Wound care places an enormous burden on healthcare resources worldwide. Despite strides in technological innovations of a wide range of options for treating wounds, hard-to-heal wounds continue to pose a challenge to physicians across the globe. Hence, enormous efforts are needed to improve our scientific understanding of the wound healing process to develop new approaches for treatment.1
Treatment of burn wounds aims to control infection and aid in rapid neovascularisation at the wound site. The final aim of burn management and therapy is wound healing and re-epithelialisation as early as possible in order to prevent infection and to reduce functional and aesthetic after-effects.2,3
Wound dressings have been fabricated in various forms using different types of materials, for example fibre mats and hydrogels, and in addition may contain additives such as drugs and drug-like molecules that target the different phases of wound healing, with the aim of eventually reducing the healing time. Many antiseptic agents, such as honey,4 silver5 and povidone-iodine6 have been used for treating burns. Silver has reemerged as a viable treatment option for infections encountered in burns, open wounds and hard-to-heal ulcers. For decades, routine management of burn wounds has centred on a standard 1% cream formulation containing silver complexed to a lipid-soluble polypropylene glycol base, along with the sulfadiazine molecule. Silver sulfadiazine (SSD), a sulfonamide class of antibiotic, exhibits its bactericidal property as soon as it encounters the bacterial cell wall of a wide range of Gram-positive and Gram-negative microorganisms, thus enhancing the rate of healing.7,8,9
SSD has been considered the gold standard for the treatment and prevention of burn infections; however, recent studies indicate that SSD retards the wound healing process.10 Although silver is known for its antibacterial and antimicrobial properties, it has been reported that higher concentrations of silver are toxic to fibroblasts.11 SSD has some undesirable effects, such as delayed development of granulation tissue, increased rate of hypertrophic scar formation, methaemoglobinaemia and limited depth of penetration in lesions.8,12 In addition to this, the glycol base is also proven to be the cause of bone marrow toxicity and neutropenia.13,14
Many pre-clinical studies have reported the use of 1% commercially available SSD cream on second-degree burn wound rat models and demonstrated its positive role in wound closure;15,16,17,18,19 and a few other studies20,21,22,23,24 have also stated its detrimental effects. A recent study by Ebrahimpour et al.15 demonstrated that faster wound closure was observed in SSD-treated rats. Lin et al.16 stated that there was a significantly higher expression of epidermal growth factor (EGF) in the SSD-treated group compared to the control group, resulting in enhanced wound contraction. On the other hand, Kiyan et al.22 reported that the thickness of epidermis and number of blood vessels formed were lower in SSD-treated groups at 25 hours post-biopsy. Similarly, two studies by Nasiri et al.23,24 described that faster wound healing was achieved in control groups compared with SSD-treated groups. Overall, the number of studies that report the positive effects of SSD in animal models is greater than studies demonstrating its negative effect. Despite the aforementioned side-effects, the benefits of SSD in wound healing are known to outweigh them, as evidenced from published literature17,18,19 and it is considered a suitable candidate in the treatment of second-degree burns.
Due to the above mentioned side-effects caused by the individual components of the marketed SSD formulations, there arises a need to revisit the exact role played by SSD in healing burn wounds. Therefore, the purpose of this systematic review was to evaluate the existing evidence on the efficacy of SSD for burn wound care in animal models which mimic the human biological system. The efficiency of SSD application on burn wounds was assessed by comparing the mean wound area on a particular day post-wounding. The results of this meta-analysis might serve as evidence to determine the effectiveness in animals. To the best of our knowledge, this analysis is the first of its kind in determining the efficacy of SSD in healing second-degree burns with respect to wound closure area in rat models. It provides relevant evidence for decision-makers in clinical therapy.
Methods
Search strategy
The search was based on the planned Population, Intervention, Comparison and Outcomes (PICO) elements where:
- P (population)—second-degree burns
- I (intervention)—SSD
- C (comparison)—cotton gauze
- O (outcome)—wound closure.
Study design
Considering the inclusion and exclusion criteria, the pre-selected articles were evaluated for titles and abstracts independently by two researchers (MVD and VP). Disagreements in the selection of articles were resolved by discussion and consensus. After initial selection, the full text of relevant articles was retrieved.
Inclusion criteria
All experimental in vivo studies that evaluated the wound healing efficacy of SSD-treated second-degree burns in rat models by measuring the wound area from post-burn infliction to the day of complete healing were included. Studies eligible for inclusion had to report wound size reduction expressed as mean area compared with that on the day post-wounding. Eligible studies also had to be indexed in PubMed, Web of Science or Google scholar from the earliest record of the database until April 2021, and be published in English.
Exclusion criteria
We excluded studies that reported third-degree burns, diabetes-induced models, in vitro studies, editorials and review articles. Data extracted from published trials were manually curated to remove duplicates. In addition, we excluded studies which used SSD for any other type of wound, or evaluated outcomes other than those established in our objective.
Data extraction
After evaluation of full-text studies that met the inclusion criteria, data were entered into an MS Office Excel sheet (2019) (Microsoft, US) with the following information: authors, publication year, animal model, number of animals in each group, mean wound closure area (expressed in % and/or cm2) along with standard deviation (SD) for SSD-treated group and control group. All data were converted to cm2 for the sake of uniformity. From the datasheet, it was observed that many studies had provided wound closure area pertaining to days 0, 3, 7, 10, 14 and 21 post-wounding, from which seven studies were chosen with more data available for days 0, 7 and 21.
Meta-analysis
Among the studies selected for the final analysis, animal groups treated with SSD were compared with control groups. The wound closure area in cm2 in both groups were the measurement of outcomes. The meta-analysis was performed using the R 3.4.4 statistical package (R Foundation for Statistical Computing, Austria) based on the method of inversion variance. Data were considered as continuous, mean±SDs were calculated, as well as the total number of animals belonging to the experimental and control groups, and converted into mean differences (treatment effect) with 95% confidence intervals (CI). The random effects model was used for analysis. The studies' statistical heterogeneity was calculated with the Chi-squared test and p<0.01 was considered statistically significant. Publication bias was evaluated for the primary outcomes by a funnel plot.
Results
Fig 1 shows the number of articles published each decade in PubMed for the keyword ‘wound’ from 1945–2021. Fig 2 shows the total number of trials identified and selected based on the inclusion criteria for systematic analysis. Out of all the hits obtained for the keywords—‘rat’, ‘silver sulfadiazine’ and ‘burn’—a total of 100 primary studies were identified as results: 52 on PubMed; 44 in Web of Science; and four in manual searches. Duplicate studies (n=28) were removed along with two more studies for which the full text was not available. Furthermore, the articles were screened for the wound closure data for both the SSD-treated and control groups. Fig 2 shows that, after independent analysis by two reviewers, only seven studies met the inclusion criteria and thus were considered for meta-analysis. A third reviewer's opinion was requested for consensus on the seven articles' selected qualification.
The sample size of these randomised trials ranged from 8–35, involving a total of 264 rat models. Of the seven chosen studies, two studies were conducted independently, each in China, Iran and Turkey, and one study was carried out in Romania. A meta-analysis was performed with the seven studies that reported wound contraction area for each group with mean±SD.
Table 1 represents the characteristics of all 70 studies identified that include treatment modalities such as hydrogels, burn liniment, microfibres, growth factors, various concentrations of SSD, aqueous and alcoholic extracts of various phytochemicals for treating second-degree and third-degree burns. The outcomes reported were primarily the macrographs of wounds as the days progressed, wound closure area and histopathology analysis, and its scoring. Out of the 70-studies, 56 studies concluded that SSD aided in faster healing of burn wounds compared with control rats. Among these 56 studies, 15 reported that SSD influenced the rate of re-epithelialisation, collagen formation, and expression of transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF)-α, thereby resulting in increased wound contraction rate. Table 2 represents the characteristics of all included studies at days 0, 7 and 21. A few of the chosen studies21,73,74,77 had missing SD at the selected time points. Weir et al.87 discussed the various methods by which meta-analysis is carried out for missing mean and SD. Ma et al.88 computed a method in which the average of the observed variances can be used in studies with missing variance. Accordingly, the mean of the available SD was used for the missing SD. The random effects model was chosen for the analysis. Fig 3 shows that at day 0, there was no difference between the treatment and control group. But as the days progressed, at day 7 (Fig 4) a considerable difference between the groups was observed since SSD, being a broad-spectrum antibiotic, would have reduced infection at the wound site, which in turn helps in deposition of collagen, resulting in faster wound closure. The healing was faster in SSD-treated groups when compared with control group on day 21, as evidenced by the diamond in Fig 5, which shows a statistically significant difference between treatment and control groups (p<0.01), mean difference –2.72 (95% CI: –4.99, –0.45).
Table 1. Characteristics of 70 studies
| No. | Title/study | Population (number of rats) | Intervention | Control | Efficacy of SSD treatment | Outcomes reported | Author, year |
|---|---|---|---|---|---|---|---|
| 1 | The efficacy of a traditional medicine preparation on second-degree burn wounds in rats | 48 | Lime salve | 1% SSD, normal saline and formulation composed of beeswax and sesame oil | Wound closure rate was 20% higher, re-epithelialisation and collagen formation was faster compared with control | Mean wound closure rate % up to day 24, histology and immunohistology analysis, angiogenesis scoring, re-epithelialisation rate, relative gene expression of VEGF, TGF-β, MMP-2, MMP-9, IL-6 and TNF-α | Ebrahimpour et al., 202015 |
| 2 | A dermal gel made of Rutilus kutum skin collagen-chitosan for deep burn healing | 64 | Collagen, chitosan, collagen-chitosan | 1% SSD and negative control | 2cm2 wound surface area compared with 1.4cm2 in control group on day 25 post-burn | Mean wound area up to day 30, histopathology analysis and scoring | Gharehgheshlagh et al., 202025 |
| 3 | Comparison among bone marrow and wheat flour mixture and standard treatment on healing second-degree burn wound in rats | 45 | Bone marrow and wheat flour | 1% SSD and negative control | Rate of wound healing faster than control | Histopathology analysis, mean wound size up to day 21 | Jafari et al., 202026 |
| 4 | Wound healing activities of Gundelia tournefortii L extract and milk cream ointment on second-degree burns of rat skin | 36 | Gundelia tournefortii L extract composite with milk cream | 1% SSD and negative control | 8% faster wound healing was observed in addition to higher histological scoring | Wound area up to day 21, histological evaluation | Javanmardi et al., 202027 |
| 5 | Effects of carnosine, ankaferd and silver sulfadiazine on an experimental burn model; roles of irisin and HSP70 | 90 | Carnosine, ankaferd | 1% SSD and negative control | Histopathology scoring was higher | Histopathology assessment for re-epithelialisation, haemorrhage and inflammatory response | Kocaman et al., 202028 |
| 6 | The effect of allogenic human Wharton's jelly stem cells seeded onto ADM in healing of rat burn wounds | 40 | ADM scaffold, hWJSC seeded onto ADM scaffold to treat third-degree burn | 1% SSD and negative control | Reduction in third degree burn was higher (54.1%) | Histology assessment | Nazempour et al., 202029 |
| 7 | Cerium nitrate treatment provides eschar stabilisation through reduction in bioburden, DAMPs, and inflammatory cytokines in a rat scald burn model | 42 | Burn with 30-minute water bathing immediately post-burn and burn with 30-minute cerium nitrate bathing immediately post-burn | Negative control | Cerium nitrate renders burnt skin into a less inflammatory state, decreases circulatory damage-associated molecular patterns | Photographs of wound up to day 7, expression of proinflammatory cytokines | Qian et al., 202030 |
| 8 | The effects of beeswax, olive oil and butter impregnated bandage on burn wound healing | 60 | Beeswax + olive oil + butter, 1% SSD | Negative control | Wound contraction was 3% higher than control group, higher expression of TGF-β1 and VEGF-α | Wound reduction up to day 14, Expression of TGF-β1 and VEGF-α, histopathologic scoring | Bayir et al., 201931 |
| 9 | Healing effects of Pergularia tomentosa L., a native medicinal plant in Bushehr province, Iran, on burn, in animal model | 21 | Pergularia tomentosa L | 3% SSD and negative control | Wound area on day 21 was half compared with control Eucerin group | % mean wound closure area up to day 21, epithelium thickness, number of blood vessels and fibroblast cells up to day 28 | Farzadinia et al., 201932 |
| 10 | Natural rubber-propolis membrane improves wound healing in second-degree burning model | 30 | Natural rubber (NR) membrane, NR-propolis membrane at 27°C and 60°C | 1% SSD and negative control | 38.3% retraction achieved compared with 32.6% in control group | Retraction % of lesion area after 10 days, histological analysis | Krupp et al., 201933 |
| 11 | Evaluation of wound healing potential of pomegranate (Punica granatum) whole fruit extract on skin burn wound in rats (Rattus norvegicus) | 21 | 2.5% standardised pomegranate extract (SPE) ointment, 5% SPE, 10% SPE | 1% SSD and negative control | Histopathology scoring same as that of control group | Histopathology scoring, no wound contraction data provided | Lukiswanto et al., 201934 |
| 12 | Characterisation of burn wound healing gel prepared from human amniotic membrane and Aloe vera extract | 40 | Aloe vera, amniotic membrane and both | Negative control | 80.2% wound contraction in control rats (no SSD group) | Evaluation of wound closure, % wound contraction up to day 24 and re-epithelialisation, histology analysis | Rahman et al., 201935 |
| 13 | Wound-healing effect of Platycodon grandiflorus (Jacq.) extract in rats | 32 | Moist exposed burn ointment, Platycodon grandiflorus extract | 1% SSD and negative control | 11% more wound contraction occurred compared with control on day 10 | Mean wound area contraction up to day 10, scanning electron mcrographs of pathological sections | Wang et al., 201936 |
| 14 | Effect of Zaoxiu ointment on wound healing in experimental second-degree burns in rats | 32 | Moist exposed burn ointment, Zaoxiu burn ointment | 1% SSD and negative control | Faster wound contraction compared with control on day 10 | Wound area contraction up to day 10, expression of MMP-2, MMP-9, VEGF and type III collagen | Wang et al., 201937 |
| 15 | The wound healing effect of Callicarpa nudiflora in scalded rats | 40 | 20% CNE and 10% CNE | 1% SSD, vaseline and negative control | Relatively faster wound healing on day 21 | Reduction in wound area up to day 21, expression of serum IL-10, VEGF, Smad 3, TGF-β1 and TNF-α | Zhang et al., 201938 |
| 16 | Therapeutic intervention of Aloe gel containing nano-sized and micron-sized silver sulfadiazine gel on second-degree burn: a comparative study | 18 | 0.25% nSSD and 0.25% mSSD gel containing Aloe gel | Negative control | Wound contraction was two times higher compared to control | % wound contraction up to day 15, histopathology analysis | Barkat et al., 201839 |
| 17 | Safety profile of silver sulfadiazine-bFGF-loaded hydrogel for partial thickness burn wounds | 24 | SSD and bFGF-loaded hydrogel formulation | Placebo formulation composed of PVA and collagen | SSD and bFGF-loaded hydrogel formulation showed no signs of irritation and sensitisation | Histopathology analysis, acute dermal irritation study, whole blood parameters, serum biochemistry parameters, acute eye irritation study | Chakrabarti et al., 201840 |
| 18 | Ciprofloxacin-lidocaine-based hydrogel: development, characterisation, and in vivo evaluation in a second-degree burn model | 12 | CbCipLid hydrogel | SSD cream, CbNa hydrogel | Maximum epithelial thickening at day 14 for SSD group | Histology scoring and analysis, epidermal thickness and continuity, % luminescence | Sanchez et al., 201841 |
| 19 | Comparative in vivo evaluation of novel formulations based on alginate and silver nanoparticles for wound treatments | 60 | 1mM Ag/alginate colloid solution, commercial wound dressing based on dry Ca-alginate microfibres, wet Ag/alginate microfibres, dry Ag/alginate microfibres | 1% SSD and negative control | Complete healing achieved on day 21 compared to control | Reduction in mean wound area up to day 25, histopathological analysis and scoring | Stojkovska et al., 201842 |
| 20 | Silver sulfadiazine nanoethogel for burn healing: characterisation and investigation of its in vivo effects | 30 | SSD nanoethosomal gel | SSD gel, 1% SSD and negative control | 8% more wound contraction compared with control | Mean wound contraction rate % up to day 21, histology parameters | Razavi et al., 201843 |
| 21 | Ankaferd blood stopper accelerates deep second degree burn wound healing in rats | 24 | Ankaferd blood stopper | 1% SSD and negative control | 100% contraction attained compared with 92.83% in control group | Mean unhealed wound area up to day 28, mean neutrophil and vessel count | Topal et al., 201844 |
| 22 | Nanosuspension-based Aloe vera gel of silver sulfadiazine with improved wound healing activity | 36 | 0.25% nanosuspension, 0.25% SSD nanogel containing Aloe vera gel, Aloe vera gel | 1% SSD and negative control | 28% faster wound contraction on day 14 | % wound contraction up to day 14, histopathological images | Barkat et al., 201717 |
| 23 | Burn healing with binahong (Anredera cordifolia (Tenore) steenis) leaves extract as a topical and systemic treatment | 25 | Topical application of 40% binahong ethanolic extract, oral application, both | 1% SSD, ointment base | Re-epithelialisation was lowered compared with control | Re-epithelialialisation, neovacularisation, inflammatory cells and histopathology analysis | Hapsari et al., 201745 |
| 24 | Evaluation of propylene glycol nanoliposomes containing curcumin on burn wound model in rat: biocompatibility, wound healing and anti-bacterial effects | 24 | 0.3% curcuminpropylene glycol containing liposomes, 0.3% free curcumin | Liposome, 1% SSD | 73.7% wound contraction achieved compared with 63.7% in control group | Mean wound reduction % up to day 18, histopathology score analysis for collagen content, re-epithelialisation, angiogenesis, inflammation and fibrosis | Kianvash et al., 201719 |
| 25 | Healing effect of Sanguisorba officinalis L extract on second-degree burns in rats | 105 | Sanguisorba officinalis L. extract | 1% SSD and negative control | Wound area smaller than control group on day 14 | Photographs of wound up to day 14, pathomorphology | Le et al., 201746 |
| 26 | Evaluation of effectiveness in a novel wound healing ointment-crocodile oil burn ointment | 24 | Crocodile oil burn ointment | 1% SSD and negative control | 16% faster healing compared to control | Healing time, mean % wound contraction up to day 28, expression of TGF-β1 and Smad3, thickness of epidermis and dermis | Li et al., 201747 |
| 27 | Therapeutic effect and mechanism of Oxytropis falcata gel on deep second-degree burn in rats | 98 | 12.5, 25 and 50g/kg of Oxytropis falcata gel | 1% SSD and negative control | Significant increase in EGF expression compared to control | Histology analysis, healing time, expression of EGF, VEGF, CD-34, IL-1β, p38 | Lin et al., 201716 |
| 28 | Wound-healing activity of Zanthoxylum bungeanum maxim seed oil on experimentally burned rats | 112 | 500 and 1000µL of Zanthoxylum bungeanum maxim seed oil | 1% SSD and negative control | Complete wound healing on day 30 as compared to 85% healing in control rats | Mean wound healing % up to day 30, wound closure time, histological examination, expression of superoxide dismutase, malondialdehyde, collagen III, MMP2, MMP9, IL-6, Il-1β | Li et al., 201748 |
| 29 | Effect of Zicao ointment on second-degree burns in rats | 105 | Zicao ointment | 1% SSD and negative control | 0.8cm2 wound area present compared with 2.6cm2 on day 14 in control group | Average wound area up to day 14 and histopathology analysis | Luo et al., 201749 |
| 30 | Heterogeneity of mast cells and expression of annexin A1 protein in a second degree burn model with silver sulfadiazine treatment | 40 | 1% SSD | Negative control | Wound healing was faster | Macroscopic and histopathologic analysis, expression of TNFα, IL-1β, Il-6, Il-10, MCP-1, macrophages, AnxA1 | Souza et al., 201750 |
| 31 | The effects of argan oil in second-degree burn wound healing in rats | 30 | Argan oil once a day, argan oil twice a day | 1% SSD and negative control | 69.6% wound contraction compared with 55.5% in control group on day 14 | Mean wound reduction up to day 14, histopathological features, expression of TGF-β1 | Avsar et al., 201651 |
| 32 | Evaluation of the wound healing potential of isoquercetin-based cream on scald burn injury in rats | 40 | 0.01%, 0.02%, 0.04%, 0.06% isoquercetin-based cream | 1% SSD and negative control | 55% contraction when compared to 13% in control group on day 21 | % mean wound reduction up to day 21, re-epithelialisation period, histopathology analysis, expression of TBARS and GSH | Bhatia et al., 201652 |
| 33 | Anti-inflammatory and wound healing activities of Aloe vera, honey and milk ointment on second-degree burns in rats | 21 | Honey, milk, and Aloe vera (HMA) ointment | Eucerin control, 3% SSD | 66.3% contraction when compared with 33.3% in control group on day 21 | % wound area up to day 21, histopathology and histomorphometry analysis | Farzadinia et al., 201653 |
| 34 | Healing effect of Terminalia chebula Retz extract on second-degree burns in rats | 105 | Terminalia chebula Retz extract | 1% SSD and negative control | 0.7cm2 wound area compared to 2.6cm2 in control group on day 14 | Average wound area up to day 14, histopathology analysis | Meng et al., 201654 |
| 35 | Ethosomal curcuminpromoted wound healing and reduced bacterial flora in second degree burn in rat | 30 | 0.2% ethosomecurcumin, 0.2 % free curcumin | 1% SSD, 30% ethanol, ethosome | 10% faster wound healing compared with control | Wound reduction area in %, quantification of bacterial species from the rat burn wounds as mean±SD, histopathology score analysis | Partoazar et al., 201655 |
| 36 | Development and characterisation of novel hydrogel containing antimicrobial drug for treatment of burns | 24 | Cubogel with and without SSD and Aloe vera | 1% SSD and negative control | 72% wound closure achieved on day 12 | % wound closure up to day 12, histopathology analysis | Thakkar et al., 201656 |
| 37 | Burn wound healing activity of Lythrum salicaria L. and Hypericum scabrum L | 30 | Lythrum salicaria extract, Hypericum scabrum extract and both | 1% SSD and negative control | 77.7% contraction when compared with 57.8% in control group on day 14 | % wound size reduction up to day 14, histology analysis | Vafi et al., 201657 |
| 38 | The healing effect of nettle extract on second degree burn wounds | 40 | Nettle extract | 1% SSD, vaseline and negative control | Faster wound closure compared with control | Wound surface area in terms of group up to day 36, PMN infiltration, collagen deposition, fibrosis and angiogenesis | Akbari et al., 201558 |
| 39 | Comparing the effect of visceral fat and barley seed ash (Hordeum vulgare L.) with silver sulfadiazine on burn wound healing in rats | 60 | Traditional medicine containing visceral fat and barley seed ash | 1% SSD, normal saline and negative control | 75.3% contraction when compared with 55.3% in control group on day 14 | Wound contraction up to day 14, histopathology analysis | Azadi et al., 201559 |
| 40 | InGaP 670-nm laser therapy combined with a hydroalcoholic extract of Solidago chilensis Meyen in burn injuries | 72 | Irradiation with an InGaP laser at 670nm, Solidago chilensis hydroalcoholic extract and both | Negative control | Number of fibroblasts, collagen content was relatively high in rats treated with hydroalcoholic extract and irradiated with laser (no SSD group) | Histology analysis, number of fibroblasts, collagen content, number of blood vessels and granulocytes, expression of TGF-β1 and VEGF on day 7, 14 and 21 | Catarino et al., 201560 |
| 41 | Wound healing activity of a traditionally used poly herbal product in a burn wound model in rats | 20 | Poly herbal cream | 1% SSD, cream base, negative control | 70.8% wound healing achieved compared with 32.2% in control group on day 14 | Wound healing % up to day 14, histopathology analysis | Fahimi et al., 201561 |
| 42 | Investigation of acute effects of Hypericum perforatum (St John's Wort-Kantaron) treatment in experimental thermal burns and comparison with silver sulfadiazine treatment | 35 | Topical Hypericum perforatum, agent gel | 1% SSD and negative control | Epidermal thickness and number of vessels formed were significantly lower than control | Histopathology analysis and scoring, epidermal thickness, number of blood vessels, hair follicles | Kiyan et al., 201522 |
| 43 | Evaluation of wound healing activity of Thunbergia laurifolia supercritical carbon dioxide extract in rats with second-degree burn wounds | 36 | 2.5%, 5%, and 10% Thunbergia laurifolia leaf extract gel | 1% SSD, gel base, negative control | 5% higher wound closure than control on day 28 | % wound closure up to day 28, re-epithelialisation time, collagen content histopathological analysis and scoring | Kwansang et al., 201562 |
| 44 | Evaluation of wound healing effect of Punica granatum L peel extract on deep second-degree burns in rats | 105 | Pomegranate husk extract | 1% SSD and negative control | 0.85cm2 wound area compared with 2.0cm2 in control group on day 21 | Average wound area up to day 21, histopathology analysis | Ma et al., 201563 |
| 45 | The healing effect of Arnebia Euchroma ointment versus silver sulfadiazine on burn wounds in rat | 50 | 5% and 10% Arnebia euchroma ointment | Normal saline, ointment base, 1% SSD | % wound contraction was 98.6% in control compared with 95.8% in SSD treated rats on day 35 | Wound area, percentage of wound contraction up to day 35, histological and bacteriological assessments | Nasiri et al., 201564 |
| 46 | Effect of Malva sylvestris cream on burn injury and wounds in rats | 50 | 5% and 10% Malva sylvestris cream | 1% SSD, normal saline and negative control | 93.2% wound healing on day 35 compared with 99.2% in control group on day 32 | Wound area, percentage of wound contraction up to day 25, histological and bacteriological assessments | Nasiri et al., 201523 |
| 47 | The effect of Terminalia chebula extract versus silver sulfadiazine on burn wounds in rats | 50 | 5% and 10% Terminalia extract cream | 1% SSD, base cream, negative control | 97.5% wound healing achieved compared with complete healing in control group on day 33 | Mean wound area up to day 30, histopathology analysis and scoring | Nasiri et al., 201565 |
| 48 | The healing effect of Scrophularia striata on experimental burn wounds infected with Pseudomonas aeruginosa in rat | 150 | Scrophularia striata ethanolic extract | 1% SSD and negative control | 2.0mm2 wound area compared with 5.0mm2 in control group on day 21 | Reduction in wound area up to day 21, collagenisation, re-epethelialisation, granulation, neovascularisation, inflammation and necrosis | Tanideh et al., 201566 |
| 49 | Comparison of healing effect of Aloe vera extract and silver sulfadiazine in burn injuries in experimental rat model | 16 | Second-degree and third-degree burn treated with Aloe vera | SSD | Complete healing by day 9 | % wound healing up to day 10 | Akhoondinasab et al., 201467 |
| 50 | Niosomally encapsulated silver sulfadiazine gel for burn treatment | 18 | 0.5% w/w niosomal SSD gel | 1% SSD and negative control | 45.6% wound contraction compared with 12.7% in control group on day 22 | Mean wound area up to day 22 | Dharashivkar et al., 201468 |
| 51 | Effect of green tea on the second-degree burn wounds in rats | 40 | Green tea | 1% SSD, vaseline and negative control | Relatively lower burn area compared with control | Mean burned area between different groups | Fatemi et al., 201469 |
| 52 | Silver sulfadiazine-based cubosome hydrogels for topical treatment of burns: development and in vitro/in vivo characterisation | 30 | SSD chitosan cubogel, SSD Carbopol cubogel, SSD chitosan/carbopol mix cubogel | Dermazine and negative control | Granulation tissue formation started at day 15, fibrosis started at day 21 for dermazine-treated group | Histopathology analysis and scoring | Morsi et al., 201470 |
| 53 | Effect of Chinese medical herbs-burn liniment on deep second-degree burn in rats | 140 | Burn liniment | 1% SSD and negative control | 0.8cm2 wound area compared with 2.0cm2 in control group on day 21 | Average wound area up to day 21, expression of ICAM-1, IL-10 and myeloperoxidase, histology analysis, MIC against standard bacterial strains | Wang et al., 201471 |
| 54 | The effect of different topical agents (silver sulfadiazine, povidoneiodine and sodium chloride 0.9%) on burn injuries in rats | 28 | 10% povidoneiodine, 0.9% sodium chloride, 1% SSD | Negative control | Decrease in inflammatory cell infiltration was observed compared with control | Histology analysis | Yüksel et al., 201472 |
| 55 | Comparison of topical sucralfate and silver sulfadiazine cream in second degree burns in rats | 48 | Sucralfate | 1% SSD, cold cream | 91% wound healing achieved against 76% in control rats at 4th week | Wound area up to day 28, thickness of granulation tissue, histology analysis | Beheshti et al., 201373 |
| 56 | Evaluation of the effect of thymoquinone treatment on wound healing in a rat burn model | 40 | Systemic thymoquinone (TQ), topical TQ, topical and systemic TQ | 1% SSD and negative control | 8.7cm2 wound area compared with 11.2cm2 in control group on day 21 | Changes in wound surface area up to day 21, extent of vascularisation, re-epithelialisation and granulation, frequency of positive cultures | Selçuk et al., 201374 |
| 57 | Antioxidant and burn healing potential of Galium odoratum extracts | 36 | 15% and 30% of methanolic extract cream (MEC) and aqueous extract cream (AEC) of Galium odoratum | 1% SSD and negative control | 88.7% wound reduction achieved against 36.3% in control group in day 14 | Wound contraction % up to day 14, histopathology analysis | Kahkeshani et al., 201375 |
| 58 | The healing effect of Arnebia euchroma in second-degree burn wounds in rat as an animal model | 48 | 10% and 20% Arnebia euchroma extract | 1% SSD and negative control | Wound reduction rate of 17.73mm2 per day compared with 5.01mm2 per day in control group | Histology analysis, mean numerical density of the fibroblasts, volume densities of the collagen bundles and vessels | Ashkani-Esfahani et al., 201276 |
| 59 | Natural products locally modulators of the cellular response: therapeutic perspectives in skin burns | 40 | Cold-cream with 10% Sambuci flos and Sambuci folium soft extracts | 1% SSD, cold cream base | 76.7% wound healing achieved against 68% in control group on day 21 | Mean burnt wound skin area up to day 21 | Mogosanu et al., 201277 |
| 60 | Crocodile oil enhances cutaneous burn wound healing and reduces scar formation in rats | 24 | Crocodile oil burn ointment | 1% SSD and negative control | 98% wound contraction achieved against 82% in control group on day 21 | Healing time, wound contraction up to day 28, expression of TGF-β1 and Smad 3 | Li et al., 201278 |
| 61 | Effect of Aloe cream versus silver sulfadiazine for healing burn wounds in rats | 48 | 0.5% powdered Aloe vera cream | 1% SSD, base cream, negative control | 4.1cm2 wound compared with 5.5cm2 on day 25 | Mean wound size up to day 25 | Hosseinimehr et al., 201079 |
| 62 | The effect of dressing with fresh kiwifruit on burn wound healing | 60 | Kiwifruit | 1% SSD and negative control | 76mm2 wound area compared with 32.4mm2 in control rats on day 21 | Changes in wound surface area up to day 21, biochemical and microbiological findings | Mohajeri et al., 201021 |
| 63 | Effect of topical external administration of recombinant human epidermal growth factor on expression of epidermal growth factor receptor and its mRNA in scald wound of diabetes mellitus rat | 136 | Streptozotocin | Negative control | External application of rhEGF when controlling blood sugar accelerates wound healing | Wound healing rate up to day 21 | Zong S al., 201080 |
| 64 | The effect of saffron (Crocus sativus) extract for healing of second-degree burn wounds in rats | 48 | 20% saffron cream | 1% SSD, cream base, negative control | 4.1cm2 wound compared with 5.5cm2 on day 25 | Average burn wound size up to day 25 | Khorasani et al., 200881 |
| 65 | Comparison between alpha and silver sulfadiazine ointments in treatment of Pseudomonas infections in third-degree burns | 60 | Third-degree burn treated with alpha ointment | 1% SSD and negative control | 75% wound contracture achieved compared to 95% in control rats in 10th week | Grading of the wounds, scar formation, positive culture and contracture | Hosseini et al., 200720 |
| 66 | An investigation on burn wound healing in rats with chitosan gel formulation containing epidermal growth factor | 64 | EGF solution, chitosan gel with and without EGF | 1% SSD and negative control | Re-epithelialisation higher compared with control | Fibroblast nucleus area at days 3, 7 and 14 | Alemdaroğlu et al., 200682 |
| 67 | Topical treatment of standardised burns with herbal remedies in model rats | 40 | Third-degree burn treated with Jomelop, HD ointment | 1% SSD and negative control | Complete wound healing occurred in 19 days as compared with 33 days for control groups | Time for complete healing, macroscopic observation and histological appearance of wound | Bečić et al., 200583 |
| 68 | Effects of hyperbaric oxygen therapy on experimental burn wound healing in rats: a randomised controlled study | 70 | SSD and hyperbaric oxygen | SSD and placebo gas | Number of blood vessels significantly less compared to experimental group | Size of oedema formation, necrosis staging, number of blood vessels, leukocyte margination | Bilic et al., 200584 |
| 69 | Absorption, excretion and tissue distribution of silver sulphadiazine | 45 | SSD | Negative Control | Absorption of SSD through dermal burn surfaces, normal skin are negligible | Concentration of silver in spleen, serum, brain, liver, bone, blood cells | Sano et al., 198285 |
| 70 | Epidermal growth factor in the healing of second-degree burns: a controlled animal study | 20 | Topical treatment with epidermal growth factor (EGF), combined treatment with EGF and AgS | 1% SSD and negative control | Complete healing occurred in 19 days compared with 35 days for control rats | Weight change in %, time to complete healing, rate of healing, mortality rate, cell proliferation | Thornton et al., 198286 |
ADM—acellular dermal matrix; bFGF—basic fibroblast growth factor; CbCipLid—carbomer ciprofloxacin-lidocaine; CbNa—carbomer hydrogel without drugs; CD-34—cluster of differentiation-34; CNE—Callicarpa nudiflora water extract; DAMPs—damage-associated molecular patterns; EGF—endothelial growth factor; GSH—reduced glutathione; HD—ointment containing an aqueous extract of Sambucus nigra L., Caprifoliaceae, Sanguisorba minor Bertol., Rosaceae, Teucrium chamaedrys L., Labiatae, Polypodium vulgare L. and Polypodiaceae; HSP70—heat shock protein 70; hWJSC—human Wharton's jelly stem cells; ICAM—intercellular adhesion molecule; IL—interleukin; InGaP—indium gallium phosphide; MIC—minimum inhibitory concentration; MMP—matrix metalloproteinase; p38—mitogen activated protein kinases 38; PMN—polymorphonuclear leukocytes; PVA—polyvinyl alcohol; rhEGF—recombinant human epidermal growth factor; SD—standard deviation; Smad—fusion of Caenorhabditis elegans Sma genes and the Drosophila Mad, Mothers against decapentaplegic; SSD—silver sulfadiazine; TBARS—thiobarbituric acid reactive species; TGF—transforming growth factor; VEGF—vascular endothelial growth factor; w/w—weight/weight
Table 2. Characteristics of included trials for days 0, 7 and 21
| Study (country) | Number of rats in each group, n | Wound area expressed as mean±standard deviation in cm2 | |||||
|---|---|---|---|---|---|---|---|
| Day 0 | Day 7 | Day 21 | |||||
| Treatment group | Control group | Treatment group | Control group | Treatment group | Control group | ||
| Beheshti, 201373 (Iran) | 16 | 1.75±0.15 | 1.75±0.10 | 1.65±0.29 | 1.70±0.33 | 0.49±0.26 | 1.14±0.31 |
| Topal, 201844 (Turkey) | 8 | 2.25±0.00 | 2.25±0.00 | 2.04±0.28 | 2.07±0.40 | 0.31±0.15 | 0.50±0.29 |
| Selçuk, 201374 (Turkey) | 8 | 20.00±0.15 | 20.00±0.10 | 14.50±0.29 | 18.00±0.33 | 8.70±0.90 | 11.20±1.20 |
| Mogosanu, 201277 (Romania) | 10 | 1.50±0.15 | 1.50±0.10 | 1.42±0.15 | 1.45±0.17 | 0.35±0.03 | 0.48±0.05 |
| Mohajeri, 201021 (Iran) | 20 | 3.14±0.15 | 3.14±0.10 | 2.75±0.29 | 2.83±0.33 | 0.76±0.37 | 0.32±0.19 |
| Ma, 201563 (China) | 35 | 3.70±0.30 | 3.70±0.20 | 2.85±0.45 | 3.00±0.40 | 0.80±0.20 | 2.00±0.20 |
| Wang, 201471 (China) | 35 | 3.70±0.30 | 3.70±0.20 | 2.80±0.40 | 3.00±0.40 | 0.85±0.15 | 2.00±0.20 |
Publication bias was assessed by visually evaluating the possible asymmetry in funnel plots which can either result from non-publication of negative results, or be caused by other factors, such as true effect size. To analyse the publication bias, a funnel plot was constructed for selected studies for day 21 (Fig 6). The study size (standard error) is represented in the vertical axis while the effect size (mean difference) is represented in the horizontal axis. Studies that involved a smaller number of animals are more widely scattered and appear towards the bottom of the graph. Fig 6 shows that the funnel plot is asymmetric in nature but then, since the number of studies are fewer, it cannot be concluded that publication bias prevails.
Discussion
Although the number of days taken for complete healing to occur (endpoint) in the chosen studies varied, day 21 was chosen for analysis. The outcome in all of the seven studies, except that investigated by Mohajeri et al.,21 favoured the wound healing process with the application of SSD post-wounding. At day 7, a larger mean difference in wound area was reported by Selçuk et al.,74 whereas at day 21, a similar trend was reported by Beheshti et al.,73 Selçuk et al.,74 Ma et al.63 and Wang et al.71 The authors compared the efficacy of SSD with their dressings.
Beheshti et al.73 compared the healing efficacy of sucralfate with that of SSD and control groups. A second-degree burn of 1.75cm2 was created on randomly categorised experimental groups (n=16). The degree of healing was evaluated by measuring the wound area on days 7, 14, 21 and 28. It was concluded that the SSD-treated group showed a 91% healing rate whereas a rate of only 76% was observed in the control group, although the maximum healing rate of 100% was exhibited by sucralfate-treated rats. Topal et al.44 studied the effect of Ankaferd Blood Stopper (ABS, Ankaferd Health Products Ltd., Turkey) and SSD in healing partial-thickness wounds in rats. The size of the unhealed wound at days 7, 14, 21 and 28 with respect to the initial wound area of 2.25cm2 was measured in rats, with each group having eight animals. The mean difference between the SSD-treated group and the control group was almost zero until day 7, but a larger difference (0.31cm2 versus 0.5cm2) was observed on day 21, emphasising that SSD aided in better healing. Moreover, complete healing was observed in ABS- and SSD-treated groups on day 28 in contrast to 0.23cm2 of the wound left unhealed in control rats.
Selçuk et al.74 performed an in vivo study in burn wound rat models to understand the role of thymoquinone (TQ), an active ingredient in Nigella sativa. A deep second-degree burn was inflicted on the back of rats covering an area of 20cm2. The changes in the wound size were recorded at pre-determined time points until day 21, in all rats, which were divided into five groups of eight each. At the end of the study, the mean unhealed wound area was 8.70±0.90cm2 and 11.20±1.20cm2 in the SSD-treated and control groups, respectively. The mean difference between SSD-treated and control groups remained higher from day 7 onwards. The rate of wound closure was similar in SSD and intraperitoneally administered TQ animal groups.
Mogosanu et al.77 wrote an article that discussed the role of many phytochemicals and natural remedies available to treat burn wounds. They described the role and effects of active ingredients found in natural remedies available to treat skin wounds. The anti-inflammatory, antimicrobial, immunomodulatory and antioxidant properties are a few characteristics of natural medicinal products that enhance the wound healing process. In their work, a burn of 1.5cm2 was created in rats randomly divided into four groups of 10 animals each. On day 21, 90.66%, 84.66%, 76.66% and 68.00% healing were observed in rats treated with cold-cream with 10% Sambuci flos soft extract, cold-cream with 10% Sambuci folium soft extract, SSD and control groups, respectively.
Mohajeri et al.21 studied extensively the wound healing effects of kiwifruit in rat models for which animals were grouped into three sets of 20 animals each. After the creation of a wound (3.14cm2 area), the animals were closely monitored to evaluate the wound size every two days. Post-wounding, animals that were treated with 3mm-thick sliced fresh kiwifruit (Group K) exhibited faster wound healing, and from day 11 onwards, similar wound closure was observed in control rats (Group C) and SSD-treated rats (Group S). Finally, on day 21, a wound area of 0.76±0.37cm2 remained unhealed in the SSD-treated group in contrast to a lesser wound size of 0.32±0.19cm2 (p<0.0001) in the control group, whereas complete wound closure was observed in Group K.
Ma et al.63 evaluated the wound healing efficacy of Punica granatum L. peel (pomegranate husk extract (PHE)). The rats were randomly divided into groups of 35 animals each and a burn wound of 3.70cm2 was created on each rat. On day 21, the mean wound area of rats treated with PHE was 0.21±0.07cm2 and with SSD was 1.15±0.1cm2, which was significantly smaller than that of the control group (2.42±0.2cm2) (p<0.01). These results prove that PHE is a promising medicinal herb for the management of deep second-degree burns. Wang et al.71 studied the role of burn liniment, which is a Chinese medicine formula, in treating deep second-degree burns of 3.70cm2. All the rats were randomly grouped into four groups with 35 animals in each group. The mean wound area treated with burn liniment was 0.1±0.1cm2, while a larger mean difference was observed on day 21 between the SSD-treated group and control group (0.85±0.15cm2 versus 2.00±0.20cm2), which was attributed to the anti-inflammatory and antibacterial activity of burn liniment.
SSD has been used as a topical agent in the treatment of burns. The results obtained through this analysis, comprising 264 animals, can be considered more significant than the results of individual studies. All the studies except one21 showed favourable wound healing effects with the application of SSD compared with control rats. Regarding the reduction in wound area, meta-analysis clearly showed an unambiguous result favouring SSD treatment. Most of the studies showed different results with respect to healing time.
Limitations
This review does have some limitations because of the small animal numbers in each group, and that the groups were also heterogenous, which may have neglected the detection of significant differences between the tested interventions. Regarding possible study biases, all studies involved rats which had second-degree burns inflicted. This finding is of great interest as topical silver, notably SSD cream, has been used as a standard in the treatment of burn wounds.
Conclusion
It is proven that the silver present in SSD interacts with wound exudate and exhibits its antimicrobial action, by which wound closure is enhanced. Thus, the results of this systematic review and meta-analysis substantiate the fact that 1% SSD enhances the wound healing rate of burn wounds in rat models. Taking the results of all the studies together, the authors provide supportive but not conclusive evidence about the effectiveness of SSD in controlling burn wound infection in animals. There are many reports stating the adverse effects of SSD. A comprehensive investigation is required to assess its drawbacks and side-effects.
Reflective questions
- What are the mechanisms by which silver sulfadiazine causes delayed burn wound healing?
- How can side-effects be controlled by manipulating the dose of silver sulfadiazine being applied to treat burn wounds?
- What are the other silver-based dressings that cause detrimental effects?