal Communication with Medicines Information, Martindale Pharma.21.07.2010
19. Ross JR, Dargan PI, Jones AL and Kostrzewski A. A case of hypomagnesaemia due to
malabsorption unresponsive to oral administration of magnesium glycerophosphate, but responsive to
oral magnesium oxide supplementation. Gut 2001; 48: 857-858.
20. Arasaradnam R and Bolton R. Hypomagnesaemia due to malabsorption is not always responsive
to oral magnesium oxide supplementation alone. Gut 2002; 50: 897-900.
Quality Assurance
Emma Templeman, South West Medicines Information, Bristol
Date Prepared
3rd August 2010
Checked by
Julia Kuczynska, South West Medicines Information, Bristol
Date of check
4th August 2010
From the NHS Evidence website www.evidence.nhs.uk
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Medicines Q&As
Search strategy
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Medline
 exp MAGNESIUM AND exp MAGNESIUM COMPOUNDS AND exp MAGNESIUM
DEFICIENCY
 (Magnesium and glycerophosphate).ti,ab
 exp MAGNESIUM DEFICIENCY AND exp ADMINISTRATION, ORAL
 exp MAGNESIUM OXIDE OR exp MAGNESIUM HYDROXIDE AND exp
MAGNESIUM DEFICIENCY
Embase
 exp MAGNESIUM AND exp MAGNESIUM DEFICIENCY AND exp
HYPOMAGNESEMIA
 exp HYPOMAGNESEMIA OR exp MAGNESIUM HYDROXIDE OR exp
MAGNESIUM OXIDE AND exp ORAL DRUG ADMINISTRATION
 exp GLYCEROPHOSPHATE, MAGNESIUM OR (Magnesium and
glycerophosphate).ti,ab
 exp MAGNESIUM AND exp GLYCEROPHOSPHATE
Micromedex (magnesium monograph)
Cochrane Library “magnesium”, “hypomagnesaemia”
In-house databases and resources
Manufacturers/suppliers:
 Martindale Pharma, email, 20.07.10, 21.07.10, 28.07.2010
 Special Products, email 20.07.2010
 GlaxoSmithKline Consumer Healthcare 23.07.10 and 26.07.2010
 KoRa Healthcare Ltd, email, 23.07.2010
 IDIS World Medicines, email 27.07.2010
 Mitovie Pharma, email 28.07.2010, 29.07.2010
 University College Hospital NHS Foundation Trust, email 28.07.2010
Internet Search
 BNF 59, BNFC 2010-2011 “magnesium”, “hypomagnesaemia”
 Electronic Medicines Compendium “magnesium”
 Medicines Complete (Martindale and AHFS) “magnesium”
 Clinical Knowledge Summaries “magnesium”, “hypomagnesaemia”
 National Electronic Library for Medicine “magnesium”, “hypomagnesaemia”, “magnesium
glycerophosphate”, “magnesium oxide”
 NICE “magnesium”, “hypomagnesaemia”
 Google Scholar “oral magnesium preparations and hypomagnesaemia” and “comparison
of oral magnesium preparations”
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From the NHS Evidence website www.evidence.nhs.uk
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