71 J Med Dent SciT. Inoue et al.J Med Dent Sci 2016； 63： 71－77

The present study investigates how effectively lidocaine ions are transported across a cellophane membrane through the application of either a direct current (DC) or alternating current (AC). The cellophane membrane was set on a parallel-plate-type acrylic cell with platinum electrodes at both ends, filled with a donor cell of a 1 % aqueous solution of lidocaine and a receptor cell with distilled water. Lidocaine concentrations were measured for 60 min while the following voltages were applied, with changes every 10 min: 3 V DC and 7.5 V sine wave AC; frequency at 1 kHz. As a result, lidocaine concentrations in the receptor cell increased in a time-dependent manner. Significant increases in lidocaine concentrations were observed in groups where the voltage combination consisted of DC 30 min/AC 30 min, DC 50 min/AC 10 min, DC 60 min and AC 10 min/DC 50 min, compared with the passive diffusion group or in groups where voltage application was performed for 20, 30 , 40, 50 and 60 min. Significant increases were also observed in groups where the voltage combination consisted of AC 60 min, DC 10 min/AC 50 min, AC 30 min/DC 30 min and AC 50 min/DC 10 min, compared with the passive diffusion group or in groups where voltage application was performed for 40, 50 and

60 min. These results suggest that lidocaine was delivered more rapidly with DC than with AC, and that its ions are transported faster when voltage is switched from DC to AC than from AC to DC, which is presumably due to the contribution of electrorepulsion by DC voltage application and the vibration energy infiltration mechanism owning to AC. Iontophoresis in combination with DC and AC was found to enable highly efficient drug delivery that shares the benefits of both forms of current application.

Key words: Iontophoresis, Direct current, Alternating current, Lidocaine

1. Introduction

Iontophoresis (IOP) is a method for enhancing the physical skin absorption of drugs using an electric field. As a drug delivery system, it can accelerate the absorption of drugs by skin tissue1. IOP uses two methods for voltage application: direct current (DC) and alternating current (AC)2. The most commonly used method is DC-IOP. Indications include palmar hyperhidrosis, surface anesthesia, oncotomy, eardrum surgery, postoperative analgesia, cancer pain, and hormone replacement therapy3. However, DC-IOP can cause side- effects such as burns and reddening due to skin electrode polarization; and thus, it poses problems including requiring the restriction of application time and decreasing the penetration efficiency4. 5. In contrast, Shibaji et al. previously reported on drug transportation

Corresponding Author: Takutoshi Inoueection of Anesthesiology and Clinical Physiology, Department of Oral Restitution, Division of Oral Health Science, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, JapanE-mail: inoanph@tmd.ac.jpReceived May 27；Accepted September 2, 2016

Original Article

Drug delivery and transmission of lidocaine using iontophoresis in combination with direct and alternating currents

Takutoshi Inoue1), Tomoaki Sugiyama2), Toshiyuki Ikoma2), Hideaki Shimazu3), Ryo Wakita1) and Haruhisa Fukayama1)

1) Section of Anesthesiology and Clinical Physiology, Department of Oral Restitution, Division of Oral Health Science, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University2) Materials and Chemical Technology, Tokyo Institute of Technology 3) Laboratory of Physiology and Biological Engineering, Faculty of Health Sciences, Kyorin University

72 J Med Dent SciT. Inoue et al.

with AC-IOP and identified the possibility of lidocaine ion transportation in ｉｎ ｖｉtｒｏ experiments using sine waves (500 Hz, 1 kHz, 10 kHz, 100 kHz, 1 MHz)6, 7. They also reported that lidocaine ions enhanced rat skin permeation in ｉｎ ｖｉｖｏ experiments7, 8. In such cases, electrode polarization was unlikely, due to polarity changing over time, which enabled prolonged voltage application9. However, compared with DC-IOP, the drug penetration was not sufficient. Therefore, improved penetration efficiency through a new voltage application method is needed.

Nakajima et al. reported that there were no major differences in lidocaine transmission between DC-IOP and AC-IOP in ｉｎ ｖｉtｒｏ experiments. However, ｉｎ ｖｉｖｏ experiments demonstrated that DC-IOP transmission was greater 20 min after voltage application, while AC-IOP transmission was greater DC-IOP from 40 min onward10. In addition, Gaurav et al. performed DC-IOP and AC-IOP lidocaine transmission tests ｉｎ ｖｉtｒｏ and reported that 1 h of DC-IOP was comparable to 2 h of AC-IOP11. That is, DC-IOP works more effectively than AC-IOP. They suggest that efficiency is expected to further increase by transmitting lidocaine using DC-IOP during the initial phase of voltage application and thereafter using AC-IOP. Therefore, in the present study, we investigated how effectively lidocaine ions are delivered across a cellophane membrane by switching the electric field between DC-IOP and AC-IOP in different combinations.

2. Materials and Methods

2.1 Materials2.1.1 Membrane

For the present experiment, we used a cellophane membrane (Futamura Chemical Co., Ltd., Nagoya, Japan) that was 36 µm thick and 2–3 nm in pore size, which is larger than lidocaine molecules by a factor of 2 : 1.

2.1.2 Lidocaine hydrochloride solutionLidocaine hydrochloride (C₁₄H₂₂N₂O • HCl; FW 270.8;

H₂O content 1 mol/mol) was purchased from Sigma-Aldrich Co., Ltd (St. Louis, MO, USA). One percent lidocaine hydrochloride was dissolved in distilled water; pH was 4.6.

2.1.3 Structure of the experimental cellFig. 1 shows the cell structure. The equipment

consisted of an acrylic circular cell comprised of two chambers with platinum electrodes (20 mm in diameter and 0.2 mm thick) set at both ends of the cell in parallel with a membrane. The cell length was 10 mm, and the

cellophane membrane was set in the middle of the cell. The usable diffusion surface area was approximately 3.1 cm2. A donor layer was filled with 1 % aqueous solution of lidocaine hydrochloride (3.0 mL, pH 4.6), and a receptor layer was filled with distilled water (3.0 mL). The cell was then maintained at a constant temperature in a temperature tank (36.5 ℃).

1.2 Methods2.2.1 Electric current application

AC-IOP was set up with a sine wave (7.5 V; 1 kH)10. DC-IOP was set up with 3 V (Fig. 2)10. After the cell was filled with the aqueous solution of lidocaine and distilled water, either DC-IOP or AC-IOP was applied. During the 60 min of voltage application, either DC or AC voltage was switched after a fixed amount of time had elapsed, as shown in Fig. 3. When DC-IOP application was followed by AC-IOP application, the combinations were as follows: 10 min DC/50 min AC (hereafter D1/A5), 30 min DC/30 min AC (D3/A3), and 50 min DC/10 min AC (D5/A1). When AC-IOP application was followed by DC-IOP application, the combinations were as follows: 10 min AC/50 min DC (A1/D5), 30 min AC/30 min DC (A3/D3) and 50 min AC/10 min DC (A5/D1). For comparison and contrast, we added one group where only DC voltage was applied for 60 min (D6), another group where only AC voltage was applied for 60 min (A6), and a passive group where no voltage was applied for a total of 9 groups.

2.2.2 Lidocaine concentrationLidocaine concentrations in the receptor cell were

measured using Hayashiʼs protocol, where 20 µL of aqueous lidocaine solution was collected from the receptor layer every 10 min using a micropipette (20–200 µL, Nichiryo, Tokyo, Japan) for up to 60 min (Fig. 3)12.

＋－

Ｐｌａｔｉｎｕｍ ＰｌａｔｅＥｌｅｃｔｒｏｄｅ

Ｃｅｌｌｏｐｈａｎｅ Ｍｅｍｂｒａｎｅ

Ｒｅｃｅｐｔｏｒ Ｃｈａｍｂｅｒ（Ｄｉｓｔｉｌｌｅｄ Ｗａｔｅｒ）

Ｄｏｎｏｒ Ｃｈａｍｂｅｒ（１％Ｌｉｄｏｃａｉｎｅ ｈｙｄｒｏｃｈｌｏｒｉｄｅ）

Ｔｈｅｒｍｏｃｏｕｐｌｅ Ｍｉｃｒｏｐｒｏｂｅ

Figure 1. The design of the experimental systemThe system consisted of a drug delivery cell with two chambers (donor and receptor), a thermocouple microprobe, and a power device.

73Lidocaine Transport by DC-IOP and AC-IOP

The samples were diluted by a factor of 1 : 25 with distilled water and measured with a spectrophotometer (U - 3310; absorbance range, ︲ 2 – 4 Abs; precision, ± 0.002 Abs: Hitachi, Ltd., Tokyo, Japan). Lidocaine sample absorbance occurred at a wavelength of 262 nm (Ultraviolet light) with an optical path length of 10 mm.

2.2.3 TemperatureA microprobe thermometer (BAT-12, Physitemp, NJ,

USA) was used to measure the temperature of the donor layer every 10 min from the start of voltage application and up to 60 min afterward.

2.2.4 Statistical analysesAll values are shown in terms of mean ± standard

deviation. Current dependency relative to lidocaine concentration changes was evaluated by two-way analysis of variance (ANOVA). The Tukey method was used for analysis of lidocaine concentration and temperature changes. Statistical significance was set at p < 0.05. We used EZR (Saitama Medical Center, Jichi Medical University) for statistical analysis13.

3. Results

3.1 Lidocaine concentration changes3.1.1 Concentration changes when switching from

DC-IOP to AC-IOPFig. 4 shows the lidocaine concentrations in the

receptor layer during passive diffusion or with only DC-IOP or AC-IOP and the lidocaine concentration changes when switching from DC-IOP to AC-IOP. Compared with passive diffusion, lidocaine concentrations increased significantly 20, 30, 40, 50 and 60 min after IOP when energized with D3/A3, D5/A1, and D6 (p < 0.05). With D1/A5 and A6, concentrations increased significantly compared with passive diffusion from 40, 50 and 60 min after IOP (p < 0.05). The lidocaine concentrations in all groups were significantly higher 40, 50 and 60 min after IOP than in the passive diffusion (p < 0.05).

０ １０ ２０ ３０ ４０ ５０ ６０ （ｍｉｎ）Ｔｉｍｅ

１

１

６６

Figure 3. Experimental protocol. Every 10 min for 60 min, 20 µL of the lidocaine solution was taking from the receptor layer using a micro-pipette 　　　　　　　

DC-IOP AC-IOP

（ａ） （ｂ）

Ｔｉｍｅ（ｓ） Ｔｉｍｅ（ｓ）０ ０

ＥＡＣ

-ＥＡＣ

Ｖｏｌｔａｇｅ（Ｖ）

Ｖｏｌｔａｇｅ（Ｖ）

ＥＤＣ

Figure 2. Experimental Waveforms(a) Sine wave (7.5 V; 1 kHz)(b) Direct current (3 V) EAC and EDC represent applied voltage.

74 J Med Dent SciT. Inoue et al.

3.1.2 Concentration changes when switching from AC-IOP to DC-IOP

Fig. 5 shows the lidocaine concentration in the receptor layer during passive diffusion or with only DC-IOP or AC-IOP and the lidocaine concentration changes when switching from AC-IOP to DC-IOP. Compared with

passive diffusion, lidocaine concentrations increased significantly from 20 to 60 min after IOP with A1/D5 and D6 (p < 0.05). Significant increases in concentrations were also seen from 40, 50 and 60 min after IOP with A3/D3, A5/D1 and A6 and compared with passive diffusion (p < 0.05).

0

5

10

15

20

25

0 10 20 30 40 50 60

A6D1/A5D3/A3D5/A1D6Passive

ｍｅａｎ±ＳＤ （n＝ ）P＜

** *

*

*

****

*

*

***** *

**

*

Ｌｉｄｏｃａｉｎｅ

ｃｏｎｃｅｎｔｒａｔｉｏｎ（ｍｍｏｌ/ｌ）

Ｔｉｍｅ（ｍｉｎ）

*

Figure 4. Changes in lidocaine concentration. switching from DC-IOP to AC-IOP, only DC-IOP, only AC-IOP and passive diffusion(●) A6, (○) D1/A5, (▲) D3/A3, (△) D5/A1, (■) D6, (□) Passive.*p < 0.05 vs passive

Ｌｉｄｏｃａｉｎｅ

ｃｏｎｃｅｎｔｒａｔｉｏｎ（ｍｍｏｌ/ｌ）

Ｔｉｍｅ（ｍｉｎ）

0

5

10

15

20

25

0 10 20 30 40 50 60

D6A1/D5A3/D3A5/D1

A6Passive

ｍｅａｎ±ＳＤ （n＝ ）P＜

*

**

**

*

*

*

*

*

*

*

*

*

*

*

*

**

Figure 5. Changes in lidocaine concentration. switching from AC -IOP to DC-IOP, only DC-IOP, only AC-IOP and passive diffusion(●) A6, (■) D6, (◆) A1/D5, (◇) A3/D3, (▲) A5/D1, (□) Passive.*p < 0.05 vs passive

75Lidocaine Transport by DC-IOP and AC-IOP

3.2 Temperature changes (Fig. 6, 7) The donor layer temperature increased in all groups,

but remained constant after 40 min at approximately

35 ℃. No statistically significant differences were found in temperature changes compared with passive diffusion (p > 0.05).

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60

A6D1/A5D3/A3D5/A1

D6Passive

ｍｅａｎ±ＳＤ （n＝ ）P＜

Ｔｉｍｅ（ｍｉｎ）

Ｔｅｍｐｅｒａｔｕｒｅ（℃

）

Figure 6. Temperature of donor chamber. switching from DC-IOP to AC-IOP, only DC-IOP, only AC-IOP and passive diffusion(●) A6, (○) D1/A5, (▲) D3/A3, (△) D5/A1, (■) D6, (□) Passive.*p < 0.05 vs passive

Ｔｅｍｐｅｒａｔｕｒｅ（℃

）

Ｔｉｍｅ（ｍｉｎ）

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60

D6A1/D5A3/D3A5/D1

A6Passive

ｍｅａｎ±ＳＤ （n＝ ）P＜

Figure 7. Temperature of donor chamber. switching from AC-IOP to DC-IOP, only DC-IOP, only AC-IOP and passive diffusion(●) A6, (■) D6, (◆) A1/D5, (◇) A3/D3, (▲) A5/D1, (□) Passive.*p < 0.05 vs passive

76 J Med Dent SciT. Inoue et al.

4. Discussion

4.1 Lidocaine concentration4.1.1 Possible penetration mechanism

In the present experiment, compared with passive diffusion, there was a significant increase in lidocaine drug transfer from 20, 30, 40, 50 and 60 min after IOP with D6, and from 40, 50 and 60 min after IOP with A6.

The principle of drug delivery using DC-IOP can be expressed as the sum of electrorepulsion, electroosmosis, and passive diffusion14. It is thought that the delivery of ionized substances consists mainly of electrorepulsion, but the effect of electroosmosis should also be considered15.

In contrast, the principle of drug delivery using AC-IOP may be expressed as the sum of vibration energy and passive diffusion. Shibaji et al. reported the enhancement effect mechanism of AC-IOP. It is thought that lidocaine ions in an aqueous solution maintain a constant Stokes radius through a Coulomb interaction with water molecules. However, if the ions receive vibration energy, the Coulomb interaction is cut off and the Stokes radius decreases while the diffusion coefficient increases2, 6.

We presume that this is because electrorepulsion added direct pressure to lidocaine ions with DC-IOP and transferred the electric charge, resulting in more rapid delivery. On the other hand, it is believed that with AC-IOP, the diffusion coefficient increases due to vibration energy but delivery requires more time. In other words, during the early phase of lidocaine transport, electrorepulsion is presumably larger than vibration energy.

4.1.2 Switching from DC-IOP to AC-IOP D3/A3, D5/A1 and D6 showed a significant difference

in lidocaine transfer compared with passive diffusion from 20, 30, 40, 50 and 60 min after IOP. This is thought to be a result of the rapid delivery of lidocaine ions in the earlier phase of voltage application with a large contribution from electrorepulsion.

D1/A5 showed a significant difference in lidocaine transfer compared with passive diffusion 40, 50 and 60 min after IOP. This may be interpreted as a resemblance to AC6, as the total amount transferred with DC 10 min is small, and the influence of vibration energy due to subsequent AC-IOP is large. Therefore, we think that efficiency increases with a minimum of 30 min of DC-IOP, which activates the initial phase of electrorepulsion.

It is considered that AC-IOP after DC-IOP may slowly deliver lidocaine ions by using the vibration energy from AC-IOP, starting from a state in which lidocaine

ions have been rapidly delivered by electrorepulsion from the initial phase of DC-IOP. Electrorepulsion added direct pressure to lidocaine ions. By switching from DC-IOP to AC-IOP, the vibration energy cuts off Coulomb interaction, and decreases stokes radius. Lidocaine ions are expected to be transmitted from the early to late phases of transmission, and adverse reactions to DC-IOP may be avoided by switching to AC-IOP.

4.1.3 Switching from AC-IOP to DC-IOP We also found a significant difference when applying

voltage for 40, 50 and 60 min with A3/D3 and A5/D1 compared with passive diffusion. This is thought to be due to the slow separation of lidocaine ions from water molecules and their delivery due to vibration energy in the initial phase of voltage application.

For A1/D5, a significant difference compared with passive diffusion was found when voltage was applied for 20, 30, 40, 50 and 60 min. This is similar to DC6, as the total amount transferred with AC 10 min is small, causing minor effects, and the influence of electrorepulsion from DC-IOP is large.

The initial phase of AC-IOP may primarily involve an increase in the diffusion coefficient due to vibration energy. The vibration energy given to the lidocaine ion, Coulomb interaction is cut off, Stokes radius decreases. By switching from AC-IOP to DC-IOP, electrorepulsion added direct pressure to lidocaine ions with DC-IOP and transferred the electric charge. The rise in lidocaine concentration during the initial phase of application is slow and if voltage is applied for less than 40 min, no significant transmission of lidocaine ions is achieved. And, Fig.5 showed that the transport of lidocaine ions using A6, A3 / D3 and A5 / D1 showed similar curves. Hence, A3 / D3 and A5 / D1 are considered similar to A6.

4.2 Temperature changesNo significant differences in temperature were found

in the present experiment. This suggests that combining DC-IOP and AC-IOP does not cause reddening or burns due to elevated temperature.

In the previous study by Nakajima et al., significant differences in temperature between DC-IOP and AC-IOP were found when voltage was applied for 30-60 min10. Although the cells they used for DC-IOP and AC-IOP were similar to ours, no significant temperature differences were found between DC-IOP and AC-IOP in our experiment. This is presumably due to differences in waveform, as we used a sine wave while they used a square wave. In other words, compared with DC-IOP,

77Lidocaine Transport by DC-IOP and AC-IOP

greater temperature increases are not found with sine waves than square waves.

5. Conclusions

In the present study, we found that drug delivery of lidocaine with D6 is rapid but slow with A6. In addition, while lidocaine concentrations increased significantly compared with passive diffusion from 40, 50 and 60 min after IOP with A3/D3 and A5/D1, lidocaine concentrations also increased significantly from 20, 30, 40, 50 and 60 min after IOP with D3/A3 and D5/A1. This difference is presumably due to the electrorepulsion from DC during the initial phase of voltage application and the infiltration mechanism of the vibration energy from AC. Furthermore, the initial phase of voltage application with D1/A5 and A1/D5, each first phrase is too short, similar to A6 and D6, respectively. According to the results of the present study, iontophoresis in combination with DC and AC appears to facilitate effective drug delivery while harnessing the benefits of each current.

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