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Subcutaneous magnesium in the advanced cancer setting
  1. Stephen J Fenning,
  2. Steinunn R Boyce,
  3. Paul Wilson and
  4. Fran Stretton
  1. Victoria Hospice, Victoria Hospital, Kirkcaldy, UK
  1. Correspondence to Dr Stephen J Fenning, Victoria Hospice, Victoria Hospital, Hayfield Road, Kirkcaldy KY2 5AH, UK; s.fenning{at}nhs.net

Abstract

Hypomagnesaemia can arise from a variety of causes but is particularly prevalent in cancer populations. This case report describes a patient with recurrent symptomatic hypomagnesaemia, on the background of advanced ovarian cancer and a high-output ileostomy, who was successfully managed on a daily continuous subcutaneous infusion of magnesium via a syringe pump. There is limited published information on the subcutaneous administration of magnesium and, to our knowledge, this is the first case to report its routine delivery over 24 hours in a syringe pump. This novel but effective approach for administering magnesium can be delivered in the community and can, therefore, prevent repeated hospital admissions for patients with recurrent symptomatic hypomagnesaemia who would otherwise need intravenous replacement.

  • Drug administration
  • Pharmacology
  • Pain
  • Symptoms and symptom management
  • Terminal care

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Case presentation

A 66-year-old woman was admitted to the acute medical unit with drowsiness and reduced oral intake. She was obese and a heavy ex-smoker, with evidence of mild airways obstruction on recent pulmonary function tests. She had had a total abdominal hysterectomy for menorrhagia in her 30s. Her serum magnesium was measured as 0.39 mmol/L but all other blood tests were unremarkable. There was no clinical evidence of sepsis.

Eight months earlier, she had been diagnosed with a high-grade serous papillary carcinoma of probable ovarian origin. One month after this, she was admitted with bowel obstruction. Laparotomy revealed a significant volume of peritoneal disease, particularly in the proximal small bowel mesentery, and she underwent formation of a defunctioning ileostomy. She subsequently received three cycles of palliative carboplatin chemotherapy, achieving some disease response, but treatment had to be discontinued due to persistent chemotoxicity. As her tumour was weakly oestrogen-receptor positive, she was commenced on letrozole as maintenance therapy.

In the seven months following her surgery, she had been recurrently hypomagnaesaemic due to a combination of excessive electrolyte loss from a high-output ileostomy and severe renal wasting of magnesium secondary to the platinum-based chemotherapy regimen. She had been admitted on three separate occasions with symptomatic hypomagnesaemia, typically lassitude with either muscle tremors or paraesthesia, and, each time, had received intravenous magnesium replacement (20 mmol intravenous magnesium sulfate in 500 mL 0.9% NaCl infused at various rates, ranging from 6 to 12 hours) (see table 1).

Table 1

A summary of all admissions involving inpatient treatment of hypomagnesaemia, listed in order of time post ileostomy formation

Between admissions, she was prescribed oral magnesium aspartate sachets but her medication adherence at home was known to be poor. Alternative strategies to manage her magnesium level in the community were explored but were limited by the resource capability of the local health service. For example, during an acute admission in which hypomagnesaemia was incidentally identified, she received intravenous magnesium replacement followed by a successful trial of overnight subcutaneous magnesium (20 mmol in 500 mL 0.9% NaCl over 12 hours) to act, in effect, as a maintenance therapy. Unfortunately, neither the District Nursing Service nor Hospital at Home (a community-based multidisciplinary acute care team) were able to deliver these subcutaneous infusions routinely once she was discharged.

On the evening of this admission, the patient received 20 mmol magnesium sulfate intravenously. The following day, she was feeling better and magnesium levels had risen to 0.81 mmol/L. She was then commenced on a daily continuous subcutaneous infusion of magnesium: 8 mmol magnesium sulfate (4 mL of magnesium sulfate 50% injection) made up to 32 mL with water for injection to provide an isotonic solution, delivered in a 50 mL syringe via a CME T34 (McKinley) syringe pump. The subcutaneous line was placed in the abdomen because, previously, the patient had developed subcutaneous site reactions in her arms.

Magnesium levels remained stable throughout her inpatient stay (0.83 mmol/L on discharge, 6 days later). There were no acute complications associated with delivering magnesium via a syringe pump. Once discharged home, the District Nursing Service visited each day to renew the pump. Bloods were initially checked weekly and then less frequently thereafter. At no point did the patient’s serum magnesium fall below 0.70 mmol/L. She died 2 months after discharge.

Discussion

Magnesium is the second most abundant intracellular ion after potassium and is essential for bone mineralisation, muscular relaxation and neurotransmission. Magnesium deficiency can result from inadequate dietary intake of magnesium, reduced absorption of magnesium from the gastrointestinal tract (e.g. diarrhoea, bowel resection, stoma, fistulae) or increased renal excretion of magnesium, often caused by endocrinopathy or drugs, such as alcohol, diuretics and chemotherapies/immunotherapies. Therefore, although the prevalence of hypomagnesaemia among hospital inpatients has been estimated at 11%, this figure is thought to be greater in cancer populations where many of the aforementioned contributory factors commonly arise.1

Mild or asymptomatic hypomagnesaemia is typically treated by giving oral magnesium. Severe and symptomatic hypomagnesaemia generally requires intravenous magnesium replacement. However, there is very limited published information on the subcutaneous administration of magnesium sulfate. The three published case reports each describe different concentrations of magnesium and different infusion regimens. In 1991, a 63-year-old patient, with persistent hypomagnesaemia following a total regional pancreatectomy, was successfully treated for 24 months with a daily 10 hour subcutaneous infusion of 14 mmol (8 mL) magnesium sulfate and 7 mL of sterile water.2 In 2005, a 56-year-old woman, with a high-output ileostomy after bowel surgery for Crohn’s disease, developed recurrent hypomagnesaemia despite oral and then weekly intravenous magnesium replacement.3 Her levels were eventually maintained on a twice-weekly subcutaneous infusion of saline (1 L) and magnesium (4 mmol), but the authors do not specify the infusion rate or duration of treatment. In 2009, a 71-year-old man with high ileostomy losses following surgery for rectal cancer had his hypomagnesaemia initially corrected with a subcutaneous infusion of 12 mmol magnesium sulfate in 1000 mL saline over 12 hours.4 Once home, he then self-administered a subcutaneous infusion of 3 mmol magnesium sulfate in 500 mL saline over 6 hours each day. His magnesium levels were maintained within the normal range for 137 days.

The only known study examining subcutaneous magnesium replacement included eight patients with permanent short bowel, defunctioning stomas or upper gastrointestinal fistulae.5 Here, patients self-administered 2–4 mmol magnesium sulfate in 500-1000 mL 0.9% saline for 6–12 hours overnight on 3–7 days a week, with a mean initial dose of 8–28 mmol/week. Their weekly dose was titrated according to weight, fluid balance and serum biochemistry, with all patients achieving equilibrium at a total dose of 8–14 mmol/week. Magnesium levels remained within the normal range for the month-long duration of the study.

To our knowledge, ours is the first case in which a continuous subcutaneous infusion of magnesium sulfate (over 24 hours via syringe pump) has been successfully used to maintain serum magnesium levels in a patient with recurrent hypomagnesaemia. As the osmolarity of magnesium sulfate injection is high and may be irritant, it was ensured that the infusion solution was isotonic and delivered into abdominal tissue. Our approach appears to be safe but will need to be evaluated further, in case series or, ideally, in well-designed clinical trials, to become adopted into routine clinical practice.

Conclusions

The daily administration of magnesium by continuous subcutaneous infusion in a syringe pump appears to be an effective means of maintaining serum magnesium levels in patients with recurrent hypomagnesaemia. Importantly, this management can be delivered in the community setting and, therefore, in selected patients, repeated hospital admissions for intravenous magnesium replacement may no longer be necessary.

References

Footnotes

  • Contributors All authors looked after the patient and were involved in the writing of the case report. SF submitted the study.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; internally peer reviewed.