Fluid delivery and infusion devices, and methods of use thereof

A medical device, comprising:

• an infusion device comprising a fluid reservoir and a transcutaneous access tool fluidly coupled to the fluid reservoir, the transcutaneous access tool configured to deliver a therapeutic fluid subcutaneously to a patient, wherein:
• the infusion device operates in a stand-by mode prior to the therapeutic fluid being introduced into the fluid reservoir and in the stand-by mode during filling of the fluid reservoir to a predetermined fill level with the therapeutic fluid,
• the infusion device is operable to generate a signal indicative that the fluid reservoir has been filled, and upon generating the signal indicative that the fluid reservoir has been filled, the infusion device uses the signal to cause infusion of the therapeutic fluid from the fluid reservoir after a predetermined infusion delay time period, and
• the predetermined infusion delay time period is a time sufficient to allow a first therapeutic composition already in the patient to decrease from a first concentration level in the patient when the first therapeutic composition was introduced to the patient to a second concentration level in the patient.