A 73-YEAR-old man flatlined on the way to hospital after an adverse reaction to milk of magnesia which he was taking to relieve his constipation, according to a medical report.

The case study in the latest edition of the British Medical Journal notes that the man had already been diagnosed with a number of health issues, including end stage kidney disease.

He was given daily doses of milk of magnesia for constipation.

After developing persistent nausea and vomiting, he was taken to hospital. En route in the ambulance the man had a severely lowered heart rate and he flatlined.

Cardiac life support procedures were initiated and when he was admitted to hospital, he was initially diagnosed with a heart attack, complicated with cardiogenic shock and/or sepsis.

However, tests later revealed high levels of serum magnesium found in his system. He was diagnosed with hypermagnesemia - a condition that is usually rare because the kidneys are effective in excreting any excess magnesium. He underwent dialysis to purify his blood.

Authors of the case study warned that in patients with impaired kidney function like this man, extreme symptomatic hypermagnesemia can occur when therapeutic doses of contraindicated magnesium-containing laxatives or antacids are ingested.

They said clinicians should be aware of this life-threatening condition in patients with significant kidney dysfunction and should avoid prescribing magnesium-based laxatives to them.

Patients, they said, should be educated regarding the safe use of magnesium containing over-the-counter products, such as milk of magnesia or remedies for gas, indigestion or heartburn.