Actually the sooner you start Actemra, the better. It helps you to taper faster and with fewer flares. I was taking 60 mg a day of prednisone when I started Actemra.

It takes up to 2 months for Actemra to take full effect, so you need to be taking prednisone during that time to control your GCA (or PMR in some cases).

Also, you can't just stop taking prednisone when you start Actemra. Depending on the dose of prednisone and the amount of time you take it, your adrenal glands stop producing cortisol. I think any dose of 10 mg or higher (or maybe even lower) for more than a couple of weeks can shut down the adrenal glands. If you stop taking prednisone all at once, your body will not produce the cortisol you need, and it can make you extremely ill, or even kill you. So you have to slowly taper the dose of prednisone you take to allow your adrenal glands to start working again. For most people the adrenal glands start working again when the prednisone dose gets down to about 5 mg a day or a little lower. I have been tapering prednisone for a whole year to get down to 2 mg per day, and it will take almost 2 more months to get down to no prednisone, and that assumes I don't have a flare or a problem with adrenal insufficiency.

There are a lot of threads on this forum about how to taper prednisone safely so that you don't have a flare of your disease or run into problems with your adrenal glands not making enough cortisol.