Disclosed herein is a method for determining a dosing prescription for a medicament in a patient undergoing CRRT. The method generally includes administering to the bloodstream of the patient a fluorescent agent; administering to the patient at least one dose of the medicament; performing CRRT on the patient after administering the fluorescent agent to the patient; exposing the fluorescent agent to visible or infrared light; monitoring transcutaneously a change in the spectral energy from the fluorescent agent over a period of time; correlating a change in intensity of the spectral energy from the fluorescent agent to a clearance rate of the fluorescent agent from the bloodstream in the patient; calculating a clearance rate of the medicament in the patient; determining an amount of the medicament in the bloodstream of the patient as a function of time; and adjusting a dosing prescription of the medicament to the patient.