Dietary magnesium supplementation in cats with chronic kidney disease: A prospective double‐blind randomized controlled trial

Abstract Background Plasma total magnesium concentration (tMg) is a prognostic indicator in cats with chronic kidney disease (CKD), shorter survival time being associated with hypomagnesemia. Whether this risk factor is modifiable with dietary magnesium supplementation remains unexplored. Objectives Evaluate effects of a magnesium‐enriched phosphate‐restricted diet (PRD) on CKD–mineral bone disorder (CKD‐MBD) variables. Animals Sixty euthyroid client‐owned cats with azotemic CKD, with 27 and 33 allocated to magnesium‐enriched PRD or control PRD, respectively. Methods Prospective double‐blind, parallel‐group randomized trial. Cats with CKD, stabilized on a PRD, without hypermagnesemia (tMg >2.43 mg/dL) or hypercalcemia (plasma ionized calcium concentration, (iCa) >6 mg/dL), were recruited. Both intention‐to‐treat and per‐protocol (eating ≥50% of study diet) analyses were performed; effects of dietary magnesium supplementation on clinicopathological variables were evaluated using linear mixed effects models. Results In the per‐protocol analysis, tMg increased in cats consuming a magnesium‐enriched PRD (β, 0.25 ± .07 mg/dL/month; P < .001). Five magnesium supplemented cats had tMg >2.92 mg/dL, but none experienced adverse effects. Rate of change in iCa differed between groups (P = .01), with decreasing and increasing trends observed in cats fed magnesium‐enriched PRD and control PRD, respectively. Four control cats developed ionized hypercalcemia versus none in the magnesium supplemented group. Log‐transformed plasma fibroblast growth factor‐23 concentration (FGF23) increased significantly in controls (β, 0.14 ± .05 pg/mL/month; P = .01), but remained stable in the magnesium supplemented group (β, 0.05±.06 pg/mL/month; P =.37). Conclusions and Clinical Importance Magnesium‐enriched PRD is a novel therapeutic strategy for managing feline CKD‐MBD in cats, further stabilizing plasma FGF23 and preventing hypercalcemia.