Introduction

There are four specific uses of antibiotics in medicine: prophylaxis (preventing the occurrence of infection), metaphylaxis (treating a group of patients or individuals when only a single patient is showing clinical signs), therapy (controlling an existing infection), and growth promotion (used in food animal production).¹ Although using antibiotics for metaphylaxis and growth promotion is most often seen in food animal production, prophylactic and therapeutic usage of antibiotics is common in both human and veterinary medicine. The use of prophylactic antibiotics is a highly debated topic among the medical community. Antibiotics are commonly used perioperatively and postoperatively as a method to prevent the formation of infection and surgical complications, but factors such as inappropriate choice of antimicrobials, improper dosage, and long-term use of antimicrobials play an important role in the emergence of multidrug-resistant bacteria.² Multidrug-resistant bacteria can result in chronic inflammation and increased risk of bacterial zoonotic transmission to owners and veterinarians.³

When properly applied in specific situations, preoperative and perioperative antimicrobial therapy reduces postoperative morbidity and mortality.⁴ However, postoperative antimicrobials are not necessary in all situations. With permanent pacemaker infections in humans, patients treated with both preoperative and postoperative antibiotics had similar rates of infection as those treated with preoperative antibiotics alone.⁵ In the case of antibiotic prophylaxis following rumenotomies in cattle, there was no significant difference in rate of infection between animals who received a single preoperative dose of antibiotic and those who were treated for an additional 7 days following surgery.⁶ For dogs undergoing orthopedic implant surgery, surgical site infection rates were similar in cases using perioperative antibiotics and postoperative prophylactic antibiotics course for 6 days following surgery.⁷ One study evaluating the use of prophylactic cephalexin treatment in acute radiation-induced dermatitis in dogs revealed that there was no significant difference in prevalence of bacterial infection or overall quality of life between dogs given prophylactic cephalexin and those that were not.⁸

Antimicrobial stewardship is a growing issue across the world in human and veterinary medicine. The American Veterinary Medical Association has subsequently formed a task force for antimicrobial stewardship and has created multiple policies regarding judicious use of antimicrobials. Within the policy titled “Antimicrobial stewardship definition and core principles,” one of the core principles is to select and use antimicrobial drugs judiciously. This is supported by using an evidence-based approach for making a diagnosis and determining whether an antimicrobial drug is indicated.⁹

Punch biopsies are regularly performed by veterinarians, especially veterinary dermatologists, to evaluate various skin conditions. In people, these procedures are considered to be clean procedures and postoperative antibiotics are not recommended.¹⁰ To date, there is no evidence-based medicine to support or refute the use of prophylactic antibiotics after cutaneous punch biopsies in veterinary medicine. The objective of this retrospective study was to evaluate the rate of bacterial infections, after cutaneous punch biopsies in small animals, without postoperative antibiotics to determine whether prophylactic antibiotics are necessary. Based on previous evidence, from both veterinary and human medicine, it was hypothesized that the rate of surgical site infections would be low and indicate that postoperative antibiotic usage is not necessary in animals receiving punch biopsies.

Materials and Methods

The medical records at the University of Illinois at Urbana-Champaign Veterinary Teaching Hospital were searched through for small animals (dogs and cats) that had a punch biopsy of the skin performed by the dermatology service (faculty or dermatology house officer) between January 1, 2013, and December 31, 2018. Inclusion criteria were small animals that received a punch biopsy of the skin and a follow-up appointment in 10–14 days for suture removal with the service. Any animal that was receiving antibiotics at the time of the punch biopsy was excluded. If any clinical signs consistent with inflammation (papules, pustules, crusts, and ulcerations) were noted at the biopsy site at the suture removal, tape cytology was performed to evaluate for any secondary infection. Erythema was not included as this could have been the normal wound healing process or a suture reaction. When bacteria were identified on cytology, a culture swab was rolled onto the affected area for collection of the sample. The culture swab was submitted for aerobic bacterial culture to identify the organism along with the susceptibility of that organism.

All procedures were performed and evaluated in a similar manner before the procedure and afterward. Before performing the punch biopsy, each biopsy site was evaluated cytologically to rule out the presence of a secondary bacterial infection. If the hair was dense, it could have been cut shorter with scissors to allow better visualization of the skin and apposition of the skin for suturing purposes. None of the sites were scrubbed or cleaned with any antiseptic solution. The area was anesthetized locally with a 1:9 volume mixture of sodium bicarbonate 8.4%^a and lidocaine 2%^b and a total volume of 1 mL injected subcutaneously in each location. Some patients were sedated for the biopsy with a 5 μg/kg dose of dexmedetomidine IV^c. Either a 6 mm or 8 mm punch biopsy was performed in each area, and the biopsy site was closed with 3-0 nylon suture in a single cruciate pattern or two simple interrupted sutures. The owner was instructed to monitor the site for any swelling, discharge, irritation, or any other signs of inflammation. No preventive measures to stop self-trauma were done, such as bandaging or E-collars. Also, no antibiotic or topical medication was dispensed after the biopsy. All suture sites were evaluated at 10–14 days and sutures were removed at that time.

Data were collected from medical records and included the following: species, signalment, concurrent disease present at the time of biopsy, concurrent medications (systemic and topical), location of the biopsy site (divided into head, trunk, and limbs), histopathology results of biopsy, and the presence of secondary bacterial infections after the biopsy was performed, including culture results if performed. Concurrent medications were divided into antifungals, anti-inflammatory, medications managing chronic disease (hypothyroid, atopic dermatitis, arthritis, etc.), and immunomodulatory/immunosuppressive. The biopsy sites were divided into head, trunk (neck, thorax, and abdomen), and limbs. Biopsy results were divided into cutaneous masses (neoplastic and nonneoplastic such as cysts), autoimmune and immune-mediated, inflammatory disorders (suspect allergic dermatitis), infectious diseases, endocrine disorders, keratinization disorders, alopecic disorders, and congenital disorders.

The data collected for biopsies of dogs over the study period were composed of a cohort sample with all undergoing an outpatient surgical biopsy for dermatologic diagnostic testing. Using this as the framework, the data were arranged to reflect dichotomous categories as they relate to complications from the biopsies. Relative risks were calculated to measure these associations to provide added understanding of the complication incidence observed in these patients. The presence of bacterial infection was considered the condition or outcome, whereas diagnosis, location, and concurrent medications were the exposures.

Results

Bacterial Infections

A total of 287 files were reviewed, but only 182 animals had follow-up data. An additional 28 animals were excluded, as they were receiving previously prescribed systemic antibiotics at the time of the biopsy. This resulted in a total population of 154 animals—128 dogs and 26 cats.

At the time of suture removal, three dogs had signs of inflammation and cocci bacteria were identified via cytology at the biopsy site. In addition, all of the biopsy sites appeared to have closed appropriately in all cases regardless of infection status. This amounted to a postoperative infection rate of 1.9% (3/154). Because all of the postoperative infections occurred in dogs, evaluating only the 128 dogs in the study determined an infection rate of 2.3% (3/128). A 10 yr old cocker spaniel with an underlying condition of diabetes mellitus was receiving insulin and artificial tears. Biopsy was performed on the dorsal aspect of the right hind paw and revealed a sebaceous adenoma. Subsequent bacterial culture at suture removal revealed a methicillin-resistant Staphylococcus pseudintermedius. An 8 yr old Yorkshire terrier had previously been diagnosed with atopic dermatitis but was not receiving concurrent medications for this condition. Biopsy was performed on the right neck and revealed a cutaneous histiocytoma. Subsequent bacterial culture at suture removal revealed a methicillin-susceptible Staphylococcus epidermidis. A 6 yr old shar pei with a history of shar pei fever and mast cell tumors was not receiving concurrent medications. Biopsy of the ventral abdomen revealed a mast cell tumor. Subsequent bacterial culture at suture removal revealed a methicillin-resistant Staphylococcus schleiferi. Pyoderma was not identified on the histopathology report in any of the above three dogs. All three cases were treated with systemic antimicrobial therapy for 21–28 days, which resolved the bacterial infections. One feline patient developed crusting around the biopsy site, but no organisms were seen on cytology, so it was not cultured. This patient was ultimately diagnosed with pemphigus foliaceus, so the crust was likely due to underlying disease and not a complication of the procedure itself.

The only statistically significant relative risk of developing infections after biopsy was 0.06 (P = .007, 95% confidence interval [CI] 0.01–0.93) when the diagnosis was a dermatologic disease compared with a cutaneous mass (Table 1). If the biopsy was taken from the trunk (including the neck, thorax, and abdomen) of the animal, the relative risk of developing complications was 2.16 (P = 0.61, 95% CI 0.16–59.91) times greater than if the biopsy was taken from the animal’s head or limbs, which was not statistically significant (Table 2). If the animal was taking medications concurrently, the relative risk of developing complications was calculated to be 0.64 (P = 1.00, 95% CI 0.02–8.86), which was not statistically significant (Table 3). Statistical evaluation of the concurrent disease, at the time of biopsy, was not performed, owing to a large number of variables and very small sample size within each category (Table 4).

TABLE 1 Results of the Biopsies Based on the Dermatologic Disorder Along with Bacterial Infections in Dogs

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TABLE 2 Location of the Biopsies Along with the Bacterial Infections in Dogs

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TABLE 3 Concurrent Medication Being Administered Along with Bacterial Infections in Dogs

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TABLE 4 Concurrent Disease at the Time of Biopsy and Bacterial Infections in Dogs

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Discussion

To our knowledge, this is the first study that examines the prevalence of infection following cutaneous punch biopsies in small animals and risk of infection related to medication, location, and type of cutaneous disease. Antimicrobial stewardship is of utmost importance, and antibiotics should be used following evidence-based medicine. The data support the hypothesis of a low postoperative infection rate after cutaneous punch biopsies when no bacterial infection is present at the time of the procedure. This strongly supports not using prophylactic antibiotics with cutaneous punch biopsy procedures when no bacteria are identified on cytology before the procedure. If bacteria are present before the biopsy, it is recommended to clear this infection to minimize the risk of postoperative infections before the procedure.

All of the dogs that developed postoperative bacterial infections had a diagnosis of a neoplastic cutaneous mass. Those with nonneoplastic dermatologic disease had a 94% relative reduced risk of infection compared with those with neoplasia as listed in Table 1. These postoperative infections cases included one of each of the following neoplasia diagnoses: sebaceous adenoma, cutaneous histiocytoma, and mast cell tumor. The dogs in this category were also variable in their age and breed presentation. With the small sample size and number of dogs infected, we were unable to statistically evaluate if age or breed had a factor. Considering the underlying diseases of these dogs (atopic dermatitis, shar pei fever, and diabetes mellitus), it is understandable that these dogs are predisposed to secondary bacterial infections that could happen anywhere on their skin.^11–13 When looking at concurrent medications, it is interesting that none of the dogs receiving immunomodulatory/immunosuppressive medications had any bacterial infections noted.

This study is limited owing to its retrospective nature and the loss of more than 100 cases because of a lack of follow-up information. Ideally, having a larger prospective study with a set criterion for inclusion and data collection would be the most beneficial. Because significantly fewer cats were evaluated in this study compared with dogs, the complication rate of 0% should be interpreted carefully, indicating a larger sample size needed to evaluate cats further. In addition, there was such a large variety of concurrent medications, concurrent disease, and diagnosed disease that amounted to small numbers in each group. This makes statistical interpretation difficult, not knowing if these comorbidities have a factor.

Additional information may have been missed owing to incomplete medical records, which could have led to underestimation of infection rates. It is difficult to know if some clients were regularly cleaning the biopsy site and putting topical medication on the area to prevent infection. Clients could have also tried to prevent the animals from physically removing the sutures or causing trauma by placing an E-collar on the animal. Although it was not recommended to implement these steps in our patients, clients could have decreased the infection rate in our population by performing these measures proactively. Additionally, a determination could not be directly identified if the dogs acquired an infection from the inflammation of the sutures, if the dog was licking and traumatizing the area, or if the concurrent disease was responsible for the infection or if it was caused by the cutaneous neoplasia itself.

Antimicrobial stewardship should be at the forefront of all veterinarians’ minds and used appropriately. When looking at the potential benefit of antibiotic usage following surgical procedures, one must consider both the benefits and the risks of administration, including adverse reactions of the patient to the medication, increased cost to the client, and the development of antimicrobial resistance. To retain the efficacy of currently available antibiotics and control the development of resistance to antimicrobial agents, the safest way is to limit their use as much as possible.¹⁴ Antimicrobial stewardship guidelines should be considered every day in our veterinary practices based on evidence-based medicine.

Conclusion

Based on our results, postoperative complications are very uncommon with cutaneous punch biopsies of our dogs and cats, and the administration of prophylactic antibiotics following punch biopsies is likely unnecessary. If a bacterial infection is present on cytology, it is recommended to treat with antibiotics and delay the biopsy until the infection is resolved. Small changes, such as limiting the dispensing of prophylactic antibiotics, could have large benefits in decreasing antimicrobial resistance in the future.