THE MERCK VETERINARY MANUAL
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Bacterial Cystitis in Small Animals

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Bacterial cystitis is infection and inflammation of the urinary bladder. Clinical signs are pollakiuria, hematuria, dysuria, and urinating in inappropriate places. Hematuria may be more noticeable at the end of the urine stream. An animal may exhibit pain on palpation of the caudal abdomen, and the bladder may feel thickened or irregular. Bacterial cystitis is occasionally diagnosed in an asymptomatic animal when a routine urinalysis is performed. Chronic glucocorticoid administration, hyperadrenocorticism, and diabetes mellitus are frequently associated with asymptomatic urinary tract infections.

Urinalysis often shows increased protein and hemoglobin on the dipstick. The WBC part of the dipstick (ie, nitrate) is inaccurate in dogs and cats and should not be used. The urine pH may be alkaline (7.5–9.0) if the bacteria are urease positive (eg, Staphylococcus or Proteus). An alkaline urine pH by itself is not abnormal, however, as diet and other factors can affect urine pH. Urine sediment should be examined microscopically. Increased numbers of WBC, RBC, and/or bacteria are consistent with cystitis. Bacteria can be confused with stain precipitate; filtering the stain or evaluating the sediment without staining is advised. Lack of visible bacteria in the sediment does not rule out urinary tract infection.

If clinical signs and/or urinalysis are suggestive of infection, a urine culture and antimicrobial susceptibility should be performed. Cystocentesis is the preferred method for sample collection, followed by sterile urethral catheterization or a midstream free catch into a sterile collection cup. A quantitative culture is necessary to interpret the result, especially with samples not collected by cystocentesis. Ideally, the culture should be set up within 2 hr of collection. If the laboratory is off-site, the sample should be refrigerated and processed by the laboratory within 24 hr. If the specimen cannot be refrigerated, commercial collection kits that contain preservatives can be used to maintain a stable bacterial population at room temperature for 24 hr. Laboratories that can provide both quantitative culturing and a minimum inhibitory concentration-based method for antimicrobial susceptibility testing are preferred.

Simple bacterial cystitis is treated for 2 wk with a broad-spectrum antibiotic that achieves a high concentration in the urine. Appropriate initial choices include amoxicillin (10–20 mg/kg, PO, bid-tid), cefadroxil (22–30 mg/kg, PO, bid), cefpodoxime (5–10 mg/kg, sid, FDA-approved for dogs only), or ormetoprim-sulfadimethoxine (27 mg/kg, PO, day one, then 13.5 mg/kg, PO, sid). A repeat urine culture 3–7 days following therapy is recommended. If positive, another antibiotic based on the new susceptibility results is given for a longer treatment period (eg, 3–4 wk). Very resistant or recurrent infections should be treated for 4–6 wk. Every course of treatment should be followed by a urine culture, even if the signs have resolved. In animals that have a history of chronic or recurrent infections, a urine culture should be done every month for 3 mo following successful therapy. If all of these cultures are negative, then a urine culture every 2–4 mo for the next year is advisable. Because resistance to antibiotics can develop during therapy, antimicrobial susceptibility testing should be performed on every positive urine culture.

Animals with resistant or recurrent bacterial cystitis should be evaluated for an underlying cause. Survey abdominal radiographs are frequently diagnostic for cystic calculi. Negative survey films should be followed by double contrast cystourethrography, ultrasonography, and/or cystoscopy to rule out radiolucent urocystoliths, anatomic defects, and neoplasia. The history may reveal chronic glucocorticoid use. A serum biochemical profile and CBC are important to rule out predisposing systemic diseases. Other diagnostic considerations include feline immunodeficiency virus, feline leukemia virus, and hyperthyroidism in cats; and hyperadrenocorticism in dogs.

In cases that respond to therapy but continue to have frequent bouts of cystitis without an identifiable cause, low-dose prophylactic antibiotics can be used to prevent ascending bacteria from establishing an infection according to the following protocol: 1) a therapeutic course of an antibiotic for the current infection is completed, 2) no antibiotics are given for 3 days, to allow collection of urine for a post-treatment culture, and 3) the prophylactic protocol is immediately started. Prophylaxis consists of using a broad-spectrum antibiotic (eg, amoxicillin, cefadroxil) at one-third of the total daily dose, given at bedtime, indefinitely. Every 6–8 wk, the antibiotic should be stopped for 3–7 days to obtain a sample for repeat urinalysis and culture. Every new infection should be treated with a therapeutic course of an antibiotic based on culture and susceptibility results. The treatment antibiotic will likely be different than the prophylactic antibiotic. The most valuable therapeutic antibiotics (eg, fluoroquinolones, second- or third-generation cephalosporins) should be reserved for resistant infections. If the recurrent infection is resistant to the prophylactic antibiotic, this antibiotic can still be used for future prophylaxis after the infection is eradicated. Encouraging frequent voiding during the daytime is helpful in preventing recurrent infections.

Last full review/revision July 2011 by Melissa S. Wallace, DVM, DACVIM

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