SUMMARY. Moist exposed burn ointment (MEBO) is a sesame-oil-based ointment for burns produced in China. An animal trial was carried out in a guinea-pig model to compare MEBO treatment with 1% bacitracin ointment in contact burns. Forty female guinea-pigs sustained contact burns inflicted by means of a brass cylinder heated to 60 °C. Some of the wounds were treated with MEBO and some with 1% bacitracin ointment. Follow-up included wound biopsies and planimetry. No differences were demonstrated in the rate of wound healing when wound planimetry was analysed. There was no statistically significant difference in the histological wound-healing patterns.
Partial-thickness thermal injuries constitute the majority of burns. Superficial partial-thickness burns (SPTB) usually heal within 21 days unless wound infection causes the destruction of surviving epidermal adnexae in the dermis. This risk motivated the common use of topical antimicrobials for SPTB as well as for deep burns. The different methods for the local treatment of burns are still controversial. Local infection and burn wound sepsis are severe problems in the treatment of thermally injured patients. Burn wound cultures are negative during the first few hours. However, the burn wound becomes rapidly colonized: gram-positive cocci are present within 24 h and gram-negative aerobes within 3 to 7 days. In untreated wounds, surface colonization may lead to the invasion of healthy tissue. Early surgical excision and the use of topical antimicrobials were reported to decrease the infection rate, significantly improving the survival rate in burn patients in the last 25 years.1 Various topical antimicrobials and antiseptics are used in the treatment of burns.2,3 The local treatment of burns may cause further problems. The beneficial effect of the decrease in bacterial counts in deeper tissue may be confounded by other effects that delay wound healing, as shown in some experimental studies. Most of these topical treatments require one or two dressing changes every day, which are painful and costly.4,5
Moist exposed burn ointment (MEBO) was developed in China (Rongxiang Pharmaceutical). It is a sesame-seed-oil-based ointment used for burn treatment. The protocol calls for almost no debridement of the wound and no shower or medical cleansing. The “old” remnants of the ointment with any debris (liquefaction of necrotic tissue) are gently removed with a wooden tongue depressor. Fresh ointment is applied every 4 h in open fashion. During a tour in China we were told that thousands of patients had been treated with this ointment with good results. We were allowed to examine some of the patients and received the clinical impression that some of the patients with SPTB were enjoying a painless course of healing.
During our visit we were unable to assess the general success of the treatment and complication rates and we therefore decided to conduct a small-scale animal trial in order to compare MEBO ointment with a familiar topical treatment possessing similar physical properties. We carried out this animal trial in a guinea-pig model and compared MEBO treatment with 1% bacitracin ointment in deep and superficial partial-thickness contact burns.
Forty female guinea-pigs (average weight, 250 ± 50 g) were housed in separate cages and climatized for one week. They were given food and water ad libitum. The animals were anaesthetized with ketamine 30 mg/kg and xylazine hydrochloride 10% 2 mg/kg. They were then chemically depilated using Orna-19 (Alpha Cosmetica, Israel) cosmetic depilatory cream, and each animal sustained two contact burns with a 1 kg brass cylinder (diameter 3 cm) heated to 60 °C in a thermostatic bath. Each animal received two contact burns, one on each side of the back. Table I describes the various experimental groups.
<% createTable "Table I","Treatment regime according to group",";Group;N° animals;Burn;Right side;Left side@;1;8;DPTB;MEBO 4 h;Bacitracin 4 h@;2;10;SPTB;MEBO 4 h;Bacitracin 4 h@;3;10;SPTB;MEBO 12 h;Bacitracin 12 h@;3a;2;Sham;MEBO 12 h;Bacitracin 12 h@;4;10;DPTB;No treatment;No treatment@;Total;40;~;~;~","DPTB = deep partial-thickness burn; SPTB = superficial partial-thickness burn",5,400,true %>Group 1: Eight animals received deep partial-thickness burns (DPTB) (60 °C bilateral contact burns for 50 sec). The right-side wound was treated with MEBO every 4 h, 4 times a day, with a 12-hour break at night. The left-side wound was treated with 1% bacitracin ointment.
Group 2: Ten animals received SPTB (60 °C bilateral contact burns for 30 sec). Five animals were treated with MEBO and five with 1% bacitracin ointment, according to the same timetable protocol as group 1.
Group 3: Ten animals received bilateral SPTB (60 °C for 30 sec). Five animals were treated bilaterally every 12 h with MEBO and five with 1% bacitracin ointment. Two additional animals were depilated on both sides of the body but not burned. One of these was “treated” with MEBO and the other with bacitracin.
Group 4: Ten animals received bilateral DPTB (60 °C for 50 sec). None of these animals received any treatment (Table I).
Before every ointment application, the remnants of the previous ointment were gently removed using a wooden tongue depressor. The wound was protected with a round plastic cap sutured to the healthy skin around the wound in order to prevent the animal from licking or rubbing off the ointment.
Treatment continued for 21 days post-burn. Follow-up (on days 1, 3, 7, 10, 14, and 21) included 3 mm punch biopsies and planimetry. The animals were sacrificed on day 21, and a horizontal strip of skin was sampled from each wound. Microscopic examination of the skin specimens was carried out after staining with haematoxylin and eosin. The biopsies were examined and assessed for the following five histological criteria (maximum score for normal skin, 10):
Two of the animals in group 1 died on day 14. In group 2 (bacitracin subgroup) two animals died on day 10 and one (MEBO subgroup) died on day 14. In group 3 one animal (bacitracin subgroup) died on day 8. In group 4 there was no mortality. The mortality rate differences were not significant, but the mortality rate in groups 1, 2, and 3 was 10-30%, which is significantly higher than a mortality rate acceptable for this model. Sham burns treated with either bacitracin or MEBO did not cause mortality.
No differences were demonstrated in the rate of wound healing when wound planimetry was analysed in each group. In the first group all wounds healed within 21 days. In the second group wounds healed within 14 days. In the third group wounds did not reach full closure by day 21. In the fourth group all wounds healed within 21 days (Fig. 1). The trends of wound-healing histological patterns were better for MEBO subgroups on days 14 and 21 but the differences were not statistically significant. The patterns were similar in burns that received no treatment (Fig. 2). Some skin irritation and hyperaemia were noticed in animal receiving bacitracin application but without burns.
<% immagine "Fig. 1","85_fig_1.gif","No differences were demonstrated in wound healing in any group. The results are expressed as the percentage of the wound square from the primary burn wound", 350 %> <% immagine "Fig. 2","85_fig_2.gif","Trend of wound-healing histological patterns in the various groups", 350 %>The mortality rate in small contact burns is usually low in animals and humans. The relatively high mortality rate (10%-30%) in some of our subgroups was therefore alarming. We could not define any ongoing concomitant disease in the experiment. We were concerned that digesting the ointment might intoxicate the animals, but no reduction in mortality was found when we protected the wound with plastic caps. The difference in mortality rates between the subgroups calls for a more wide-scale experiment.
The lack of differences in wound healing rate, with only a tendency towards wound histology improvement in the MEBO group, suggested that for this model MEBO is as effective a treatment as bacitracin. No sign of wound sepsis was observed in either group, i.e., no differences were demonstrated in either group in PMN in the wound or in bacterial invasion of healthy tissue.
The similarities between the groups can be attributed to the properties of the oil base of the ointment applied over the burn wound in the open treatment modality.
One per cent bacitracin ointment is used in the treatment of many of our out-patients if the burns are small and superficial. MEBO is an ointment with similar physical properties but without documented antimicrobial properties. It seems that antimicrobial properties did not play any role in this wound-healing model.
Our small-scale study compared MEBO and 1% bacitracin ointment on deep and partial-thickness contact burns. We found no statistically significant differences in the healing rates of MEBO and 1% bacitracin-ointment-treated burns when compared with burn wounds that received no treatment.
RESUME. Le MEBO (moist exposed burn ointment - onguent pour les brûlures exposées humides) est un onguent basé sur l’huile de sésame pour le traitement des brûlures fabriqué en Chine. Les Auteurs ont effectué une recherche expérimentale utilisant un modèle de cobaye afin de comparer le traitement avec le MEBO avec le traitement utilisant l’onguent de bacitracine 1%. Quarante cobayes du sexe féminin ont subi des brûlures de contact moyennant un cylindre de cuivre chauffé à 60 °C. Certaines lésions ont été traitées avec le MEBO et d’autres avec l’onguent de bacitracine. Le traitement successif comprenait la biopsie des lésions et la planimétrie. Les Auteurs, sur la base des résultats de l’analyse de la planimétrie, n’ont pas observé aucune différence pour ce qui concerne le rythme de la cicatrisation des lésions. Il n’y avait pas de différence statistiquement significative dans les caractéristiques histologiques de la cicatrisation des lésions.
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