http://www.geocities.com/HotSprings/Spa/9971/creatine.html Creatine is eventually degraded into creatinine which is excreted by the kidneys. Creatinine is filtrated in the kidneys via passive diffusion thus its excretion does not require additional energy input. Excess creatine is also excreted in the urine through passive diffusion. Early studies indicated that most of the creatine is stored in the body since it did not appear in regular urine samples (8,9,10).