Antiseptics on Wounds: An Area of Controversy (PART TWO)
A three-percent solution of hydrogen peroxide is commonly used as a wound antiseptic. The three-percent solution demonstrates in-vitro broad-spectrum efficacy. Its greatest activity is towards Gram-positive bacteria, but the presence of catalase in these bacteria makes dilutions below three percent less effective. In a similar fashion, catalases present in tissues can render hydrogen peroxide even less bactericidal in vivo. Although hydrogen peroxide is very commonly used, surprisingly few studies have been conducted to examine its effect on the wound healing process and its efficacy as a wound antiseptic.
Animal and human studies have shown hydrogen peroxide to have no negative effect on wound healing. Lineaweaver, et al., did not find retardation of reepithelization in a rat model after irrigation of the wound with three-percent hydrogen peroxide. However, at the in-vitro component of the same study, he found minimal bactericidal effect of hydrogen peroxide. Gruber, et al., found acceleration of reepithelization in a rat model and in a clinical trial. However, bullae were formed on or about the day of healing in most of the patients, suggesting possibly that hydrogen peroxide should not be used in newly formed epithelium.
In another study by Tur, et al., hydrogen peroxide was found to significantly increase the blood flow in ischemic ulcers in a guinea pig model. The increased blood flow may be due to new vessel formation through activation of metalloproteinases. Interestingly, the blood flow was increased even in places distant to the local application of hydrogen peroxide. No explanation was given for this finding. However, the authors found no difference in the wound-healing rate. This may be due to the limited sensitivity of the method they used to evaluate the clinical response (visual determination of the non-necrotic area).
In a clinical study evaluating the effectiveness of hydrogen peroxide on reducing the infection rate of appendectomy wounds, no toxic effects were found, but it was found to be ineffective. Similarly, in another clinical study in human blister wounds contaminated with Staphylococcus aureus, hydrogen peroxide was found not to retard the healing but neither did it decrease bacterial load.
In conclusion, hydrogen peroxide appears not to negatively influence wound healing, but it is also ineffective in reducing the bacterial count. However, it may be useful as a chemical debriding agent. The American Medical Association concluded that the effervescence of hydrogen peroxide might provide some mechanical benefit in loosening debris and necrotic tissue of the wound.
Acetic acid is frequently used in wounds as a 0.25-percent or 0.5-percent solution. It is bactericidal against many Gram-positive and Gram-negative organisms, especially Pseudomonas aeruginosa. No delay of reepithelization has been found in animal and human models. Although one study found that acetic acid initially delayed reepithelization, after the eighth day, this effect did not persist. In the same study, it was not shown to influence tensile wound strength. In two human uncontrolled studies, acetic acid was found to be beneficial in wounds infected with Pseudomonas aeruginosa.[83,84] In a study with patients with venous leg ulcers, gauze dressings wetted with acetic acid were shown to effectively decrease the number of Staphylococcus aureus and Gram-negative rods. Pseudomonas was not reduced significantly.
Although several in-vitro studies found acetic acid to be cytotoxic,[31,86] the in-vivo studies do not confirm these findings. The authors believe that acetic acid can continue being used topically in contaminated wounds where an agent is needed in order to eliminate the chances of infection.
Chlorhexidine has been commonly used in disinfectant and antiseptic solutions. Chlorhexidine antiseptic solutions are used mainly in urology, gynecology, dentistry, and in the treatment of wounds. It is highly bactericidal.
Several animal studies have tested the efficacy and safety of chlorhexidine on wounds. It has been found to have mild inhibitory effects on wound healing in guinea pigs. Chlorhexidine diacetate was found to accelerate wound healing in full-thickness wounds in beagles. Chlorhexidine was also found to be relatively safe for use as a surgical wound irrigation solution, since only the higher concentrations tested (0.05%) caused slight tissue toxicity in rats. Lower concentrations (0.02%) are recommended for wound irrigation. In other studies, it was found to cause inhibition of granulation tissue in guinea pigs and decreased tensile strength of wounds in rats. However, Brennan, et al., found no decrease in collagen production in a rat model, and Shahan, et al., also in a rat model, found decreased tensile strength 48 hours after the treatment and significantly increased strength at 96 hours, since chlorhexidine decreased the healing time.
In human studies, chlorhexidine rinses were shown effective in reducing microbial complications when used perioperatively in patients that received dental implants. Conversely, in another study, it was found to be ineffective to reduce wound sepsis rate and length of hospital stay in patients that had undergone appendicectomy. The authors speculate that reinfection from within as an explanation for the lack of chlorhexidine efficiency.
Chlorhexidine appears to be relatively safe with little effect on the wound healing process, and its use may favor healing of open wounds in risk for infection. However, the results from studies to date are insufficient to draw conclusions about the use of chlorhexidine on open wounds. More human trials need be performed to assess its efficacy and safety.
Silver compounds have widely been used as wound antiseptics, mainly in burns. Silver sulfadiazine (SSD) and silver nitrate (AgNO3) are among the most commonly used. Silver sulfadiazine is the most broadly used treatment for the prevention of infection in patients with burn wounds.[95,96] Combinations of SSD with cerium nitrate and nanocrystalline silver releasing systems (Acticoat®, Westaim Biomedical, Exeter, New Hanover) have been developed in order to increase its efficacy and/or reduce its toxicity. Newer silver formulations appear to increase the rate and degree of microbial killing, decrease exudate formation, and can remain active for days.
Animal studies examining the effects of SSD and AgNO3 on wounds have showed no significant effect on epithelization rate. SSD was also found to increase the rate of neovascularization. In another study in rats, silver compounds were found to promote wound healing, reduce the inflammatory and granulation phases of healing, and influence metal ion binding. Moreover, Geronemus, et al., found increased reepithelization rate in domestic pigs with the use of SSD.
Yet, Leitch, et al., found SSD to cause inhibition of wound contraction in an acute wound rat model. Likewise, Niedner, et al., found a slight, nonsignificant reduction of granulation tissue formation with the use of AgNO3.
Among human studies, the authors present only those on patients suffering from wounds other than burns, as there is currently no controversy for the use of silver compounds on burn patients, as mentioned above. Kucan, et al., examined the effects of SSD on bacterial counts in patients with infected chronic pressure ulcers. He found SSD to be effective in decreasing the bacteria below 105/gr tissue in all the ulcers treated. In a randomized trial with venous ulcers, SSD one-percent cream was proved to statistically reduce the ulcer size compared to the placebo, while in another study it was found to be well tolerated and effective on wound cleansing and granulation tissue formation. Livingstone, et al., studied the effect of AgNO3 and an antibiotic solution (neomycin plus bacitracin) on reducing autogenous skin graft loss due to infection in patients with thermal injury. They found both medications to be effective in comparison to the control group (Ringer’s lactate solution), but the antibiotic solution was associated with the rapid emergence of drug-resistant organisms, while AgNO3 was not.
Nanocrystalline silver compounds have been found to increase the reepithelization rate of meshed autografts and appear to be promising for the treatment of other chronic wounds as well. The anti-inflammatory effects of silver could be associated with the vehicle, which reduces wound drying, reducing therefore inflammation (moist wounds have been found to be significantly less likely to be infected). More clinical trials are needed for the evaluation of nanocrystalline silver.
Summarizing, it appears that silver compounds do not have a negative effect on wounds and maybe accelerate wound healing clinically. Their in-vivo antimicrobial activity is not in question.
The use of antiseptics on wounds is currently being viewed with skepticism. Results from in-vitro studies have shown that antiseptics are toxic not only against bacteria and other microorganisms but also against human cells essential to the wound healing response. These findings resulted in a series of animal and human studies in order to evaluate the in-vivo activity of antiseptics. However, it seems that in human subjects, pronounced cytotoxicity, found in vitro, was not confirmed. In the majority of clinical trials, antiseptics appear to be safe and were not found to negatively influence wound healing. Their antimicrobial efficiency, with the exception of hydrogen peroxide, seems satisfactory as well. Randomized controlled studies to evaluate the effect of each antiseptic on the different kinds of wounds (acute, venous, diabetic, or pressure ulcers) are indicated to provide greater evidence regarding the benefits of antiseptic use on wounds. Efforts to develop superior antiseptic formulations are likely to and should continue. Development of cadexomer iodine, which not only does not negatively influence wound healing but also accelerates healing even in noninfected wounds, and development of improved silver delivery systems, which release silver more efficiently than previous formulations while enhancing re-epithelization, are paradigms of the therapeutic potential of antiseptics. Vehicles that contribute to the maintenance of an optimal moist environment may be more appropriate as delivery systems of antiseptics than the current ones, since moist environments result in both increased wound healing rate and enhancement of antimicrobial penetration to wounds.
Antiseptics need not be omitted from the therapeutic armamentarium of wound care. In patients and wound types with high risk of infection, antiseptics may be used to prevent wound infection that would have deleterious effects on wound healing. Antiseptics present advantages over topical antibiotics, since they do not cause the emergence of drug-resistant bacteria and have broader antimicrobial spectrum and lower sensitization rates.
In conclusion, after review of the literature, most antiseptics, especially newer formulations, appear to be relatively safe and efficient in preventing infection in human wounds. The advantages of antiseptics on wounds may outweigh possible disadvantages, and their position in wound care management should be reconsidered.
The authors would like to thank Laura Bolton, PhD, for her support for this article.