Abstract: A subcutaneous drug delivery device having a housing having an internal reservoir in communication with a drug delivery needle via a fluid path. An expandable chamber disposed adjacent to the reservoir forces drug from the reservoir to the needle when supplied with a gas. A flow regulating chamber, in communication with the fluid path, is capable of volumetric changes in response to temperature and/or pressure changes. An increase in the volume of the flow regulating chamber increases flow resistance to the needle and thereby counteracts the corresponding increase in delivery rate resulting from the expansion of the expandable chamber due to the same volumetric changes in response to temperature and/or pressure. The device also includes an improved filling system that enables the reservoir within the device to be filled with drug from a source without regard to filling position and with a decreased risk of injury from needles.