Low doses of recombinant human erythropoietin does not affect C-terminal FGF23 in healthy men.

Recombinant human erythropoietin (rhEpo) can improve human performance, but misuse remains difficult to detect. C-terminal fibroblast growth factor 23 (cFGF23) was recently demonstrated to increase following injection of a single high dose rhEpo, but the effect of more frequent low doses is unknown. Using a randomized double-blind placebo-controlled design, we investigated whether two weeks with three weekly subcutaneous injections of 50 IU/kg Eprex (low-dose) or 20 IU/kg Eprex (micro-dose) increase cFGF23 levels compared with saline (placebo) injections in 24 healthy males. Venous blood was sampled at day -3, 0, 1, 3, 11, 14, 18 and 25 of the treatment and analyzed for cFGF23 and erythropoietin concentration ([EPO]). The level of cFGF23 was similar at days -3, 0, 1, 3, 11, 14, 18 and 25 with the low-dose (23±4, 26±5, 23±7, 27±6, 25±8, 24±10, 22±5 and 24±7 RU/ml, respectively), micro-dose (23±6, 25±5, 23±8, 28±9, 27±7, 25±9, 25±5 and 23±6 RU/ml, respectively) and placebo (23±6, 24±6, 26±7, 26±6, 31±6, 31±7, 24±4, and 27±8 RU/ml, respectively) treatment. The correlation coefficient between plasma [EPO] and plasma cFGF23 levels was R2 =0.01 and insignificant. The results demonstrate that cFGF23 is not sensitive to low doses of subcutaneous rhEpo injections in healthy males.