My older dog's pee is dark brown and red after UTI meds, what's wrong?

Hello and thank you for reaching out to Petco Pet Education Center, formerly Petcoach. I'm sorry to hear that Gracie has been urinating frequently and that it is red-tinged. It is possible that she has a UTI that is not responding to the particular antibiotics that your veterinarian initially prescribed, which can be a problem especially in older pets. Your veterinarian should perform a urinalysis and a urine culture and susceptibility (if they haven't already) to see if there is an infection present and to what particular antibiotics it is susceptible. Another possible cause of Gracie's signs could be urinary bladder stones, which can cause irritation of the bladder, leading to frequent urinations that are often red-tinged. Most bladder stones are visible on abdominal x-rays, which may be recommended by your veterinarian. Other stones require an abdominal ultrasound to see. An abdominal ultrasound would also be able to detect any other abnormalities in the bladder, for example, a tumor. I recommend ensuring she has plenty of access to water, and having her seen by your veterinarian at their next available appointment. I hope this is helpful!