Medicines Q&As
Q&A 14.5
Can magnesium sulfate be given subcutaneously?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
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Date prepared: 23rd October 2013
Background
Hypomagnesaemia can arise from a variety of causes. Some of the most common include
gastrointestinal disorders characterised by excessive losses in diarrhoea, stoma or fistula, or
deficiency may occur, for example, as a result of certain drug treatments or in alcoholism (1). The
reference range for plasma magnesium is approximately 0.75 – 1.05 mmol/L (2).
Sometimes it is impossible or inconvenient to use the oral, intravenous or intramuscular routes to
correct magnesium deficiency. This can be the case, for example, in patients with chronic intestinal
malabsorption of magnesium who are regularly admitted to hospital with symptomatic
hypomagnesaemia requiring intravenous replacement. If it were possible to offer patients such as
these regular subcutaneous magnesium, then repeated admissions to hospital could be avoided.
Answer
There is very limited published information available describing the subcutaneous administration of
magnesium sulfate and a wide range of concentrations have been used.
In a 1991 case report a 63-year old patient, who developed severe and persistent hypomagnesaemia
following a total regional pancreatectomy, was successfully treated for 24 months with
subcutaneously administered magnesium sulfate (3). The dose was titrated to magnesium sulfate
14mmol (8ml) and 7ml of sterile water administered subcutaneously via a microinfusion pump over 10
hours overnight. On one occasion two 1-cm dark coloured superficial skin abscesses were reported,
which were attributed to a delayed absorption as a result of the needle being placed too superficially.
No further skin complications occurred and serum magnesium levels were maintained within a low
normal range.
A further case report described a 56-year old woman with a high-output stoma following bowel
resections for Crohn’s disease, who had persistent hypomagnesaemia despite intravenous and
subsequently oral magnesium supplementation (4). She was treated with twice-weekly home
subcutaneous saline (1 litre) and magnesium (4mmol) infusion, together with oral
1α-hydroxycholecalciferol (500 nanograms/day), which maintained her serum magnesium levels. The
infusion rate and duration of treatment are not stated.
In a more recent case report, a 71-year old man with a high-output ileostomy and subsequent
hypomagnesaemia was treated initially in hospital with subcutaneous magnesium sulfate 12mmol in
one litre of saline over 12 hours (5). He was then discharged home and self-administered
subcutaneous infusions of 500ml of saline solution with 3mmol of magnesium sulfate over 6 hours
each day. Serum magnesium levels maintained within the normal range for 137 days after discharge
were reported.
One small study of eight patients with gastrointestinal failure who self-administered overnight
subcutaneous rehydration fluids utilised low concentrations of magnesium sulfate (e.g. 2 – 4mmol
Mg2+ in 500ml to 1 litre) (6). Subcutaneous fluid infusions were administered over 6-12 hours on 3-7
days/week and the initial magnesium sulfate dose was 8-28 mmol/week, which was adjusted
according to plasma magnesium levels. This proved safe and effective.
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Medicines Q&As
In the UK, magnesium sulfate injection is available as a 10%w/v (0.4mmol/ml Mg2+), or 20%w/v
(0.8mmol/ml Mg2+) or 50% w/v (2mmol/ml Mg2+) licensed preparation (7). However, the osmolarity of
magnesium sulfate 10% injection and above is high and may be irritant so should be diluted before
infusion (8). These magnesium sulfate preparations are not, however, licensed for subcutaneous
administration.
An isotonic solution of magnesium sulfate is 6.3% w/v in water (approximately 0.25mmol/ml Mg2+) (9).
It would seem a wise precaution if considering the administration of magnesium subcutaneously, to
start by using isotonic solutions where possible. This would reduce the likelihood of pain or tissue
damage at the injection site. One report has suggested that, since magnesium sulfate is a salt and
may cause skin irritation, it should only be given in the abdominal subcutaneous adipose tissue,
together with site rotation (3). Serum magnesium and electrolyte levels should be monitored regularly
(4).
Summary

Limited evidence suggests that magnesium sulfate may, with caution, be given by
subcutaneous infusion, in individual cases where other routes are impractical or impossible
(3-6).

Only one small study and three case reports have been published and the concentrations of
magnesium sulfate and administration schedules that have been used are variable (3-6).

Since the osmolarity of magnesium sulfate injection is high and may be irritant, the
concentration should be kept as low as possible and ideally should not exceed 6.3%
(approximately 0.25mmol/ml Mg2+).

One report has suggested that, since magnesium sulfate is a salt and may cause skin
irritation, it should only be given in the abdominal subcutaneous adipose tissue, together with
site rotation (3).

Magnesium sulfate injection is not licensed for subcutaneous infusion and use in this way is
therefore the responsibility of the prescriber.

Serum magnesium and electrolyte levels should be monitored regularly (4).

Local policies on the subcutaneous administration of fluids should be consulted, if available.
Limitations
Only three case reports and one small study have described the use of subcutaneous magnesium
sulfate in humans.
There are no data on long-term benefits or harm.
In view of the lack of data, local policies should be consulted where available.
References
1) Joint Formulary Committee. British National Formulary. London: BMJ Group and
Pharmaceutical Press. Electronic edition. Accessed via http://www.bnf.org/ on 1st November
2013
2) Longmore M, Wilkinson I, Turmezei T et al. Oxford Handbook of Clinical Medicine. 7 th Edition.
Oxford University Press;2007, p742
3) McDermott KC, Almadrones LA, Bajorunas DR. The diagnosis and management of
hypomagnesemia: a unique treatment approach and case report. Oncology Nursing Forum
1991; 18(7): 1145-1152.
4) Tsao SKK, Baker M, Nightingale JMD. High-output stoma after small-bowel resections for
Crohn’s disease. Nature Clinical Practice Gastroenterology and Hepatology 2005; 2(12): 604608.
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5) Alfaro Martinez JJ, Botella Romero F, Lamas Oliveira C et al. Severe hypocalcemia
6)
7)
8)
9)
secondary to hypomagnesaemia, successfully treated by self-administered subcutaneous
magnesium. Nutrición Hospitalaria 2009;24:354-356.
Martinez-Riquelme A, Rawlings J, Morley S et al. Self-administered subcutaneous fluid
infusion at home in the management of fluid depletion and hypomagnesaemia in gastrointestinal disease. Clinical Nutrition 2005; 24:158-163.
UKMi Medicines Q&A 210.4 Magnesium sulfate injection: converting between millimoles,
milligrams and percentage w/v. Date prepared 22nd January 2013. Accessed via
http://www.evidence.nhs.uk/search?q=%22Magnesium+sulfate+injection%3A+converting+bet
ween+millimoles%2C+milligrams+and+percentage+w%2Fv%22 on 19th November 2013.
Magnesium sulphate intravenous monograph. Injectable Medicines Guide. Accessed via
http://www.injguide.nhs.uk/ on 1st November 2013.
Wade A (editor). Pharmaceutical Handbook. 19th Edition. London: Pharmaceutical Press;1980
p.257.
Quality Assurance
Prepared by
Kate Pickett, Medicines Q&A Pharmacist (based on earlier work by Dr Simon Wills), Wessex Drug
and Medicines Information Centre, University Hospital Southampton NHS Foundation Trust.
Date Prepared
23rd October 2013
Checked by
Sue Gough (based on the Q&A previously checked by Nicola Watts), Wessex Drug and Medicines
Information Centre. University Hospital Southampton NHS Foundation Trust.
(With thanks to Peter Rhodes, Principal Pharmacist for Technical Services, University Hospital
Southampton NHS Foundation Trust.)
Date of check
18th December 2013
Search strategy
 Embase (via NICE Evidence Search):
 [exp MAGNESIUM CHLORIDE/sc or exp MAGNESIUM/sc or exp MAGNESIUM
SULFATE/sc]
 [exp MAGNESIUM CHLORIDE/ or exp MAGNESIUM/ or exp MAGNESIUM SULFATE/] and
exp SUBCUTANEOUS DRUG ADMINISTRATION/ and exp HYPOMAGNESEMIA/
 [exp MAGNESIUM CHLORIDE/ or exp MAGNESIUM/ or exp MAGNESIUM SULFATE/] and
hypodermoclysis.af
 Medline (via NICE Evidence Search:
 [exp MAGNESIUM CHLORIDE/ or exp MAGNESIUM/ or exp MAGNESIUM SULFATE/] and
[exp INJECTIONS, SUBCUTANEOUS/]
 CINAHL (via NICE Evidence Search):
 [exp INFUSIONS, SUBCUTANEOUS/ or exp INJECTIONS, SUBCUTANEOUS/] and [exp
MAGNESIUM COMPOUNDS/ or exp MAGNESIUM/ or exp MAGNESIUM SULFATE/]
 [exp MAGNESIUM COMPOUNDS/ or exp MAGNESIUM/ or exp MAGNESIUM SULFATE/]
and exp HYPODERMOCLYSIS/
 British Nursing Index (1985 onwards) (via NICE Evidence Search):
 SUBCUTANEOUS.af and MAGNESIUM.af
 MAGNESIUM.af and HYPODERMOCLYSIS.af
 Drugdex. Accessed via http://www.micromedexsolutions.com/micromedex2/librarian
 Electronic Medicines Compendium. Accessed via http://www.medicines.org.uk/emc/
 NICE Evidence. Accessed via www.evidence.nhs.uk
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Medicines Q&As
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British National Formulary. Accessed via www.bnf.org
AHFS Drug Information. Accessed via www.medicinescomplete.com
Martindale. Accessed via www.medicinescomplete.com
Trissel. Handbook on Injectable Drugs. Accessed via www.medicinescomplete.com
Injectable Medicines Guide. Accessed via http://www.injguide.nhs.uk/Home.asp
Technical Services expert
In-house texts
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Available through NICE Evidence Search at www.evidence.nhs.uk