Magnesium is vital for many biochemical processes, activating over 300 enzyme systems including those involved in carbohydrate metabolism, protein synthesis, oxidative phosphorylation and the synthesis of ATP, DNA and RNA. Magnesium is the physiologic calcium antagonist.
Magnesium regulation depends on renal excretion. The excretion capacity of the kidney ranges widely depending on the plasma Mg2+ concentration. Excess plasma calcium (Ca2+) or Mg2+ activates a calcium receptor in the kidney that
Magnesium deficiency has many consequences, including chronic fatigue states and delirium, muscle weakness and tetany, disordered glucose metabolism, numerous myocardial arrhythmias, vascular disorders and electrolyte disturbances, particularly of potassium. The generally accepted normal range for total serum Mg2+ is 0.75–1.0 mmol l–1. However, since magnesium is primarily an intracellular ion, whole body magnesium depletion may exist in the presence of normal or even elevated plasma Mg2+
Hypermagnesaemia to control eclamptic convulsions was first reported by Lazard15 and popularised by Pritchard in 1955.16 Subsequently, it was used with some success as a tocolytic.17, 18
Pharmacologically, magnesium is a calcium competitor that is effective, not only at the dihydropyridine receptors, but also at other calcium channels unaffected by traditional calcium channel antagonists. Magnesium is also an effective antagonist of the N-methyl-d-aspartic acid (NMDA) receptor in the central
While magnesium is now the agent of choice for the prevention of eclamptic convulsions, the argument as to whether all pre-eclamptic patients should be given magnesium is not resolved. Although magnesium is very safe, it is not entirely without risk, particularly in areas where monitoring may be limited, and consideration has to be given to the benefit/risk ratio of using the agent against the exposure of a large number of patients to a therapy which most of them do not need. There are also
Magnesium has widespread relevance to obstetric practice. Deficiencies may contribute to various disease states, and correction of these deficits may improve maternal and child health. The ion is undoubtedly the agent of choice for the prevention and control of eclamptic convulsions. The role in tocolysis is less clear and is largely driven by individual experience and preference, rather than hard evidence. Similarly, while current data suggest that it may protect against the development of
The author has no conflicts of interest to declare. Magnesium is the drug of choice to prevent convulsions in pre-eclampsia and eclampsia, but there is uncertainty as to which patients with mild disease need treatment. Magnesium may be of benefit in tocolysis, but the level of evidence is inadequate to make firm recommendations. Magnesium treatment in pre-term labour may offer protection to the premature neonatal brain, but the level of evidence is inadequate for firmPractice Points