Successful management of primary hypomagnesaemia with high-dose oral magnesium citrate: a case report

We report a 40-d-old female infant who presented to our clinic with afebrile generalized convulsive episodes due to severe hypomagnesaemia with secondary hypocalcaemia. Laboratory investigations revealed mild hypoparathyroidism, which was to return normal following magnesium (Mg) treatment, and normal fractional renal excretion of Mg (0.8%). After the diagnosis of primary hypomagnesaemia was established, the patient was discharged with oral Mg subcarbonate and intramuscular Mg sulphate. On regular follow-up until the age of 4 y, the child was asymptomatic. Mean serum calcium levels remained normal, while mean serum Mg levels remained subnormal. During this 4-y period, oral Mg dose was gradually increased while the doses and frequency of administration of parenteral Mg were decreased. Additionally, oral Mg subcarbonate was switched to Mg citrate because of its side effects. Finally, parenteral Mg was discontinued as the dosage of oral Mg supplementation reached a level of 90 mg/kg/d elemental Mg citrate, without any gastrointestinal side effects. Some screening tests were performed to evaluate the complications of chronic hypomagnesaemia. Bone age, bone densitometry, ECG and renal sonography were all normal. Our patient is now 5 y old and symptom free.

Treatment with high doses of oral Mg was successful in keeping our patient symptom free and normocalcaemic, but cannot fully normalize serum Mg concentrations. Thus, during the regular follow-up of patients with primary hypomagnesaemia, the main target must be to increase oral Mg supplementation to a dosage which can maintain normocalcaemia rather than normomagnesaemia.