Bioelectrochemistry 56 (2002) 233 – 236
`
`www.elsevier.com/locate/bioelechem
`
`Clinical evaluation of safety and human tolerance of electrical sensation
`induced by electric fields with non-invasive electrodes
`
`L. Zhang*, D.P. Rabussay
`
`Genetronics, Inc., 11199 Sorrento Valley Rd., San Diego, CA 92121-1334, USA
`
`Received 17 December 2001; received in revised form 24 January 2002; accepted 28 January 2002
`
`Abstract
`
`This paper reports the first clinical safety study of human tolerance of electrical sensation using non-invasive, flexible surface-type
`electrodes and exponentially decaying electric pulses. The study evaluated the effect of electric fields in the absence of a drug and an
`anesthetic, and was performed in light of potential applications in the field of erectile dysfunction (ED). Twenty impotent patients who had
`previously received injection or intraurethral therapies were enrolled in the study. Voltage escalations from 50 to 80 V (in 10-V increments)
`with a single pulse of 3-ms duration were performed with meander-type electrodes placed on the shaft and part of the glans of the penis. The
`electric fields-induced sensation was assessed via a pain scale from 0 to 10. All 20 patients, who were free to withdraw from the study at any
`point, completed the voltage escalation study. No clinical safety concerns were apparent and no skin irritation was observed after electric
`treatment. Our initial study indicates that the pulses in the tested voltage range were well tolerated by most patients. In previous animal
`experiments under analogous experimental conditions, the application of 50 V has been found effective for transdermal drug delivery into the
`penis. D 2002 Elsevier Science B.V. All rights reserved.
`
`Keywords: Electrical sensation; Human; Skin; Electroporation; Impotence; Anesthesia
`
`1. Introduction
`
`Skin is a potentially attractive target tissue for local and
`systemic delivery of therapeutics. It is easily accessible,
`constantly regenerating, and provides a large surface area.
`Transdermal drug delivery also offers potential advantages
`over other delivery routes such as injection or oral medi-
`cation: convenience, non-invasiveness, and potentially
`fewer side effects for local treatments. However, the skin’s
`highly resistive outer layer, the stratum corneum, presents a
`strong barrier to the delivery of therapeutic levels of most
`drugs. Electroporation (EP) of skin is a powerful tool for
`decreasing the resistance of the stratum corneum and to
`enhance drug penetration. Recent progress in understanding
`the mechanism and effectiveness of EP in cutaneous drug
`delivery has been summarized in [1]. Although about 200
`patients have been treated under local or general anesthesia
`with EP in the context of electrochemotherapy of tumors
`[2,3], very few studies have assessed the tolerability of EP
`on healthy skin without anesthesia [4]. For further clinical
`
`* Corresponding author. Fax: +1-858-410-3397.
`E-mail address: lzhang@genetronics.com (L. Zhang).
`
`applications, it is important to answer key questions such as:
`How painful is EP? Is EP safe?
`Since nerve sensations and pain are subjective experi-
`ences, the threshold of tolerability of the electrical treatment
`is expected to vary from subject to subject. Only human
`studies can provide direct answers to the question whether
`pain experienced during electrical treatment is acceptable or
`not.
`The level of sensation or pain induced by equal stimuli
`depends largely on the concentration of sensory receptors in
`the skin, which varies with the anatomical location, as well
`as the individual’s subjective threshold. The penile skin,
`especially at the glans, is one of the most sensitive locations
`in the human body due to the high density of nerve endings
`and vascularization. In cooperation with others, we had
`previously shown in rabbits that
`topical application of
`vasodilators to the penis, when followed by EP of the penile
`surface, caused various degrees of erection [5]. No erection
`was observed with the control groups (either EP alone no
`drug or drug alone no EP). It indicates that EP increases the
`permeability of the skin tissue for transdermal delivery.
`These encouraging results and the potential of providing
`an alternative treatment for impotent patients prompted us to
`assess the tolerability and safety of electric fields in patients
`
`1567-5394/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.
`PII: S 1 5 6 7 - 5 3 9 4 ( 0 2 ) 0 0 0 5 7 - 9
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`234
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`L. Zhang, D.P. Rabussay / Bioelectrochemistry 56 (2002) 233–236
`
`suffering from erectile dysfunction (ED). ED is a medical
`disorder for men. It has been estimated that it is prevalent in
`2% of men aged 40 years, and in 50% of the male
`population that is 70 years and older. ED affects more than
`20 million men in the US. Intracavernosal
`injection of
`vasodilators, such as prostaglandin E1 (PGE1, alprostadil,
`CAVERJECTR),
`is still a commonly,
`though now less
`frequently, used treatment of ED. It is very painful and
`carries a high risk of corporal fibrosis at frequent usage [6].
`Another approach is transurethral delivery of penile suppo-
`sitories (alprostadil, MUSER), which can also be painful
`and is less effective than injection [7]. More recently, an oral
`formulation of sildenafil citrate (VIAGRAR) has become
`available and is now the first line of treatment. However, the
`use of VIAGRAR is associated with side effects, and cannot
`be used without significant risk by ED patients with
`cardiovascular disease or patients who depend on medica-
`tions containing nitrates.
`The goal of the study reported here was to investigate the
`safety of electric field and the tolerability of electrical
`sensation in the absence of a drug and an anesthetic. This
`is the first clinical study approved by an Institutional
`Review Board (IRB) determining the sensation caused by
`electric field using non-invasive electrodes. Electrical sen-
`sation (pain) was assessed by 20 ED patients via a scale
`ranging from 0 to 10 following voltage escalations. In order
`to develop a clinical viable treatment with electroporation,
`we should consider both aspects: (1) maximize the effi-
`ciency of electroporation, and (2) minimize the pain asso-
`ciated with electrical sensation induce by electric fields.
`Therefore, the patients’ response obtained from this study
`will be valuable information for determining the feasibility
`of further development in the field of electroporation with
`potential medical applications.
`
`2. Experimental
`
`2.1. Study design
`
`This IRB-approved clinical study was conducted by
`MDS Harris (Lincoln, NE) in Phoenix, AZ. Twenty ED
`patients were enrolled in this study. Each patient signed an
`Informed Consent Form prior to receiving the treatments.
`Subjects were divided into two groups: 10 subjects who had
`undergone the intracavernosal injection treatment, and 10
`subjects who had used the transurethral therapy. During the
`screening period, subjects were given a demonstration of the
`Genetronics Transdermal Delivery Device (exponential
`pulse generator and a surface-type meander electrode) and
`received an electrical pulse on their forearm. Those subjects,
`who did not wish to continue, were free to withdraw at that
`time. Subjects who consented to continue proceeded with
`the screening process. The medical screening process
`involved medical history, physical examination, and clinical
`laboratory tests (hematology, serum chemistry, urinalysis,
`
`HIV antibody screen, and urine screen for alcohol and drugs
`of abuse). On the scheduled study day, subjects self-admin-
`istered (under supervision) the Genetronics Transdermal
`Delivery Applicator which covers the penile shaft and part
`of the glans. Each subject initially received a single pulse at
`50 V. If the subjects tolerated the 50 V without any severe or
`serious adverse experiences,
`they could continue with
`voltage escalation in 10-V increments up to a maximum
`of 80 V, depending upon their tolerance for the procedure.
`The pulse length was always set at 3 ms. There was at least a
`1-h rest period between voltage escalation applications.
`After each pulse application, every subject filled out a form
`about the experienced sensation and rated the sensation of
`pain on a scale ranging from 0 to 10, with zero indicating no
`sensation and 10 indicating excruciating pain. Vital signs
`(blood pressure, pulse) were evaluated prior to, and follow-
`ing each treatment. Urinalysis was conducted from a sample
`obtained at the end of the voltage escalations for each
`subject. The subject used the same set of meander electrodes
`throughout the voltage escalation.
`
`2.2. Pulse generator and electrode
`
`The pulse generator was equipped for clinical use and
`delivers exponential pulses (Genetronics, San Diego, CA).
`The Transdermal Delivery Applicator consisted of two
`
`rectangular meander-type electrode patches (25 cm each),
`
`attached to the inside of an inflatable cuff which is normally
`used to measure the blood pressure on the arms of infants
`(Tycos Instruments, Arden, NC). The meander electrode
`patch consisted of an array of interweaving electrode fingers
`with alternating polarity [8]. Each electrode finger was 0.2
`mm wide and was separated by a 0.2-mm gap from its
`neighboring electrodes. The gap was filled with insulator to
`eliminate some bypass current between the adjacent electro-
`des. The patient aligned the two meander electrode patches
`lengthwise along the sides of the mid-shaft such that the
`electrodes also extended onto the sides of the glans.
`
`2.3. Test procedure
`
`The pulse generator was calibrated before each pulse
`application. The surfaces of the electrodes were cleaned
`with alcohol swabs and allowed to dry thoroughly. The
`patient cleaned the penile skin surface on both sides (left
`and right) of the midshaft and on the glans with alcohol
`swabs and let the skin dry thoroughly. Next, the patient
`moistened the penile skin using a cotton ball wetted with the
`saline solution (sham drug). After that, the patient posi-
`tioned the meander electrode patches as described above,
`wrapped the cuff around the penis and secured the cuff by
`closing the VelcroR fasteners. The patient then inflated the
`cuff slowly until
`the cuff and electrodes made uniform
`contact with the surface of the penis, usually at a pressure
`of 20 – 30 mm Hg. The electrodes were connected to the
`pulse generator and a single pulse was delivered. At the end
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`L. Zhang, D.P. Rabussay / Bioelectrochemistry 56 (2002) 233–236
`
`235
`
`the cuff was deflated and removed
`of the procedure,
`together with the electrodes.
`
`3. Results and discussion
`
`Patients were subjected to single pulses of 50 – 80 V
`escalating in 10-V increments and delivered for 3 ms. The
`patients were asked to rate the pulse sensation on a scale of
`0, no pain, to 10, excruciating pain. The results of this study
`are shown in Table 1. Pain scores up to and including level 5
`were considered tolerable. The percentage of tolerability at
`each voltage level was calculated by multiplying the number
`of subjects rating the degree of sensation up to level 5 by
`100 and dividing this result by 20 (the total number of
`patients enrolled). At 50 V, the tolerability of pulse sensation
`was 100%, and 65% of the ratings fell between no pain and
`mild (0 to 2). At 60 and 70 V, tolerability declined slightly
`to 93%, with 30% of the ratings still between 0 and 2. When
`the voltage increased to 80 V, the tolerability dropped to
`75% due to the fact that 25% of the patients marked pain
`scores from 6 to 9. In summary, all patients passed the single
`pulse tests (50 – 80 V, 3 ms) without rating the sensation
`excruciating. Across the voltage escalation range from 50 to
`80 V, the overall of the tolerability was 90% (72 out of 80
`scores). No side effects of electrical
`treatment were
`observed or reported according to clinical examination of
`the patients before and after the tests.
`Many different factors affect the sensation generated by
`electrical pulses delivered to the skin, including voltage,
`current, current density, pulse length, frequency, waveform,
`and body location. In this study we evaluated one of the
`most important factors, i.e., voltage. Aside from its direct
`effect on nerve stimulation, voltage also influences the
`amount of current flow. It is known that above the percep-
`tion threshold, the quality of sensation changes with increas-
`ing current and the degree of pain increases nonlinearly [9].
`One effect of delivering an electrical pulse of the magnitude
`we applied in this study is the breakdown of the insulating
`layer of the skin, the stratum corneum, thus allowing higher
`
`Table 1
`Summary of electrical sensation assessment in ED patients
`
`current flow into and through the skin [10]. This, in turn,
`increases the level of sensation. With increasing applied
`voltages,
`the electrical resistance of the skin decreases
`significantly. Therefore, it is not surprising that the level
`of sensation can escalate substantially with a relatively small
`increase in applied voltage. This phenomenon was observed
`in our study when the voltage was elevated from 50 to 80 V.
`For electroporation enhanced transdermal drug delivery, a
`high degree of breakdown of the skin impedance is desir-
`able. However, in the treatment of patients a compromise
`has to be found that allows sufficient drug permeation
`through the porated skin tissue while not generating unac-
`ceptable pain in creating the pores. In experiments with
`rabbits under similar pulsing conditions, an applied voltage
`of 50 V was effective in delivering a sufficient amount of
`PGE1 transdermally into the penis to cause a full or partial
`erection in all treated animals (n=9). The application of the
`same voltage to humans was tolerable to 100% of the
`patients tested. Knowing that the thickness of human penile
`skin differs from the rabbit’s, and even if the voltage has to
`be increased to 80 V in order to achieve effective drug
`delivery in humans, that voltage would still be tolerable to
`90% of the patients we tested.
`Besides voltage and current, another important factor is
`anatomical location. As mentioned, the penis is one of the
`most sensitive areas of the body and the application of 80 V
`caused significant distress to 25% of the patients. On the
`contrary, in a different study on topical delivery of lidocaine,
`where we tested the pain response to electroporation with
`meander electrodes targeting the forearm skin,
`the pain
`scores were mostly below levels 2 and 3 [4]. In that study,
`the pulse conditions were actually more intense (80 V, 10
`ms, two cycles of six pulses each). Both in the study just
`mentioned and in the study reported here, no skin irritation
`was observed post electrical treatment. However, in a rat
`study with caliper electrodes, where the skin-fold was
`electroporated between two flat, parallel metal plates, the
`appearance of erythema was reported [11]. In this case, not
`only were the upper-most
`layers,
`including the stratum
`corneum affected by the electrical pulses, but also the
`
`Twenty patients were given one electrical pulse each at escalating voltages from 50 to 80 V. After each pulse, every patient scored his subjective sensation
`(pain) according to the scale given above. Pain scores up to and including level 5 were considered tolerable.
`
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`
`underlying tissue. This points out the advantage of electrode
`designs such as the meander electrodes which allow the
`initial electric fields to be mostly localized within the
`superficial layers of the skin, thereby avoiding undesirable
`effects, including pain, in underlying tissues.
`In summary, this study provides evidence that electrical
`treatment with the purpose of enhancing transdermal drug
`delivery appears feasible, even in sensitive areas like the
`penis. Previous studies mentioned above, which included
`actual drug delivery by electroporation in animals and
`humans, make it likely that under the pulsing conditions
`we found acceptable in this study, effective drug delivery
`may be achieved even in the absence of anesthesia. The
`electrode applicators and delivery conditions used here can
`be optimized further depending on the disease target and
`medical requirements.
`
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