How often can I take Methylprednisolone 4 mg. dosepk? I am 70 yrs. old and have, among other things, fibromyalgia , osteoporosis , and arthritis. This was prescribed for an inflamed piriformis muscle , and after taking the first day s 6 pills, the pain is mostly gone. This is a pain that has come and gone for years, It sometimes is so bad I cannot walk.