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Antimicrobial Agents and Chemotherapy, October 2008, p. 3633-3636, Vol. 52, No. 10
0066-4804/08/$08.00+0 doi:10.1128/AAC.00637-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Penetration of Chlorhexidine into Human Skin 
T. J. Karpanen,1*
T. Worthington,1
B. R. Conway,1
A. C. Hilton,1
T. S. J. Elliott,2 and
P. A. Lambert1
Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, United Kingdom,1
Selly Oak Hospital, University Hospital Birmingham NHS Foundation Trust, Raddlebarn Road, Selly Oak, Birmingham B29 6JD, United Kingdom2
Received 15 May 2008/
Returned for modification 4 July 2008/
Accepted 25 July 2008

ABSTRACT
This study evaluated a model of skin permeation to determine
the depth of delivery of chlorhexidine into full-thickness excised
human skin following topical application of 2% (wt/vol) aqueous
chlorhexidine digluconate. Skin permeation studies were performed
on full-thickness human skin using Franz diffusion cells with
exposure to chlorhexidine for 2 min, 30 min, and 24 h. The concentration
of chlorhexidine extracted from skin sections was determined
to a depth of 1,500 µm following serial sectioning of
the skin using a microtome and analysis by high-performance
liquid chromatography. Poor penetration of chlorhexidine into
skin following 2-min and 30-min exposures to chlorhexidine was
observed (0.157 ± 0.047 and 0.077 ± 0.015 µg/mg
tissue within the top 100 µm), and levels of chlorhexidine
were minimal at deeper skin depths (less than 0.002 µg/mg
tissue below 300 µm). After 24 h of exposure, there was
more chlorhexidine within the upper 100-µm sections (7.88
± 1.37 µg/mg tissue); however, the levels remained
low (less than 1 µg/mg tissue) at depths below 300 µm.
There was no detectable penetration through the full-thickness
skin. The model presented in this study can be used to assess
the permeation of antiseptic agents through various layers of
skin in vitro. Aqueous chlorhexidine demonstrated poor permeation
into the deeper layers of the skin, which may restrict the efficacy
of skin antisepsis with this agent. This study lays the foundation
for further research in adopting alternative strategies for
enhanced skin antisepsis in clinical practice.

INTRODUCTION
Effective skin antisepsis is essential in preventing infections
associated with invasive procedures, such as intravascular catheter
insertion or surgery. A range of skin antiseptic agents are
available in the clinical setting, such as povidone-iodine and
chlorhexidine compounds at various concentrations with alcoholic
or aqueous solutions. However, a 2% (wt/vol) chlorhexidine solution
is the recommended agent to be used prior to invasive procedures
according to the EPIC (evidence-based practice in infection
control) and CDC guidelines (
18,
19). Two percent chlorhexidine
digluconate (CHG) has been shown to significantly reduce intravascular
catheter-related infections (
14), yet 2% (wt/vol) CHG in 70%
(vol/vol) isopropyl alcohol demonstrates activity superior to
that of aqueous CHG solution in a preoperative skin preparation
(
9) and in vitro carrier tests (
1). However, little is known
about the kinetics of chlorhexidine skin permeation from either
of these solutions (
11,
25). Microorganisms colonizing the skin
not only reside on the skin surface but are also found to inhabit
hair follicles and lower skin depths (
8). Many antimicrobial
agents exhibit restricted permeation of the skin (
8) and fail
to reach the deeper layers, including the hair follicles, which
harbor coagulase-negative staphylococci (
2,
7,
8,
13,
15) and
propionibacteria (
13). Commensal microorganisms may therefore
persist at the site of incision following skin antisepsis (
4,
22), and such resident organisms may cause infection when the
protective skin barrier is breached during surgical procedures
(
12,
20,
26). Therefore, effective and rapid permeation of the
applied antiseptic agent into the deeper layers of the skin
is essential in preventing infections associated with invasive
procedures.
The aim of the current study was to use the Franz-cell skin model (6) to determine the penetration profile for CHG through excised human skin and to evaluate the skin permeation of 2% (wt/vol) aqueous CHG into the skin using this model.

MATERIALS AND METHODS
Materials.
CHG, diethylamine (high-performance-liquid-chromatography [HPLC]
grade), dimethyl sulfoxide, phosphate-buffered saline (PBS),
sodium heptane sulfonate (HPLC grade), and Tween 80 were purchased
from Sigma-Aldrich (Dorset, United Kingdom). Acetic acid and
methanol (both HPLC grade) were purchased from Fisher Scientific
(Leicestershire, United Kingdom).
Skin samples.
Full-thickness human skin samples were obtained from patients undergoing breast reduction surgery, and full ethical committee approval was obtained prior to this study (REC 2002/169). The full-thickness human skin was frozen on the day of excision and stored at –70°C until required.
Quantification of CHG.
HPLC was used to measure the amounts of CHG in the skin samples obtained during the permeation studies. The analyses were performed using an Agilent 1200 series HPLC system (Agilent Technologies, United Kingdom). The samples were run at a flow rate of 1.2 ml/min at room temperature through a reverse-phase chromatography column (CPS-2 Hypersil 5-µm column; dimension, 150 by 4.6 mm [Thermo Electron Corporation, United Kingdom]), with UV detection at 254 nm. The isocratic mobile phase consisted of a methanol:water mixture (75:25) with 0.005 M sodium heptane sulfonate and 0.1% (vol/vol) diethylamine adjusted to pH 4 with glacial acetic acid. The HPLC method was validated by repeating a series of standardized CHG concentrations five times and plotting a graph of peak area versus CHG concentration. The level of detection (LOD) and level of quantification (LOQ) were calculated from the standard curve according to the following equations: LOD = (3 x standard deviation)/slope; LOQ = (10 x standard deviation)/slope.
Skin permeation studies.
Skin permeation studies were performed with vertical Franz diffusion cells (Fig. 1). The receptor compartment was filled with 29 ml of PBS, maintained at 37°C by using a circulating water jacket, and agitated by stirring with a magnetic bar. Skin samples were thawed in PBS at room temperature, dried with an absorbent towel, and mounted on Franz diffusion cells with the stratum corneum (SC) uppermost, facing the donor compartment. The surface area exposed to the test compound was 3.14 cm2 (2 cm in diameter). All entrapped air between the skin and receptor fluid was removed, and the skin was left to equilibrate for 30 min to reach the skin surface temperature of 32°C.
Twenty percent (wt/vol) aqueous CHG was diluted with distilled
water and 0.1% (vol/vol) Tween 80 to obtain the final test solution
of 2% (wt/vol) CHG. One milliliter of test solution was spread
over the skin surface in the donor compartment, and the compartment
was sealed with a moisture-resistant film (Parafilm M, Alcan
packaging) to prevent evaporation. One milliliter of receptor
fluid was removed every 30 min for 2 h, every hour between 2
to 6 h, and at 8 h, 12 h, and 24 h. Fluid removed from the receptor
compartment was immediately replaced with an equal volume of
fresh PBS solution. All samples were filtered through a 0.45-µm
nylon filter (Kinesis, United Kingdom) and analyzed by HPLC.
The assay was performed in triplicate and on two different donor
skin samples.
CHG penetration profile studies.
Excised full-thickness human skin samples were mounted on the Franz diffusion cells as described above and exposed to 2% (wt/vol) CHG for 2 min, 30 min, and 24 h. Following exposure, the skin samples were removed, washed with PBS, and dried with an absorbent towel. The skin samples were immediately sprayed with a cryospray (Bright Instruments) and frozen at –20°C. Punch biopsy samples (7 mm in diameter) were cut from each frozen sample in triplicate and placed on a cork disc in embedding compound (Bright Instruments, Cambs, United Kingdom). The frozen samples were sectioned horizontally with a microtome (Bright Instruments) into 20-µm sections (from the surface to a depth of 600 µm) and 30-µm sections (from depths of 600 to 1,500 µm). Each section was placed in an Eppendorf tube and the total weight of each skin sample determined. Chlorhexidine was extracted from the skin by placing 1 ml of HPLC mobile-phase solution in each tube, followed by incubation of the sealed tubes at 60°C for 1 h. Following this, the samples were analyzed by HPLC and the concentration of CHG (µg/mg of skin) determined. Control skin (skin without treatment) was analyzed parallel to the test samples. Effective elution and recovery of CHG from the skin by this method were confirmed prior to the experiment by injecting a standardized quantity of CHG (128 µg) into 10 skin samples, extracting the CHG, and determining the recovered amount (94.4 ± 1.82%; data not shown).

RESULTS
HPLC validation.
The mean retention time for CHG was 3.6 min. There were no intervening
peaks from endogenous contaminating compounds within skin samples.
The HPLC method gave a linear response (
r2 = 0.999) over the
concentration range of 0.0039 µg/ml to 128 µg/ml.
The level of detection and level of quantification were calculated
at 0.016 µg/ml and 0.052 µg/ml, respectively.
Skin permeation studies.
No CHG was detected in the receptor compartment during the 24-h exposure of excised full-thickness human skin to 2% (wt/vol) aqueous CHG.
CHG retention studies.
After 2 min, 30 min, and 24 h, concentrations of chlorhexidine within the skin were highest in the surface 100-µm sections and reduced below depths of 300 µm (Fig. 2 and 3). The concentrations of CHG within the top 100-µm sections of skin were 0.157 (± 0.047) µg/mg tissue and 0.077 (± 0.015) µg/mg tissue after 2-min and 30-min exposures to 2% (wt/vol) CHG, respectively (Fig. 2). The concentration of CHG within deeper layers (below 300 µm) fell to less than 0.002 µg/mg tissue following both 2-min and 30-min exposures. The difference between the amounts of chlorhexidine within the top layers between 2 min and 30 min of exposure was not significant (P > 0.05) (Student's t test, INSTAT2; Graphpad, San Diego, CA). The concentration of CHG was significantly higher within all skin sections following 24 h of exposure to CHG than with the shorter exposure times. The concentration of CHG was 7.88 (± 1.37) µg/mg tissue within the upper 100-µm sections and less than 1 µg/mg of tissue at depths of 300 µm and below.

DISCUSSION
This study demonstrates that 2% (wt/vol) chlorhexidine, the
antiseptic agent recommended within EPIC and CDC guidelines
for skin antisepsis prior to central venous catheter insertion,
poorly permeates into deeper layers of the skin after 2 min
and 30 min of exposure to the antiseptic. The concentrations
of CHG within the upper 100-µm sections of skin were 0.157
(± 0.047) µg/mg tissue and 0.077 (± 0.015)
µg/mg tissue after 2 min and 30 min, respectively. If
1 g of tissue is estimated to equal 1 ml, these levels are higher
than the concentrations required to kill many common skin microorganisms,
such as
Staphylococcus epidermidis, under in vitro conditions
(
10). Below 300 µm, the CHG concentration remained less
than 0.002 µg/mg tissue, which may not be effective for
eradicating microorganisms on the skin (
17), especially microorganisms
residing deep in the hair follicles. Furthermore, chlorhexidine
activity is reduced in the presence of organic compounds, such
as fatty acids, and at lower pHs (
16) and therefore may reduce
the efficacy of skin antisepsis with CHG. An exposure time of
2 min was used to reflect the clinical conditions used prior
to surgery (
5). Although the 2-min study appears to show a larger
amount of bound chlorhexidine than the 30-min study, there is
variability in concentrations measured in the top layers, as
is expected with the shorter exposure period (
24), and the difference
between 2 min and 30 min of exposure is not significant (
P >
0.05). It is likely that a steady state has not yet been reached
at 2 min. A similar phenomenon was reported by Wagner et al.
(
23). Skin was also exposed to 2% (wt/vol) CHG for 24 h, and
the concentration of CHG in the deeper sections, i.e., beyond
300 µm, was less than 1 µg/mg tissue. These levels
of CHG are more than the minimum bactericidal concentrations
for many skin commensals (
10); however, this level of CHG was
obtained only after a prolonged time of contact of the skin
with CHG. In this study, no detectable levels of CHG were recovered
from the receptor compartment, suggesting that aqueous CHG does
not permeate through the full thickness of excised skin and
is retained within the tissue. These results support previous
research on another CHG-based compound, chlorhexidine phosphanilate,
which was also shown not to permeate through full-thickness
skin samples (
25).
In this study, a model for studying the delivery of CHG into excised full-thickness human skin was evaluated. Skin permeation studies are commonly performed in vitro with vertical or horizontal diffusion cells using skin or artificial membranes. This study was performed using vertical diffusion cells (Franz-type diffusion cells) to evaluate the delivery of CHG through excised full-thickness human skin. Such conditions mimic the in vivo environment by maintaining the physiological receptor fluid at body temperature and the skin surface temperature at 32°C (6, 23). Skin permeation studies generally evaluate drug delivery through the skin by measuring drug diffusion into the receptor fluid through the SC or epidermis, which are the main barriers for skin permeation. However, the use of stripped skin layers, such as isolated SC or epidermal layers, for drug permeation studies may influence the results, with possible retention of the drug in the dermal layers of the skin. Full-thickness skin was used in this study to determine the location of CHG throughout the skin, rather than studying the flux of the drug through the barrier layers. Following exposure to CHG, the full-thickness human skin was sectioned to a depth of 1,500 µm by sequential sectioning with a microtome, producing a total of 60 sections per skin sample. Skin sectioning has been used in many previous studies (21); however, the SC is often removed by tape stripping prior to sectioning of the skin. In this study, the full-thickness skin samples were sectioned throughout the sample without prior removal of the surface layers. This study demonstrates that the CHG permeation through the full-thickness skin was not linear, which was expected due to the variation in structure at various layers. The top 100-µm layer of the skin, which contains SC (average of 10 to 20 µm thick) and other epidermal layers (50 to 100 µm thick), contained the largest amount of CHG following exposure to 2% (wt/vol) CHG over all time points studied. Previous research has shown that the main permeation barrier for skin absorption is the SC (3, 11, 25), which is thought to be due to its high-lipid matrix and packed layers of keratinized epithelial cells. Furthermore, this study found that below 300 µm, at the dermal layer, the level of CHG remained constantly low. Depending on the body site, dermis contains hair follicles and other skin appendages, including sebaceous glands and sudoriferous glands (sweat-producing glands), which are of interest in skin antisepsis since they may be niches for microbial colonization of the skin following skin antisepsis (7, 8). It is generally recognized that skin antisepsis does not sterilize the skin; our study confirms this and demonstrates that it may be due to poor permeation of chlorhexidine into the deeper layers of the skin.
In conclusion, this study showed poor permeation of chlorhexidine through excised full-thickness human skin after 2 min and 30 min of exposure to aqueous 2% (wt/vol) CHG. The levels of CHG were highest within the top 100-µm sections of skin and remained consistently low within the deeper layers. Furthermore, the model presented in this study is a valuable tool in determining a permeation profile for chlorhexidine through human skin in vitro. This study lays the foundation for further research within this area with a view to potentially adopting alternative strategies for enhanced skin antisepsis in clinical practice.

ACKNOWLEDGMENTS
This work was supported by EPSRC CASE grant CNA/05/09 with funding
from Insight Health Ltd., United Kingdom.

FOOTNOTES
* Corresponding author. Mailing address: Life and Health Sciences, Aston University, Aston Triangle B4 7ET, United Kingdom. Phone: (44) 121 204 3951. Fax: (44) 121 204 4187. E-mail:
karpantj{at}aston.ac.uk 
Published ahead of print on 1 August 2008. 

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Antimicrobial Agents and Chemotherapy, October 2008, p. 3633-3636, Vol. 52, No. 10
0066-4804/08/$08.00+0 doi:10.1128/AAC.00637-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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