Magnesium by injection - the only way to guarantee getting magnesium levels up in the body

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The only way that I can guarantee to raise serum magnesium to a therapeutic level is to give it by injection. I prefer people to use the small volume daily injections. Because the magnesium sulphate is a hypertonic solution, it can sting, so adding a little lignocaine helps (but is, of course, optional).

Giving yourself a magnesium injection

Use a 0.5 ml disposable insulin syringe. The needle is very fine and this makes for a virtually painless insertion. Take off the protective white cap over the plunger and the orange cap over the needle. The plunger is set at 0.05ml, so push this down so there is no air in the barrel of the syringe. Firstly draw up about 0.05 ml of lignocaine (whilst you are trying it to see if you need it and if it suits you), then fill up the rest of the syringe with magnesium sulphate. This gives you about 0.55 ml of clear liquid.

You can inject in several different sites. Start with the roll of fat round the tummy button that everyone has when they sit down. This is where most diabetics inject. You can also use the front or outside muscle of the leg between the knee and the hip, or the upper outer quadrant of the buttock. Hold the syringe like a dart, rest the needle against the skin at 90° (right angles) to the skin, push gently, bit harder, until suddenly the needle slides through. You just have to go through the skin. Inject slowly over say 30 seconds, then withdraw the syringe when empty. Hold a wad of cotton wool firmly against the site for one minute.

Then massage the area of injection gently for TWO MINUTES to disperse the magnesium. Everyone is a risk of getting injection lumps but I hope this gentle massage will make this less likely! DISPOSE OF THE SYRINGE AND NEEDLE SAFELY IN THE ENCLOSED SHARPS BIN OR BY USING A SAFE CLIP. DO NOT RE-USE NEEDLES! Take full sharps bins or safe clips to either your chemist or GP surgery or local hospital for safe disposal.

I prefer these subcutaneous injections because they cause less tissue damage and bruising compared to the intramuscular injection.

You will also find excellent instructions in the guide on giving subcutanous injections published by the National Institutes of Health, Cilnical Center: Giving a subcutaneous injection

Larger volume injections

If you can't face injecting yourself several times a week, then larger volume injections can be given weekly. A suggested regime is 1 gm/2 mls given intra-muscularly weekly for 10 weeks.

The injection is painful because one is injecting a hypertonic solution. It is best given at room temperature or blood heat, i.m., either into triceps, deltoid, or glutens maximus slowly over 1-2 minutes. For a 2ml injection I usually use an orange needle. Magnesium is a powerful vasodilater. Even if one takes care to check the tip of the needle is not in a vein, sometimes there is such a powerful local vasodilatation that the vessels open up and an i.v. injection is inadvertently given. This does not matter much, except that the patient develops a generalised vasodilatation, feels hot and alarmed, goes red and may faint (if upright).

In fact it is partly this effect which is taken advantage of in the treatment of acute myocardial infarction or acute stroke. In both these conditions there is a local obstruction of blood supply. I use i.v. magnesium (2-5mls of 50%) as a bolus to treat both these conditions - often with dramatic effects. With acute MIs there is often immediate pain relief as either the obstruction is relieved or good collateral circulation restored. Furthermore, magnesium is antiarrhytmic. Trials with magnesium have clearly demonstrated benefit and magnesium is used as a front line medication in many hospitals (2).

How long should injections continue for?

At least 8 weeks at the above rates of dosing. If the injection sites get sore, you can try moving to other methods, eg, oral, skin, bath, per rectum or nebuliser. Please refer to Magnesium Magnesium by nebuliser and Magnesium Per Rectum handouts.


1. Lancet 337: 757-60 (1991).

2. Lancet 339, 1553-1558 (1992) "Intravenous magnesium sulphate is a simple, safe and widely applicable treatment. Its efficacy in reducing early mortality of myocardial infarction is comparable to, but independent of, that of thrombolytic or antiplatelet therapy". Woods KL, Fletcher S, Roffe C, et al.

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