Responsible dermatology in general practice

If you’re in general practice, you are likely seeing dermatology cases on an almost daily basis. These cases can be frustrating and often require antimicrobials as part of the treatment. But are we using these antimicrobials in a responsible way?

“It’s a legitimate concern—multidrug resistance in our world,” said Julia Miller, DVM, DACVD, an assistant clinical professor, section of dermatology in the Department of Clinical Sciences at Cornell University’s College of Veterinary Medicine in Ithaca, New York. At the recent Fetch dvm360® conference in Charlotte, North Carolina, Miller presented a practical approach to dermatology cases in general practice, with the intention of maximizing antimicrobial stewardship.

Key Concepts in Antimicrobial Stewardship

According to Miller, the 4 pillars of antimicrobial stewardship are drug, duration, dose, and time. All these pillars must be accurately addressed when using antimicrobials responsibly, according to Miller.

“I don’t like thinking of antimicrobial stewardship as just ‘Don’t use this drug, do use this drug,’” Miller said. “It’s more complicated than that because if you choose the appropriate antibiotic—but you do not choose the right dose and you don’t give it long enough—that’s bad antimicrobial stewardship.”

Multi-drug resistant (MDR) infections are well-known threats to both human and animal health. They have been named a top global public health concern by the World Health Organization. As part of their responsibility to uphold public health, veterinarians must be judicious in using antibiotics.

Additionally, some consequences of MDR infections are unique to veterinary medicine. “When we develop multidrug resistance, we are talking about increased costs for treatment,” Miller said. “Now we have to use big-gun antibiotics that cost an awful lot more money. That’s going to take more visits. It’s going to take cultures and susceptibilities to make sure we’ve got it right.”

Higher costs for treatment and more visits may also increase the stress on owners, especially in cases of limited finances. The emotional impact on the client can be even larger in severe cases, which sometimes result in euthanasia.

Right Time: Is an antibiotic really needed?

“The first step in good antimicrobial stewardship is to make sure that you need an antibiotic,” Miller said. Staphylococcus pseudintermedius, the most common cause of superficial bacterial folliculitis in dogs, is the No. 1 reason antimicrobials are used in canine dermatology cases. Other species of Staphylococcus occur in canine patients at lower frequencies.

Many skin patterns that are consistent with Staphylococcus species infectioncan be observed on physical examination; however, proof of infection requires cytology. “You don’t treat liver disease without blood work, so stop treating [Staphylococcus]without cytology,” Miller said. For example, a patient with pustules could have a Staphylococcus species infection, but pemphigus and other autoimmune disease, contact hypersensitivity, and drug reactions are each a differential diagnosis requiring distinct treatments.

Miller noted that some classic Staphylococcus species lesions can be difficult to collect cytology samples from due to their dry nature. Patients with epidermal collarettes, excessive scale, or a moth-eaten haircoat in short-coated breeds such as bulldogs are highly suspicious for Staphylococcus species infection. Combining cytologic and physical examination findings is the best way to approach these cases and determine if antibiotic treatment is warranted.

Right Drug: Choosing Between Topical and Systemic Antibiotics

When it comes to superficial Staphylococcus infections, veterinarians have a variety of treatment options, including topical and systemic antimicrobials. “Superficial[Staphylococcus] can almost always be treated topically,” Miller said.

However, successful treatment requires owner compliance in bathing or application of topical medications. Miller acknowledged that not all owners will be compliant with topical treatment, making oral medications the better choice in some cases. “The No. 1 thing for antimicrobial stewardship is getting the treatment done,” she said.

Miller encouraged practitioners to treat cases of superficial bacterial folliculitis topically when possible. When discussing treatment plans with clients, keep the plan simple. Veterinarians or technicians should have an honest conversation about the owner’s ability to treat topically. Asking clients if they can do the baths or apply the topical products as prescribed can save time and frustration for both the client and veterinary team. If the answer is no, consider systemic options.

In some cases, systemic antimicrobials are preferred from the beginning. For Miller, these cases include the presence of furunculosis, which is characterized by red, palpably thickened skin; folliculitis that is nonresponsive to appropriate topical therapy; patients with immune compromise; and when owner compliance is a concern.

When using systemic antimicrobials, empirical antibiotic selection can be appropriate in many cases, especially in patients presenting with a first-time infection. First-tier antimicrobials in dermatology include clindamycin, cephalexin, cefpodoxime, cefovecin, amoxicillin clavulanate, and trimethoprim with sulfadiazine or sulfamethoxazole.^1,2 Without culture and sensitivity, doxycycline and minocycline may be considered as second-tier choices.^1,2

Right Dose and Duration: Empirical Antibiotic Use in Dermatology

When choosing among first-tier antibiotics, Miller encourages veterinarians to consider several factors, including patient size (this affects which medications can be dosed appropriately in their commercially available formulations), historical use of antimicrobials, history of adverse effects, and the effect of dosing frequency on client compliance.

Although cephalexin is known by many veterinarians as a first-line agent for treating bacterial pyoderma, Miller stressed that the minimum effective dose is 22 mg/kg by mouth twice daily. Higher doses up to 30 mg/kg can be used but are more likely to have gastrointestinal adverse effects. “If it’s not the drug that fits the weight [of the pet], then it’s not the right drug,” Miller said. In cases when appropriate dosing of cephalexin is not possible, consider other first-tier agents.

Miller also cautioned veterinarians when choosing clindamycin empirically. She shared that although it can be an excellent first-line antimicrobial for dermatology cases, resistance develops quickly. Even if the pet has never been treated with clindamycin, resistance can develop if there is a long history of using other antimicrobials.³ Additionally, if selecting clindamycin based on culture and susceptibility testing, veterinarians should ensure that the bacteria is also sensitive to erythromycin. Clindamycin resistance can be induced in bacteria that has already developed erythromycin resistance.

When considering the duration of treatment, continuing 7 days past clinical resolution is recommended. Although lesions may appear visually resolved after only a week of treatment, deeper infection may still be present. Thus, standard recommendations are to dispense a 21-day course of antimicrobials in cases of superficial bacterial folliculitis.¹

Culture and susceptibility testing is never wrong. It should be utilized in cases in which treatment with multiple antimicrobials has failed, multiple antimicrobials have been previously used at short durations (<10 days), and there is a history of fluoroquinolone use.⁴ Cytology should always be performed in these cases to confirm the presence of bacteria and aid in interpretation of results. Fluoroquinolones, chloramphenicol, and rifampin should be reserved for use based on culture and susceptibility testing.^1,2

Take-home Points

Although it may be tempting in dermatology cases to treat empirically based on the clinical appearance of the dog, practitioners should confirm the presence of a bacterial infection through cytology. Therapeutic choices should be made collaboratively with the client to maximize compliance, and when antimicrobials are chosen, practitioners should ensure they choose the right drug at the right time and prescribe it at the appropriate dose and duration.

General practitioners “are the front line of good antimicrobial stewardship,” Miller said.

Kate Boatright, VMD, a 2013 graduate of the University of Pennsylvania, is a practicing veterinarian and freelance speaker and author in Western Pennsylvania. She is passionate about mentorship, education, and addressing common sources of stress for veterinary teams and recent graduates. Outside of clinical practice, Boatright is actively involved in organized veterinary medicine at the local, state, and national levels.

References

1. Hillier A, Lloyd DH, Weese JS, et al. Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis (Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases). Vet Dermatol. 2014;25(3):163-e43. doi:10.1111/vde.12118
2. Hnilica KA, Patterson AP. Small Animal Dermatology. A Color Atlas and Therapeutic Guide. Elsevier, 2017.
3. van Damme CMM, Broens EM, Auxilia ST, Schlotter YM. Clindamycin resistance of skin derived Staphylococcus pseudintermedius is higher in dogs with a history of antimicrobial therapy. Vet Dermatol. 2020;31(4):305-e75. doi:10.1111/vde.12854
4. Faires MC, Traverse M, Tater KC, Pearl DL, Weese JS. Methicillin-resistant and -susceptible Staphylococcus aureus infections in dogs. Emerg Infect Dis. 2010;16(1):69-75. doi:10.3201/eid1601.081758