Self-powered vapor pressure delivery device

Claim 1

A self-powered dispenser for administering an active agent internally to a mammal consisting essentially of: a. a hollow casing whose inner surface defines an active agent impermeable chamber and whose outer surface defines the exterior of the dispenser; b. an outlet in said casing communicating from said chamber to said exterior of the dispenser; c. a bladder positioned within said chamber the inner surface of said bladder defining a sealed inner chamber, the active agent being contained in said chamber externally of said bladder and in contact with the outer surface of said bladder, said bladder being formed of a flexible material and being expandable in response to a pressure increase within the inner chamber from an initial state in which the volume defined by the outer surface of the bladder is less than the volume of said chamber to an expanded state in which the outer surface of the bladder conforms approximately to the shape of said chamber and the volume defined thereby is approximately the volume of said chamber; d. a self-actuated active agent flow resisting means within said outlet for metering the discharge of agent from said chamber at a substantially constant rate; and e. a liquified gas propellant having a vapor pressure greater than one atmosphere at the physiological temperature of the mammal contained within said inner chamber; whereby when said dispenser is placed internally of the mammal said propellant vaporizes in response to said physiological temperature causing said bladder to expand continuously from said initial state to said expanded state and thereby concurrently and continuously displace active agent from said chamber via said outlet and said means in vivo at a controlled rate.