Calciphylaxis

A 58-year-old woman with end-stage renal disease on hemodialysis for 6 years presents with sudden onset of intensely painful violaceous reticular patches on her abdomen and thighs, progressing to stellate purpuric plaques with black eschar formation over 2 weeks. She is on warfarin for atrial fibrillation. Labs show PTH 920 pg/mL, serum calcium 10.2 mg/dL, phosphate 6.8 mg/dL (Ca × PO4 product 69). Skin biopsy reveals medial calcification of dermal arterioles with intimal hyperplasia and microthrombi. The condition marked **B** in the diagram is suspected. Which of the following is the MOST APPROPRIATE first-line intervention to reduce pain and promote wound healing in this patient?