Published: June 2010
Prescriber Update 31(2): 13
Healthcare professionals are advised that an association between omeprazole treatment and hypomagnesaemia has been identified. The data sheets for medicines containing omeprazole are in the process of being updated to include information about this association.
A safety signal was initially detected from adverse reaction reports describing cases of hypomagnesaemia in patients taking omeprazole. In 2008, two case reports of hypomagnesaemia and hypocalcaemia were identified by CARM; however at the time there was insufficient evidence to confirm an association. Since then a growing body of evidence has confirmed this association, including a further report of hypomagnesaemia to CARM, and the publication of case reports in the literature1-3 , and by the Netherlands Pharmacovigilance Centre.4
Most case reports of hypomagnesaemia have been associated with long-term use of omeprazole at normal doses (20 - 40mg per day); magnesium levels normalised after stopping treatment. Reports of hypomagnesaemia were usually also associated with hypocalcaemia, with some patients displaying symptoms of severe hypocalcaemia and hypomagnesaemia (seizures, cardiac arrhythmia, tetany, severe vomiting leading to other electrolyte disturbances and psychiatric symptoms).
Magnesium has an important influence on calcium homeostasis through decreased parathyroid hormone secretion and diminished responsiveness of skeletal and renal tissue to parathyroid hormone.4 Although the mechanism by which omeprazole induces hypomagnesaemia is unclear it has been postulated that it may be due to reduced absorption of magnesium through an active transport mechanism.1
Medsafe advises healthcare professionals to be alert to the possibility of hypomagnesaemia in patients taking omeprazole and displaying symptoms such as muscle cramps, weakness, irritability or confusion.