This application is a continuation of application Ser. 5 The present invention provides an electrochemically
No. 046,937 filed May 5, 1987, now abandoned, which driven drug dispenser wherein an electrochemical
is in turn a continuation-in-part of application Ser. No. pump provides a controllable source of varying pres
729,860, filed May 2, 1985, abandoned. sure for accurately delivering a small quantity of a drug
at a desired delivery rate over an extended period of
BACKGROUND OF THE INVENTION 10 time. A drug dispenser according to the invention is
This invention relates generally to devices for the implantable, has no moving parts, and achieves the
infusion of drugs into the human body, and, more par- desired delivery rate by means of an electronic control
ticularly, to pump driven devices for the highly accu- ler
rate infusion of small quantities of drugs. An electrochemical pump is a pump in which an The administration of drugs to a patient can be ac- 15 electrochemically active fluid is pumped from one comcomplished through a variety of methods, including partment across an electrolytic membrane into another gravity, mechanical pumps, pressurized gases and os- compartment by an electric current. The fluid is ionized mosis. A gravity dispenser utilizes the force of gravity m the one compartment and the ions are propelled to dispense a drug suspended above the patient. The trough the membrane and are recombined into fluid m delivery rate of the drug is adjusted by means of the 20 the other compartment. _ pressure head, the height of the drug above the patient, A draS denser according to the invention includes and by a restriction of the outlet line leading to the a container, separating means dividing the container patient. However, the delivery rate of the gravity dis- m*° a. dTM8 chambf and a PumP chamber,- an elef °" Penser is difficult to control accurately because of f ^ally active fluid m the pump chamber, an exchanges in the height of the drug as it is dispensed to the 25 tT0?tlc membrane dividing the pump chamber into first .. . , ... . °,.. . , and second compartments, electrodes on opposing sides patient, changes in the posture of the patient and even . , v , . f . .
• x- • *t u i * *!. *■*» ui J of the membrane, and means to provide an electric
variations in the back pressure of the patient s blood. the dectrodes The elJtric current
More miportantly, however, the patient is greatly re- md frQm Qne rtment t0 the other /a Je
stncted in mobility, since the drug must be constantly 3Q determined b the ma^knde of the current. As the
suspended in a container above the patient. A typical fluid flows mtQ the sec*nd c0 artment it exerts es.
controller for adjusting the delivery rate of the gravity sufe Qn the s atin means t0 discharge a drug from
force dispenser is disclosed m U.S. Pat. No. 4,300,552 to {he drug chamber. Control means varies the magnitude
Cannon. of the current to discharge the drug at a predetermined
Other methods for administering drugs eliminate the 35 rate
need for suspending the drug above the patient and, In the absence of ^ current, the fluid diffuses
therefore, greatly improve the mobility of the patient. thr0Ugh the membrane at a characteristic rate of diffu
Mechanical pump dispensers generally consist of an sion ... t0 any difference between the pres
electrically driven mechanical pump. These pumps sure of the fluid in one compartment and the pressure of
provide accurate control of the delivery rate of the 40 the ^d m t^e other. The control means varies the
drug, but incorporate moving parts, which can wear out current with reference to this diffusion rate such that
and break down. These pumps also consume relatively the net rate of flow of the fluid, being equal to an alge
large amounts of power. Other dispensers employ a bnuc sum 0f the pumping rate and the diffusion rate,
pressurized gas to administer the drug to the patient. discharges the drug at the predetermined rate.
Generally, these dispensers are large and bulky, and not 45 The drug may be discharged through a delivery port
easily portable. Furthermore, regulation of the delivery and cneck valve, a permeable membrane, or the like,
rate is often difficult. Typical pressurized gas dispensers The fluid may comprise hydrogen or oxygen or the like,
are disclosed in U.S. Pat. No. 2,766,907 to Wallace, Jr. The separating means may comprise a flexible dia
and U.S. Pat. No. 4,237,881 to Beigler et al. phragm, a sliding wall, or some other device through
Osmosis driven dispensers depend on solutes that 50 which pressure can be communicated from the pump
exhibit an osmotic pressure gradient against water. The chamber to the drug chamber.
delivery rate provided by these dispensers is determined The control means may linearly vary the current at a
by the type of solute used and, therefore, the delivery rate proportional to the diffusion rate to discharge the
rate cannot be varied during operation. Representative drug at a constant rate, or the current may be intermit
osmotic dispensers are disclosed in U.S. Pat. No. 55 tently varied to deliver the drug at a pulsating rate.
3,995,632 to Nakano et al., U.S. Pat. No. 4,034,756 to Pressure sensing means may be included in one of the
Higuchi et al. and U.S. Pat. No. 4,439,196 to Higuchi. compartments to sense the pressure for more precise
Electrically controlled osmotic dispensers are disclosed control. The membrane may include a non-electrolytic
in U.S. Pat. No. 3,923,426 to Theeuwes and U.S. Pat. portion which may be selected according to its diffusion
No. 3,894,538 to Richter. 60 characteristics.
Many patients require a continuous infusion of small It will be appreciated from the foregoing that a drug
quantities of drugs over a period which may be many dispenser according to the invention can achieve accu
hours or even several days in duration. Such drugs rate delivery rates at low dosage levels over an ex
sometimes must be dispensed at constant, precisely-con- tended period of time in a portable, implantable unit. A trolled rates; in other cases, the drugs must be dispensed 65 complex delivery schedule can readily be implemented in a cyclical, pulsating fashion, or at a controlled van- by electronically varying the pumping current. Other
able rate. Accordingly, there is a need for a portable, aspects and advantages of the invention will become implantable drug dispenser that can accurately dispense apparent from the following detailed description, taken
