Deep pyoderma with rods on cytology: how to treat it
6-year-old Labrador Retriever with painful nodules, draining tracts with haemorrhagic exudate and crusts on the lateral thighs. Cytology of the exudate shows degenerate neutrophils, macrophages and intracellular rods. Deep skin scrapings are negative.
What is the most appropriate therapeutic approach?
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A. Empirical cefalexin for 3 weeks and reassess
Cefalexin covers staphylococci well, but rods suggest Gram-negative bacteria (Pseudomonas, E. coli, Proteus) with unpredictable susceptibility. Moreover, 3 weeks is usually too short for deep pyoderma.
B. Topical chlorhexidine alone, without systemic antibiotics
Topical therapy is a very useful adjunct, but it does not reach the dermis or subcutis: deep pyoderma with furunculosis needs systemic treatment.
C. Prednisolone to reduce inflammation and pain
Corticosteroids are contraindicated in active deep infection: they promote its spread. Inflammation in furunculosis is partly due to free keratin and hair in the dermis and subsides as the infection is controlled.
D. Culture and susceptibility testing of a deep sample, systemic antibiotic based on the result maintained until clinical and cytological resolution, plus antiseptic baths
Correct. In deep pyoderma, culture (from a biopsy or a closed lesion, not the surface) is always indicated, especially when rods are seen. Treatment usually lasts weeks (often 4–6 or more) and is stopped after confirming cure at a recheck, not by the calendar.
lightbulb Key takeaway
Deep pyoderma = always culture, long treatment and reassessment before stopping. Look for underlying causes such as demodicosis, endocrinopathies or allergies, and remember that rods on cytology change the empirical choice.
References: ISCAID: Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis (Hillier et al., 2014)
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.