Foster J et al. (2006) Influence of commonly used drugs on the accuracy of cystatin C-derived glomerular filtration rate. Pediatr Nephrol 21: 235–238

Researchers from the Children's Hospital of Eastern Ontario, Canada, have found that various doses of several commonly used renal drugs do not affect cystatin-C-based estimates of pediatric glomerular filtration rate (GFR). This evidence refutes previous findings that certain drugs such as corticosteroids might alter cystatin C concentrations, thus showing that cystatin C might well be an accurate indicator of GFR in children with renal disease.

Foster and colleagues retrospectively analyzed 71 children (2.6 months to 18 years of age) with renal disease, who were taking at least one commonly used renal medication such as tacrolimus, ciclosporin, an angiotensin-converting-enzyme inhibitor, losartan, or a corticosteroid. Ratios of directly measured GFR : cystatin-C-based GFR were calculated for each drug at various doses, with a ratio of 1 indicating agreement.

None of the drugs influenced the ratio of measured GFR : cystatin-C-based GFR in a dose-dependent manner. Only the antibacterial drug co-trimoxazole was associated with a GFR ratio significantly <1 (P = 0.045), which could have been related to the small number of patients on each study drug. The study did not confirm previous data that showed a dose-dependent increase in cystatin C in adults taking prednisone; however, the authors acknowledge that their study might not have been sufficiently powered to detect a change in cystatin-C-based GFR at low GFRs. Despite these limitations, they support the use of cystatin C concentration for the calculation of GFR in children.