Claims for Patent: 5,246,418

Summary for Patent: 5,246,418

Title:	Iontophresis system having features for reducing skin irritation
Abstract:	An iontophoresis drug delivery system includes a device which is attachable to the skin of an animal and having a drug reservoir, an electrolyte reservoir, and electrodes electrically communicating with the reservoirs and with the skin of the animal. An electronic circuit for controlling the rate or amount of current or voltage applied to the electrodes of the device includes a constant voltage and current generator, and a switching circuit for switching between applying either a constant current to the electrodes or a constant voltage. Current and voltage sensors are attached to the electrodes and provide feedback signals which are compared with predetermined threshold signals to control through feedback the amount of constant voltage and constant current applied to the electrodes.
Inventor(s):	Haynes; John L. (Chapel Hill, NC), Sage, Jr.; Burton H. (Raleigh, NC)
Assignee:	Becton Dickinson and Company (Franklin Lakes, NJ)
Application Number:	07/808,754
Patent Claims:	1. An operable iontophoretic drug delivery system comprising: a drug reservoir adapted to be attached to the skin of an animal; a first electrode in said drug reservoir; an electrolyte reservoir adapted to be placed in communication with the skin of an animal; a second electrode in said electrolyte reservoir; circuit means for providing electrical communication between said first and second electrodes, said circuit means including means for connection to a source of electrical power; means for providing substantially constant voltage between said electrodes, in said circuit means, including means for monitoring current through said first electrode; means for providing substantially constant current to said first electrode, in said circuit means; and switching means, in said circuit means, for switching from said means for providing constant voltage to said means for providing constant current when said current monitored by said monitoring means reaches a predetermined value. 2. The operable iontophoresis drug delivery system of claim 1 further including means for measuring the current passing through said first electrode and for accumulating the total current passing through said first electrode. 3. The operable iontophoresis drug delivery system of claim 2, further including means for terminating power to said first electrode when accumulated total current reaches a predetermined value. 4. The operable iontophoresis drug delivery system of claim 1, wherein said drug reservoir contains an ionic compound selected from the group consisting of therapeutic compounds, diagnostic compounds and drugs. 5. The operable iontophoresis drug delivery system of claim 1, wherein said first electrode includes a conductive element selected from the group consisting of silver, silver/silver chloride, gold, copper, molybdenum and lead. 6. The operable iontophoresis drug delivery system of claim 1, wherein said drug reservoir and said electrolyte reservoir are part of a common housing. 7. The operable iontophoresis drug delivery system of claim 6, wherein said housing is made of plastic. 8. The operable iontophoresis drug delivery system of claim 6, wherein said housing includes a removable release sheet covering both reservoirs and a portion of said housing adapted to contact the skin of an animal. 9. The operable iontophoresis drug delivery system of claim 1, wherein said drug reservoir and said electrolyte reservoir include an adhesive coated surface for attachment to the skin of an animal. 10. An operable iontophoretic drug delivery system comprising: a drug reservoir adapted to be attached to the skin of an animal; a first electrode in said drug reservoir; an electrolyte reservoir adapted to be placed in communication with the skin of an animal; a second electrode in said electrolyte reservoir; circuit means for providing electrical communication between said first and second electrodes, said circuit means including means for connection to a source of electrical power; means for providing substantially constant voltage between said electrodes, in said circuit means, including at least one of means for monitoring current through said first electrode and means for monitoring voltage between the first and second electrodes; means for providing substantially constant current to said first electrode, in said circuit means; switching means, in said circuit means, for switching between said means for providing constant voltage and said means for providing constant current when at least one of the monitored current and monitored voltage equals a predetermined value; and power limiting means in said switching means for causing a transition from one constant voltage and constant current to a constant power provided to the first and second electrodes if a predetermined power, monitored by said power limiting means, is reached. 11. An operable iontophoretic drug delivery system comprising: a drug reservoir adapted to be attached to the skin of an animal; a first electrode in said drug reservoir; an electrolyte reservoir adapted to be placed in communication with the skin of an animal; a second electrode in said electrolyte reservoir; circuit means for providing electrical communication between said first and second electrodes, said circuit means including means for connection to a source of electrical power; means for providing substantially constant voltage between said electrodes, in said circuit means, including at least one of means for monitoring current through said first electrode and means for monitoring voltage between the first and second electrodes; means for providing substantially constant current to said first electrode, in said circuit means; switching means, in said circuit means, for switching between said means for providing constant voltage and said means for providing constant current when at least one of the monitored current and monitored voltage equals a predetermined value; and power limiting means, in said switching means, for causing a transition from one constant voltage and constant current to a constant power provided to the first and second electrodes if a predetermined power is reached. 12. The operable iontophoresis drug delivery system of claim further including means for measuring the current passing through said first electrode and for accumulating the total current passing through said first electrode. 13. The operable iontophoresis drug delivery system of claim 11, wherein said drug reservoir contains an ionic compound selected from the group consisting of therapeutic compounds, diagnostic compounds and drugs. 14. A circuit for connecting a pair of electrodes of an iontophoretic drug delivery system comprising: means for connecting said circuit to a source of power; means for providing substantially constant voltage between said electrodes; means for providing a substantially constant current to one of said electrodes; means for monitoring current through one of said electrodes; means for switching from said means for providing constant voltage to said means for supplying constant current when said current monitored by said monitoring means reaches a predetermined value. 15. A circuit for connecting to a pair of electrodes of an iontophoretic drug delivery system comprising: means for connecting said circuit to a source of power; means for providing substantially constant voltage between said electrodes; means for providing a substantially constant current to one of said electrodes; at least one of means for monitoring current through one of said electrodes and means for monitoring voltage between the electrodes; means for switching between said means for providing constant voltage and said means for providing constant current when at least one of the monitored current and the monitored voltage equals a predetermined value; and power limiting means in said switching means for causing a transition from one of said constant voltage and constant current to a constant power provided to the electrodes if a predetermined power between said electrodes is reached. 16. A method for iontophoretic drug delivery through the skin of an animal using an iontophoretic drug delivery device having an ionic compound containing reservoir, a first electrode in said ionic compound containing reservoir, an electrolyte containing reservoir, and a second electrode in said electrolyte containing reservoir comprising the steps of: (a) attaching said iontophoretic drug delivery device to the skin of an animal; (b) causing electrical power to flow between said electrodes at a constant predetermined voltage; (c) monitoring the current while said power is being delivered at constant voltage; (d) when said monitored current reaches a predetermined current causing the electrical power between said electrodes to change from constant voltage to constant current at said predetermined current; and (e) continuing to cause electrical power to flow between said electrodes at a constant predetermined current. 17. The method for iontophoretic drug delivery of claim 16, having additional steps comprising: (f) monitoring and accumulating the total current passing between said electrodes; and (g) terminating electrical power provided to said electrodes when the accumulated total amount of current, corresponding to the delivery of the desired amount of ionic compound into the skin of the animal, has been reached. 18. A method for iontophoretic drug delivery through the skin of an animal using an iontophoretic drug delivery device having an ionic compound containing reservoir, a first electrode in said ionic compound containing reservoir, an electrolyte containing reservoir, and a second electrode in said electrolyte containing reservoir comprising the steps of: (a) attaching said iontophoretic drug delivery device to the skin of an animal; (b) causing electrical power to flow between said electrodes at at least one of a constant predetermined voltage and a constant predetermined current; (c) at least one of monitoring the current to one of the first and second electrodes while said power is being delivered at constant voltage and monitoring the voltage between the first and second electrodes while said power is being delivered at a constant current; (d) when at least one of the monitored current and monitored voltage equals a predetermined value, causing the electrical power between the first and second electrodes to change between a constant voltage and a constant current; (e) monitoring power between said electrodes; and (f) if the monitored power reaches a predetermined value, causing the power to the electrodes to change from one of constant voltage and constant current to a constant power provided to the electrodes. 19. In combination: a drug delivery device attachable to a patient for supplying a drug to the patient by iontophoresis, the drug delivery device including a pair of electrodes; and an electronic circuit coupled to the electrodes of the drug delivery device and selectively providing at least one of a controlled voltage and a controlled current to the electrodes, the electronic circuit comprising: adjustable voltage and current generating means coupled to the electrodes of the drug delivery device and providing one of a selectively adjustable current and voltage to the electrodes; means for sensing the current provided to the electrodes of the drug delivery device, the current sensing means generating a sensed current feedback signal which is proportional to the sensed electrode current; means for sensing voltage provided to the electrodes of the drug delivery device, the voltage sensing means generating a sensed voltage feedback signal which is proportional to the sensed electrode voltage; means coupled to the current sensing means for comparing the sensed current feedback signal with a predetermined current threshold signal and generating a current state signal in response to the comparison thereof; feedback signal selector means, the feedback signal selector means being responsive to at least the current state signal and receiving at least the sensed current feedback signal and sensed voltage feedback signal and generating a feedback signal corresponding to at least one of the sensed current feedback signal and the sensed voltage feedback signal in response to at least the current state signal; setpoint selector means, the setpoint selector means receiving a preselected voltage limit signal and preselected desired drug delivery current signal and being responsive to at least the current state signal, the setpoint selector means generating a setpoint signal corresponding to at least one of the voltage limit signal and the desired delivery current signal in response to at least the current state signal; and means for subtracting the feedback signal from the setpoint signal, the subtracting means generating an error signal corresponding to the difference between the feedback signal and the setpoint signal; the voltage and current generating means being responsive to the error signal and adjusting at least one of the current and voltage provided to the electrodes in response thereto. 20. A combination as defined by claim 19, wherein the adjustable voltage and current generating means includes a variable pulse generator and a pulse to power converter coupled to the variable pulse generator, the variable pulse generator being responsive to the error signal and generating a pulsed output signal which varies in correspondence to the error signal, the pulse to power converter being responsive to the output signal of the variable pulse generator and generating an output voltage which varies in correspondence to the pulse generator output signal. 21. A combination as defined by claim 19, wherein the electronic circuit further comprises: multiplication means, the multiplication means receiving the sensed current feedback signal and the sensed voltage feedback signal and effectively multiplying the sensed current feedback signal and sensed voltage feedback signal together and generating a sensed power feedback signal in response to the multiplication thereof, the sensed power feedback signal being provided to the feedback signal selector means; and means coupled to the multiplication means for comparing the sensed power feedback signal with a predetermined first power limit signal and generating a power state signal in response to the comparison thereof; wherein the feedback signal selector means is responsive to one of the current state signal and the power state signal, the feedback signal generated by the feedback signal selector means corresponding to one of the sensed current feedback signal, the sensed voltage feedback signal and the sensed power feedback signal in response to one of the current state signal and the power state signal; and wherein a preselected second power limit signal is provided to the setpoint selector means, the setpoint selector means being responsive to one of the current state signal and the power state signal, the setpoint signal generated by the setpoint selector means corresponding to one of the voltage limit signal, the desired delivery current signal and the second power limit signal in response to one of the current state signal and the power state signal. 22. A combination as defined by claim 19, wherein the electronic circuit further comprises: output enable switch means, the output enable switch means being coupled to the circuit in series between one of the electrodes of the drug delivery device and the voltage and current generating means, the output enable switch means being responsive to a dose state signal and selectively interrupting current flow provided to said one of the electrodes in response thereto; and total drug dose sensing means, the total drug dose sensing means receiving a predetermined total dose signal and comparing the total dose signal with a signal substantially representative of the quantity of drug administered to the patient by the drug delivery device and generating the dose state signal in response to the comparison thereof. 23. A combination as defined by claim 22, wherein the total drug dose sensing means includes: means for determining the quantity of current over time provided to the electrodes of the drug delivery device, the current quantity determining means providing an accumulated current signal in response thereto, the accumulated current signal being the signal substantially representative of the quantity of drug administered to the patient by the drug delivery device; and means coupled to the current quantity determining means for comparing the accumulated current signal with the total dose signal and generating the dose state signal in response to the comparison thereof. 24. A combination as defined by claim 19, wherein the electronic circuit further comprises: output enable switch means, the output enable switch means being coupled to the circuit in series between one of the electrodes of the drug delivery device and the voltage and current generating means, the output enable switch means being responsive to an excess current limit signal and selectively interrupting current flow provided to said one of the electrodes in response thereto; and means for comparing the sensed current feedback signal with a predetermined excess current threshold signal and generating the excess current limit signal in response to the comparison thereof. 25. A combination as defined by claim 19, wherein the adjustable voltage and current generating means includes a power amplifier circuit, the power amplifier circuit being responsive to the error signal and generating an output voltage which varies in correspondence to the error signal, the output voltage being provided to the electrodes of the drug delivery device. 26. A combination as defined by claim 19, wherein the adjustable voltage and current generating means includes a variable pulse generator, the variable pulse generator being responsive to the error signal and generating a pulsed output voltage which varies in correspondence to the error signal, the pulsed output voltage being provided to the electrodes of the drug delivery device.