Recirculating implantable drug delivery system

Details Recirculating implantable drug delivery system Recirculating implantable drug delivery system

1999-02-26

2001-03-06

Seidel, Richard K. (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Infrared, visible light, ultraviolet, x-ray or electrical...

C604S890100

Reexamination Certificate

active

06198966

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods and apparatus for delivering drug therapy to the human body. More particularly, the invention relates to implantable apparatus and methods for delivering drug therapy using a recirculating carrier fluid.
2. Description of the Related Art
In conventional implantable drug delivery devices, drug is dissolved in a carrier fluid and the drug/carrier fluid combination is stored in a reservoir and a closely controlled dosage metered and delivered to the body. Drug concentration in the carrier fluid is typically kept very low. One reason for this is that many drugs become unstable at higher concentrations or may precipitate out of the carrier fluid, resulting in blockage within the delivery device. Another reason is that high concentrations of drug may lead to local toxic effects during delivery and would require very low infusion rates beyond the controllable range of many delivery devices. Also, inadvertent leakage of carrier fluid bearing large concentrations of drug would present a danger to the human body.
Since the concentration of drug in the carrier fluid is typically very low, often on the order of a few micrograms to a few milligrams per milliliter of carrier, relatively large volumes of carrier fluid must be stored within the implantable drug delivery device and periodically replenished by refilling from sources external to the human body. For example, in the SYNCHROMED® infusion pump, manufactured by Medtronic, Inc. of Minneapolis, Minnesota, at least half of the total device volume is occupied by the pump reservoir, which stores carrier and drug. In a morphine administering application, morphine sulfate is dissolved in water at a concentration of less than 50 milligrams per milliliter. Thus, less than 5-percent of the fluid stored in the pump reservoir is actually active drug. In prior art devices, further reduction of the pump size, although desirable, is not achievable without corresponding loss in drug storage capacity.
Some known systems, such as the one disclosed in U.S. Pat. No. 5,643,207, have utilized endogenous body fluids as carrier fluids in order to provide more compact delivery devices. However, such systems present difficulties in controlling the concentration of drug in the physiological fluids and, due to the chemical make-up of physiological fluids, are limited in the types of drug that may be delivered using such systems. There is thus a need for a drug delivery system which eliminates the need for large storage capacity yet which is capable of extended delivery without refilling.
SUMMARY OF THE INVENTION
The aforementioned problems are solved by the invention which provides a drug delivery system which recirculates the carrier fluid in closed-loop fashion, thereby requiring only a relatively small amount of carrier fluid for operation. In a preferred embodiment, the invention provides a drug reservoir and a pump which provides carrier fluid to a recirculating path. The recirculating path is preferably in the form of a dual-lumen catheter which provides a supply leg to a drug delivery interface and a return leg from the drug delivery interface to the pump. A metering device maintains the concentration of drug within the supply leg of the recirculating path. A drug delivery interface is provided between the recirculating path and the living body in the form of a semi-permeable membrane which permits a flow of drug from the recirculating path, yet which prevents a net outflow of carrier fluid from the recirculating path. In another preferred embodiment, drug concentration sensors are provided to measure the concentration of drug in the recirculating path or in the human body and to actively adjust the metering device accordingly.
A primary advantage of the present invention is that rate of drug infusion through the drug delivery interface is a function of the difference in concentration across the interface; the rate of drug infusion is substantially independent of the flow rate of fluid through the recirculation path.


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