the dividing wall 15 a and the one way valve 17 a into septum 44 a of the implant device 10 a the one way valve provides a flow path 23 a as shown in fig7 a and fig7 b between the first and the second compartments 11 a and 13 a when the valve 17 a is in the open position the first compartment 11 a has a piston 83 a connected to a driving means and the second compartment 13 a has a follower 28 a which is in flow communication with the movement of the piston 83 a the wall of the second chamber 22 a is collapsible as represented by a bellows wall 56 a as shown in fig6 a the second fluid 24 a which is inert to the drug fluid and body tissues serves as a filler fluid in communication with the first fluid chamber to fill the space evacuated by the movements of the piston and the follower to prevent creation of a partial vacuum that could negatively impact the movement of the piston and the follower both piston 83 a and follower 28 a separate second fluid 24 a from first fluid 20 a the piston is driven by a drive means for infusing the first fluid through outlet 34 a and reducing the volume of the first fluid in the first compartment in this divided drug chamber configuration the drug dosage dispensed at each step of the piston forward movement is a small fraction of the amount for an un divided configuration furthermore a catheter 48 a is attached to outlet 34 a of first chamber 18 a in communication with the first fluid 20 a the wall 51 a of the first chamber.