Treatment with magnesium is neither helpful nor harmful after heart
attacks
Intravenous magnesium confers no benefit to patients with acute myocardial
infarction, a study published this week in The Lancet shows (2002;360:1189).
There has been some debate as to whether magnesium, a readily available
and cheap therapy, should be used to treat high risk patients following
a heart attack. Despite promising results from work in animals, conflicting
results have been reported in clinical trials.
Around 6,200 patients with acute ST-elevation myocardial infarction (STEMI)
were randomised to receive either magnesium sulphate (given as a 2g intravenous
bolus over 15 minutes followed by a 17g infusion over 24 hours) or matching
placebo in the Magnesium in Coronaries (MAGIC) trial.
Patients were stratified according to their eligibility for reperfusion
therapy — those aged 65 years or older who were eligible for reperfusion
therapy and those of any age not eligible for reperfusion therapy. All
patients received study treatment within six hours of the onset of symptoms.
The researchers found there was no difference between the two groups
in the proportion of patients dying (15.3 per cent for those treated with
magnesium versus 15.2 per cent for those given placebo; odds ratio 1.0,
95 per cent confidence interval P=0.96). They also found no evidence that
any subgroup of patients either benefited from or were harmed by treatment.
The researchers comment that the null effect of the magnesium in the
trial was not expected based on the results of previous trials. They suggest
that publication bias and inadequate sample sizes could have led to overestimation
of magnesium’s benefit. Also, the proposed cardioprotective effects
of magnesium might overlap with those of current therapies not used routinely
in earlier trials. “The combination of mechanisms proposed for magnesium’s
beneficial effects in STEMI . . . could be superseded by the effects of
current medical regimens that include aspirin, beta-blockers, and angiotensin-converting
enzyme inhibitors.” These agents also increase concentrations of
myocardial magnesium and minimise urinary losses of magnesium, they say.
“In view of the totality of the available evidence, in current coronary
care practice there is no indication for the routine administration of
intravenous magnesium to patients with STEMI at any level of risk,”
the researchers conclude.
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