Lower urinary tract infections: From diagnosis to treatment
Translated from Patricia Dowling, DVM, MSc, DACVIM (Large Animal), DACVCP, Western College of Veterinary Medicine, Saskatoon, Saskatchewan, Canada
Bacterial urinary tract infections
Bacterial urinary tract infections are frequently diagnosed in dogs and cats. Although bacterial cystitis can occur in dogs of both sexes and all ages, in cats it is observed primarily in spayed females and animals older than 10 years. The antimicrobial agents used for treatment have not changed significantly, but there is growing concern about increasing antibiotic resistance. Therefore, careful and responsible use of antimicrobial medications is essential. There are new recommendations regarding which types of bacteriuria should be treated, which antibiotics should be considered as first-line therapy, and how long treatment should last.1
Diagnosis
The correct diagnosis of an infection requiring treatment is paramount. A complete urinalysis is indicated in dogs and cats with clinical signs of a urinary tract infection.
Indications for urine culture and resistance testing include:
- The medical history (e.g., sporadic or recurrent infections)
- Clinical symptoms (e.g., painful urination, blood in urine, frequent urination, abnormal urinary flow patterns)
- Visible evidence of bacteria in urine sediment
- Signs of pyuria (pus in urine)
Since urinary tract infections (UTIs) occur predominantly in older cats—typically those with underlying health conditions—urine culture and antibiotic susceptibility testing are recommended at the time of initial diagnosis. However, reports from several veterinary clinics indicate that the correct diagnosis and appropriate use of antibiotics often do not align between dogs and cats. In a recent, unpublished study by the author, it was found that approximately 40% of the diagnoses of bacterial UTIs in dogs made in practice were not confirmed by urinalysis, and that urine cultures and antibiotic susceptibility testing were not performed in an accredited diagnostic veterinary laboratory.
Although the insufficient use of diagnostic laboratory services may be due to factors such as cost and delays between sampling and results, administering antibiotics to patients without an infection requiring treatment is a serious misuse of these drugs.
Types of urinary tract infections
Once a urinary tract infection has been diagnosed, the exact type of infection should be determined before selecting an antimicrobial treatment plan.
Sporadic bacterial cystitis
Sporadic bacterial cystitis (SBC, also known as simple urinary tract infection) arises from a temporary breach of the body's defense mechanisms. Affected animals typically exhibit symptoms of a lower urinary tract infection and respond quickly to appropriate treatment. Clinical symptoms rarely or never recur thereafter. Because most antibiotics reach high concentrations in urine, SBCs are usually isolated infections that respond well to appropriate first-line therapy (see table).
If the diagnosis of infection is correct, treatment in dogs can be empirical – based on knowledge of the commonly isolated pathogens and their typical susceptibility to the antibiotics used.1 However, this does not apply to young to middle-aged cats, in which clinical signs of lower urinary tract disease are more likely to indicate feline urological syndrome (formerly known as feline idiopathic cystitis).
When selecting an antibiotic, the pharmacokinetics and pharmacodynamics of the active ingredient, possible side effects (for both the animal and the owner), ease of administration, and cost should be taken into account.
Antibiotic concentrations achieved in urine are more important than serum concentrations in the treatment of sporadic urinary tract infections. Urine concentrations typically exceed serum levels because most antibiotics are excreted in their active form in the urine. If a concentration at least four times the minimum inhibitory concentration (MIC) is achieved throughout the entire dosing interval, efficacy against the pathogen is ensured at approximately 90 mg/dL.⁴
Therefore, despite a resistance finding in the susceptibility test, amoxicillin can be used in a primary SBC infection by Escherichia coli or Staphylococcus pseudintermedius Amoxicillin/clavulanic acid is considered the first-line treatment due to the extremely high urinary concentrations. Initial or empirical treatment with amoxicillin/clavulanic acid is not recommended.¹–³
Since the symptoms of SBC are usually caused by inflammation, the use of NSAIDs (non-steroidal anti-inflammatory drugs) can also be considered – however, with caution in cats. Antibiotic treatment should only be started if the clinical symptoms persist or worsen. New recommendations suggest administering antimicrobial therapy for only 3 to 5 days, even though the package insert often indicates longer treatment durations. If the symptoms resolve after the short course of treatment, further urine tests or cultures are not necessary.
Antimicrobial treatment options for urinary tract infections
The following options are listed in order of preference according to the principles of responsible antibiotic use.
First choice
- Amoxicillin
Dosage: 11–15 mg/kg, orally, every 8–12 hours
Recommended first-line therapy for SBCs. Dosing every 8 hours may improve efficacy. Ampicillin should be avoided due to its low bioavailability. Not suitable for prostatitis or pyelonephritis due to impaired tissue perfusion. - Sulfadiazine/Trimethoprim
Dosage: 15–30 mg/kg, orally, every 12 hours
Suitable as a first-line therapy for SBC, but less frequently used clinically due to potential side effects in dogs and its unpleasant taste in cats. It can be considered for prostate infections. However, enterococci are naturally resistant. - Cephalexin and Cefadroxil
Dosage: 12–25 mg/kg, orally, every 12 hours
First-generation cephalosporins; a potential first-line option for SBCs if amoxicillin is unsuitable. Enterococci are naturally resistant. Due to poor tissue penetration, not recommended for prostatitis or pyelonephritis. - Nitrofurantoin
Dosage: 5 mg/kg, orally, every 6–8 hours
Can be considered as a first-line option for SBC when amoxicillin is unsuitable and multidrug-resistant pathogens are present. Not suitable for use in prostatitis or pyelonephritis, as therapeutic concentrations cannot be achieved in these tissues.
Second choice
- Amoxicillin/Clavulanic acid
Dosage: 12.5–25 mg/kg, orally, every 12 hours
No proven advantage over amoxicillin in SBC, unless susceptibility data demonstrate high resistance to amoxicillin but sensitivity to the combination. Tissue penetration is also insufficient in cases of prostatitis or pyelonephritis. - Cefpodoxime
Dosage: 5–10 mg/kg, orally, every 24 hours (in dogs)
A third-generation cephalosporin, reserved for cases with documented resistance to first-generation cephalosporins. Enterococci are inherently resistant. - Cefovecin
Dosage: 8 mg/kg, subcutaneously, once; repeat dose possible after 7–14 days
Also a third-generation cephalosporin, intended for documented cases of resistance to first-line drugs. Enterococci exhibit natural resistance.
Third choice
- Enrofloxacin
Dosage:- Dogs: 5–20 mg/kg, orally, every 24 hours
- Cats: 5 mg/kg, orally, every 24 hours
Reserved for multidrug-resistant pathogens, but can be used as a first-line treatment for prostatitis and pyelonephritis. Its use in cats is limited due to the risk of retinopathy.
- Marbofloxacin
Dosage: 2.75–5.5 mg/kg, orally, every 24 hours
Reserved for multidrug-resistant pathogens and uropathogenic E. coli (UPEC), but can also be considered as a first-line treatment for prostatitis and pyelonephritis. - Orbifloxacin
Dosage: 2.5–7.5 mg/kg, orally, every 24 hours
Similar to marbofloxacin – reserved for multidrug-resistant pathogens and UPEC, but possible as a first-line treatment for prostatitis and pyelonephritis. - Pradofloxacin
Dosage:- Dogs: 3–5 mg/kg, orally, every 12 hours
- Cats: 3–7.5 mg/kg, orally, every 24 hours
Reserved for multidrug-resistant pathogens and UPEC, it can also be considered as a first-line treatment for prostatitis and pyelonephritis. Pradofloxacin shows higher activity against some bacteria than enrofloxacin, marbofloxacin, and orbifloxacin. It is not approved for use in dogs in the USA but is available in other countries. Furthermore, it does not cause retinopathy in cats.
- Chloramphenicol
Dosage:- Dogs: 40–50 mg/kg, orally, every 8 hours
- Cats: 50 mg per cat, orally, every 12 hours
Reserved for multidrug-resistant pathogens and UPEC. May be considered for pyelonephritis or prostatitis when fluoroquinolones are not an option. However, due to the risk of myelosuppression (particularly in cats) and a potential risk of idiosyncratic, dose-independent aplastic anemia in humans, chloramphenicol should be used with caution.
- Doxycycline
Dosage: 5 mg/kg, orally, every 12 hours
Reserved for methicillin-resistant Staphylococcus aureus and UPEC. May be considered as an alternative in pyelonephritis or prostatitis when fluoroquinolones are unsuitable. Special care should be taken in cats, as tablets or capsules may pose a risk of esophageal ulceration. It is recommended to administer each tablet or capsule with approximately 6 mL of water using a syringe. - Fosfomycin
Dosage: 40 mg/kg, orally, every 8–12 hours (in dogs)
Reserved for multidrug-resistant pathogens. Can be used every 8 hours in cases of pyelonephritis or prostatitis if fluoroquinolones are not an option.
Recurrent bacterial cystitis
Recurrent bacterial cystitis arises from a persistent underlying disorder of the urinary tract or immune system that leads to at least three episodes of urinary tract infections in the preceding 12 months or at least two episodes in the last 6 months.1 The underlying pathophysiology can vary and is not always effectively treatable, so long-term, repeated antibiotic therapy is usually of little success.
- Reinfection This occurs when, after successful treatment (documented by a negative urine culture), a new infection with a different bacterial species or strain develops. In such cases, further diagnostic measures should be considered to identify treatable predispositions. Treatment is then the same as for sporadic cystitis – long-term antibiotic therapy is not recommended.
- Relapse Relapse occurs when the original infection has not been completely eliminated despite treatment. Relapses can occur secondarily due to pathological conditions such as biofilm formation, urolithiasis, or pyelonephritis, which prevent a sufficient concentration of the antibiotic from being achieved at the site of infection. Escherichia coli is the most frequently isolated pathogen causing urinary tract infections in dogs and cats.⁵–⁸
Relapses in a E. coliInfections can occur due to unique virulence factors that allow the pathogen to penetrate the uroepithelium, multiply there, and evade high urinary concentrations of antibiotics.⁹,¹⁰ Therefore, if repeated detection of E. coli – especially if the resistance pattern remains constant – to a uropathogenic E. coli (UPEC) infection should be considered. In cases of recurrent urinary tract infections, it is important to ensure that adequate antibiotic concentrations are achieved in the urine and bladder to eliminate the infection. The choice of antibiotic, dosage regimen, resistance pattern, and owner compliance should be reviewed, as few drugs are effective in treating intracellular or biofilm infections.111 Furthermore, a high rate of antibiotic resistance has been documented in dogs with UPEC.10,121
graph
graph: Pathogenesis of UPEC infections:
The bladder uroepithelium is a pseudostratified transitional epithelium lined by large surface cells (facet cells) (A). UPECs reaching the bladder attach to the surface of the facet cells via pili (B). Following adhesion, UPECs penetrate the cytoplasm of the facet cells (C) and replicate (D).
They then form intracellular bacterial communities (E) that are protected from antibiotics because the antibiotics do not penetrate the cells in sufficient concentrations. The host's immune response recruits neutrophils, and infected cells can be shed and excreted in the urine, contaminating the environment and transmitting the infection to new hosts (F). Alternatively, bacteria from the intracellular community can develop a filamentous morphology and reattach to other facet cells in the bladder lumen (G), thus restarting the infection cycle.
Subclinical bacteriuria
Subclinical bacteriuria is not uncommon in otherwise healthy animals, in patients with comorbidities (e.g., diabetes mellitus, chronic kidney disease), or in those undergoing immunosuppressive therapy. Despite concerns that secondary complications such as sepsis or pyelonephritis might occur, there is little evidence that subclinical bacteriuria increases the risk of clinical urinary tract infections or other infectious complications in dogs or cats.13,14
In human medicine, subclinical bacteriuria is generally not treated, even in immunocompromised patients. While treatment may lead to the short-term elimination of bacteriuria, recolonization is common and associated with increasing antibiotic resistance. Therefore, it is now recommended that if bacteria are detected in the urine but there are no clinical signs of a urinary tract infection, urine culture or susceptibility testing should not be performed, and the animal should not be treated with antibiotics. Even the detection of a multidrug-resistant pathogen does not necessarily justify treatment.
The clinical decision as to whether a patient without symptoms (for example, due to a spinal cord injury or immunosuppressive treatment) should be treated must be made on an individual basis.
Treatment
First-line therapy for patients with sporadic bacterial cystitis is the administration of amoxicillin for 3 to 5 days.¹ If clinical symptoms resolve after this short course of therapy, no further diagnostic measures or treatments are necessary. Recurrent infections should be managed as for SBC, with particular attention paid to identifying underlying abnormalities. Relapses may occur due to complex pathologies, where UPEC and biofilms require special therapeutic considerations. Patients with subclinical bacteriuria should not be routinely treated with antimicrobials, even in the presence of comorbidities.
Frequently asked questions about lower urinary tract infection
What are urinary tract infections and what symptoms can occur in dogs and cats?
Urinary tract infections (UTIs) affect the lower urinary tract, primarily the bladder and urethra. In dogs and cats, they are usually bacterial infections caused by the entry of pathogens – often Escherichia coli or Staphylococcus spp. – originate in the urinary tract. Typical symptoms include:
Painful urination (dysuria): Affected animals often show signs of discomfort or pain when urinating.
Frequent urination (pollakiuria): Increased but frequent urination in small amounts may occur.
Blood in the urine (hematuria): Visible blood or a reddish tint in the urine is a common symptom.
Altered urinary flow pattern: Some animals exhibit a weak or interrupted urine stream, which may indicate altered anatomy or inflammation.
General malaise: Fever, reduced activity or loss of appetite can also be signs of infection, especially if the infection has spread to the kidneys (pyelonephritis).
UTIs are more common in older cats, especially spayed females. Early detection and treatment are important to avoid complications and maintain the animal's quality of life.
How is a urinary tract infection diagnosed?
The diagnosis of a urinary tract infection is made through a systematic and multi-stage approach that ensures the correct treatment is administered. Key diagnostic steps include:
Medical history and clinical examination: The Veterinarian First, a detailed medical history is taken and the animal's behavior is observed. Symptoms such as painful urination, frequent urination, or blood in the urine are noted.
Urinalysis: A complete urinalysis is essential. This involves examining parameters such as pH, specific gravity, the presence of white blood cells (pyuria), red blood cells, and bacteria. This examination provides initial indications of an infection.
Urine culture and antibiotic susceptibility test: A urine culture is performed, particularly in cases of recurrent infections or where there is a risk of antibiotic resistance. This involves isolating the bacteria and testing their sensitivity to various antibiotics. These tests help determine the best possible therapy and ensure the targeted use of medication.
Other imaging techniques: In some cases, especially when anatomical anomalies or structural changes are suspected, additional imaging techniques such as ultrasound or X-rays may be used.
These meticulous diagnostic steps ensure that not only is a urinary tract infection diagnosed, but also its precise type and possible causes are identified. This allows for targeted and effective treatment to be initiated.
What types of urinary tract infections are there and how do they differ?
Urinary tract infections can be divided into different categories, and this distinction is particularly helpful in choosing the right treatment. The most important types are:
Sporadic bacterial cystitis (SBC):
This is the most common form and results from a temporary breakdown of the body's defense mechanisms. Symptoms appear suddenly and usually subside after a short course of antibiotics, typically lasting 3 to 5 days. Re-infection is rare unless there are underlying causes.
Recurrent bacterial cystitis:
In this form, at least three infections occur within 12 months or two within 6 months. This is often due to a persistent urinary tract disorder or an insufficient immune response. The cause can be either new pathogens (reinfection) or the recurrence of the same pathogens (relapse).
Subclinical bacteriuria:
This refers to the detection of bacteria in the urine without the presence of clinical symptoms. This is not uncommon, especially in older animals or those with chronic conditions such as diabetes or kidney disease. This form is generally not treated, as it is not associated with an increased risk of serious complications, and treatment can often lead to recolonization with resistant bacteria.
Distinguishing between these forms is important because it directly influences treatment strategy and the use of antibiotics. While sporadic infections usually respond well to a short course of therapy, recurrent infections often require further diagnostic testing to identify precursor diseases.
What treatment options are available and how is the choice of antibiotic made?
The treatment of urinary tract infections depends primarily on the type and severity of the infection, as well as the results of antibiotic susceptibility tests. Here are some important points regarding treatment:
First-line therapy for sporadic cystitis:
For most uncomplicated cases, amoxicillin is recommended for a period of 3 to 5 days. This therapy is based on the fact that amoxicillin is excreted in high concentrations in the urine, which means that even if a resistance pattern is detected in laboratory testing, an effective response can still be achieved.
Selection of the antibiotic:
Besides pure efficacy, pharmacokinetics (how the drug is distributed and eliminated in the body) and pharmacodynamics (how the drug works) play an important role. Potential side effects, ease of administration, and cost are also taken into account. Thus, there are various options, from cephalosporins to fluoroquinolones, which are considered in complicated cases such as prostatitis or pyelonephritis.
Treatment of recurrent infections:
In cases of recurrent infections, it is important to identify and treat the underlying causes. Long-term, repeated use of antibiotics is generally not recommended, as it can lead to an increased risk of resistance.
Non-antibiotic approaches:
In cases of mild inflammation, non-steroidal anti-inflammatory drugs (NSAIDs) can also be used to reduce the inflammatory response. Supportive measures, such as increasing fluid intake, can also be helpful in flushing out the bacteria.
The combination of precise diagnostics and the selection of a suitable, often empirically used antibiotic ensures that the therapy is targeted and unnecessary drug use is avoided.
How can you prevent a recurrent urinary tract infection and what should be considered during long-term treatment?
The prevention of urinary tract infections and the management of recurrent cases are important aspects of veterinary care. Here are some approaches to prevention and long-term management:
Identification and treatment of underlying causes:
Anatomical or functional disorders of the urinary tract, such as kidney stones or structural abnormalities, are frequently present and predispose to recurrent infections. Comprehensive diagnostics, often supplemented by imaging procedures such as ultrasound, can help identify such causes and treat them effectively.
Optimization of hygiene measures:
Regular and thorough hygiene, especially for cats, can reduce the risk of reinfection. This includes cleaning the litter box and ensuring the animal has access to fresh water at all times.
Adapted diet and lifestyle:
A balanced diet that contributes to overall health and urinary tract function is important. In certain animal species or breeds, the supplementation of cranberry products or other natural preparations may be beneficial, although the scientific evidence for this varies.
Avoiding unnecessary antibiotic therapy:
Responsible antibiotic use (antibiotic stewardship) is crucial to prevent resistance. Treatment should be avoided, especially in cases of subclinical bacteriuria, as this often leads to recolonization and resistance.
Regular checks:
In animals that have repeatedly suffered from urinary tract infections, regular check-ups (urine analyses and cultures) are advisable in order to react to changes early and monitor the course of the infection.
A combination of preventive measures, targeted therapy and regular monitoring can significantly reduce the risk of recurrent urinary tract infections, thus sustainably improving the animal's quality of life.
Conclusion
Urinary tract problems are an important issue for many pet owners. Lower urinary tract infections This is a common problem. Many dogs and cats suffer from Lower urinary tract infections. Timely diagnosis of Lower urinary tract infections can significantly facilitate treatment. Even if Lower urinary tract infections Although the process is often uncomplicated, a thorough examination is necessary.
The causes of Lower urinary tract infections are diverse and range from bacterial pathogens to structural abnormalities. A common cause of Lower urinary tract infections is bacterial colonization by Escherichia coli. Furthermore, hormonal imbalances can also lead to... Lower urinary tract infections contribute. Veterinarians emphasize that Lower urinary tract infections often caused by inadequate hygiene or accompanying illnesses. Early detection of Lower urinary tract infections is essential to avoid complications.
The diagnosis of Lower urinary tract infections Diagnosis is made through a combination of clinical examination and laboratory analyses. A urinalysis provides clues about Lower urinary tract infections and supports the decision for further diagnostic testing. Culture tests confirm Lower urinary tract infections and help choose the appropriate antibiotic. Modern techniques make it possible to, Lower urinary tract infections to identify precisely. The knowledge about Lower urinary tract infections It significantly improves the success of the treatment. Long-term studies show that early intervention significantly improves the success of the treatment. Lower urinary tract infections They can be checked more quickly.
The treatment of Lower urinary tract infections It depends on the type and severity of the illness. In many cases, Lower urinary tract infections Treated with short-term antibiotic therapy. Recurrent Lower urinary tract infections They often require a detailed investigation of the underlying causes. Veterinarians recommend that, in the case of Lower urinary tract infections It is also important to take preventative measures. An adapted diet can help, Lower urinary tract infections to prevent this. Regular checkups minimize the risk of Lower urinary tract infections. With proper care, Lower urinary tract infections often successfully avoided.
In summary, it is important to, Lower urinary tract infections to recognize it as a serious health problem. Preventive measures can help. Lower urinary tract infections often avoided. Timely diagnosis ensures that Lower urinary tract infections They can be treated quickly. Advanced diagnostic methods make it possible to, Lower urinary tract infections to identify precisely.
Choosing the right antibiotic is crucial to Lower urinary tract infections to combat it effectively. Veterinarians should always ensure that Lower urinary tract infections regular checkups can prevent recurring problems. Lower urinary tract infections be detected early. Good communication between Veterinarian and the owner contributes to this, Lower urinary tract infections to manage optimally. The long-term goal is to, Lower urinary tract infections to avoid completely. With proper management, Lower urinary tract infections significantly improve the quality of life for the animals.
Note: This article was originally published in February 2022 under the title "Lower Urinary Tract Infections".
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