Systems and methods for sustained medical infusion and devices related thereto

A medical device for delivering therapeutic fluid to a body of a patient, the device comprising:

• a first unit comprising a first portion of a fluid transfer system;
• a second unit coupleable to the first unit, the second unit comprising a reservoir for holding the therapeutic fluid, and a second portion of the fluid transfer system coupleable to the first portion of the fluid transfer system when the first unit is coupled to the second unit;
• a cradle configured for releasably receiving the first unit, the cradle comprising a releasable mechanism for coupling both the first and second units when engaged;
• and
• a cannula unit coupleable to the second unit, the cannula unit comprising a cannula for insertion into the body of the patient;
• wherein upon coupling the first, second, and cannula units, and insertion of the cannula into the body of the patient, fluid communication is established from the reservoir to the body, via the cannula, without the use of tubing external to the coupled first and second units.