Canine pyoderma is a bacterial infection of the skin, most often caused by Staphylococcus pseudintermedius, a commensal of the dog. It is classified by the depth of infection as surface, superficial or deep pyoderma, and it is one of the leading reasons for prescribing antimicrobials in dogs.
This frequency gives the skin a special place in the fight against antimicrobial resistance, because canine staphylococci and their resistance genes can pass to humans. In addition, the skin can be sampled and treated from the outside. An antiseptic can therefore often replace a systemic antibiotic. The guidelines published in 2025 by the International Society for Companion Animal Infectious Diseases (ISCAID) cover all three depths of pyoderma for the first time and markedly shorten treatment durations. Our colleague Anette Loeffler presented them in two lectures at the 35th European Veterinary Dermatology Congress (ESVD-ECVD-ISVD, Bilbao, 11-13 September 2025): one on the real need for and duration of antibiotic therapy, the other on the guidelines themselves.
1 The real need for systemic antimicrobials
1.1 Reducing their use
The US Centers for Disease Control and Prevention (CDC) have made antibiotic resistance their top priority, with the aim of reducing the annual rate of outpatient antibiotic dispensing.
Antimicrobial use guidelines have two aims: a good outcome for the patient and judicious use of these drugs. They rely on the literature as far as possible, then fill the gaps with experience and consensus.
Unlike the internist, the dermatologist can replace a systemic antimicrobial with a topical one. Trials confirm that topical treatment can appropriately replace systemic treatment. The guidelines therefore give topical treatment the highest strength, graded A, in surface and superficial pyoderma. Topical treatment reaches the follicle well: an ex vivo study by Dr Loeffler’s team, using a fusidic acid suspension at 10 mg/g, shows penetration down to the follicular infundibulum, at concentrations far above the usual minimum inhibitory concentrations (MICs) of S. pseudintermedius.
1.2 Some deep pyodermas can resolve without antimicrobials
Dr Loeffler presented a case series by Dr Christine Cain of 22 dogs with post-grooming furunculosis, a deep Pseudomonas pyoderma that follows bathing and abrasive grooming and can lead to septicaemia as early as the next day, with a risk of death. In this study, 17 dogs recovered on a systemic antimicrobial. One received prednisolone only, and four received a cephalosporin even though Pseudomonas did not respond to it. These five dogs therefore recovered without an active antimicrobial. Likewise, in a study of generalised demodicosis, 16 dogs treated with an acaricide and benzoyl peroxide washes, without a systemic antimicrobial, all recovered. According to our colleague, they did not recover more slowly than the 28 dogs that also received a systemic antimicrobial.
For our colleague, these observations show that not all deep pyodermas are the same. Some might stem from an excessive immune response, which glucocorticoids would calm. Others might stem from sterile inflammation, in which the isolated bacterium is merely a coincidence. These are her hypotheses, and further data are therefore needed.
1.3 Dysbiosis, infection and criteria for cure
Pyoderma involves commensals in most cases. The question is therefore what allows them to proliferate and creates dysbiosis, and then what turns dysbiosis into infection. Dr Loeffler considers the definitions of infection and carriage of little clinical use, because they predate molecular techniques. Restoring the skin barrier is probably what prevents these commensals from proliferating. Dermatology also lacks a criterion for cure. The physician can obtain sterile urine; the dermatologist never obtains sterile skin and does not want to, because the goal is normally colonised skin. Nor are the lesions specific, since a pustule may be that of pemphigus.
1.4 What antimicrobials really cost
Safety is not a good argument against antimicrobials, because they are very safe. Studies on pyoderma report gastrointestinal upsets in about 10 % of cases.
The concern comes from the microbiome, which sequencing now allows us to study. Antibiotic therapy acts first on the resistome, the full set of resistance genes: under selection pressure, bacteria adapt. A human study showed spread of resistance within the skin microbiome after a systemic antibiotic. In dogs, amoxicillin-clavulanate and cefalexin increase faecal shedding of resistant Escherichia coli.
Antibiotic therapy then acts on host health: in humans it is associated, especially in childhood, with inflammatory bowel disease. The gut microbiome is being studied in obesity, allergies, diabetes and Alzheimer’s disease. Animal data are scarce, but past antimicrobial use shows that the association exists. By contrast, in a longitudinal study by Lluís Ferrer’s group of six atopic dogs, four weeks of ciclosporin followed by four weeks of prednisolone at an anti-inflammatory dose did not alter the skin microbiota.
2 The ISCAID guidelines: scope and method
Pyoderma is very common, and antimicrobial resistance has become a major problem. According to Dr Loeffler, an extensive human and veterinary literature shows that current guidelines reduce overall antimicrobial use, especially that of reserve drugs. These drugs must still work on the day someone is admitted to hospital with a serious infection. Indeed, staphylococci and their resistance genes can pass from animals to humans. This risk is, however, low for methicillin-resistant S. pseudintermedius (MRSP), higher for resistant S. aureus (MRSA) and unknown for S. coagulans.
These guidelines are the first to cover every depth of pyoderma and both topical and systemic antimicrobials. Each case is decided individually, according to the dog’s general condition. Every veterinarian must know the resistance patterns, drug availability and regulations of their own country, which vary even within Europe. National veterinary organisations can also use them to draft their own guidelines. The text, published in May, is available in full.
The method combines a systematic review of studies published up to 23 December 2023 with grading of the evidence according to the SORT taxonomy, which gives each recommendation a strength from A (at least one good-quality randomised trial) to C (consensus). All the authors then voted on each recommendation, which was discussed again until unanimity was reached. Finally, fifteen external veterinarians, general practitioners and specialists from several continents, critically reviewed the text.
3 Diagnosis before antimicrobials
3.1 Cytology in every case
Cytology remains undervalued and underused. Our colleague sees it neglected in the case queries she receives every day, although this test costs no more than a strip of adhesive tape and a good microscope. For Dr Loeffler, no dog should receive an antimicrobial without prior cytology, surgical wounds included. It is essential in every suspected case of pyoderma, because many lesions are also seen in sterile diseases: the pustule is the primary lesion of pemphigus foliaceus, and papules are common in atopic dermatitis. The sensitivity of cytology reaches 93 % in superficial pyoderma. The absence of cocci therefore does not completely rule out the diagnosis.
No threshold number of cocci defines infection. One looks for cocci in active division, in pairs and then in groups of four, because these regular groupings prove that they are bacteria and not artefacts. Several findings support pyoderma. The first is the presence of intracellular bacteria, because they have multiplied enough to attract neutrophils. The second is extracellular bacteria with nuclear streaming, the remains of DNA from dead neutrophils. DNA is a very stable molecule that stretches out on the slide. Very large numbers of bacteria without inflammatory cells define bacterial overgrowth syndrome, in which the immune system does not react.
3.2 Culture and susceptibility testing
When to perform them is debated. Culture and susceptibility testing are ultimately recommended whenever systemic treatment is being considered. Cost is a barrier: about £100 to £120 where Dr Loeffler works, up to 500 dollars in North America. The guidelines therefore ask laboratories for a reasonable price, because this test benefits everyone.
Culture is never contraindicated, but it is not always necessary. The money for an unnecessary culture is better spent on a shampoo or a flea product. Culture is not used for diagnosis, because healthy skin also carries staphylococci. Diagnosis relies on clinical signs and cytology. Nor is culture used to choose a topical product, whether shampoo or ear drops. The laboratory grows the bacterium, then measures a zone of inhibition or an MIC. It then translates that measurement into “resistant” or “susceptible” using clinical breakpoints, set from pharmacokinetic and pharmacodynamic data. These breakpoints apply only to systemic administration, and none exist for topical products. The R and S on the report therefore mean nothing in that setting. Occasionally, a swab is used to screen for a multidrug-resistant bacterium.
Culture is always preceded by cytology. If the report lists four bacteria, one is tempted to prescribe a fluoroquinolone; if cytology shows only cocci, the bacterium responsible is S. pseudintermedius, and a beta-lactam is enough.
3.3 Empirical choice and risk factors
Choosing without culture remains an option, but it requires a risk assessment. In superficial pyoderma, more than 90 % of infections are caused by S. pseudintermedius. Every clinician knows the frequency of MRSP in their region. An antibiotic is chosen empirically only if the risk of methicillin resistance is low, and only from among first-tier drugs: clindamycin, cefalexin, cefadroxil, amoxicillin-clavulanate. Amoxicillin-clavulanate was debated, because human medicine now regards it as precious and uses it the way we use fluoroquinolones. Clindamycin and cefalexin are sufficient for uncomplicated superficial pyoderma.
Culture is always strongly recommended when a risk factor is present: previous antimicrobial use, past MRSP or MRSA infection, recurrent pyoderma, more than one course of systemic antimicrobials in six months, a resistant staphylococcus in the dog or its household, no improvement after five to seven days of a properly administered antibiotic, new lesions during treatment, rods or mixed flora on cytology.
3.4 The primary cause, from the first episode
Dr Loeffler’s favourite recommendation is that pyoderma is always secondary to a primary cause, to be investigated from its very first occurrence. “Idiopathic” pyoderma is no longer tenable. The possible causes are many (parasites, allergies, endocrinopathies). The choice of tests is a matter of clinical judgement. In surface pyoderma, a problem of conformation and skin folds is often found. In deep pyoderma, the possibility of demodicosis must never be overlooked.
4 Surface pyoderma
The guidelines include three presentations: acute moist pyotraumatic dermatitis (“hot spot”), intertrigo or skin fold pyoderma, and bacterial overgrowth syndrome. These are dysbioses, in which microbial proliferation remains confined to the upper layers of the epidermis. For these forms, the very term pyoderma has become controversial, because the bacteria do not invade the tissues. Treatment therefore has three components: reducing microbial proliferation, reducing inflammation by treating the primary cause, and relieving pain. This last component is now written into the guidelines, because these lesions can be painful.
A topical antimicrobial is the treatment of choice, with the highest strength. Dr Loeffler regrets still seeing surface infections treated systemically, whereas topical treatment alone has proved equivalent to systemic treatment in pyotraumatic dermatitis. Beware: a hot spot can resemble pyotraumatic furunculosis. This deep pyoderma is recognised by its satellite lesions and calls for different treatment. Chlorhexidine has the best evidence.
Inflammation sustains these conditions. Combining the topical antimicrobial with a topical glucocorticoid, a short systemic course of five to seven days or a Janus kinase inhibitor is recommended. One trial even showed that a prednisolone cream alone led to faster healing than an antibiotic cream alone.
Healing is generally achieved within seven to fourteen days. Follow-up can rely on the owner: if the owner is satisfied, a recheck is not essential; if the owner judges progress insufficient, the dog is seen again with cytology. When the cause, such as a skin fold, cannot be corrected, the antiseptic is continued as prevention, sometimes for life.
5 Superficial pyoderma
Superficial pyoderma affects the epidermis and the hair follicle. It includes exfoliative pyoderma, impetigo, mucocutaneous pyoderma and superficial bacterial folliculitis, by far the most common form. Diagnosis relies on clinical signs and cytology. Pemphigus foliaceus, which mimics folliculitis, is suspected when there are lesions on the pinnae, the bridge of the nose or the footpads, and acantholytic keratinocytes on cytology.
The recommendation is topical treatment alone: superficial pyoderma does not need a systemic antimicrobial. A topical product alone was effective in 12 of the 13 published trials, eight of them randomised. The guideline gives strength A to chlorhexidine 2-4 %, benzoyl peroxide 2.5 % and a few other agents. A randomised trial by Stefano Borio’s group showed that topical treatment alone is as effective as a systemic antimicrobial. In that trial, after four weeks, 31 dogs treated with 4 % chlorhexidine shampoo and solution had done as well as 20 dogs on amoxicillin-clavulanate at 25 mg/kg twice daily. The guidelines thus provide the argument to put to owners, even though topical treatment works a little more slowly, with a response in two to three weeks. Trials show improvement from the first or second week and cure of most dogs within three to four weeks.
A veterinary recheck is needed to confirm that every lesion has resolved and to pursue the search for the primary cause if it has not already been identified.
Systemic treatment is reserved for cases that have not responded to topical treatment alone, or where topical treatment is not feasible, and not for mere convenience. The literature gives no clinical reason to prefer it to topical treatment. The dog’s temperament or the owner’s abilities may nevertheless require it, as may lesions that have not improved sufficiently after two weeks of topical treatment. In the absence of risk factors, the first-tier empirical drugs are those active against S. pseudintermedius: amoxicillin-clavulanate, first-generation cephalosporins, clindamycin.
The duration has been shortened to two weeks, with a veterinary recheck scheduled before the end of the course to decide whether to stop or continue. Treatment is not continued until the hair regrows, but until the primary lesions (papules, pustules and erythematous collarettes) have resolved. Alopecia may persist for up to six weeks after these lesions have healed. Residual erythema with cytology free of bacteria does not justify continuing. Improvement should begin within five to seven days; otherwise the dog is seen sooner for cytology and culture. The aim, according to Dr Loeffler, is to replace “just in case” prescribing with regular follow-up and adjunctive topical therapy. Adjunctive topical therapy is recommended whenever possible, because it might shorten systemic treatment.
6 Deep pyoderma
The key sign of deep pyoderma is the haemorrhagic crust, because the infection has reached the dermis and its blood vessels. This proximity to the vessels explains the severity of the disease, which can spread through the bloodstream and progress to septicaemia. The lesions are painful. Haemopurulent discharge, nodules, fistulae, ulcers and furuncles also point to depth. A furuncle is a ruptured follicle that forms a red to violaceous papule more than 3 mm across, from which pus drains. Presentations, generalised or localised, include extensive folliculitis-furunculosis, the pyotraumatic form, lick dermatitis, interdigital nodules, callus pyoderma, chin pyoderma and post-grooming furunculosis. Atopic dermatitis is probably the most common cause of deep pyoderma, but demodicosis, hypothyroidism, hyperadrenocorticism and tumours must also be considered.
Deep lesions always require systemic treatment. Its choice must in every case be based on culture, because S. pseudintermedius accounts for only about 60 % of the organisms involved, leaving a 40 % risk of error for an empirical choice. S. pseudintermedius accounts for 63 % of the 428 isolates from seven studies. The rest include streptococci, Pseudomonas aeruginosa, E. coli and enterococci, some of which are intrinsically resistant to lincosamides. Amoxicillin-clavulanate has little activity against Pseudomonas and cephalosporinase producers. Anaerobic culture is always added. The sample must come from the deep infection (fistula exudate after cleaning, or a biopsy), because a surface swab often misses the right bacterium.
Here, the cost of culture is offset by that of ineffective empirical treatment, because deep pyoderma takes a long time to treat. According to Dr Loeffler, while awaiting culture results, early cytology-guided treatment is justified if the dog is at risk of septicaemia: cefalexin when cocci are seen, a fluoroquinolone when rods are seen. But there is often time to wait a few days. This interval is used to put good pain relief in place. As soon as the dog is no longer in pain, adjunctive topical therapy is recommended in every case.
Reassessment takes place after three weeks. If the infection lesions (crusts, pustules, pus, fistulae) have resolved and cytology is clean, treatment is stopped, even if alopecia persists. If there is no improvement at all, cytology is repeated and a sterile process is considered. If the lesions regress and then plateau, treatment is adjusted according to a new susceptibility test. It is very rare to need more than six weeks of an appropriate antimicrobial.
7 Duration of antibiotic therapy: where the new recommendations come from
7.1 What human medicine contributes
Brad Spellberg’s group in California has published many opinion articles arguing that, with antibiotics, shorter is better. Dozens of randomised trials have compared short and long courses. Dr Loeffler cites two. In the first, 121 patients with cellulitis all received five days of levofloxacin. Some then continued for five more days, the others received a placebo. The outcome was the same with five days of treatment as with ten. In the second, 200 patients hospitalised with a soft tissue infection had more treatment failures on the long course, with possible selection bias. Human medicine also knows the opposite, courses of more than a year against persistent bacteria in chronically ill patients, but there human lives are at stake, not an allergic dog. Published in 2014 to update those of 2005, the human guidelines on skin infections set five to seven days for impetigo, erysipelas and cellulitis, far from the three weeks long taught for dogs.
7.2 Veterinary recommendations without evidence
An opinion article entitled Hostage to history asked whether the durations taught were merely a legacy. There is no evidence on the duration of treatment for superficial pyoderma, nor on the possibility of stopping at clinical cure; but there is none for continuing beyond it either.
Dr Loeffler traces several editions of guidelines. In 2014, a consensus recommended three to four weeks for superficial pyoderma, continuing treatment for seven days after clinical cure. For deep pyoderma, it recommended four to six weeks or more, continuing for fourteen days after clinical cure. The World Association for Veterinary Dermatology guidelines on resistant staphylococci, published in 2017, were based on a true systematic review: of 220 articles, it retained 48 randomised trials or prospective studies. None studied duration itself, because all compared one drug with another. In 2021, according to our colleague, an update looked for evidence for that extra week and found none.
7.3 Stopping at clinical cure, with a recheck
In the absence of evidence for treatment “beyond cure”, the authors aligned themselves with human medicine: duration depends on clinical response, and treatment stops when the signs have resolved, in superficial and deep pyoderma alike. This is expert opinion, driven by antimicrobial stewardship.
Two safety nets accompany these durations. The first is a recheck by a veterinarian, at two weeks for superficial pyoderma and at three weeks for deep pyoderma. The second is the search for the primary cause from the first episode, not after two years of recurrences. Dr Loeffler admits that these durations may feel uncomfortable, but she says she is satisfied with them. She acknowledges, however, that she sometimes departs from them for the difficult cases at her referral centre.
Conclusion
Cytology comes before any antimicrobial, because only cytology confirms a bacterial origin. The primary cause is investigated from the first episode, because pyoderma is always secondary. Surface pyoderma is treated with a topical antimicrobial and sometimes an anti-inflammatory, superficial pyoderma with topical treatment alone, and deep pyoderma with a systemic antimicrobial chosen on the basis of culture. Empirical choice is reserved for dogs at low risk of resistance and for first-tier drugs. Duration is no longer set beyond clinical cure: two weeks and then a recheck for superficial pyoderma, three weeks for deep pyoderma.
These recommendations rest largely on consensus, for lack of trials, and our colleague does not hide it. She proposes better characterising deep pyodermas, some of which heal without antimicrobials; defining the boundary between dysbiosis and infection; finding an objective criterion for cure; finally comparing different treatment durations; and measuring the effect of antimicrobials on the canine microbiome and that of anti-inflammatories in prevention.
References
Loeffler A. New ISCAID canine pyoderma guidelines. In: 35th European Veterinary Dermatology Congress (ESVD-ECVD-ISVD), Bilbao, 11-13 September 2025.
Loeffler A. Real need and duration of antibiotic therapy. In: 35th European Veterinary Dermatology Congress (ESVD-ECVD-ISVD), Bilbao, 11-13 September 2025.
Loeffler A, Cain CL, Ferrer L, Nishifuji K, Varjonen K, Papich MG, et al. Antimicrobial use guidelines for canine pyoderma by the International Society for Companion Animal Infectious Diseases (ISCAID). Vet Dermatol. 2025;36(3):234-82.
