Antiseptics on Wounds: An Area of Controversy (PART ONE)

Part One Introduction Antiseptics are agents that destroy or inhibit the growth and development of microorganisms in or on living tissue. Unlike antibiotics that act selectively on a specific target, antiseptics have multiple targets and a broader spectrum of activity, which include bacteria, fungi, viruses, protozoa, and even prions.[1,2] Several antiseptic categories exist, including alcohols (ethanol), anilides (triclocarban), biguanides (chlorhexidine), bisphenols (triclosan), chlorine compounds, iodine compounds, silver compounds, peroxygens, and quaternary ammonium compounds.[1] The most commonly used products in clinical practice today include povidone iodine, chlorhexidine, alcohol, acetate, hydrogen peroxide, boric acid, silver nitrate, silver sulfadiazine, and sodium hypochlorite. Antiseptic uses and indications vary. Several antiseptic agents mainly focus on cleansing intact skin and are used for prepping patients preoperatively and prior to intramuscular injections or venous punctures, pre- and postoperative scrubbing in the operating room, and hand washing by medical personnel. Some also contain detergents, which render them too harsh for use on nonintact skin.[3] The usefulness of antiseptics on intact skin is well established and broadly accepted. However, the use of antiseptics as prophylactic anti-infective agents for open wounds, such as lacerations, abrasions, burns, and chronic ulcers, has been an area of intense controversy for several years. Two official guidelines have been released recently concerning antiseptic use on wounds. Povidone iodine has been Food and Drug Administration (FDA)-approved for short-term treatment of superficial and acute wounds.[4] The statement includes that povidone iodine has not been found to either promote or inhibit wound healing. On the other hand, guidelines for the treatment of pressure ulcers by the US Department of Health and Human Services strongly discourage the use of antiseptics and promote the use of normal saline for cleansing pressure ulcers.[5] In clinical practice, antiseptics are broadly used for both intact skin and wounds, although concerns are raised based upon their effect on human cells and wound healing. Opinions are conflicting. Some authors strongly disapprove the use of antiseptics in open wounds.[6–8] On the other hand, others believe antiseptics have a role in wound care, and their use may favor wound healing clinically.[9,10] Reasons to use antiseptics on wounds. The main rationale for using antiseptics on open wounds is prevention and treatment of infection and, therefore, increased rate of the healing process. It is established that infections may delay healing, cause failure of healing, and even cause wound deterioration.[11] Microbial pathogens delay wound healing through several different mechanisms, such as persistent production of inflammatory mediators, metabolic wastes, and toxins, and maintenance of the activated state of neutrophils, which produce cytolytic enzymes and free oxygen radicals.[12] This prolonged inflammatory response contributes to host injury and delays healing. Moreover, bacteria compete with host cells for nutrients and oxygen necessary for wound healing.[13] Wound infection can also lead to tissue hypoxia, render the granulation tissue hemorrhagic and fragile, reduce fibroblast number and collagen production, and damage reepithelization.[7,14–16] Consequently, although creation of an optimal environment for the wound healing process is currently the primary objective of wound care, addressing infection still plays a critical role in wound management. Despite the universal acceptance of the detrimental role of infection on wound healing, the exact significance of increased bacterial load on wounds is still an area of debate. All chronic wounds are colonized by bacteria population, and it is known colonized wounds can heal.[17,18] However, in addition to clinical infection, it seems that bacterial number above a critical concentration can decrease the wound healing rate and may have deleterious effects on the wound healing process. The role of bacteria in the chronicity of nonhealing wounds is under investigation. Likely, a state of bacterial contamination that can produce subclinical tissue damage exists.[19] This may be caused by shear number or by other properties of the bacterial process. Increased bacterial numbers in pressure ulcers have been implicated as significant participants of chronic ulceration.[20] Several studies have demonstrated that bacterial number above 10(5) or 10(6) organisms per gram can cause local disease to skin or can delay wound healing.[21–24] Quantification of bacteria within wounds is not the sole predictor of the risk of infection, since several individualized factors, such as presence of foreign material and concomitant diseases, can decrease the ability of the hosts to defend themselves. Moreover, the nature of the wound and the virulence of microbes involved are important.[25] In addition to use of antiseptics to reduce bacterial load of a wound, several other approaches have been developed, including debridement, cleansing and pulsating jet lavage for removal of the devitalized tissue, and application of topical antibiotics. Another argument for the use of antiseptics on wounds to prevent wound infection is that antiseptics may be preferable to topical antibiotics with regard to development of bacterial resistance. Antibiotic resistance of skin wound flora has emerged as a significant problem, and measures to prevent it should be taken.[26] Generally, antiseptics aim at eliminating all pathogenic bacteria of the wound, while antibiotics are effective only to certain bacteria that are sensitive to them. Although resistance toward antiseptics has been reported, it is to a significantly lesser degree than reported with antibiotic usage.[18] According to McDonnell, et al., some acquired mechanisms of resistance (especially to heavy metals) are clinically significant, but in most cases the results have been speculative.[1] Moreover, development of resistance against povidone iodine, which is the most commonly used antiseptic today, does not exist.[27] Payne, et al., state that the sensible use of antiseptics could help decrease the usage of antibiotics, preserving their advantage for clinically critical situations.[28] Antiseptics are also considered superior to topical antibiotics when their rates of causing contact sensitization are compared. Aminoglycosides, especially neomycin, have a much higher sensitization rate compared to povidone iodine.[3] Moreover, patients allergic to one antibiotic may acquire cross-allergy to other antibiotics, as well. The sensitization rate to povidone iodine, the most commonly used antiseptic, has been found to be only 0.73 percent.[3] Arguments against antiseptics. A main concern for clinicians prior to applying a topical agent on an open wound is safety. Agents that are cytotoxic or cause delay in wound healing are used with reservation. The strongest argument against the use of antiseptics on wounds is that antiseptics have been found, primarily using in-vitro models, to be cytotoxic to cells essential to the wound healing process, such as fibroblasts, keratinocytes, and leukocytes.[29–31] However, this cytotoxicity appears to be concentration dependent, as several antiseptics in low concentrations are not cytotoxic, although they retain their antibacterial activity in vitro.[27] Since the in-vitro results are not always predictive of what may happen in vivo, numerous studies have been conducted on animal and human models. The results of these studies are conflicting and will be presented later in the article. A second reason against the use of antiseptics on open wounds, as first stated by Fleming in 1919,[32] is that antiseptics are not as effective against bacteria that reside in wounds as they are against bacteria in vitro. The presence of exudate, serum, or blood seems to decrease their activity. However, in practice, several bacteriological studies have shown that antiseptics can decrease bacterial counts within wounds.[33,34] In order to draw conclusions regarding the appropriateness and usefulness of antiseptic use on wounds, the authors have chosen to review the results of animal and human studies of the most common antiseptics used currently. Iodine Compounds Since the first discovery of the natural element iodine in 1811 by the chemist Bernard Courtois, iodine and its compounds have been broadly used for prevention of infection and treatment of wounds.[35] However, molecular iodine can be very toxic for tissues, so formulations composed by combination of iodine with a carrier that decreases iodine availability were developed. Povidone iodine (PVP-I) results from the combination of molecular iodine and polyvinylpyrrolidone. Povidone iodine is available in several forms (solution, cream, ointment, scrub). The scrub form contains detergent and should be used only on intact skin. Cadexomer iodine consists of spherical hydrophilic beads of cadexomer-starch, which contain iodine, is highly absorbent, and releases iodine slowly in the wound area. It is available as an ointment and as a dressing. Numerous studies have been conducted in order to determine the safety and efficacy of iodine compounds on wound healing. Effects of iodine compounds on the bacterial load of wounds. Povidone iodine. Several animal studies have examined the effects of povidone iodine on the bacterial load of wounds. These results have not proven the efficacy of povidone iodine; however, the results of numerous clinical trials show that it is effective in reducing the bacterial load of wounds. Rodeheaver, et al.,[36] studied the bactericidal activity of povidone iodine solution in contaminated wounds in Hartley guinea pigs and the potential therapeutic benefit. Although they found that it can significantly reduce bacterial load 10 minutes after the application of the antiseptic, this effect did not persist. Four days after a single PVP-I application, there was no decreased rate of infection or decreased bacteria number. Another study[37] that evaluated contaminated 12-hour old lacerations in a guinea pig model failed to find any decrease of wound bacterial counts after irrigation with PVP-I in comparison to normal saline. However, the authors mention that this may be due to the formation of a proteinaceous wound coagulum and point out that even parenteral antimicrobials are ineffective in preventing infection in animal models if administered alone more than three hours after wounding. However, most of the human trials performed prove the efficacy of povidone iodine in clinical situations. Georgiade, et al.,[38] applied PVP-I ointment on burn wounds in 50 patients and showed that control of bacterial growth was effective. There was not a control group in this study; however, the control of bacterial growth showed a significant correlation to the frequency of PVP-I application. Gravett, et al.,[39] studied the effect of one-percent PVP-I solution in the prevention of infection in sutured lacerations in 395 patients. Their data suggest that use of one-percent PVP-I solution prior to suturing reduces the incidence of wound infection. In a recent study[40] on clinically noninfected venous leg ulcers, the combination of PVP-I with hydrocolloid dressing was shown to reduce bacterial clumps, neutrophilic vasculitis, and phagocytic infiltration and increase the healing rate in comparison to the hydrocolloid dressing alone. One of the most cited studies is the one conducted by Viljanto[41] in surgical wounds in 294 pediatric patients. He found that a five-percent PVP-I aerosol, which contained some excipients (glycerol, citrate-phosphate buffer, polyoxyethylated nonylphenol), increased the infection rate. In order to explain these results, he used the cellstic method, which consists of placing a cellulose sponge inside a silicone-rubber tube between the wound edges. Wound exudate fills the sponge, and cells migrate into the sponge. He found that the five-percent aerosol caused pronounced leukocyte migration, a five-percent solution without excipients caused slighter inhibition, while the one-percent solution was practically no different to the control (saline). Subsequently, spraying wounds with a one-percent PVP-I solution had no effect on wound healing while it significantly decreased infection rate. Interestingly, povidone iodine has been found to have increased bactericidal activity in lower concentrations.[42] Conversely, some studies have not confirmed those previously mentioned results. PVP-I soaking was not found to significantly decrease bacterial counts in acute, traumatic, contaminated wounds that required debridement, while saline soaking caused increased counts. PVP-I solution was not found to be an effective substitute to wound cleaning and debridement.[43] However, PVP-I irrigation has been shown to be effective in several other studies,[44–46] so it is not obvious if the lack of effect of PVP-I in this study should be attributed to the antiseptic itself or to the method used. In another study with infected chronic pressure ulcers, PVP-I solution was found to reduce bacterial levels but was no more effective than saline.[47] Cadexomer iodine. The efficacy of cadexomer iodine has been shown in both animal and human models. Mertz, et al.,[48] examined the effect of cadexomer iodine dressing on partial-thickness wounds in specific pathogen-free pigs contaminated with or without methicillin-resistant Staphylococcus aureus (MRSA). Applied daily, cadexomer iodine was found to significantly reduce MRSA and total bacteria in the wounds in comparison to no treatment control and vehicle (cadexomer) at all time points studied (1, 2, and 3 days after inoculation). The reduction was most pronounced at day 3. In an uncontrolled small study series (n = 19), Danielsen, et al.,[49] used cadexomer iodine in ulcers colonized with Pseudomonas aeruginosa and found negative cultures in 65 percent and 75 percent of patients after 1 and 12 weeks of treatment, respectively. Effects of iodine compounds on the wound healing process. Povidone iodine. Literature regarding the effect of povidone iodine on wound healing in animal wound models is conflicting. Reasons for this discrepancy may be differences in the parameters of wound healing evaluated, the variety of assessment times, iodine concentrations and control groups, and the diversity of animal wound models (partial thickness, full thickness, burn wounds, ischemic wounds, etc.). The type of animal used appears to be of importance, as different animals show different healing responses. Loose-skinned animals (mice, rabbits, guinea pigs) heal mainly through contraction, while the primary mechanism of healing in tight-skinned animals (pigs) is epithelization, and healing in tight-skinned animals more closely resembles the human healing response.[50] It should be emphasized that none of the animal studies examined the effect of povidone iodine in chronic wound models, as an animal model equivalent to human chronic wounds does not exist. Briefly, in some studies povidone iodine was found to cause no inhibition on wound re-epithelization,[51,52] while in others it retarded healing.[53] As far as the tensile strength of the wound is concerned, PVP-I has been reported to cause increase,[54] reduction,[56] have no effect,[55] and cause either reduction or no effect depending on the assessment time.[29] It has also been found to have no effect on collagen56 and granulation tissue production or nonsignificant reduction.[57] Moreover, it has been shown to increase revascularization.[53] In another study measuring the corneal toxicity of antiseptics, povidone iodine was found to be nontoxic in rabbit corneas.[58] Clinical studies evaluating the influence of PVP-I in wound healing are numerous. Most of them have shown no decrease of the wound healing rate from the use of povidone iodine. The aforementioned study by Viljanto[41] found no effect on wound healing when a one-percent solution is used. Niedner[59] reviewed the cytotoxicity of PVP-I and concluded that “the normal course of wound healing (suction blister60) as well as the disturbed one (Mohs therapy[61] and burns[62]) is not negatively influenced by PVP-I.” Piérard-Franchimont, et al.,40 examined the effect of PVP-I in combination with hydrocolloid dressing on venous leg ulcers. The control group was treated with compression hydrocolloid dressings alone. Using planimetric evaluation, they showed that the rate of leg ulcer healing was accelerated in the PVP-I–treated group in comparison to control, especially the first four weeks of treatment. Lee, et al., in a noncontrolled study found reduction of infection and promotion of healing in patients with long-standing (6 months to 16 years) decubitus and stasis ulcerations.[63] Knutson, et al.,[64] reported their five-year experience and concluded that the combination of sugar and PVP-I enhanced healing of burns, wounds, and ulcers and reduced the requirements for skin grafting, antibiotics, and the hospital costs. However, they do not mention what “standard care” thecontrol group received; neither is it clear if this improvement is due to PVP-I, to sugar, or to the combination. Mayer, et al.,[9] reviewed the in-vivo studies examining the effects of the various PVP-I formulations on wound healing. They reported five human studies using PVP-I solution, three with PVP-I ointment, and three with PVP-I cream. In all these studies, PVP-I was not found to negatively influence wound healing in comparison to the control group or to other treatments. Burn wounds are, in many ways, different than the other acute wounds, and they have a higher risk of infection that not only can delay wound healing but also can cause a significant risk for the patient’s life. Steen[65] reviewed the use of PVP-I in the treatment of burns. After reviewing in-vitro animal and human studies, he concluded that PVP-I has concentration-dependent cytotoxicity. The higher the complexity of the system studied (in-vivo > ex-vivo > in-vitro studies) the less detectable the effects are. He did not exclude the possibility that PVP-I may cause slight retardation in wound healing but believed the benefits of the microbicidal effects of PVP-I should not be ignored. Since large areas usually need to be treated in burn patients, risks of systemic toxicity of increased PVP-I absorption were reviewed, as well. For several more reviews of PVP-I use on wounds, see references 9, 10, 27, 66, and 67. Cadexomer iodine. In animal models, cadexomer iodine has been reported to increase epidermal regeneration and epithelialization in both partial-thickness and full-thickness wounds.[33,68] However, cadexomer iodine appears to have no effect on granulation tissue formation, neovascularization, or wound contraction.[59] Cadexomer iodine has also been the subject of many clinical studies. In these studies, cadexomer iodine has been found to be effective and beneficial to wound healing. Nine clinical trials comparing the effects of cadexomer iodine with other treatments on chronic venous ulcers showed enhancement of wound healing. The other treatments that were compared to cadexomer iodine included various “standard treatment” (cleansing with diluted hydrogen peroxide or dilute potassium permanganate baths and covering with either zinc paste dressings or nonadherent dressings, mainly paraffin-impregnated or saline dressings, or saline wet-to-dry compressive dressings, or gentian violet and polymyxin-bacitracin ointment, or support bandaging/stocking and a dry dressing),[69–74] dextranomer,[75] and hydrocolloid dressing or paraffin gauze dressings.[76] In one study, no control group was used, since the main purpose of the study was to examine the safety of cadexomer iodine with regard to development of sensitivity.[77] In several studies, the ulcers had been recalcitrant to previous treatments. All studies found cadexomer iodine not only to cause no inhibition on wound healing but to accelerate it. Moreover, observations of reduction of pain, removal of pus, debris, and exudate, and stimulation of granulation tissue formation were made.[71] The reduction of exudate could be considered an expected action of cadexomer iodine, since cadexomer iodine is designed to absorb large quantities of exudate (each gram can absorb 3mL of fluid) and then results in slow release of iodine. Apelqvist, et al.,[78] examined the effects of cadexomer iodine in cavity foot ulcers in diabetic patients and found no clinical difference in comparison to other treatments (gentamicin solution, streptodornase/streptokinase, or dry saline gauze) but considerable less costs. In a randomized trial, Moberg, et al.,[79] compared cadexomer iodine (n = 16) with standard treatment (n = 18) in patients with decubitus ulcers. Cadexomer iodine significantly reduced pus, debris, and pain of the ulcers and accelerated the healing rate. After eight weeks of treatment, the ulcer areas were reduced by 76 and 57 percent in the cadoxemer iodine and standard treatment group, respectively. Six ulcers treated with cadexomer iodine were completely healed, while only one with standard treatment was healed. Summarizing the review of numerous in-vivo studies of iodine compounds the authors can conclude that in humans PVP-I and cadexomer iodine do not have a negative influence on wound healing, while cadexomer iodine causes an acceleration of healing in chronic human wounds. Both can be effective in reducing bacteria number and decreasing infections. Results from animal studies depend on many variables and should be interpreted with cautiousness. Studies of PVP-I have more conflicting results, especially with animal models, and have caused concern on many clinicians. Nevertheless, the results from the studies evaluating cadexomer iodine are clear and leave no doubt that this newer iodine compound is effective without having any negative influence on wound healing rate. Inversely, an acceleration of wound healing has been observed. (Article continued in PART TWO.)