Welcome to Justanswer! I am Dr. Altman and happy to assist you both today!
I am so sorry Toby is showing these symptoms. Is the calvapet also known as Clavaseptin in the UK? Is there another name on the bottle because doing a search of antibiotics in the UK calvapet is not showing up.
There are a handful of causes of urination that has blood in it:
1.) A urinary tract infection
2.) Bladder stones that traumatize the bladder and cause bleeding
3.) A bladder tumor, most likely in a senior pet
4.) Trauma- hit by car, muscle trauma of some kind
Ideally until you are able to get to your veterinarian, please increase water intake. You can do this by supplementing the dry food with water and flavoring the water (maple syrup for example) as well. Increasing the water intake will help "flush" out the bladder and reduce the pain associated with the bleeding.
Collecting a first morning sample in a tupperware container and refrigerating the sample if more than an hour old to have your vet evaluate the sample will help determine the cause of the blood in the urine.
Your vet will run a urinalysis, potentially do a urine culture to look for bacteria, an X-ray to rule out a bladder stone, and bloodwork to ensure there is not a metabolic cause or kidney issues causing the symptoms. If you do start antibiotics today please let your veterinarian know tomorrow because it can effect urine culture results and urinalysis findings even just 24 hours later
Diagnosing the issue will help determine how best to treat the blood in the urine to get your pet comfortable swiftly
Below is more information on this condition in dogs, called hematuria (blood in urine):
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