Q&A 14.6
Can magnesium sulfate be given subcutaneously?
Prepared by UK Medicines Information (UKMi) pharmacists for NHS healthcare professionals
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Date prepared: 1st August 2016
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 theseregular 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 12mmolin 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 andthe initial magnesium sulfate dose was 8-28 mmol/week, which was adjusted according to plasma magnesium levels. This proved safe and effective.
A conference abstract has been published of a retrospective review of 21 patients who received subcutaneous infusions of saline withadded magnesium (7). A 10 year review of medical, dietetic and pharmacy records of patients receiving home subcutaneous fluids was conducted by analysing an “Intestinal Failure” database. Patients had hypomagnesaemia due to a variety of reasons including Crohn’s/Ulcerative colitis, surgical complications and mesenteric infarction. Patients received varying doses of magnesium (mean 21 ± 9.8 (8–40) mmol per week) and fluid (Mean infusion volume was 4 ± 2.1 (0.5–7) litre/week)which were self-administered. In most patients this treatment was well tolerated and treatment continued for longer than one year. Stopping of subcutaneous fluids was most commonly due to a failure of the subcutaneous tissues to accept the infusion fluid, but eight patients were continuing on treatment at the time of the review.
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 (8).However, the osmolarity of magnesium sulfate 10% injection and above is high and may be irritant so should be diluted before infusion (9).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+) (10). 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.
Published evidence appears to be limited to small studies and case reports, and the concentrations of magnesium sulfate and administration schedules that have been used are variable.
Sincethe 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.
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.
Local policies on the subcutaneous administration of fluids should be consulted, if available.
Limitations
Evidence for the use of subcutaneous magnesium sulfate in humans is limited and of poor quality. There are limited 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 on 1stAugust 2016
2)Longmore M, Wilkinson I, Turmezei T et al. Oxford Handbook of Clinical Medicine. 7th 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): 604-608.
5)Alfaro Martinez JJ, Botella Romero F, Lamas Oliveira C et al. Severe hypocalcemia secondary to hypomagnesaemia, successfully treated by self-administered subcutaneous magnesium. Nutrición Hospitalaria 2009;24:354-356.
6)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 gastro-intestinal disease. Clinical Nutrition 2005; 24:158-163.
7)Small M, Brundrett D, Nightingale J, PWE-235 Long term subcutaneous saline and magnesium administration in patients with a short bowel. 10 year outcomes. Gut 2015;64:A315. Available via
8)UKMi Medicines Q&A 210.5 Magnesium sulfate injection: converting between millimoles, milligrams and percentage w/v. Date prepared 26th May 2016. Accessed via on 1st August 2016
9)Magnesium sulphate intravenous monograph. Injectable Medicines Guide.Accessed via 1st August 2016.
10)Wade A (editor). Pharmaceutical Handbook. 19th Edition. London: Pharmaceutical Press;1980 p.257.
Quality Assurance
Prepared by
Joshua McKie, (based on earlier work by Dr Simon Wills),Southampton Medicines Advice Service, University Hospital Southampton NHS Foundation Trust.
Date Prepared
1st August 2016
Checked by
Sam Owen,Southampton Medicines Advice Service. 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
10th August 2016
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 OVID):
- [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
- Electronic Medicines Compendium. Accessed via
- NICE Evidence. Accessed via
- British National Formulary. Accessed via
- AHFS Drug Information. Accessed via
- Martindale. Accessed via
- Trissel. Handbook on Injectable Drugs.Accessed via
- Injectable Medicines Guide. Accessed via
- Technical Services expert
- In-house texts
1
Available throughNICE Evidence Search at