<p>A medication infusion pump (10) is provided for substantially constant flow delivery of medication from medication chamber (12) through catheter (16) to a patient. The pump (10) comprises compact housing (18) adapted for implantation into the body of a patient, wherein housing (18) defines a hollow interior forming medication chamber (12). An inlet port (14) on housing (18) permits transcutaneous access to and filling of medication chamber (12) within housing (18). A flexible propellant reservoir (24) filled with fluid propellant occupies a portion of medication chamber (12) to apply a substantially constant pressure to the medication for a substantially constant flow through an elongated capillary tube (30), and catheter (16) to the patient. Capillary tube (30) is spooled within housing (18) at the perimeter thereof in association with an annular filter (28) of large surface area to prevent impurities, and particulate from entering and clogging capillary tube (30). Inlet port (14) includes a click plate (88) for providing a positive feedback indication of proper registration between inlet port (14) and refillneedle (66).</p>
