gms | German Medical Science

It has been reported recently that two skin antiseptics based on 85% ethanol are equally effective in 10 and 2.5 minutes on the skin of the forehead [1]. In clinical practice the actual application time for a skin antiseptic is often less than 10 minutes on skin with a high density of sebaceous glands. That is why we wanted to find out if two skin antiseptics based on 63% propan-2-ol (iso-propanol) and so far studied with an application of 10 minutes are equally effective on the resident flora of the forehead with an application time of 2 min.

The efficacy was evaluated using the test method of the German Society for Hygiene and Microbiology. It was first established in 1991 [2] and includes a 10 minute reference procedure which was established based on data by Christiansen et al. in 1987 and justified by its optimum efficacy on the resident skin flora [3]. In Germany, a 10 minute application time on skin with a high density of sebaceous glands was the standard application time until 2008 when shorter application times as short as 1 min were allowed [4]. The data sets with a 10 minute application time were obtained using the method version of 1991 [2], all other data sets were obtained using the last method version of 2002 [5]. Each experiment was performed in a reference-controlled cross-over design. A minimum of 20 volunteers was recruited per experiment. The skin of the forehead was randomly divided into five areas of approximately five cm². One area was chosen to determine the baseline bacterial density. Two areas were used for application of the reference alcohol (10 minutes), one for each of the different sampling times. Another two test areas were used for application of the skin antiseptic (2 or 10 minutes), one for each of the different sampling times. A cotton swab was soaked with the skin antiseptic and swabbed over the marked test field. The procedure was repeated up to five times in order to keep the skin moist with the skin antiseptic for the entire application time. Ethical approval for studying the efficacy for skin antisepsis was obtained from the ethics committee of the University Hospital Kiel, Germany (1991). The study was conducted in accordance with the ethical principles that have their origins in the current version of the Declaration of Helsinki (52^nd WMA General Assembly, Edinburgh, Scotland, October 2000). Informed consent was obtained from each participant.

The following preparations were used: propan-2-ol (70%, v/v) as the reference alcohol, a clear skin antiseptic based on 63% [w/w] iso-propanol (Cutasept F, Bode Chemie GmbH, Hamburg, Germany; “skin antiseptic A”), and a coloured skin antiseptic based on 63% [w/w] iso-propanol (Cutasept G, Bode Chemie GmbH, Hamburg, Germany; “skin antiseptic B”).

Each sampling area was marked so that the standard size of 5 cm² was clearly visible. A cotton swab was soaked in tryptic soy broth (TSB). The sampling area was rigorously rubbed for about 10 s as described before [6]. The swab was transferred into 5 ml TSB containing a combination of neutralizing agents for inactivation of residual biocidal activity [7]. The following neutralizing agents were used: 3% Tween 80, 3% saponine, 0.1% histidine and 0.1% cysteine. This combination of neutralizing agents was found to be valid for neutralization of the skin antiseptics (data not shown). The tube was vortexed for 30 s. A serial dilution was done in TSB. From appropriate dilution steps aliquots of 1 ml were spread on tryptic soy agar (TSA) in duplicate.

Two marked skin areas on the forehead were treated with the reference alcohol, two other ones with one of the two skin antiseptics. After each type of treatment two samples were taken (post-values). The first sample was taken immediately after completion of the application (10 or 2 min after beginning of the application). The second sample was taken 30 minutes after beginning of the application (20 or 28 min after completion of application). Between each product application, a rest period of at least one week elapsed in order to allow the reconstitution of normal skin flora.

The plates were incubated for a total of 48 h at 36°C, and the colony-forming units (CFU) from plates were counted. For calculation purposes, plate count values ≤300 CFU were accepted. Plate count values of 0 were reset to 1, because the log₁₀ of 0 is undefined, and the log₁₀ of 1 = 0. The weighted mean of CFU was calculated taking into account the number of CFU per plate and the corresponding dilution step. The weighted mean was multiplied by the dilution factor in order to obtain the number of CFU per mL in the sampling liquid. All pre- and post-values were expressed as log₁₀ values. For each sample from each volunteer, the logarithmic reduction factor (RF) was calculated as the difference between the log₁₀ baseline value and the log₁₀ post-values. A product is considered effective for skin antisepsis if the mean RF at both sampling times is not significantly lower than the corresponding mean RF of the 10 min reference treatment (one sided Wilcoxon matched-pairs signed-ranks test; p>0.1).

Skin antiseptic A applied for 10 min reduced the bacterial density on the forehead by 1.67 log₁₀-steps (10 min after beginning of the application) and 1.69 log₁₀-steps (30 min after beginning of the application) and was equally effective in comparison to the reference procedure (Table 1 [Tab. 1]). Two experiments were performed with the clear skin antiseptic A applied for 2 minutes. In both experiments, skin antiseptic A was equally effective at both sampling points (p>0.1).

Skin antiseptic B was studied in two experiments (Table 1 [Tab. 1]). Application for 10 minutes was equally effective than the 10 min reference procedure in the immediate effect (1.26 versus 1.25 log₁₀ reduction) and after 30 min (1.28 versus 1.29 log₁₀ reduction; p=0.968). When applied for 2 minutes it was also equally effective immediately after the application (1.68 versus 1.87 log₁₀ reduction; p=0.255) and 30 min after beginning of the application (1.75 versus 1.80 log₁₀ reduction; p=0.492).

For the first time we were able to demonstrate that the efficacy of two iso-propanol-based skin antiseptic is achieved on the forehead within 2 min and does not require a 10 min application time. This could be shown for a clear and a coloured skin antiseptic both based on 63% (w/w) iso-propanol. Extending the application time with any of the two skin antiseptics beyond 2.5 min has, based on our data, no additional effect on the bacterial density and can therefore be regarded as unnecessary.

Although the efficacy of iso-propanol on the resident skin is considered to be weaker compared to ethanol and n-propanol [8], it is nevertheless one of the most commonly used types of alcohol for skin antisepsis both in Europe and the US and is considered to be safe and effective for this purpose [9]. Its efficacy is often underestimated especially when a combination with other active agents is used [10].

The clinical advantage is substantial if the application time on skin with a high density of sebaceous glands is reduced from 10 to 2 min without any loss of efficacy. Although data were obtained on the forehead other skin areas are also known to have a high density of sebaceous glands such as the skin on back or the chest [11] which underlines the relevance of our data especially in spine surgery or open thoracic and cardiac surgery. But this will only be possible for preparations with sound evidence that a short application time yields the same efficacy as a long application time.

The clear and coloured skin antiseptics which were tested in our study and which were applied for 2 min on the skin of the forehead fulfilled the efficacy requirements for skin antisepsis. The shorter application time on skin with a high density of sebaceous glands will allow acting more efficiently in clinical practice.

CFU – Colony-forming units
RF – Reduction factor
TSA – Tryptic soy agar
TSB – Trypric soy broth

The first and last authors are paid employees of Bode Chemie GmbH, Hamburg, Germany.

GK and NN designed the study, all authors analysed the data, GK wrote the manuscript, and all authors read and approved the final manuscript.

The study was funded by Bode Chemie GmbH, Hamburg, Germany. The sponsor participated in the study design, analysis and interpretation of data, writing of the manuscript and the decision to submit the manuscript for publication.