This randomized, Open Label Phase 2 study published in JAMA Oncology compared various dosing schedules of prednisone and one for dexamethasone which are used with Zytiga (abiraterone acetate). As you may know, some form of steroid is necessary for use with Zytiga to compensate for its inhibition of natural cortisol production. If not compensated, patients on Zytiga would suffer from a metabolic syndrome known as mineralocorticoid excess (hyperaldosteronism) resulting in hypertension and hypokalemia (low potassium) which could lead to metabolic alkalosis, tetany (muscle cramping) and irregular heart rhythms.
The various prednisone regimens included 5mg once per day, 2.5mg twice per day, and 5mg twice per day. Dexamethasone was given as 0.5mg once per day. For each of these subgroups, the following percentage of patients had no mineralocorticoid excess (a good thing!):
Prednisone 5mg twice daily: 70.6%; Dexamethasone: 70.3%; Prednisone 2.5mg twice daily: 60%; Prednisone 5mg once daily: 36.8%.
Perhaps of even greater interest, here are the numbers for months of radiographic progression-free survival for each group:
Dexamethasone: 26.6 months; Prednisone 5mg twice daily: 18.5 months; Prednisone 5mg once daily: 15.3 months; Prednisone 2.5mg twice: 12.8 mo.
Total lean body mass decreased in the prednisone groups and total body fat increased in the prednisone, 5 mg, twice daily and dexamethasone groups. In the dexamethasone group, there was an increase in serum insulin and insulin resistance, while total bone mineral density decreased.
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