When my 10 year old son was about 8 his endo added prendisone for his evening dose instead of cortef because his 17 ohp was high and she didn’t want to increase his cortef dose.  She told us that prendisone lasts longer in the system than cortef so night time was a good time to use the prendisone.  We did that for about 2 years and since his levels stabilized, she took him off the prendisone and replaced it with the cortef.  The evening prendisone dose was equivalent to the cortef he was on.  Hope that helps.

Judy