It is not really accurate to say that a dose of dex lasts 30-something hours. That misconception comes from mixing up the idea of plasma half life vs. biological (or cell) half life.

Look at this chart, or any other chart that shows the relative properties of the different glucocorticoids. http://web.uct.ac.za/depts/mmi/jmoodie/h02tab.html You’ll notice that there are TWO columns that have to do with half-life. Half-life refers to the amount of time that it will take for HALF the medication to be cleared out of the system. The column that we are interested in is PLASMA half-life....what we can measure in blood...not biological half-life.

For example, look at the plasma half-life of hydrocortisone. It is 1-2 hours. This means that if you give 10 mg. of hydrocortisone, HALF that amount (~5 mg) will remain after 1-2 hours. After another 2-4 hours, 2.5 mg will remain (half of 5) After 3-6 hours, 1.25 (half of 2.5) will remain. And so on and so forth. This is where the notion that a dose of hydrocortisone lasts about 6 hours comes from.

Now look at the plasma half life of dexamethasone. It is 3-4.5 hours. If you go through the same sort of number crunching with a dose of dex, it will show that a dose of dex lasts about 16 hours in the bloodstream....NOT 30 or more.

Sure, if you calculated using biogical half-life, that dose of dex would last much, much longer. But, then, so would a dose of hydrocortisone. In fact, if looking at the biological half-life of hydrocortisone, that same 10 mg dose would last about 36 hours, not 6-8. So, we are talking about two very different things.

As for the believing or not believing the 80:1 dex:hydro potency....the number is an approximate one, but it seems to fall right in line with the amounts of hydro and dex that MR quoted. E.g. using an 80:1 ratio, 0.25 mg of dex (a relatively modest amount for an adult) would be equivalent to 20 mg of hydro (also a relatively modest amount); 0.375 mg would be equivalent to 30 mg; and 0.5 mg (a large dose) would be equivalent to 40 mg hydro (also a large dose). So, to me, this seems to support, not refute, the 80:1 ratio????

Bottom line: I have absolutely no personal interest in whether someone uses hydrocortisone or dexamethasone.  I would say...do what you are comfortable  with and---most of all---what your doctor is familiar with.  At the same time,  I also think it is important to dispel some of the "old wives tales" that seem to follow dex around.