Introduction—Oral and intravenous replacement of minerals such as magnesium and calcium are usually straightforward in clinical practice, the choice generally being governed by the preparation most readily available. There are very few data comparing efficacy and absorption profiles of different magnesium salts. This case report highlights the importance of considering alternative preparations of oral magnesium salts in patients who appear unresponsive to one preparation, rather than moving on to chronic intravenous therapy via a Hickman line. In the case of patients with small bowel shortening, the use of magnesium oxide should be considered.

Case report—A 39 year old Jamaican woman presented with a three day history of paraesthesia and cramps in her hands and feet. Her past medical history included an emergency laparotomy for a septic abortion resulting in extensive resection of both the small and large bowel, ileostomy formation, a left nephrectomy, and a hysterectomy. This surgery had been performed 15 months previously in Jamaica. She had recently begun to pass increasing volumes of liquid secretions into her ileostomy, up to 4–8 litres/day.

On examination she was clinically dehydrated with positive Trousseau's and Chovstek's signs but neurological examination was otherwise normal. The stoma was functioning but copious amounts of clear stomal fluids were noted to be pouring from it. Initial blood tests revealed a normochromic normocytic anaemia (haemoglobin 11.8 g/dl). Renal function was abnormal (sodium 140 mmol/l, potassium 3.2 mmol/l, urea 9.5 mmol/l, creatinine 248 nmol/l) and she had a low corrected calcium (1.9 mmol/l), …