I had very similar experience when I first tried Repatha. I had the lowest 140 mg injectionable. The pain in my back happened again on 2nd injection and I want to mention that I've had back issues for years. I continued with Repatha 2x month and switched to Praluent for cost reasons and not sure if medication is causing back issues but my back seems worse. However, my cholesterol dropped from 2022 when I started from 302 to 160s and I still maintain #s from 153/160s. I have 4 coronary stents in LAD so I "feel" I don't have a choice and ALL other pill statins (I've tried them all) hurt my joints/bones/muscles much more. I have genetic "familial" cholesterol. There are many new RX on the horizon.