Overview

Topical antimicrobial dressings are used to minimize microbial growth in wounds. There has been an increase in the use of these dressings following concerns over antimicrobial resistance, however clinical evidence to support their use remains sparse. These dressings can be used on acute and chronic wounds which are critically colonized or infected (41).

Recently polyhexamethylene biguanide (PHMB) (which has an effect on bacterial cell metabolism) has been introduced. They are effective against a range of microorganisms including Pseudomonas aeruginosa and Staphylococcus aureus, common in many chronic wounds. The routine use of antimicrobial dressings is however not recommended (41). 

 

Honey: examples: Medihoney and Manukapli Honey. Indications: Chronic ulcers, infected, necrotic sloughy wounds, fungating wounds, surgical and superficial wounds. Pros: safe in diabetic patients, bacterial resistance to honey has not been observed. Cons: Could initially make the wound appear larger and some patients may complain of pain due to a drawing sensation. Contraindications: Medical honey should not be used in the presence of calcium or sodium alginate, very deep wounds or where there is undermining or tracking with sinuses as the plant waxes can potentially block sinuses. (41)

 

Iodine: examples: iodoflex and iodosorb. Indications: Malodorous, infected wounds, minor burns, ulcers. Pros: Absorbs copious amounts of exudate, applied under film dressing to allow viewing of wound. Cons: brown stain on skin, slight stinging sensation. Contraindications: Hyperthyroid disorder. (41)

 

Silver and charcoal: examples: Acticoat. Indications: Infected wounds, ulcers, Burns, malodorous wounds. Pros: Bactericidal – kills pathogens such as MRSA. Cons: Questions remain regarding accumulation toxicity and resistance, Should be used with care, most require secondary dressings, skin discoloration. Contraindications: Allergy, some can’t be used with oil based products or topical antimicrobials. (41)

 

Silver containing dressings

Description: Silver has antiseptic and anti-inflammatory properties and is a broad spectrum antibiotic. It is biologically active in its soluble form as Ag+ or Ag0 clusters. Ag+ is the ionic form present in silver nitrate, silver sulfadiazine, and other ionic silver compounds. Ag0 is the uncharged form of metallic silver present in nanocrystalline silver.

Acticoat are three or five layered dressing constructs of a silver mesh containing silver nanocrystals applied to either side of a rayon/polyester core. Nanocrystalline silver utilizes nanotechnology to release clusters of extremely small and highly reactive silver particles. The smaller the particles of silver, the greater the wound surface area that will be in contact with silver, increasing bioactivity and silver solubility.

 

Acticoat is made by physical vapour deposition (argon gas is introduced into a vacuum chamber acting as an anode. When an electric current is passed into the chamber, argon ions knock out the silver atoms travelling towards the substrate to be coated, depositing and developing nanocrystals). These changes to the lattice structure of the crystal result in a high energy, meta-stable form of elemental silver. Research has demonstrated that sustained-release silver products have a bactericidal action providing effective management of odour and exudate, thus reducing the risk for colonization and preventing infection (69).

 

Mechanisms Involved: When moistened with sterile water and placed on the wound, Acticoat releases clusters of highly reactive silver cations, causing electron transport, inactivation of bacterial cell DNA, cell membrane damage and binding of insoluble complexes in micro-organisms. If re-moistened, it produces a controlled release of clusters of silver cations onto the wound, for up to 3 or 7 days therefore maintaining a moist environment to promote wound healing. Free silver cations destroy micro-organisms immediately by blocking cellular respiration and disrupting the function of bacterial cell membranes. This occurs when silver cations bind to tissue proteins, causing structural changes in the bacterial cell membranes which in turn cause cell death. Silver cations also bind and denature the bacterial DNA and RNA, thus inhibiting cell replication (69). 

 

Costs and Evidence: Research indicates nanocrystalline silver is an effective antimicrobial dressing for treating wounds especially burns and chronic wounds. Acticoat™ reduces inflammatory processes, promotes wound healing and is less toxic than other forms of silver dressings due to the prolonged release of silver onto the wound. There has been no in vivo reports of toxicity of nanocrystalline silver on keratinocytes or fibroblasts. Acticoat™ is cost effective, reduces pain and has a longer wear time, thus limiting the frequency of dressing changes. There has been no reports of resistance to Acticoat dressings (69).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Honey containing dressings

Description: Honey primarily contains sugar (75–79%) and water (20%). Other components of honey are proteins, vitamin B, minerals and antioxidants such as flavonoids, ascorbic acid, catalase and selenium. Organic acids make up 0.57% of the honey and are responsible for its acidity. The main enzymes in honey are invertase, amylase and glucose oxidase. Honey is easily contaminated during production so medical grade honey should be sterilized by gamma irradiation so that micro-organisms are killed without jeopardizing antibacterial activity (71).

 

Mechanisms Involved: The antibacterial effect of honey is based on several mechanisms. Hydrogen peroxide is produced by glucose oxidase (an enzyme) when the honey is diluted by wound exudate. Hydrogen peroxide activates neutrophils through a nuclear transcription factor. Phytochemicals (or flavonoids) are antioxidants and directly inhibit phagocytosis, preventing formation of the superoxide free radicals and protect tissues from further damage (71).

 

Bacterial growth requires a water activity (amount of ‘free’ water) of 0.94–0.99. However, since honey has a low water activity of 0.56–0.62, this prevents bacterial growth. The high sugar content of honey draws fluid from the wound by osmosis and extracts water from bacteria resulting in its death. Finally, the acidity of honey (pH 3.2- 4.5) further inhibits the growth of micro-organisms, since the optimal pH for most of these organisms lies between 7.2 and 7.4. Honey has been shown to reduce inflammation, prevent surgical debridement, deodorise and accelerate tissue growth. It’s been found to affect the structure and activity of various bacteria (71).

 

Costs and Evidence: Available evidence indicated a greater efficacy of honey compared with alternative dressings for superficial or partial thickness burns. Medihoney Antibacterial Medical Honey (Medical grade, Leptospermum sp.) by Derma Sciences Europe, Ltd, is priced at £9.90, factoring unit costs only. This treatment can therefore be relatively costly. (54) In the study of MRSA, the bacteria were susceptible to “relatively low” concentrations of manuka honey. Combining honey with the antibiotic oxacillin (and to a small extent vancomycin) altered the structure of these drugs, making them potentially more effective. This was measured as the minimum inhibitory concentration (the concentration of drug needed to slow growth or kill the organisms). In the study of Pseudomonas bacteria, honey induced “significant changes” in the bacteria’s protein expression, which is likely to be detrimental to its survival. In the study of Streptococcus pyogenes, honey inhibited the growth of bacterial biofilms (71).

 

 

 

 

 

 

 

 

 

 

 

Iodine containing dressings

Description: Iodine is a highly effective agent that has been used to treat wounds for more than 170 years. It has a broad spectrum of antimicrobial activity with efficacy against mycobacteria, fungi, protozoa and viruses. It can be used to treat acute and chronic wounds. It is also relatively inexpensive and easy to use, but is often underused as a topical antiseptic due to its perceived toxicity. Iodine is a natural dark violet, non-metallic element that plays a key role in human metabolism. It is essential for the production of thyroid hormones and iodine deficiency results in hypothyroidism. It occurs naturally as iodide ions in sea water, fish, oysters and certain seaweed. It can also be found in vegetables grown in iodine-rich soil and dairy products. It has been described as ‘the most potent antiseptic available (75).

 

Safety: Iodophors were developed in the 1950s to overcome the side effects associated with elemental iodine. These were found to be safer and less painful, but just as effective as elemental iodine, allowing widespread use. Bonding iodine with another molecule makes it less toxic and instead of high concentrations of iodine being released in a single application, iodine is slowly released from the reservoir carrier molecule over a long period of time. Iodophors are preparations that bind iodine to a solubilising agent or carrier. The water-soluble complex allows the slow release of a low concentration of free iodine when the carrier comes into contact with wound exudate. This controlled release of low concentrations of iodine helps to minimise the negative side effects of using free elemental iodine (75).

 

Modern preparations: The two most commonly used iodophors in modern wound dressings are Povidone iodine (a chemical complex of polyvinylpyrrolidone and elemental iodine) and Cadexomer iodine (an iodine and polysaccharide complex), such as Iodoflex® and Iodosorb® which can be used as antiseptic fillers, particularly in cavity wounds. Povidone iodine preparations were introduced in the 1960s and it is now the most common iodophor used clinically. It is available as solutions, ointments, sprays and wound dressings (75).

 

Mechanisms Involved: Iodine’s exact antimicrobial mode of action is not fully understood, but it may be associated with its ability to rapidly penetrate the cell wall of micro-organisms. Schreier et al investigated the effects of Polyvinylpyrrolidone on microbial cells and found that it affects the structure and functions of enzymes and cell proteins; and damages bacterial cell function by blocking hydrogen bonding and altering the membrane structure. Multiple modes of action ensures rapid death of microbes and prevention of bacterial resistance. As the microbicidal action of iodine is related to several directly toxic effects on the cell wall, rather than through specific molecular pathways (as used by antibiotics), resistance is highly unlikely and reports of iodine-resistant strains are exceptionally rare (75).

 

Costs and Evidence: There is substantial in vitro evidence demonstrating that Polyvinylpyrrolidone is a highly effective broad spectrum antimicrobial. Activity has been demonstrated against both common bacterial wound isolates and antibiotic-resistant species. It was determined that more than 99% of MRSA cells were killed within 10 seconds of exposure to PVP-I. Mertz et al found that cadexomer iodine significantly reduced MRSA and total bacteria in partial thickness porcine wounds compared with a no-treatment control and a vehicle group (75).