[Answered]: R.S

R.S. is a pregnant woman who has been stabilized on phenytoin for 15 years. She is in her third trimester and her phenytoin plasma concentration is found to be 7.0 mg/L. The therapeutic range of phenytoin is 10–20 mg/L when the plasma protein binding is normal (fu = 0.1). R.S.’s albumin level is measured and found to be low, and her fu value for phenytoin is estimated to be 0.15. Is the measured phenytoin concentration therapeutic, toxic, or subtherapeutic?