We thank Iversen et al. for their commentary on our article.1 Kidney function is a critical consideration for drug development, approval, and use as it alters pharmacokinetics and pharmacodynamics. Glomerular filtration rate (GFR), the best overall index of kidney function, is complicated to measure directly. Thus, GFR is estimated in most settings. Different methods to estimate GFR are used in drug development and clinical practice. Such inconsistencies may result in confusion and discordance in drug dosing.