Nosocomial infections contribute to morbidity and mortality. More than one-half of all epidemics of nosocomial bacteremia or candidemia reported in the world literature between 1965 and 1991 were derived from vascular access in some form.1 The source of infection may be endogenous (blood-borne infection or from the patient’s skin) or exogenous sources (nurses, doctors, hospital workers, or from contaminated medications or equipment). Details regarding infections due to infusion therapy are well described elsewhere.1 EMLA® cream (eutectic mixture of lidocaine 2.5% and prilocaine 2.5%) is a topical and transdermal analgesic. The application of EMLA cream is indicated for topical anesthesia of the skin in connection with needle insertion,2 and other invasive procedures for both adults and children.3,4 We described EMLA cream’s antibacterial effect in vitro.5
In this study we compared the impact of EMLA cream and an alcohol-containing skin disinfectant (Skinsept Pur®) on the colony forming unit (cfu) numbers of intact human skin bacterial flora.
We tested pharmaceutical preparations of EMLA 5% cream (lidocaine 25 mg, prilocaine 25 mg, carboxypolymethylene, polyoxyethylene hydrogenated castor oil, sodium hydroxide, purified water) that contains no preservative (Astra®, Södertälje, Sweden) and Skinsept Pur alcohol–based disinfectant that contains 46% ethyl alcohol, 27% propylalcohol, 1% benzyl alcohol and 0.29% hydrogen peroxide (Ecolab, Düsseldorf, Germany).
After ethical committee approval, 20 healthy volunteers who had given written consent were included in the study. Bacterial samples were taken with Envirocheck® RODAC GKZ contact plates (Replicate Organism Detection and Counting, containing Tryptic soy agar with Tween® (polysorbate) 80, lecithin, histidine and sodium thiosulphate [Merck KGaA, Darmstadt, Germany]). First, a sample was taken from the back of both hands. EMLA was then randomly applied to the right or left hand according to the manufacturer’s recommendations. Approximately half of a 5 g tube was applied as a thick layer of cream to the skin (approximately 10 cm2). The area was covered with one of the enclosed occlusive dressings. After 1 h, the dressing was removed and the EMLA cream was wiped off with a sterile swab. The other hand was disinfected with Skinsept Pur. The alcohol-based disinfectant was sprayed 3 times with 1 min intervals between the applications. Other samples were taken 1, 2, 3, 4, 6, and 12 h later from both hands. The plates were incubated for 24 h at 37°C and for an additional 24 h at room temperature for the slower growing micrococci. The number of cfu was then assessed.
The volunteers remained in an interview room for the first 6 h. After that, they were asked to either remain in the interview room or in the hospital building (library, doctor’s room) until the end of the study (12 h). Although the volunteers were told not to engage in any physical activity which could result in contamination of the back of their hands, including activity that could result in sweating before the last sample was taken, they were not observed. Hand-washing was only allowed with nonbactericidal soap if they had to use the lavatory. None of the volunteers used the restroom within the first 5 h. There was no statistical difference between the two groups in visiting the bathroom during the remainder of the study period.
The null hypothesis was that EMLA and Skinsept® have equal effects on the bacterial flora of intact human skin. Statistical significance of the differences between the two groups was assessed by using the Mann-Whitney U-test. Differences between cfu at different sampling times within one group were determined by analysis of variance. For both statistical comparisons, a P value <0.05 was considered significant.
There was no statistical difference between the cfu on the right or left hand at the beginning of the study before the treatment (0 h). The number of cfu on the skin decreased significantly from 0 h after both EMLA or Skinsept Pur treatment from 44.9 ± 1.3 (42.4 ± 7.0) to 0.9 ± 0.17 (1.61 ± 0.47) cfu/cm2, respectively (mean ± sem) (P < 0.0001). The cfu was statistically different from 0 h within each group (EMLA or Skinsept®) at each sampling time (Fig. 1). There was no statistical difference between the cfu after EMLA or Skinsept Pur treatment at 1, 2 or 3 h. The difference was significant at 4 h (P = 0.0019), 6 h (P = 0.003) and 12 h (P = 0.02). The cultured bacteria from the skin did not change throughout the study period and were Staphylococcus epidermidis, other coagulase negative staphylococci, micrococci and Corynebacteria sp.
In a previous study, we demonstrated that EMLA cream has antibacterial property in vitro, with a bacteriocidal effect for E. coli and P. aeruginosa and a significant reduction in the cfu of Micrococcus sp, S. aureus and methicillin-resistant S. aureus within 1 h.5 Berg et al.6 recently confirmed our in vitro results. The results of this study suggest that EMLA cream has antibacterial property in vivo as well. EMLA cream is bactericidal initially and has a superior bacteriostatic effect compared to Skinsept Pur between 4 and 12 h. The newly developed aqueous alcoholic solutions are as equally effective as conventional reagents such as chlorhexidine gluconate and povidone-iodine in preventing surgical site infection.7
Recent guidelines, such as the American Society of Regional Anesthesia Consensus Conference and the United States Center for Disease Control, suggest the use of an alcohol-based chlorhexidine solution for skin disinfection before central venous cannulation and regional anesthesia.8,9 We compared an alcohol-based skin disinfectant without chlorhexidine to EMLA because it is still used in everyday practice in many hospitals prior to peripheral venous cannulation.10 The penetration of alcohol into skin is limited due to the high rate of evaporation. Using human epidermal membranes, the permeability coefficient of ethanol is 8 × 10−4 cm/h.11 A previous study proved that an alcohol-based skin disinfectant (Isozid H®) could not protect the equipment (needles and guidewires) penetrating the skin for central venous cannulation from bacterial contamination in 74%.12
EMLA cream penetrates into deeper skin layers. EMLA provides cutaneous analgesia to depths of 2 mm after 60 min and to 3 mm after 120 min.13 The above-mentioned results may explain the longer lasting antibacterial effect of EMLA. EMLA also influences skin blood flow that may affect bacterial survival.14 A previous study reported that lidocaine 2% or prilocaine 2% solution had some antimicrobial effect. In the previous studies, the incubation time was 18 h and their combined effect on bacteria was not evaluated.15 The other components of EMLA were not tested.
There have been no published studies investigating the effect of EMLA cream on microorganisms in vivo on intact skin. One clinical study investigated the impact of EMLA cream on the bacterial flora of leg ulcers.16 The authors reported that after treatment with EMLA for 30 min there was no significant difference on the bacterial flora in the EMLA- treated patients compared with the controls. They only examined the bacteriological results qualitatively, not quantitatively, and did not give any details of the microbiological methods.
Our results suggest that the use of EMLA cream (with no preservatives) reduces the bacterial count on intact human skin. Further clinical studies are needed to answer whether the use of EMLA cream could reduce the infectious complications after surgery or other skin-related procedures and could help to eradicate infected skin lesions.
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