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Suggested Guidelines For Using Antimicrobials In Bacterial Skin Infections: Antimicrobial choice, treatment regimens and compliance*
By: Michael Ephraim Vergara, DVM, Technical Services Associate
*Excerpts from the published study of the same title by L. Beco, E. Guaguere, C. Lorente Mendez, C. Noli, T. Nuttall, M. Vroom (Veterinary Record, February 9, 2013)
Therapy: selecting an appropriate antibiotic
Systemic or topical treatment?
Once a pyoderma has been diagnosed, it is important to consider if the infection is deep, severe and/or generalized enough to warrant treatment with systemic antibiotics.
Preferred alternatives for mild, surface and/or focal infections include topical antimicrobial shampoos and sprays, or even topical antibiotics if topical antiseptics do not clear the infection. Topical antiseptic treatments can hasten to clear the infection, or will greatly reduce the need for systemic therapy (Scott et al 2001, de Jaham 2003, Murayama et al 2010).
If systemic antibiotics are considered the best approach, there are five relevant points to take into consideration:
- The vast majority of skin infections are associated with coagulase positive staphylococci.
- The skin is the largest organ of the body, and its blood supply is comparatively poor.
- The length of treatment will depend on the depth of the infection.
- Most cases of canine pyoderma are secondary to other pathologies, which must be addressed to obtain a clinical cure.
- Using topical antiseptic treatment will hasten to clear the infection
Choice of antibiotic:
The vast majority of skin infections in companion animals are associated with coagulase-positive staphylococci, with Staphylococcus pseudintermedius (part of the Staphylococcus intermedius group [SIG]) the most common causative agent in canine pyoderma (Devriese et al, 2005; Bannoehr et al, 2007).
Clinical trials have been conducted on canine pyoderma cases on systemic antibiotic therapies and efficacies of different drugs have been established. It is possible to use this efficacy data and SIG susceptibility data to estimate the probability of successful management of staphylococcal skin infections with different antibiotics, and classify them into first-, second- and third-line antibiotics.
First-line antibiotics include established and well-tolerated narrow and broad-spectrum drugs with anti-staphylococcal activity. They are no less potent than higher-tier drugs in the correct circumstances, and are appropriate for empirical treatment of uncomplicated canine pyoderma. First-line drugs include cefadroxil, cefalexin, clavulanateamoxicillin, clindamycin, and lincomycin. Cefpodoxime and cefovecin can be included as first-line antibiotics where medication may be difficult, and/or compliance is, or likely to be, poor (Van Vlaenderen et al, 2011). Long-term injectable or once-daily palatable oral antibiotics are useful if there is, or is likely to be, poor adherence to the treatment regimen, problems with communicating the treatment regimen to the owner, and/or multiple therapies within a treatment regimen.
Second-line antibiotics should only be used when there is culture evidence that first-line drugs will not be effective. These antibiotics are not appropriate for empirical antibiotic treatment (Authier et al, 2006). Second-line antibiotics include newer broad-spectrum drugs important to animal and human health where the development of resistance is of greater concern. Second-line antibiotics include cefovecin, cefpodoxime, difloxacin, enrofloxacin, marbofloxacin, orbifloxacin, and pradofloxacin. The recent decline in staphylococcal susceptibility to fluoroquinolones is probably due to the common use of these drugs (Prescott et al, 2002). To limit the emergence of resistance, fluoroquinolones should only be used wheresecond-line antimicrobials are necessary (Authier et al, 2006).
Third-line antibiotics are very important to animal and human health, especially for the treatment of multidrug-resistant organisms. Resistance towards these drugs is of great concern and/or they have greater potential for adverse effects. Most of these drugs are not licensed for animals, and there are few safety and efficacy data. Third-line antibiotics must only be used when there is culture evidence of sensitivity, no first- or second-line antibiotics are effective, and topical antimicrobial therapy is not feasible or effective (Authier et al, 2006). Thirdline antibiotics include aminoglycosides, azithromycin, ceftazidime, chloramphenicol, clarithromycin, florphenicol, imipenem, phosphomycin, piperacillin, rifampin, tiamphenicol, and ticarcillin. The development of resistant bacteria in human health is a big concern. In their ethical role of healthcare professionals, veterinarians should never use drugs deemed critically important to human health (eg, vancomycin, teicoplanin, linezolid, etc) in animals. Some countries, moreover, expressly prohibit the use of human antibiotics not licensed for animals (eg, azithromycin, ceftazidime, clarithromycin, imipenem, phosphomycin, piperacillin, rifampicin, ticarcillin, and others), so those antibiotics should preferably be avoided, even if there is evidence of sensitivity. Clinicians are responsible for ensuring that it is legal to use non-licensed drugs in their countries.
Antibiotic dose, duration and compliance issues
The skin is the largest organ of the body, and its blood supply is comparatively poor (Scott et al, 2001). Antibiotics should, therefore, be used at the upper end of their dose range in pyoderma. Animals should always be weighed to allow accurate dosing. If necessary, slightly overdose – never underdose.
For cefadroxil: 22 to 30 mg/kg every 12 hours orally (Angarano and MacDonald 1989, Frank and Kunkle 1993), or 30 to 40 mg/kg every 24 hours orally (Noli and Scarampella 1999).
The duration of treatment will depend on the depth of the infection. Superficial pyodermas typically need two to three weeks of treatment. Deep pyodermas can be greatly improved after two weeks, but full resolution often takes four to six weeks or longer (Carlotti and Ovaert 1988, Angarano and MacDonald 1989, Guaguère and Marc 1989, Paradis et al 1990, Scott et al 2006, and Carlotti et al, 1995).
Poor compliance or adherence to treatment is likely to compromise efficacy and encourage resistance. Compliance problems include underdosing, missed doses and stopping treatment early (Barter et al1996, Grave and Tanem 1999), and compliance declines with twice daily or more frequent dosing and treatment regimens with more than one drug. Furthermore, owners may find it difficult or dangerous to administer drugs to some animals. Thus, discussing potential problems openly and honestly with owners helps to select the most appropriate drug and dosing regimen. Compliance can be improved by:
- Using long-duration injectable drugs or once-daily drugs.
- Using palatable drugs and drugs that the owner is able to administer safely.
- Convincing the owner of the importance of correct treatment.
- Giving written instructions and use precise terminology – for example, ‘every 12 hours’ instead of ‘twice daily’.
- Good follow-up and communication.
- Minimizing the number of different drugs or treatments.
In this day when antibiotic resistance is an emerging problem in veterinary and medical care and constitutes a threat to animal welfare and public health, a proper approach in dealing with bacterial infections is a must. But more importantly, if good hygiene routines can be practiced to prevent and control infections and minimize zoonotic risk, that would be so much better.