Tomcat Urethral Obstruction Treatment Overview

By Lisa Murphy DACVECC

Causes of a urethral obstruction (UO) are varied but include idiopathic obstruction (which in more recent studies was > 50% of cases evaluated) and less commonly, uroliths and urethral plugs. Much research has also been done into the treatment of urethral obstruction in cats secondary to Feline Lower Urinary Tract Disease (FLUTD)/Feline Idiopathic Cystitis. Aside from actually removing the obstruction in the short term, few treatments have been proven to significantly reduce recurrence with upwards of 20% of cats experiencing a recurrence within 6 months. 

Here I summarise some of the common treatments. As always, please feel free to comment or to email me with questions (

Intravascular volume resuscitation

Cats with urethral obstruction presenting in cardiovascular collapse require ‘shock doses’ of intravenous fluids (e.g. 10-20 ml/kg bolus followed by constant reassessment of the patient’s perfusion status repeating boluses as needed).

Studies looking at the use of different types of fluids, more specifically 0.9% sodium chloride (saline) vs. Normosol R (similar to buffered LRS or Hartmann’s solution), did not show any difference in outcome or clinically significant reduction in plasma potassium levels. Cats given NormR had a more rapid normalisation of their acid-base balance. For more on this topic see this podcast episode.


Hyperkalemia occurs commonly in cases with severe obstruction from urine retention. Reduced glomerular filtration rate with secondary acute kidney injury (AKI) from the initial UO may also promote hyperkalaemia. These patients can present in shock-like states from severe hyperkalemia.

Typically, this is recognised by inappropriately severe bradycardia and cardiac dysrhythmia. Common dysrhythmias include atrial standstill and ventricular premature complexes. There is no set blood potassium level at which dysrhythmias will occur – although they are more common at levels > 8.5 mmol/l. Treatment is usually recommended above this level although some cats will not show clinically significant signs of hyperkalaemia even at this level. It is important to treat each patient as an individual.

Treatment options include:

  • Intravenous fluid therapy: improves renal perfusion and renal excretion of potassium; dilutes potassium in the extracellular compartment.
  • Calcium gluconate (0.5-1 ml/kg IV over 15 mins): can temporarily (approximately 20 minutes) reduce the cardiotoxic effects of hyperkalemia. It does not reduce plasma potassium levels and needs to be followed up with definitive management.
    • [S Jasani: the risk-benefit profile for the use of calcium gluconate in cats with clinically significant hyperkalaemia is very favourable in my opinion. I encourage a liberal approach to administer this therapy, potentially more than once.]
  • Dextrose (glucose) (0.5-1 ml/kg IV) and insulin (0.5 u/kg regular (neutral, soluble) insulin) to drive potassium into the intracellular compartment. Although both substances have a fast onset of action, use of insulin requires close monitoring of blood glucose over subsequent hours.

Decompressive cystocentesis

There has been much controversy about the safety of this procedure in these patients and until recently I definitely was in the camp of never doing this. Nowadays I will discuss the potential risks of this procedure with owners where I consider the procedure necessary.

Advantages of this procedure include:

  • Buying time for the patient by helping correction of the electrolyte derangements at least temporarily until a more definitive treatment can be performed
  • Potentially may help with unblocking
  • Rapid relief of symptoms
  • Need for minimal to no sedation
  • Helping to restore glomerular filtration which helps reduce worsening kidney injury

Potential risks of this procedure include:

  • Bladder rupture. However, in a retrospective study of 47 cats who had this procedure performed, no cat developed a ruptured bladder. An indwelling catheter was placed following decompressive cystocentesis in these cats and they were managed as standard thereafter.
  • Uroabdomen. A published study evaluated the use of repeat decompressive cystocentesis in cases where owners did not have the finances to pursue indwelling urinary catheter placement. Of the 15 cats evaluated, 73% were discharged, some of which had more than ten cystocentesis procedures performed. Of the non-survivors, three did develop uroabdomen and one haemoabdomen. Non-survivors also tended to have higher creatinine and required more frequent cystocentesis so perhaps this procedure should be avoided in sicker cats.
    • [S Jasani: information from this study has been shared here as it relates to the topic under discussion. However, I personally have very serious welfare concerns about this study protocol and remain to be convinced that an alternative more patient-friendly yet affordable protocol could not have been implemented.]

[S Jasani: as with Lisa, I do not promote the use of decompressive cystocentesis as first-line treatment. If performed, please be sure to drain the bladder as fully as possible to achieve maximum benefit possible.]

Catheter types and size, does it matter?

Is there a perfect catheter? The short answer is we don’t know. Each type of catheter has their own advantages and disadvantages.

  • Polyprolylene (or ‘Tom cat’) catheters are one of the more rigid options. They can help relieve the obstruction but also have higher risks of urethral trauma. They are likely uncomfortable for the cats if they are left indwelling.
  • Polyvinvyl (red rubber) catheters are commonly placed after the obstruction is relieved. They are much less irritant and offer more comfort for the cat.
  • More recent is the ‘Slippery Sam’ or polytetrafluroethylene which is very useful for unblocking without causing too much irritation to the urethra. However, it only comes in one size (3.5fr) and one length. Furthermore, the connection apparatus for this can be difficult and come apart easily. Please note that while we know some people still do this, some years back the manufacturers changed their recommendation to say that these catheters should not be left indwelling.

As far as catheter size, the jury is also still out. The 5fr catheter has the potential benefits of less luminal obstruction from clots, less likelihood of the cat urinating around it, and easier flushing of saline. However, one study looking at the use of 3.5fr and 5fr urethral catheters showed higher reobstruction rates with 5fr catheters within 24 hours (19% with 5fr vs. 6.7% with 3.5fr). This study was retrospective so the effects of different aetiologies of UO and differences in disease severity are difficult to interpret.

Finally, there is the question of how long to leave an indwelling catheter in place. In general, I would recommend leaving it in place at least until the cat’s blood work abnormalities have resolved and the urine grossly looks clear. No benefit has been proven on whether to leave it in for 24 or 48 hours.


Depending on the study you read, bacteriuria has been shown in anywhere from < 2% up to 40% of cats with UO. What is known is that ‘prophylactic’ antibiotics do not prevent the development of urinary catheter-associated infections. In general, the younger a UO patient the less likely they have an infectious cause or component although they may develop one while the catheter is indwelling. Urine microbiology could be considered at the time of catheter removal or 3 days post removal. The practice of submitting the tip of the catheter for microbiology is also difficult to recommend because the tip has a high contamination rate which could cause false positives.

Urethral relaxants 

Medications most commonly used for this include acepromazine, phenoxybenzamine and prazosin which mainly function via alpha-1 antagonism leading to smooth muscle relaxation. Since smooth muscle is only present in the proximal third of the penile urethra these relaxants may not be very effective. One study showed a possible benefit of prazosin vs. phenoxybenzamine with lower recurrence of UO rates. A more recent study showed no beneficial effect of prazosin vs. placebo for the incidence of recurrent UO. 


Several anti-inflammatories have been studied for UO. Cats given prednisolone vs. a placebo did not show any improved survival. More recently, a study evaluating the use of meloxicom in cats with UO showed no difference in recurrence of UO or recovery from clinical signs compared to cats given a placebo. At this time, there’s no evidence showing a reduction in recurrence of UO with the use of anti-inflammatories. Intravesicular administration of pentosan sulphate, which is a glycosaminoglycan, also did not result in reduced recurrence or clinical signs.


Amitriptyline is a tricyclic antidepressant which has anticholinergic, anti-histaminergic, sympatholytic, analgesic and anti-inflammatory properties. It has been used for human interstitial cystitis cases. Some studies have been performed evaluating this drug in non-obstructive FLUTD cases and have not shown any improvements. In one study, it may have increased the risk of FLUTD recurrence.

Post-obstructive diuresis

Post obstructive diuresis is an uncommon phenomenon that can occur in these patients. It may occur due to several factors including:

  • accumulation of osmotically active substances in the blood
  • tubular epithelial dysfunction
  • medullary washout
  • antidiuretic hormone dysfunction
  • increased natriuretic factors accumulating during obstruction 

Typically it is recognised by increased urine production (> 2ml/kg/hr). In one study, it tended to occur within 6 hours of resolution of the UO via a urinary catheter.  This study also showed cats with an admission pH of < 7.35, hyperglycaemia, hyperosmolality and azotaemia were more likely to experience this phenomenon. In some cases, the diuresis can last several days (one cat in the aforementioned study experienced it for 84hr).

Post-obstructive diuresis can lead to dialysis disequilibrium syndrome which is characterised by neurological symptoms from rapid decreases in peripheral osmolality. As the osmolality decreases, cerebral oedema occurs leading to an increase in intracranial hypertension (ICH).   Symptoms can range from vomiting and lethargy to more severe signs including seizures, obtundation and cardiac dysrhythmias. Should neurological signs occur, administration of a hyperosmolar osmotic agent (mannitol/hypertonic saline) is recommended for the ICH. Ideally one would also slow the decrease in osmotically active solutes (BUN in particular) although this can be difficult to achieve in these patients. 


In general, recurrence rates are anywhere between 20-45% in the first few months post-obstruction. Factors that may affect recurrence include the use of a 5fr urethral catheter and use of phenoxybenzamine but not the duration of catheterisation, administration of antimicrobials, use of pain medications or presence of an infection at admission. Independently, only increasing dietary water content was associated with decreased recurrence.

[S Jasani: the emphasis in this paragraph on recurrence should very much be on ‘…that MAY affect recurrence’. While Lisa kindly gives up her time to write these blogs posts, she is not able to simultaneously provide full evidence-based medicine critiques of the references listed. Type of study, methodology, sample size, size of any effect reported, etc. all need to be considered before drawing conclusions that may affect your personal clinical practice.]


Kruger, J.M., Conway, T.S., Kaneene, J.B., Perry, R.L., Hagenlocker, E., Golombek, A. and Stuhler, J., 2003. Randomized controlled trial of the efficacy of short-term amitriptyline administration for treatment of acute, nonobstructive, idiopathic lower urinary tract disease in cats. Journal of the American Veterinary Medical Association, 222(6), pp.749-758.

Ostroski, C.J. and Cooper, E.S., 2014. Development of dialysis disequilibrium‐like clinical signs during postobstructive management of feline urethral obstruction. Journal of veterinary emergency and critical care, 24(4), pp.444-449.

Hetrick, P.F. and Davidow, E.B., 2013. Initial treatment factors associated with feline urethral obstruction recurrence rate: 192 cases (2004–2010). Journal of the American Veterinary Medical Association, 243(4), pp.512-519.

Cooper, E.S., 2015. Controversies in the management of feline urethral obstruction. Journal of Veterinary Emergency and Critical Care, 25(1), pp.130-137.

Reineke, E.L., Thomas, E.K., Syring, R.S., Savini, J. and Drobatz, K.J., 2017. The effect of prazosin on outcome in feline urethral obstruction. Journal of Veterinary Emergency and Critical Care.

Dorsch, R., Zellner, F., Schulz, B., Sauter-Louis, C. and Hartmann, K., 2016. Evaluation of meloxicam for the treatment of obstructive feline idiopathic cystitis. Journal of feline medicine and surgery, 18(11), pp.925-933.

Osborne, C.A., Kruger, J.M., Lulich, J.P., Johnston, G.R., Polzin, D.J., Ulrich, L.K. and Sanna, J., 1996. Prednisolone therapy of idiopathic feline lower urinary tract disease: a double-blind clinical study. Veterinary Clinics: Small Animal Practice, 26(3), pp.563-569.

Delille, M., Fröhlich, L., Müller, R.S., Hartmann, K. and Dorsch, R., 2016. Efficacy of intravesical pentosan polysulfate sodium in cats with obstructive feline idiopathic cystitis. Journal of feline medicine and surgery, 18(6), pp.492-500.

Francis, B.J., Wells, R.J., Rao, S. and Hackett, T.B., 2010. Retrospective study to characterize post-obstructive diuresis in cats with urethral obstruction. Journal of feline medicine and surgery, 12(8), pp.606-608.