From Dog
Radiographs of a dog with severe pyothorax. Note the blurring of the cardiac silhouette, scalloping of the lung margins, interlobar fissure lines, rounding of the lung margins at the costophrenic angles, and dorsal elevation of the trachea.[1]

Pyothorax is an umbrella term for any disease which presents with free-forming pus or multiple abscesses in the thoracic cavity.

This is a relatively infrequent presentation in dogs and commonly associated with a secondary bacterial infection.

Causes include:

  • Penetrating chest trauma or bite wounds[2]
  • Inhaled small plant parts[3] or migrating foreign body such as grass awn[4]
  • Necrotic pulmonary mass due to neoplasia - e.g. lymphoma
  • Parasites
- Spirocerca lupi[5]

Regardless of cause, secondary infections invariably ensue and in dogs, purulent pleural effusion is usually composed of a mixture of obligate anaerobic and facultative bacteria[6], including:

- Escherichia coli
- Nocardia spp
- Fusobacterium spp
- Bacteroides spp
- Actinomyces viscosus
- Streptococcus spp
- Staphylococcus spp
- Clostridium spp
- Rhodococcus equi
- Klebsiella spp
- Peptostreptococcus spp
- Mycoplasma spp
- Porphyromonas spp
- Prevotella spp
- Pasteurella spp
- Propionibacterium spp
- Pseudomonas spp

Affected dogs are usually febrile, dyspneic and lethargic. Auscultation usually reveals muffled heart sounds and moist rales over dorsal lung fields.

Diagnosis is usually determined by thoracocentesis, but radiographic findings are usually confirmatory of a suspicion, based on presenting clinical signs. Immediate bacterial/fungal cultures are required, but treatment should be commenced immediately due to the often prolonged time for culture or PCR assay determination. Thoracoscopy may assist both diagnosis and treatment[7].

A differential diagnosis would include hemothorax, chylothorax and other causes of dyspnea such as heartworm disease.

Treatment usually requires pleural lavage via thoracostomy-tube drainage and heparin treatment or thoracostomy followed by aggressive antimicrobial agents.

Invasive (surgical) versus noninvasive treatment of pyothorax in dogs leads to a better long-term outcome in most canine patients[8], underlying the importance of pleural lavage as a critical part of eliminating bacteria within the pleural space[9]. Recurrent pyothorax often leads to a poorer prognosis.

Aggressive antimicrobial therapy is indicated in most cases[10].

Drug Dosage in dogs
Amikacin 5–10 mg/kg IV, IM, or SC q8–12h
Amoxycillin/clavulanate 22 mg/kg PO q8–12h
Ampicillin 20–40 mg/kg IV, IM, SC, or PO q6–8h
Cefazolin 15–25 mg/kg IV, IM, or SC q4–8h
Cephalexin 25–60 mg/kg PO q8h
Chloramphenicol 50 mg/kg IV, IM, SC, or PO q6–8h
Clindamycin 5–11 mg/kg IV, IM, SC, or PO q8h
Enrofloxacin 5–20 mg/kg IV, IM, SC, or PO q24h
Erythromycin 10–20 mg/kg PO q8h
Gentamicin 6 mg/kg IV, IM, or SC q24h
Metronidazole 10–15 mg/kg IV or PO q12h
Penicillin G 20,000–100,000 U/kg IV, IM, SC, or PO q4–8h
Rifampin 10–20 mg/kg IV, IM, or PO q12–24h
Tetracycline 20–50 mg/kg PO q8–12h
Trimethoprim–sulfamethoxazole 30–60 mg/kg IV or PO q12h


  1. Scott, JA & Macintire, DK (2003) Canine Pyothorax: Clinical Presentation, Diagnosis, and Treatment. Vetlearn 25(3):180
  2. Shahar R et al (1997) A technique for management of bite wounds of the thoracic wall in small dogs. Vet Surg 26(1):45-50
  3. Frendin J (1997) Pyogranulomatous pleuritis with empyema in hunting dogs. Zentralbl Veterinarmed A 44(3):167-178
  4. Peláez MJ & Jolliffe C (2012) Thoracoscopic foreign body removal and right middle lung lobectomy to treat pyothorax in a dog. J Small Anim Pract 53(4):240-244
  5. Mylonakis ME et al (2008) Canine spirocercosis. Compend Contin Educ Vet 30(2):111-116
  6. Walker AL et al (2000) Bacteria associated with pyothorax of dogs and cats: 98 cases (1989-1998). J Am Vet Med Assoc 216(3):359-363
  7. Monnet E (2009) Interventional thoracoscopy in small animals. Vet Clin North Am Small Anim Pract 39(5):965-975
  8. Boothe HW et al (2010) Evaluation of outcomes in dogs treated for pyothorax: 46 cases (1983-2001). J Am Vet Med Assoc 236(6):657-663
  9. Piek CJ & Robben JH (1999) Pyothorax in nine dogs. Tijdschr Diergeneeskd 124(9):276-280
  10. Johnson MS & Martin MW (2007) Successful medical treatment of 15 dogs with pyothorax. J Small Anim Pract 48(1):12-16