The Congested Cat: Antibiotic Use in Feline Upper Respiratory Tract Disease

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Feline upper respiratory tract disease (URTD) is a common presentation in general practice and can be classified as acute (≤10 days duration) or chronic (>10 days duration).¹ The diagnostic and therapeutic approach to these cases can vary based on the duration, severity, and clinical signs at presentation.

MEET ANNIE

Annie, an 8-year-old female spayed domestic longhair cat, was presented to her veterinarian because she appeared to be struggling to breathe. Her owners reported several days of upper respiratory congestion, which seemed to worsen at night, and that her appetite had decreased. Although she had shown some interest in food, she would swallow, then gag when presented with food. Annie lived with 1 other cat that was clinically normal; both were indoor-only but did have access to a screened-in patio.

On physical examination, Annie appeared to be over-conditioned at 12.6 lb (5.7 kg), with a BCS of 7/9. Temperature, pulse, and respiratory rate were within normal limits. Serous ocular discharge and evidence of mucopurulent discharge around the nares were observed. Upper respiratory congestion was audible, with decreased airflow bilaterally based on a glass slide fog test. On auscultation, referred upper respiratory sounds were present, and a wheeze was occasionally heard at peak inspiration. When the laryngeal area was auscultated, rattling was heard, suggesting turbulent airflow. The remainder of the physical examination was unremarkable.

Although viral rhinitis caused by infection with feline herpesvirus-1 (FHV-1) or feline calicivirus (FCV) is the most common cause of infectious URTD empiric antibiotic therapy is recommended if a cat shows signs of fever, lethargy, and/or anorexia, along with mucopurulent nasal discharge.¹ Some bacteria, including Mycoplasma spp, Chlamydia felis, Bordetella bronchiseptica, and some Streptococcus spp, are the primary pathogens involved in cases of bacterial URTD.¹ In cases in which a cat is presented with mucopurulent nasal discharge but maintains normal appetite and attitude, a 10-day observation period is recommended before considering antibiotic therapy.^1,2 Symptomatic treatment targeted at managing inflammation and maintaining appetite should be the primary treatment for cases of acute URTD. If fever, lethargy, and/or anorexia begin during the observation period, empiric antibiotic therapy should then be considered.¹

Diagnostics in a patient with signs of URTD are focused on determining if there is an underlying disease process other than viral rhinitis (eg, pneumonia, other systemic diseases). Nasal cytology and culture are not recommended in the acute phase of the disease due to the high chances of growth of a nonpathogenic commensal organism.¹ PCR testing for common primary pathogens can also be difficult to interpret, as most of these organisms can be isolated from both healthy and sick cats.¹

Baseline Diagnostic Investigation

Annie’s owners elected to perform the recommended baseline diagnostics. Serum chemistry profile showed mild azotemia (creatinine, 2.2 mg/dL; reference range, 0.3-2.1 mg/dL), with a urine specific gravity of 1.040, suggesting prerenal azotemia, although laboratory work should be repeated once Annie is clinically normal to ensure that creatinine returned to normal as well. Radiography showed a mild diffuse bronchointerstitial pattern and an alveolar pattern with air bronchograms in the right middle lung lobe. In the upper airway, there was increased radiodensity that was determined to be a result of the head being positioned in ventroflexion. Testing for feline leukemia (FeLV) and feline immunodeficiency virus (FIV) was recommended but declined, as Annie had a negative test prior to adoption 1 year ago.

Because of the severity of Annie’s clinical signs and presence of radiographic changes, Annie was prescribed antibiotic therapy along with symptomatic management.

Doxycycline is the recommended first-line antimicrobial for feline URTD by the Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Disease (ISCAID).¹ There is predictable susceptibility of B brochiseptica, C felis, Mycoplasma spp, and several commensal respiratory tract bacteria to doxycycline.¹ Tablets and capsules should be administered in a lubricated substance, followed by water or a small meal to avoid inducing esophagitis. Amoxicillin can also be considered a first-line antimicrobial for the treatment of acute bacterial URI when C felis and Mycoplasma are not highly suspected.¹

Pradofloxacin and marbofloxacin are FDA-approved fluoroquinolones for use in cats. Although fluoroquinolones can be effective against several respiratory pathogens in cats, this class of drugs has potential to induce antibiotic resistance.¹ Reserving fluoroquinolones for use in cases based on culture and susceptibility data is preferred.

Convenia® (cefovecin sodium), a third-generation cephalosporin, is commercially available and labeled for the treatment of skin infections caused by susceptible strains of Pasteurella multocida and is administered as a single subcutaneous injection.³ For susceptible skin infections in both dogs and cats, Convenia can offer benefits to both veterinarians and pet owners, as its extended-release formulation (up to 14 days) can help improve owner compliance with administration and reduce the stress of medicating a pet at home. Cefovecin is not labeled for treatment of respiratory infections, and it is not an appropriate treatment of URTD in cats. Convenia, however, does remain an excellent antimicrobial choice for treating both abscesses and wounds in cats and dogs, as well as superficial pyoderma in dogs.³

Treatment Plan

Annie was started on doxycycline. Additional symptomatic treatment for Annie included injections of Cerenia® (maropitant citrate) once daily for treatment of vomiting and diphenhydramine twice daily for nasal congestion. The owners were instructed to offer foods in a variety of textures to try to entice Annie to eat, as well as to heat up the food to create a stronger odor since Annie likely had a decreased ability to smell.

Patients with URTD will ingest some of the mucopurulent discharge from the nasal passages and sinuses that drain into the throat. The ingestion of this discharge likely contributes to the nausea and vomiting experienced by some of these patients. Hyporexia and anorexia likely occur secondary to nausea and nasal congestion, which impedes the ability of a cat to smell its food. Cerenia injectable is labeled for the treatment of acute vomiting in cats older than 4 months of age.⁴

Case Progression

Annie was presented the next day for a recheck examination due to worsening clinical signs, including worsening anorexia. Mucopurulent discharge was present bilaterally from the nares, but she remained afebrile. Open-mouth breathing was observed, and thoracic auscultation was unchanged. Hospitalization for more intensive supportive care, including intravenous fluids, was discussed. Diphenhydramine was discontinued, and subcutaneous dexamethasone with vitamin B12 was added to Annie’s care plan. The Cerenia injection was repeated, and doxycycline was continued.

The following day, Annie showed mild interest in food but vomited after eating. Nasal congestion had increased, and although airflow was detected through the right nostril, the left nostril was producing blood-tinged mucopurulent discharge. Due to the continued progression of clinical signs, the veterinarian and owners elected to anesthetize Annie for a nasal flush, collection of samples for culture and susceptibility testing, and sedated oral and pharyngeal examination.

Because aerobic cultures lack susceptibility in detecting Mycoplasma spp, B bronchiseptica, and C felis, common pathogens in feline URTD, a negative aerobic culture does not eliminate the possibility of a bacterial component. In cases of chronic URTD, advanced diagnostics are recommended, including nasal biopsy for histopathology, advanced imaging, rhinoscopy, and nasal lavage for the collection of cytology, aerobic culture, Mycoplasma spp culture or PCR, and fungal culture.¹ Culture and susceptibility results should be interpreted with caution, as positive cultures can be obtained from the nasal passages of healthy cats.¹

Case Outcome

Annie recovered uneventfully from anesthesia and was boarded at the clinic during the day for continued care. She was started on doxycycline, once-daily Cerenia injections, and saline nasal drops. Annie recovered fully within 10 days of initial presentation. Ultimately, aerobic culture was negative for bacterial growth.

Conclusion

Upper respiratory infections are a common ailment among cats, particularly in shelter populations. Although most of these infections are viral in origin, monitoring for signs of secondary bacterial infection is important. Judicious use of antibiotics continues to be a critical focus for both human and veterinary medicine. Therefore, understanding the signs of bacterial involvement in URTD and the most commonly implicated bacteria is important when choosing antimicrobial therapy. Along with monitoring for secondary bacterial infections, diagnostics, supportive care, and managing nausea, vomiting, and anorexia can play a critical role in patient recovery.

CONVENIA IMPORTANT SAFETY INFORMATION

People with known hypersensitivity to penicillin or cephalosporins should avoid exposure to CONVENIA. Do not use in animals with a history of allergic reactions to penicillins or cephalosporins. Side effects for both dogs and cats include vomiting, diarrhea, decreased appetite/anorexia and lethargy. See full Prescribing Information, ConveniaPI.com

CERENIA IMPORTANT SAFETY INFORMATION

Use CERENIA Injectable for vomiting in cats 4 months and older. Safe use has not been evaluated in cats with gastrointestinal obstruction, or those that have ingested toxins. Use with caution in cats with hepatic dysfunction. Pain and vocalization upon injection is a common side effect. In people, topical exposure may elicit localized allergic skin reactions, and repeated or prolonged exposure may lead to skin sensitization. See full Prescribing Information, CereniaPI.com