Abstract: A feedback controlled drug delivery system includes the automated sampling and analysis of a patient sample and dosing the patient based on the analysis. Automated sampling may be performed by direct analysis of the patient sample, such as for the measurement of a blood sample coagulation state or a glucose level. The drug delivery system includes a sample set that has a bidirectional patient tube that allows for delivery of the patient sample to an analyzer, and at another time, the infusion of a therapeutic drug. A controller receives a measurement from the analyzer, and based on that measurement, adjusts the delivery of the therapeutic fluid. The sample set has a quick--clear Leur fitting that allows for more effectively clearing a first fluid from a Leur fitting when starting a second fluid. The system also has a reagent cassette holder that protects, using a foam gasket, a reagent on a sample slide.