The first problem is the dilutions. Dosages of adrenaline are (or were) mentioned in dilution. 1:1000 & 1:10000. There begins the confusion.
Firstly, let us understand where the 1000 comes from in 1:1000. Have you seen a small vial of adrenaline? That is 1mL. It has effectively 1mg of epinephrine/adrenaline. But why is it called 1:1000? Because 1mL of water = 1g of water = 1000mg. So, the 1:1000 actually refers to 1mg of adrenaline : 1000 mg of water. Unnecessarily complex!
All you had to say was 1mg in 1mL. And that is why this labeling is now being followed in some countries.
So, there you have a small vial - a 1mL vial - with 1mg of adrenaline in it.
Now, let us look at the other form epinephrine comes in. Epinephrine also comes in a big syringe of 10mL. But even this 10mL contains only 1 mg of adrenaline. The total amount of adrenaline in this 10mL form is the same as a small vial.
What is different then? Well, when the volume increases without increase in amount, the concentration drops. The 10mL form is more dilute than the small vial. Can you guess the dilution? It is 1:10000 or more easily expressed as 1mg in 10mL.
So, the first thing to internalize is that the small 1mL vial we see has 1mg of adrenaline (it may say 1.8mg of an adrenaline salt, but the effective amount of adrenaline is 1mg). And this is a concentrated form of adrenaline.
What that also means is that the 1mg/1mL adrenaline is never used directly IV! The reason is that this can cause an arrhythmia or other damages to the heart muscles.
If you're bored reading text, watch this youtube video telling these same things.
Now, the dilute form and the concentrated form are for slightly different uses. The concentrated form is given IM in anaphylactic shock. The dilute form is given IV in cardiac arrest.
When giving IM adrenaline for anaphylactic shock, the dosage in adults is almost always 0.5mg (0.5mL of the concentrated vial). If you can remember this fact it is easy to calculate the pediatric dose as well. The adult dose can be thought of as if it applies to a 50kg person. So 0.5mg for 50kg = 0.01mg/kg and that is the pediatric dose. (This 50kg adult approximation applies for many other drugs in calculation of pediatric dose. Let me know in comments below about other drugs that can be calculated this way).
When giving in cardiac arrest, in which case the dilute form (1mg in 10mL) is used, the adult dose is the entire 1mg (or 10mL) given intravenous and repeated based on the protocol you follow.
That is all there is to know. Just a 0.5mg and a 1mg.
