Hello @123suew, I think @alanbruce @pattitoo and @murp may be able to share their experience with Fosamax. There is also another discussion that you may be interested in following.

Calcium and Vitamin D for bone density: https://connect.mayoclinic.org/discussion/calcium-and-vitamin-d-for-bone-density/

Hi,
I have PMR and have been weaning down very slowly and am now at 5 mg. of prednisone. So far, so good - no pain. I too started on prednisone about 5 months ago. I was quite sure that I had PMR but it took a couple GP's who dismissed my thinking until I finally landed on a Rheumatologist that concurred. i was one of those that had a normal ESR and CRP, but i was aware that 20% of those with PMR can have normal values.
I had a DEXA scan which showed osteopenia (lumbar and hip). My hip scores are very close to being in the osteoporosis range. My rheumatologist said I was a candidate for fosamax because of the scores and the long term use of prednisone.
I must preface with - this is just my thinking and approach right now, although that could certainly change if warranted in the future (strong family history of osteoporosis as well). I have chosen to not go on fosamax right now, because I recall the difficulty and discomfort experienced my Mother. She ended up having problems with her esophagus and afib that her Doctor thought was correlated with fosamax use. I have upped my calcium, Vitamin K, Vitamin D and take a supplement that has all the above including strontium (Bone Strength). I eat alot of calcium rich foods. I also do quite a bit of weight bearing exercise and work out with a weighted vest. All this to say, I am hoping that my next DEXA scan will not show a worsening. I am aware that fractures are not just a function of bone density but are also a result of bone strength, so hoping for the best.
Take care and just wanted to share my current thoughts right now. I know many people have not had serious side effects to fosamax.