`
`International Bureau
`
`6 :
`
`Al
`
`(43) International
`
`4 January 1996 (04.01.96)
`
`(21) International
`Num ber:
`(22) International Filing Date:
`
`Application
`
`PCT/US95/07692
`
`23 June 1995 (23.06.95)
`
`KG,KP,KR,KZ,LK,LR,LT,LU,LV,MD,MG,MN,
`
`PCT
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(51) International Patent Classification
`WO 96/00110
`(11) International Publication Number:
`A61N 1130, A61B 5/00, 10/00
`P ublication Date:
`(81) Designated States: AM, AT, AU, BB, BG, BR, BY, CA, CH,
`CN, CZ, DE, DK, EE, ES, Fl, GB, GE, HU, IS, JP, KE,
`MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK,
`TJ, TM, TI, UA, UG, UZ, VN, European patent (AT, BE,
`CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT,
`SE), OAP! patent (BF, BJ, CF, CG, CI, CM, GA, GN, ML,
`MR, NE, SN, TD, TG), ARIPO patent (KE, MW, SD, SZ,
`
`(30) Priority Data:
`
`08/265,048
`08/373,931
`
`us
`24 June 1994 (24.06.94)
`us
`10 January 1995 (10.01.95)
`
`UG).
`
`(71) Ap plicant: CYGNUS THERAPEUTIC SYSTEMS [US/US];
`
`400 Penobscot Drive, Redwood City, CA 94063 (US).
`
`(72) Inventors: TAMADA, Janet; 1622 Ralston Avenue, Belmont,
`CA 94002 (US). AZIMI, Nooshin, T.; 807 Bay Harbour
`Drive, Redwood City, CA 94065 (US). LEUNG, Lewis;
`16 Madrona Street, San Carlos, CA 94070 (US). LEE,
`Richard, K-T; 5698 Tan Oak Drive, Fremont, CA 94555
`(US). PLANTE, Phillip, J.; 655 South Fair Oaks, M-116,
`
`CA 94086 (US). BHAYANI, Bhaskar, V.; 63
`Sunnyvale,
`Mission Ridge Court, Fremont, CA 94539 (US). CAO,
`
`Michael; 308 Roosevelt A venue, Sunnyvale, CA 94086
`
`(US). TIERNEY, Michael, J.; 368 North Sixth Street, San
`Jose, CA 95112 (US). VIJAYAKUMAR, Prema; 43493
`Souther Land Way, Fremont, CA 94539 (US).
`
`Published
`With international search report.
`
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`(74) Agents: SHAY, James, R. et al.; Morrison & Foerster,
`
`755
`
`Page Mill Road, Palo Alto, CA 94304-1018 (US).
`
`(54) Title: IONTOPHORETIC SAMPLING DEVICE AND METIIOD
`216
`
`224 168
`
`160
`
`164
`
`162
`
`113� �111
`
`(57) Abstract
`
`medium (111, 113); and an iontophoretic power source (224). The conductive medium (111, 113) is either
`
`
`
`
`An iontophoresis apparatus for the transdermal monitoring of a target substance comprising: first and second collection
`reservoirs,
`the first collection reservoir comprising
`medium (111) and the second collection reservoir comprising
`a first ionically
`conductive
`a second
`
`medium (I 13); a first iontophoresis electrode (162) in contact with the first conductive
`ionically conductive
`
`medium (111) and a second
`
`iontophoresis electrode (164) in contact with the second conductive
`a sensor for detecting the target substance contained
`medium (113);
`·within at least one conductive
`containing an ionically conductive medium. The invention
`an ionically
`
`also includes a collection
`
`conductive hydrogel or a wicking material
`
`
`
`for use with an iontophoresis for the transdermal monitoring of a target substance, the collection
`comprising an
`reservoir
`reservoir
`apparatus
`hydrogel having a pH in the range of from about 4.0 to about 10.0 and an enzyme reactive
`ionically conductive
`with the target substance.
`also inc1udes a method for using the transdennal
`is a method for continuous
`
`monitoring apparatus. In particular,
`The invention
`the invention
`
`
`
`
`
`in vivo monitoring of the blood glucose level of a patient comprising the following steps: (a) placing a collection reservoir on a collection
`(b) applying electrical
`energy to the collection site to move glucose or a glucose metabolite
`site on a tissue surface of the patient;
`
`into the
`collection reservoir; (c) analyzing
`
`
`
`for concentration of glucose or glucose metabolite; (d) correlating
`
`the collection reservoir
`the concentration
`
`in step (c) with blood glucose level; and (e) performing steps (a)-(d) substantially continuously.
`determined
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`"
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`FOR THE PURPOSES OF INFORMATION ONLY
`States party to the PCT on the front pages of pamphlets publishing international
`
`Codes used to identify
`
`applications under
`
`the PCT.
`
`AT
`AU
`
`BB
`BE
`BF
`BG
`BJ
`BR
`DY
`CA
`CF
`CG
`CH
`C l
`CM
`CN
`
`CZ
`DE
`
`Aus1ria
`Aus1ralia
`Barbados
`Belgium
`Burkina Faso
`
`Bulgaria
`
`Benin
`Brazil
`Belarus
`
`Congo
`Swi1zerland
`
`Canada
`Cen1ral African Republic
`COie d'Ivoire
`
`Cameroon
`China
`Czechoslovakia
`Czech Republic
`Gennany
`
`cs
`DK Denmark
`ES
`GA Gabon
`
`Fl
`FR
`
`Spain
`Finland
`F1'1111cc
`
`GB
`G E
`GN
`GR
`HU
`IE
`
`IT
`JP
`
`KE
`KG
`KP
`
`Uoi1ed Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`
`Japan
`Kenya
`
`Democratic People's Republic
`
`Ireland
`Italy
`Kyrgysian
`of Korea
`KZ Kazakhsian
`LI
`Luxembourg
`
`KR
`
`Republic of Korea
`
`Liechtens1cin
`Sri Lanka
`
`LK
`LU
`Lal via
`LV
`Monaco
`M C
`Republic of Moldova
`MD
`Madagascar
`MG
`ML Mali
`Mongolia
`MN
`
`M R
`Maurii.ania
`MW Malawi
`NE
`Niger
`Netherlands
`Norway
`
`NL
`PL
`
`NO
`NZ
`
`New Zealand
`
`Russian Federa1ion
`
`,.
`
`Poland
`PT Ponugal
`RO
`Romania
`RU
`SD
`SE
`Sl
`SK
`SN
`TD
`
`Sudan
`Sweden
`Slovenia
`Slovakia
`Senegal
`
`Chad
`
`Togo
`Tajikistan
`and Tobago
`Trinidad
`Ukraine
`Uni1ed States of America
`Uzbekis1an
`Vie1 Nam
`
`TG
`
`TJ
`TT
`UA
`
`us
`uz
`VN
`
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`
`IONTOPHORETIC SAMPLING DEVICE AND METHOD
`
`BACKGROUND OF THE INVENTION
`This invention relates generally to the
`transdermal monitoring of the concentration of substances
`in blood and, in particular, to the use of reverse
`iontophoresis or electroosmosis for the continuous
`transdermal monitoring of blood glucose .
`Many diagnostic tests are performed on humans
`by evaluating the amount or existence of substances in
`the blood. One blood substance of interest is blood
`glucose . Typically, blood samples are removed from a
`subject by either using a syringe or by pricking the
`\
`skin. The amount of blood drawn, of course , depends upon
`the amount of blood required for testing. Thereafter,
`the blood sample may be prepared and specifically tested
`for a variety of substances using techniques well known
`in the art .
`Over the last few years methods of determining
`the concentration of·blood glucose or other substances
`without drawing blood have been developed . For example ,
`Stanley U . S . Patent No . 5 , 13 9 , 0 2 3 describes a transdermal
`glucose monitoring apparatus that uses a permeability
`enhancer, such as a natural bile sal t , to facilitate
`transdermal movement o f glucose along the concentration
`gradient between the higher glucose concentration in the
`interstitial fluid and the lower glucose concentration in
`the receiving medium.
`In some embodiments, the receiving
`medium is the aqueous portion of a hydrogel support
`adhered t o the subject ' s skin.
`Stanley measured the
`glucose concentration within the hydrogel by removing the
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`hydrogel from the subject ' s skin, placing the hydrogel in
`water and letting the glucose diffuse out of the hydrogel
`into the water . The water was then analyzed for glucose
`concentration.
`Sembrowich U . S . Patent No . 5 , 0 3 6 , 861 describes
`a glucose monitor that collects the subject ' s sweat
`through a skin patch attached to the subject ' s wrist .
`Sembrowich describes the use of iontophoresis to
`transdermally introduce a gel into the subj ect ' s skin.
`The gel contains a cholinergic agent for stimulating the
`secretion mechanism of the eccrine sweat gland and agents
`that minimize or prevent loss of glucose from the sweat
`as it travels from the sweat gland to the skin patch.
`The Sembrowich device uses electrodes to measure the
`glucose level in the collected sweat by some unspecified
`method .
`
`Schoendorfer U . S . Patent No . 5 , 07 6,273
`describes a method and apparatus for determination of
`chemical species in body fluid.
`Sweat expressed from the
`subj ect ' s skin is collected in a patch adhered to the
`subj ect ' s skin. The patch concentrates the sweat in a
`binder layer by driving off a portion of the collected
`water. The collected analyte binds with a specific
`binding partner in the patch to ·present a visual
`indication of its presence in the patch.
`Schroeder U . S . Patent No . 5 , 14 0 , 9 8 5 discloses a
`· The device
`sweat-collecting device mounted on a subj ect .
`has an electrode-based glucose detection system that can
`give a qualitative indication of blood glucose
`concentration .
`Glikfeld U . S . Patent No . 5 , 279 , 543 describes
`the use of iontophoresis to sample a substance through
`skin into a receptor chamber on the skin surfac e .
`I n one
`embodiment, Glikfeld describes an in vitro device
`consisting o f two gel electrodes attached to one side of
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`hairless mouse skin. Radiolabeled glucose is placed on
`the other side of the skin, and current is applied to the
`electrodes for a period of time. The electrodes are then
`analyzed for radioactivity content by conventional liquid
`scintillation counting.
`(See Glikfeld col . 7 , line 5 1 ,
`t o col . 8 , line 1.) Glikfeld suggests that this sampling
`procedure can be combined with a specific glucose
`biosensor or glucose selective electrodes, but Glikfeld
`does not describe how that combination might be achieved.
`(See Glikfeld col . 9 , lines 27-34 . )
`.
`
`SUMMARY OF THE INVENTION
`This invention improves on prior art
`transdermal monitoring methods and devices by providing
`an iontophoretic sampling device with an integrated
`sensor for monitoring the blood concentration of target
`substances or constituents noninvasively .
`'
`A general object of this invention i s to
`provide a means of extracting substances in the blood
`through the skin using reverse iontophoresis or
`electroosmosis .
`In a preferred embodiment , one or more
`collection reservoirs are held in contact with the
`subject ' s skin. The reservoirs contain a conductive
`medium and are in turn in contact with electrodes and a
`means for providing electric potential or current between
`the collection reservoir site and another site on the
`subject's skin. The collection reservoirs are also in
`contact with a means for sensing and/or quantifying the
`concentration of a target substance .
`This invention i s particularly advantageous
`over drawing blood from a subject when extensive time­
`consuming sample preparation is required to perf orrn a
`diagnostic test on whole blood . This invention is also
`advantageous for neonates (who have a small blood volume)
`and for subjects who must have frequent testing.
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`
`In a preferred embodiment , the collection
`reservoirs consist of an ionically conductive hydrogel or
`wicking material soaked with an ionically conductive
`medium . The advantage of using a hydrogel or wicking
`material as the extraction means is that by collecting
`the target substances into a semi -solid medium which is
`in contact with a target substance sensor, there is
`direct feedback to the subject of whether, or how much
`o f , the target substance is in the blood. Also, because
`the target substances are extracted into a hydrogel or
`other medium of small volume , the concentration of the
`substance is higher than can be obtained by reverse
`iontophoretic extraction into a liquid solution, as in
`some prior art devices .
`There are a number of different substances that
`can be sampled using the reverse iontophoresis/electro­
`( i . e . ,
`osmosis techniques described herein . Charged
`having a negative or positive ionic charge) substances
`will be extracted in the highest concentration.
`Uncharged substances will be extracted at lower, but
`still quantifiable , concentrations . An example of an
`uncharged substance is glucose . Obviously, there are
`many other substances in the body which would be of
`interest to sample and analyze . These include , but are
`not l imited to, amino acids , enzyme substrates or
`products indicating a disease state or condition, other
`markers of disease states or conditions, drugs of abuse,
`therapeutic drugs , and electrolytes .
`Different substances will be extracted at each
`electrode , as one e lectrode is positively charged and
`will attract negatively charged substances, and the other
`electrode is negatively charged and will attract
`positively charged substances . Uncharged substances may
`be extracted at either· electrode, although they are
`typically extracted at higher concentrations at the
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`step
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`5
`Each ionically conductive
`negatively charged electrode .
`medium in contact with the electrodes , therefore , may be
`analyzed for different substances .
`(although not
`The invention is particularly
`exclusively) directed to a method for continuous in vivo
`monitoring of the blood glucose level of a patient
`comprising the following steps :
`(a) placing a collection reservoir on a
`collection site on a tissue surface of the patient;
`( b ) applying electrical energy t o the
`collection site to move glucose or a glucose metabolite
`into the collection reservoir;
`(c) analyzing the collection reservoir for
`concentration of glucose or glucose metabolite ;
`(d) correlating the concentration determined in
`(c) with blood glucose level ; and
`(e) performing steps
`(a) - (d) substantially
`continuously.
`The method correlates measured glucose levels
`with blood glucose levels over a n extended period o f time
`and tracks changes in blood glucose levels .
`The invention is also particularly, but not
`exclusiveiy, directed to a glucose monitor comprising :
`first and second glucose collection reservoirs
`each containing glucose collection medium selected from a
`group consisting of water and saline solution;
`a power supply having a positive connector and
`a negative connector ;
`conductors and a switch electrically connecting
`the first and second collection reservoirs to the power
`supply positive connector and the power supply negative
`connector , the switch having· a first position in which
`the first collection reservoir is electrically connected
`to the positive.connector and the second collection
`reservoir is electrically connected to the negative
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`connector and a second position in which the second
`collection reservoir is electrically connected to the
`positive connector and the first collection reservoir is
`electrically connected to the negative connector.
`Preferably, the glucose monitor is one wherein the first
`and second collection reservoirs each further comprise an
`electrode in electrical communication with the collection
`medium and with the power supply through a conductor and
`the switch.
`The invention is described in more detail below
`with reference to the drawings .
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`Figure lA is a block diagram of a glucose
`monitoring device according to this invention .
`Figure lB shows a glucose monitoring device
`useful fQr practicing this invention in place on a
`patient .
`
`Figure lC is an exploded drawing of a
`collection reservoir assembly.
`· Figure lD is a cross- sectional drawing of the
`electrode/collection reservoir assembly of Figure lC .
`Figure 2 is a graph of the results of a blood
`glucose monitoring of a fasting subj ect
`(1) using a
`standard protocol .
`Figure 3 is a graph of the results of a blood
`glucose monitoring of a fasting subject
`( 2 ) using a
`standard protocol .
`Figure 4 is a graph of the results of a blood
`oral glucose tolerance monitoring of subject
`(1) as
`Figure 2 using a standard protocol .
`Figure 5 is a graph of the results of a blood
`(1) as
`oral glu9ose tolerance monitoring of subject
`Figure 4 showing only the cathode .
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`Figure 6 is a graph of the results of a blood
`oral glucose tolerance monitoring of a subject
`( 1 ) as
`Figure 5 at the cathode showing a 4 0 min lag time.
`Figure 7 is a graph of the results of a blood
`(1) as in Figure
`glucose monitoring of a fasting subject
`2 showing a drift in flux at the cathode.
`Figure a· is a graph of the results of a blood
`( 1 ) as in Figure
`glucose monitoring of a fasting subject
`7 showing a linear fit to the drift at the cathode in
`flux over 3 h .
`Figure 9 is a graph of the results of a blood
`(1) as in
`oral glucose tolerance monitoring of a subject
`Figure 4 showing subtraction of linear drift as in Figure
`8 from cathode flux .
`Figure 10 is a graph of the results of a blood
`oral glucose tolerance monitoring of a subject
`( 1 ) as in
`Figure 9,showing extracted glucose correlates with blood
`glucose with a 4 0 minute lag as in Figure 6 .
`Figure 1 1 is a graph of the results of an oral
`glucose tolerance monitoring of a subject ( 3 ) showing
`correlation at the anode using a standard protocol.
`Figure 1 2 is a graph of the results of an oral
`glucose tolerance monitoring of a subject (3 ) as in
`Figure 11 showing a 20 min time ·1ag.
`Figure 1 3 is a graph of the results of an oral
`glucose tolerance monitoring of a subject (4 ) showing
`higher flux and better correlation at the anode using a
`standard protocol .
`Figure 14 is a graph of the results of an oral
`glucose tolerance monitoring of a subject (4) as in
`Figure 13 showing a 20 min time lag.
`Figure 15 is a graph of the results of an oral
`glucose tolerance monitoring of a subject (5 ) showing
`correlation at both the cathode and anode using a
`standard protocol.
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`Figure 16 is a graph of the results of an oral
`(5) as Figure
`glucose tolerance monitoring of a subject
`15 showing a 20 min time lag.
`Figure 17 is a graph of the results of a blood
`oral glucose tolerance monitoring experiment on subject
`(6), right arm, using a standard protocol .
`Figure 18 is a graph of the results of a blood
`oral glucose tolerance monitoring experiment on subject
`( 6 ) , left arm, using an alternating protocol.
`Figure 19 is a graph of the results of a blood
`oral glucose tolerance monitoring experiment on subject
`( 7 ) , right arm, using a standard protocol.
`Figure 2 0 is a graph of the results of a blood
`oral glucose tolerance monitoring experiment on subject
`(7), left arm, using an alternating protocol.
`Figure 21 is a graph of the results of a
`fasting �lood glucose monitoring experiment on subject
`(6) using an alternating protocol.
`Figure 2 2 is a graph of the results of a
`fasting bloo� glucose monitoring experiment on subject
`(6) as Figure 21 showing only the cathode.
`Figure 23 is a graph of the results of a blood
`glucose monitoring of the same subject (6) as Figure 1 8 ,
`left arm, but with the drift adjusted for the cathode as
`in Figure 2 2 .
`Figure 24 is a graph of the results of a blood
`glucose monitoring of the same subject (6) as Figure 18
`but with the time lag and drift adjusted for the cathode.
`Figure 25 is a graph of the results of a blood
`glucose monitoring of the same subject (6) as Figure 1 8
`but with the drift adjusted for the anode as in Figure
`21 .
`
`Figure 26 is a graph of the results of a blood
`glucose monitoring of the same subject
`( 6 ) as Figure 18
`but with the time lag and drift adjusted for the anode.
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`Figure 27 is a graph of the results of a blood
`glucose monitoring of the same subject
`( 7 ) as Figure 2 0 ,
`left arm, but with the time lag and drift adjusted for
`the cathode .
`Figure 2 8 is a graph of the results of a blood
`glucose monitoring of the same subject
`(7) as Figure 2 0 ,
`left arm, but with the time lag and drift adjusted for
`the anode .
`
`Figure 2 9 is a graph of the results of a blood
`glucose monitoring experiment using several cycles of
`direct current and several cycles of alternating
`polarity.
`
`Figure 3 0 is a graph of the results of
`iontophoretic sampling of glucose compared to passive and
`wash controls .
`Figure 3 1 is a graph of the cumulative amount
`of gluco�e extracted passively from the skin plotted as
`a function of the square-root of time. Each line
`corresponds to a single subject.
`Figure 3 2 is a graph of the results of glucose
`sampling at pH 8 . 2 using the standard method.
`Figure 3 3 is a graph of the results of glucose
`sampling at pH 8 . 2 using alternating polarity.
`Figure 34A is a top view of an embodiment of
`the invention featuring a co-planar iontophoresis
`electrode and sensor electrodes.
`Figure 34B is a cross-sectional side view of
`the embodiment of the invention shown in Figure 34A .
`Figure 35A is a top view of another embodiment
`of the invention in which the sensor electrodes are
`located on top of the iontophoresis electrode.
`Figure 35B is a cross-sectional side view of
`the embodiment of the invention shown in Figure 3 5A.
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`Figure 36A i s a top view of an embodiment o f
`the invention in which the sensor electrodes are located
`beneath the iontophoresis electrode .
`Figure 36B is a side view of the embodiment of
`the invention shown in Figure 36A.
`Figure 37A is a top view of an embodiment of
`the invention featuring an annular iontophoresis
`electrode surrounding the sensor electrodes .
`Figure 37B is a side view of the embodiment
`shown in Figure 37A.
`Figure 38 is an exploded view of the embodiment
`of Figure 37 and a strap-on housing .
`Figure 39 is a side view showing an optical
`sensing scheme .
`Figure 4 0 is a schematic diagram showing an
`iontophoretic collection system according to this
`invention.
`Figure 41 is an exploded view of one embodiment
`of an iontophoretic collection system according to this
`invention.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
`Definitions
`Unless defined otherwise all technical and
`scientific terms used herein have the same meaning as
`commonly understood by one of ordinary skill in art to
`which this invention is directed . Although any methods
`and materials similar or equivalent to those described
`herein can be used in the practice or testing of this
`invention, the preferred methods and materials are now
`described.
`All patents and publications cited herein are
`incorporated herein by reference for the purpose of
`disclosing and describing information for which the
`patents and publications are cited in connection with .
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`WO 96/00110
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`PCT/US95/07692
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`1 1
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`The fol lowing terms are used throughout the
`application:
`By " applying electrical energy to the
`collection site to move glucose or a glucose metabolite
`into the collection reservoir" is meant applying
`electrical energy of sufficient strength and duration to
`the tissue surf ace of a patient in order to transport the
`glucose or a glucose metabolite from beneath the tissue
`at a collection site on the surface of the t issue into a
`defined collection area . This includes the method known
`as iontophoresis .
`"Iontophoresis " as used herein means a method
`for transporting positive or negative ions or even
`uncharged non-ionic substances across tissue through the
`In
`application of electrical energy to the tissue .
`conventional iontophoresis , a reservoir is provided at
`the tissµe surface to serve as a source of material to be
`transported or as a collector of material transported.
`" Reverse iontophoresis" refers to the movement
`of an ionically charged substance from the blood across
`the epithelial membrane and into a collection device
`under the influence of an applied electric potential .
`"Electroosmosis" refers to the movement of a charged or
`uncharged substance through a membrane into a collection
`device under the influence of an applied electric
`potential .
`"Reverse iontophoresis" and "electroosmosis"
`will be used·interchangeably herein to refer to the
`movement of an ionically charged or uncharged substance
`across an epithelial membrane upon the application of an
`electric potential t o the epithelial membrane through an
`ionically conductive medium.
`As used herein "sampling" or "monitoring" as
`used herein means the extraction of a substance from an
`organism through the tissue . The tissue or skin can be
`natural or artificial tissue and can b e o f plant or
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`animal nature , such as natural or artificial skin, blood
`vessel tissue, intestinal tissue and the like . The term
`"artificial" as used herein means an aggregation of cells
`of monolayer thickness or greater which are grown or
`cultured in vivo or in vitro and which function as a
`tissue of an organism but are not actually derived, or
`excised, from a pre-existing source or host . The
`subject/patient or host organism can include warm-blooded
`animals and is particularly, a mammal , such as rats ,
`mice, pigs, dogs , cats, cattle, sheep, horses and
`especially a human being. When the tissue is human skin,
`the tissue surface is the stratum corneum surf ace or
`mucosal tissue, such as in the oral, nasal or vaginal
`cavity.
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`"Epithelial layer" refers to a membrane
`surface , such as skin and mucosal membranes .
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`General Materials and Methods
`The method and apparatus of this invention may
`be used to transdermally sample and quantify or qualify
`the level of a substance in a patient ' s blood. The
`method and apparatus will be initially described as used
`to transdermally sample and quantify or qualify glucose
`or a glucose metabolite.
`I t should be understood that
`the method and apparatus o f this invention may be used to
`transdermally sample and quantify or qualify other
`substances as wel l .
`There is a need to sample and quant ify or
`qualify glucose or a glucose metabolite in the blood, for
`example, for the purpose of diabetes diagnosis and
`treatment. This preferably needs to be done without the
`invasive withdrawal of blood by a needle into a
`collection reservoir/container. For maximum benefit , the
`sampli�g and quantification also need to be performed
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`AGAMATRIX, INC. EXHIBIT NO. 1021
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`substantially continuously and the. measured glucose
`values need to track actual blood glucose levels .
`Accordingly, the method of the invention is
`useful in continuously monitoring the levels of glucose
`or a glucose metabolite from the body . The method can
`also be used for the measurement of blood glucose levels
`in either a semi-continuous or a single measurement
`method. The method can be practiced by a device that
`provides electrodes or other means for applying electric
`current to the tissue at the collection site ; one or more
`collection reservoirs or sampling chambers to receive the
`glucose ; and a glucose concentration measurement system.
`A pref erred embodiment of the method and apparatus are
`described in more detail below .
`According t o the method of this invention, a
`glucose collection reservoir is placed at a collection
`site on a tissue surface of the patient, for example , on
`the stratum corneum of the patient ' s skin or on the
`mucosal epithelium. Electrical energy is applied to the
`tissue at the collection site to move glucose or a
`glucose metabolite from the tissue into the collection
`reservoir . The collection reservoir is analyzed
`periodically to measure the glucose or glucose metabolite
`concentration therein, and this measured concentration
`value i s correlated with the patient's blood glucose
`leve l . These steps are repeated to monitor the patient ' s
`blood glucose level substantially continuously and to
`track changes in the patient ' s blood glucose level .
`In a preferred embodiment o f the method, two
`electrodes provide the electrical energy t o the tissue at
`the collection site or sites . Two collection reservoirs
`are provided, one at or near each electrode . The applied
`electrical current is preferably in the range of about
`0 . 01 to about 2 mA/cm2 .
`In applying the electrical
`energy, the polarity of the electrodes i s alternated at a
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`rate in the range of about 0.1 Hz
`(one switch every 10
`seconds) to about 1 switch every hour, so that each
`electrode is alternately a cathode or an anode . Glucose
`is collected in both reservoirs, but is most preferably
`measured in the reservoir acting as the cathode .
`In
`other words , the reservoir in which glucose concentration
`is monitored alternates as the polarity of the electrodes
`alternates .
`The reversal of polarity during the glucose
`sampling method of the invention has advantages,
`including :
`( 1 ) an unexpected enhancement of the
`correlation between blood and iontophoretically extracted
`samples under the alternating polarity method of the
`invention as compared to a non-alternating polarity
`(2) a particularly unexpected increase in the
`protocol,
`normalized flux rate, and ( 3 ) the avoidance of depletion
`of the Agel plating on Agel electrodes or pH variations
`which occur for non-alternating systems .
`The polarity switching can be manual or
`automati c . The polarity switching can be o f any
`\
`frequency, especially at frequencies between about 1
`cycle per 2 0 .seconds to about 1 cycle per 4 hours,
`preferably between about 1 cycle per 2 0 seconds to about
`1 cycle per 2 hours , more preferably between about 1
`cycle per minute to about 1 cycle per 2 hours, or between
`about 1 cycle per 10 minutes t·o about 1 cycle per hour,
`and especially about 1 cycle per half hour. By cycle is
`meant one interval of current in each direction . The
`application of electrical energy in a given cycle may
`cease during glucose analysis of the collection medium .
`In the preferred method, part or all of the
`glucose collection medium is extracted from the
`collection reservoir and analyzed for glucose
`concentration. One preferred analysis method is high
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`(HPLC ) , although other
`
`pressure liquid chromatography
`analysis methods may be used.
`To provide useful information regarding blood
`glucose levels , the glucose concentrations detected in
`the collection medium must be correlated with the
`patient ' s blood glucose .
`Collection medium glucose is
`computed in flux terms, such as nmoles/cm2•hr. This
`information must be translated into blood glucose values
`( expressed, e . g . , in terms of mg/dl) that correspond to
`the measured glucose flux.
`The correlation between blood glucose
`concentration and measure glucose flux may be expressed
`the time lag between blood
`in terms of four variables :
`glucose concentration values and measured glucose flux
`values; linear drift over time of the measured glucose
`flux values ; and the slope and intercept (i.e., the low­
`end bloo� glucose value below which no glucose flux is
`detected) of a line relating time lag and drift-corrected
`glucose flux data to blood glucose concentration.
`Correlation between measured glucose flux and actual
`blood glucose concentration is accomplished through a
`calibration procedure which relates blood glucose data
`and glucose flux data.
`Time lag is defined as the constant time shift
`between blood glucose and glucose flux curves that
`achieves a best fit in curve shape al�ng the time axis
`within predefined tolerances . The amount of time shift
`may be determined manually or automatically with the aid
`of a computer or other processor using known curve shape
`comparison algorithms . Time shift i