Inappropriate Diagnosis

• Although not very common, at times a dog is misdiagnosed. While generally an infection is the most likely cause for green discharge from the penis, there may be other underlying conditions at play. Medical conditions affecting dogs that may cause penile discharge and may not generally respond to antibiotic therapy are tumors, allergies, presence of calculi or bladder stones, foreign matter trapped under the sheath or fungal infections.
  
  

Inappropriate Antibiotic

• Laboratory tests may help identify the problem bacteria.NA/AbleStock.com/Getty Images
  
  At times dogs may be simply dealing with a bacterial infection that requires a longer course of antibiotics or that does not respond to a particular type of antibiotic. In this case the vet should take samples of the discharge for a cytology analysis and culture and sensitivity test, explains veterinarian Mary Zink, which helps determine exactly what type of bacteria the dog is dealing with so the most appropriate antibiotic can be chosen.
  
  

Inappropriate Administration

• Instances occur in which the dog may not respond to antibiotic treatment simply because the owner is not administering it correctly. The dog may appear to take the antibiotic only to spit it out later without the owner realizing this. The dog may not properly absorb the antibiotic due to vomiting or diarrhea. The owner may not have administered the drug as prescribed, skipping days or failing to administer the drug for the full course.
  
  

Inappropriate Use of Antibiotics

• The indiscriminate use of antibiotics is counter-productive since it makes their use much less effective when they are truly needed. This misuse may cause antibiotic resistance, which means an infection may be refractory to the antibiotic drug, requiring always stronger and stronger medications. Antibiotic resistance is also triggered by a dog's compromised immune system since antibiotics require a healthy immune system to be effective, according to Vet Info.