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Therapeutic caveats: Difficult urinary tract infections


The volume of urine produced by the patient should be considered when selecting dosage for antimicrobial drugs. Higher dosages are needed to maintain effective urine concentrations of drugs in polyuric patients as compared to those who are producing concentrated urine. Although signs of UTI may subside following administration of suboptimum doses of an antimicrobial agent to polyuric patients, bacteriuria may persist.

To ensure adequate concentrations of the drug in the urinary tract during treatment intervals, it is recommended that daily doses be administered shortly following micturition, and especially just prior to a period of confinement during which voiding is not permitted (such as overnight).

Caveat: Ultimately, it is the responsibility of the clinician caring for the patient to balance issues of drug safety and efficacy in order to modify drug dosages and maintenance intervals according to individual needs.

Duration of treatment How long should bacterial UTIs be treated?

Antimicrobic therapy should be continued for a sufficient period to: 1) eliminate bacteria from tissue in addition to urine, and 2) allow the urinary tract and its defense mechanisms time to recover sufficient function to prevent recurrence of UTI. Therefore, it is not possible to establish rigid timelines about the duration of antimicrobic therapy. Rather, the duration of therapy is dependent on each patient's response to therapy, and must be individualized on the basis of serial clinical and laboratory findings. Remission of clinical signs is not itself a reliable index of successful eradication of infection, nor is reduction in WBC, RBC and protein detected by urinalysis. Duration of therapy should be based on the persistent elimination of bacteria as defined by urine cultures in addition to amelioration of pyuria and clinical signs.

Table 4
For the purpose of initial therapeutic plans, we recommend that the first episode of urinary tract infection in females and neutered males be treated for approximately 10 days to two weeks provided bacteria are not isolated from urine during therapy (Table 4). For intact male dogs at risk for bacterial prostatitis, three to four weeks of treatment is recommended. In general, continue therapy for one week after resolution of pyuria, hematuria and proteinuria as documented by urinalysis. If, after a suitable period of treatment with an antimicrobial agent, urine cultures are negative but urinalyses remain abnormal, an underlying abnormality is likely.

For infrequently recurrent UTIs due to reinfections, treatment should be continued for two to three weeks. The goal is to prevent bacteria from colonizing and reproducing while the damaged site is healing and host defenses regain adequate function to prevent recurrence of infection. For chronic UTIs or recurrent UTIs due to relapses, treatment should be continued for at least three to six weeks. Deep-seated and severe infections, and infections of the kidney or prostate gland, may require more prolonged therapy (Table 4).

Caveat: When treating patients with antimicrobics for long periods, appropriate consideration should be given to adverse side effects. For example, sulfadiazine-trimethoprim combinations have been associated with anorexia, lethargy, keratoconjuctivitis sicca, anorexia, anemia and immune-complex reactions. We have identified sulfadiazine in uroliths. Practitioners should be familiar with common adverse events associated with antimicrobics to be able to place their significance in proper perspective.

Monitoring the outcome How should response to therapy be monitored?

Table 5
The following recommendations are guidelines only and should not be interpreted as rigid facts.
  • 1. With protocols designed to enhance client and patient compliance, select the least expensive, least toxic and most effective antimicrobial agent and begin therapy.
  • 2. Selection of the proper antimicrobial drug, dosage, and frequency of administration usually eliminates bacteria from the urine (but not necessarily the adjacent tissue) within two to five days. Therefore, three to five days following initiation of therapy, collect a urine sample by cystocentesis and culture it for bacteria (so-called therapeutic culture or test for efficacy). Evaluation of urine cultures at this time facilitates early recognition of ineffective therapy. Therapy is considered to be successful only if urine does not contain any viable bacteria. Even though there may be viable bacteria in surrounding tissues, the urine should be sterile. Treatment is ineffective and relapse will likely occur if the bacterial colony count has only been reduced (for example from 105 to 102). In this situation, re-evaluate the therapeutic protocol including selection of antimicrobic drugs and their routes and rates of administration.
  • 3. Consider evaluation of a urine culture and urinalysis three to five days (or sooner if necessary) prior to the scheduled discontinuation of therapy, especially if prophylactic antibiotics are to be subsequently used to prevent frequent re-infection. Therapy may be discontinued if the urine is sterile and the urine sediment is normal. If results indicate persistent infection, re-evaluation of therapy is essential. In this situation, initiation of prophylactic low-dose antimicrobial therapy is contraindicated.
  • 4. Potential causes of poor response are summarized in Table 5.


Source: DVM360 MAGAZINE,
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