Morning pain control is more important than mimicking how cortisol is regulated by the body.

Prednisone interferes with the normal functioning of the HPA axis. Some of the things our bodies do are impossible to duplicate or even closely mimic. The way the body regulates cortisol levels and inflammation is impossible to replicate with any exogenous glucocorticoid.

Endocrinologists prefer hydrocortisone for adrenal insufficiency because it is the pharmaceutical form of cortisol. However hydrocortisone is taken 2 or 3 times per day because the half-life is short ... the same as cortisol. Maintaining more consistent cortisol levels throughout the day is as important as attempting to mimic the circadian rhythm.

I think a split dose of prednisone is more useful at higher doses. It is a shock to the HPA axis to get a surge of prednisone every morning when a smaller dose might adequately regulate the inflammation. Unfortunately, the regulation of inflammation decreases after approximately 16 hours according to the half-life of prednisone. The way Prednisone is metabolized is different depending on the person and other factors. Some people are good for 36 hours with a single morning dose,

When the anti-inflammatory effects of Prednisone starts to wane --- the inflammation surges again.

I took very high doses of Prednisone for uveitis. To a certain extent, I knew if the inflammation inside my eye was "better or worse" on an hourly basis. I could adjust my dose accordingly.

I noticed the uveitis inflammation improved throughout the day after my morning prednisone dose but it didn't all go away. When I slept, the inflammation was dramatically worse the next morning. Each day was like starting over with another high dose of Prednisone.

When I spit my prednisone dose, the uveitis inflammation still improved during the day. However, when I took a smaller dose in the evening the improvement carried over to the next day. From one day to the next there was steady improvement.

Steady improvement is better than the roller-coaster effect of a high prednisone dose followed by high levels of inflammation. Granted this was for uveitis when 60 to 100 mg and tapering back to zero was routine for me. I would be the first to admit that I had no clue what to do for PMR.

I don't think a split dose is needed at lower levels of inflammation as long as a single small dose in the morning is sufficient to regulate the inflammation. Lower Prednisone doses aren't too much of a shock to the system. However, if it works for someone ... that is more important than my opinion.