A drug delivery device utilizing compressible fluid chambers for actuation is disclosed. The device includes a compressible dispensing chamber situated in a first compartment and a compressible filler-fluid chamber in flow communication with the first compartment. The compressible dispensing chamber is attached with a reciprocating plunger for dispensing the drug fluid. The drug chamber is refillable with a refill container that uses a compressible pouch containing the refill drug fluid. The refilling process is failsafe enabled by the insertion of the refill container needle only at the correct position to activate an internal contact switch. The compressible-wall configurations enable low dispensing forces without leakage of the drug fluid.
