KNOWLEDGE SUMMARY

Keywords: CATS; FELINE; PRAZOSIN; RECURRENT URETHRAL OBSTRUCTION

The efficacy of administration of prazosin in reducing the risk of recurrent urethral obstruction in male cats

Rebecca Hearne, BVMSci MRCVS^1*

¹ University of Surrey, School of Veterinary Medicine and Science, Daphne Jackson Road, University of Surrey, Guildford, Surrey GU2 7AL
* Corresponding author email: rebeccahearne@outlook.com

Vol 8, Issue 4 (2023)
Submitted 11 Jul 2022; published: 01 Nov 2023; next review: 21 Sep 2025
DOI: https://doi.org/10.18849/ve.v8i4.638

PICO question

In male cats presenting with urethral obstruction, does administration of prazosin compared with no administration of prazosin reduce the incidence of recurrent urethral obstruction within the first month of initial presentation?

Clinical bottom line

Category of research

Treatment.

Number and type of study designs reviewed

A total of three studies were included in this appraisal. Two of which were prospective double-blind clinical studies and one retrospective study.

Strength of evidence

Weak.

Outcomes reported

Both double-blind studies found no significant difference between prazosin administration and the development of recurrent urethral obstruction (rUO) when compared with a placebo. Both studies, however, did report that cats had a shorter urinary catheterisation time with prazosin administration. The retrospective study found no association between prazosin administration and the risk of rUO and found that after 14 days post discharge, significantly more 73/302 (24%) cats that received prazosin had experienced rUO compared to 11/86 (13%) of cats that did not. One study found side effects to the administration of prazosin which may be detrimental to the overall recovery.

Conclusion

Administration of prazosin does not reduce the risk of rUO within 30 days of presentation. However, the strength of evidence is weak and would benefit from further clinical studies.

How to apply this evidence in practice

The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient’s circumstances and owners’ values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources.

Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.

The evidence

One paper compared prazosin against another drug, phenyoxybenazamine (Hetrick & Davidow, 2013), however, until 2017 there were no papers that analysed the effectiveness of prazosin compared to a placebo or no drug administration.

Three papers were found which were relevant to the PICO question (Reineke et al., 2017; Hanson et al., 2021; and Conway et al., 2022). In terms of study design the two double-blind studies are much higher on the hierarchy of evidence compared to the retrospective study. However, they did not have adequate numbers of participants to draw statistically reliable conclusions. Because of this, the overall strength of evidence is weak.

Summary of the evidence

Reineke et al. (2017)

 

Hanson et al. (2021)

 

Conway et al. (2022)

 

Appraisal, application and reflection

The goal of this Knowledge Summary was to ascertain as to whether treatment with prazosin after urethral obstruction in cats, is beneficial in preventing recurrent urethral obstruction (rUO). It is hypothesised that urethral spasm is a potential cause of rUO, therefore administration of prazosin, a smooth muscle relaxant, was thought to help prevent rUO (Straeter-Knowlen et al., 1995).

The available evidence fitting to the PICO question comes from three published papers (Reineke et al., 2017; Hanson et al., 2021; and Conway et al., 2022). One study is a double-blind prospective interventional study (Reineke et al., 2017), and this study type produces the highest level of evidence as there is minimal bias from the client and the researcher. However, a downside to this study is the lack of study participants. Only 47 cats took part in this study (27 in the treatment group and 20 in the placebo group). Calculations carried out after the completion of the study suggest that a total of 1,915 cats (1149 in the prazosin-treated group and 766 in the placebo-treated group) would have been needed for an effect to be identified (Reineke et al., 2017). This lack of participants makes it difficult to generalise to the whole population. Similarly, the Hanson et al. (2021) study is a randomised double-blind study, so again ranks high on the hierarchy of evidence, however, there is a risk of type I and II statistical errors due to the small sample size and so potential lack of generalisable data. Hanson et al. (2021) states that to truly determine the statistical difference 199 study participants would be needed, as opposed to the actual study size of 65/80 cats that completed the study.

The third study is lower on the hierarchy of evidence and is a retrospective, observational cohort study (Conway et al., 2022), this means that drawing concrete conclusions from this third study is challenging as there are so many variables and areas for bias, compared to double-blinded prospective studies. For example, all cats were treated by different veterinarians at different hospitals and the collection of data is relying on the clinical notes for each animal.

Following discharge from the hospital it is very difficult to control variables within the cat’s environment which may contribute to the development of rUO. Reineke et al. (2017) made an attempt to overcome this with standardised discharge instructions for each patient which included elements such as litter tray placement, hygiene, and increasing the cats water consumption. However, it is impossible to control these variables completely. An additional variable was that there was a range of doses of prazosin used across each study (varying from 0.25 mg/cat q12hrs, 0.5 mg/cat q12hrs or 1 mg/cat per os once daily), however, despite this, similar conclusions were reached (Reineke et al., 2017; Hanson et al., 2021; and Conway et al., 2022).

Study populations were all made up of male cats presenting with urethral obstruction. There were limited exclusion criteria based on demographics (breed, age, or neutered status) in all three studies. However, two studies (Reineke et al., 2017; and Hanson et al., 2021) excluded cats with underlying diseases such as chronic kidney disease or hypertension which the cat may have been on concurrent medication for. Due to the Conway et al., (2022) study being a retrospective study there is no note of such exclusion criteria. All studies excluded cats that experienced complications such as any ruptures or tears as well as those with suspected presence of cystoliths diagnosed via imaging. Hanson et al., (2021) was the only study which included cats presenting for the first time, meaning those cats have no prior history of urethral obstruction. Having a history of urethral obstruction may impact the results as it is possible there is some degree of penile or urethral trauma associated with prior urinary catheterisation (Corgozinho et al., 2007). In addition, all three studies excluded cats with urolithiasis or crystoliths as a possible cause of urethral obstruction. Ultrasound is the most sensitive method of detecting uroliths >2 mm (Reineke et al., 2017), however, there is no way to guarantee that cats did not have any urocystoliths <2 mm. Hanson et al. (2021), used radiography to detect the presence of urocystoliths, this is not a sensitive measurement (Kyles et al., 2005) and thus cats with urolithiasis as a cause of urethral obstruction may have been inadvertently included in the study.

It was reported that cats receiving prazosin had a shorter hospitalisation time and shorter duration of urinary catheterisation than those receiving the placebo (Reineke et al., 2017). Similarly, Hanson et al. (2021) noted that cats receiving prazosin had a shorter duration of urinary catheterisation compared to the group receiving the placebo. Although, there are many variables that could have led to a shorter duration of urinary catheterisation, such as owner finances or the self-removal of the urinary catheter by the patient it can be hypothesised that prazosin is potentially beneficial in the early stages of urethral obstruction. However, the limitation of the small sample size in both these studies precludes any firm conclusions being drawn and a similar study with a greater number of study participants would be needed to prove this hypothesis.

There is a previous retrospective study (Hetrick & Davidow, 2013) again low on the hierarchy of evidence, which concluded that cats had a lower risk of rUO when administered prazosin compared to phenyoxybenazamine. However, it was not possible to determine if this was because phenyoxybenazamine increases the risk of rUO as opposed to prazosin reducing the risk. Therefore, the three studies comparing prazosin to no drugs, or a placebo are a preferable source of evidence.

Overall, it can be concluded from all three studies that there is no benefit from the administration of prazosin post urethral obstruction towards preventing rUO, compared to no administration within 14 to 30 days after the initial obstruction. However, more clinical studies are needed with larger sample sizes. In addition, the side effects of giving prazosin may have detrimental effects on patient recovery from urethral obstruction. For example, Reineke et al. (2017) noted side effects such as lethargy, diarrhea, and anorexia, all of which may contribute to the development of dehydration, leading to worsening of kidney damage and clinical signs, especially if the cat is experiencing post unblocking diuresis.

Methodology

Search strategy

 

Exclusion / inclusion criteria

 

Search outcome

 

ORCiD

Rebecca Hearne: https://orcid.org/0009-0003-4004-7161

Conflict of interest

The author declares no conflicts of interest.

References

1. Conway, D.S., Rozanski, E.A. & Wayne, A.S. (2022). Prazosin administration increased the rate of recurrent urethral obstruction in cats: 388 cases. Journal of the American Veterinary Medical Association. 260(S2), 1–6. DOI: https://doi.org/10.2460/javma.21.10.0469
2. Corgozinho, K.B., de Souza, H.J.M., Pereira, A.N., Belchior, C., da Silva, M.A., Martins, M.C.L. & Damico, C.B. (2007). Catheter-induced urethral trauma in cats with urethral obstruction. Journal of Feline Medicine & Surgery. 9(6), 481–6. DOI: https://doi.org/10.1016/j.jfms.2007.09.002
3. Hanson, K.R., Rudloff, E., Yuan, L., Mochel, J.P. & Linklater, A.K. (2021). Effect of prazosin on feline recurrent urethral obstruction. Journal of Feline Medicine & Surgery. 23(12), 1176–1182. DOI: https://doi.org/10.1177/1098612x211001283
4. Hetrick, P.F. & 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), 512–519. DOI: https://doi.org/10.2460/javma.243.4.512
5. Kyles, A.E., Hardie, E.M., Wooden, B.G., Adin, C.A., Stone, E.A., Gregory, C.R., Mathews, K.G., Cowgill, L.D., Vaden, S., Nyland, T.G. & Ling, G.V. (2005). Clinical, clinicopathologic, radiographic, and ultrasonographic abnormalities in cats with ureteral calculi: 163 cases (1984–2002). Journal of the American Veterinary Medical Association. 226(6), 932–936. DOI: https://doi.org/10.2460/javma.2005.226.932
6. Reineke, E.L., Thomas, B.A., Syring, R.S., Savini, J. & Drobatz, K.J. (2017). The effect of prazosin on outcome in feline urethral obstruction. Journal of Veterinary Emergency and Critical Care. 27(4), 387–396. DOI: https://doi.org/10.1111/vec.12611
7. Straeter-Knowlen, I.M., Marks, S.L., Rishniw, M., Speth, R.C., Wirth, W. & Knowlen, G.C. (1995). Urethral pressure response to smooth and skeletal muscle relaxants in anesthetized, adult male cats with naturally acquired urethral obstruction. American Journal of Veterinary Research. 56(7), 919–923.