Effect of Cranberry Extract on Bacteriuria in Dogs with Intervertebral Disk Herniation

In a clinical trial, cranberry extract did not reduce the incidence of bacteriuria in dogs with acute thoracolumbar disk herniation. Urine antiadhesion activity, which was not affected by cranberry supplementation, was associated with a reduced risk of Escherichia coli bacteriuria. The results of the study were recently published in the Journal of Veterinary Internal Medicine.

Researchers from North Carolina State University tested a commercial canine cranberry extract supplement (Crananidin, Nutramax Laboratories) in client-owned dogs with acute-onset nonambulatory paraparesis or paraplegia caused by thoracolumbar disk herniation. Dogs included in the study underwent surgical spinal decompression and had no signs of bacteriuria on presentation. Dogs with a history of recurrent urinary tract infection or disease that could increase the risk of urinary tract infection (such as diabetes mellitus or hyperadrenocorticism) were excluded.

Of the 94 dogs included in the final analysis, 42 were given cranberry extract according to the manufacturer’s label instructions and 52 received placebo. Treatment began 48 hours after surgery and continued for 6 weeks. Dogs were evaluated at 2, 4, and 6 weeks postoperatively. The original study design called for more patients, but the investigators closed enrollment early because an interim data analysis showed no significant treatment effect for cranberry extract.

The overall incidence of bacteriuria was 18% (17 positive urine cultures in 94 dogs). Eleven of the positive cultures were from dogs in the cranberry group and 6 were from dogs in the placebo group, a difference that was not significant. Female sex was the most significant risk factor for bacteriuria. Involuntary urination was also a risk factor, although its association with bacteriuria was not as strong as female sex. Catheterization, crystalluria, initial neurologic status, and neurologic grade were not significant risk factors for bacteriuria.

Because cranberry extract specifically targets Escherichia coli (proanthocyanidins in cranberries inhibit the adhesion of fimbriated bacteria—like some E. coli—to uroepithelial cells in vitro), the investigators compared the incidence of this bacterium between groups. Of the 17 positive cultures, 7 were identified as E. coli: 6 in the cranberry group and 1 in the placebo group.

The researchers also assessed urine antiadhesion activity in a subset of 47 samples. Thirty of the samples had positive antiadhesion activity, with no significant difference between the cranberry and placebo groups. The incidence of E. coli bacteriuria was significantly lower in dogs with positive urine antiadhesion activity. The clinical relevance of the urine antiadhesion activity test has not yet been established in dogs, say the authors, and they recommend further study of its relationship with E. coli bacteriuria.

The lack of difference in antiadhesion activity between the two groups could have been caused by poor compliance, poor bioavailability, or an inappropriate dose rate, write the authors. Dog owners administered the treatments at home, so compliance could not be confirmed. The dose by weight and once-daily dosing schedule of the cranberry supplement could also have been inadequate, they say.

The authors conclude that the trial did not show a benefit of cranberry supplementation in a population of dogs predisposed to bacteriuria. Because the results did indicate an association between urine antiadhesion activity and E. coli bacteriuria, they recommend further investigation of dose rates, frequency, and timing of proanthocyanidin supplementation in dogs.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.