 Urinary excretion of the unchanged drug ranges from 0% to as high as 18.7%, depending on various factors.The two major circulating metabolites of modafinil are modafinil acid (CRL-40467) and modafinil sulfone (CRL-41056).Both of these metabolites have been described as inactive, and neither appear to contribute to the wakefulness-promoting effects of modafinil.