Preventing recurrent hypomagnesaemia: oral magnesium glycerophosphate

Summary of possible benefits and harms

Oral magnesium glycerophosphate is listed as a possible treatment for preventing recurrence of hypomagnesaemia in the British national formulary (a reference book of information on medicines generally prescribed in the UK).

In 2011, there were just under 26,000 prescriptions for oral magnesium glycerophosphate given to people in England. This figure does not include prescriptions supplied in hospitals and the records don't include exactly why each person was given the medicine, or how well it worked. There are also other types of unlicensed oral magnesium salts available; these weren't prescribed as often as oral magnesium glycerophosphate.

No studies were identified that compared oral magnesium glycerophosphate with dummy pills (known as 'placebo' pills) or with other types of oral magnesium to prevent hypomagnesaemia from coming back. No studies of oral magnesium glycerophosphate in children were found.

Only 3 patient reports were found that looked at how well oral magnesium glycerophosphate worked for preventing hypomagnesaemia from coming back after treatment with a magnesium drip. The 3 patients were adults whose ability to absorb magnesium had been affected by having parts of their intestines removed (2 patients) or by taking a drug called omeprazole for problems with their digestive system (1 patient).

In all of these patients, taking oral magnesium glycerophosphate was not enough to maintain normal magnesium levels in their blood. The 2 patients who had had parts of their intestines removed were switched to another form of magnesium called magnesium oxide. In 1 of these patients, treatment with magnesium oxide maintained normal magnesium levels, however the other patient still needed a magnesium drip every 3 to 6 months. The third patient stopped taking omeprazole and their magnesium levels returned to normal.

The numbers of people reported on are so small that they may not be representative of what happens in all people who take oral magnesium glycerophosphate to prevent hypomagnesaemia from coming back. These reports also do not tell us how well it would work in people who have had hypomagnesaemia for reasons other than having parts of their intestines removed or taking omeprazole.

Taking oral forms of magnesium may cause diarrhoea. People whose kidneys are not working well may not be able to take oral magnesium glycerophosphate, or they may only be able to take a smaller dose of it. This is because their kidneys do not work well enough to remove any extra magnesium from the body.