I Have Lupus. I Am Currently Taking Magnesium Salicylate For

I have lupus. I am currently taking magnesium salicylate for back pain. Before I started taking it, I would wake up at 3am with excruciating back pain. I haven't had any since I started taking it. My nephrologist says I need a kidney biopsy and wants me to stop taking the magnesium FIVE DAYS before the procedure. The prospect of doing that for that long terrifies me. Can I take a clotting agent at the same time as the salicylate? Does it have to be FIVE days before? I take 1100 mg once a day (two pills) - can I reduce my dosage instead of eliminating it?