Hyperfiltration and Elevated Fractional Excretion of Magnesium in Children with Cystic Fibrosis

Several critical knowledge gaps exist in understanding and managing renal function in pediatric patients with cystic fibrosis (CF). A limited amount of data demonstrates hyperfiltration in CF, yet it is unknown how these changes in relation to intravenous (IV) aminoglycosides and evolves into chronic kidney disease in CF. Similarly, there is limited information on the fractional excretion of magnesium (FEMg) in relation to acute kidney injury induced by IV aminoglycosides. The PIANO-CF trial was a single-center study conducted at a pediatric hospital in Australia, looking at young children with CF who were admitted for IV aminoglycoside therapy. In relation to IV aminoglycoside therapy, the study evaluated the estimated glomerular filtration rate, serum magnesium, FEMg, and urine creatinine (UCr). For children with CF admitted for IV aminoglycosides, estimated glomerular filtration rate indicated hyperfiltration in 87% at baseline and 81% post-IV aminoglycosides. A significant increase in FEMg was observed with treatment, with a mean increase of 2.6% (<i>p</i> = 0.0143). FEMg values increased significantly with tobramycin administration (<i>p</i> = 0.0024 and <i>p</i> = 0.0021). Hyperfiltration rates in young children with CF were high at ∼80%. It is not known what the resulting effect of hyperfiltration has on susceptibility to acute kidney injury or the development of chronic kidney disease in CF. Finally, given the high rates of FEMg, renal wasting of magnesium in CF warrants further study.