A cartridge for supplying fluid in a transdermal drug delivery apparatus, the cartridge comprising: a body at least partially defining an interior for containing fluid for being delivered by the transdermal drug delivery apparatus, and first and second openings to the interior of the body, wherein the first and second openings are respectively proximate opposite first and second ends of the body; a self-sealing member at least partially closing the first opening; and a movable member at least partially closing the second opening, wherein at least a portion of the movable member is for being urged into the interior of the body for increasing pressure within the interior of the body, wherein the body at least partially defines: a first cavity contiguous with the first opening; a second cavity contiguous with the second opening; and characterised by a passageway connected between the first and second cavities (98, 100); wherein: the first cavity includes a cylindrical section that tapers to a frustoconical section; the second cavity is at least partially defined by a substantially concave wall; and the passageway is open proximate a central portion of the substantially concave wall. a body at least partially defining an interior for containing fluid for being delivered by the transdermal drug delivery apparatus, and first and second openings to the interior of the body, wherein the first and second openings are respectively proximate opposite first and second ends of the body; an interior for containing fluid for being delivered by the transdermal drug delivery apparatus, and first and second openings to the interior of the body, wherein the first and second openings are respectively proximate opposite first and second ends of the body; a self-sealing member at least partially closing the first opening; and a movable member at least partially closing the second opening, wherein at least a portion of the movable member is for being urged into the interior of the body for increasing pressure within the interior of the body, wherein the body at least partially defines: a first cavity contiguous with the first opening; a second cavity contiguous with the second opening; and characterised by a passageway connected between the first and second cavities (98, 100); wherein: the first cavity includes a cylindrical section that tapers to a frustoconical section; the second cavity is at least partially defined by a substantially concave wall; and the passageway is open proximate a central portion of the substantially concave wall. a first cavity contiguous with the first opening; a second cavity contiguous with the second opening; and characterised by a passageway connected between the first and second cavities (98, 100); wherein: the first cavity includes a cylindrical section that tapers to a frustoconical section; the second cavity is at least partially defined by a substantially concave wall; and the passageway is open proximate a central portion of the substantially concave wall. the first cavity includes a cylindrical section that tapers to a frustoconical section; the second cavity is at least partially defined by a substantially concave wall; and the passageway is open proximate a central portion of the substantially concave wall.