I didn't ever take sulfasalazine for PMR but I give your doctor credit for trying it. It might work for you and other people but it isn't tried very often for PMR. It is used more often for inflammatory arthritis.

I was diagnosed with reactive arthritis with uveitis about 20 years before PMR was diagnosed. That was way back in the early 1990's when I was only about 35 years old so I was too young for PMR back then. There was a study about that time that suggested sulfasalazine was an effective treatment for reactive arthritis and uveitis.
https://pubmed.ncbi.nlm.nih.gov/8961907/.
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It was funny because my rheumatologist treating PMR about 20 years later was reviewing some of my very old medical records from the 1990's. She said the notes said I had a "good response" to sulfasalazine and wanted to know what I remembered about it. She was excited about wanting me to try sulfasalazine again. I had to burst her bubble because my recollection wasn't that good. I took sulfasalazine for more than a year when I gave up on it. My experience mirrored the results of a followup study that wasn't so positive.
https://pmc.ncbi.nlm.nih.gov/articles/PMC1752243/