Hello, I'm Dr. Deb.
I recently came online and see that your question about Darla hasn't been answered. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
I'm sorry that Darla appears to have a uti. In general, I prefer to confirm that this is the problem before starting antibiotics but I can say that this drug can be given for this particular problem and her symptoms certainly sound consistent with one.
It's not a commonly prescribed antibiotic for some reason but in the published guidelines for treatment of urinary tract disease in dogs and cats, the Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases recommends that nitrofurantoin is a “good second-line option for simple uncomplicated UTI, particularly when multidrug-resistant pathogens are involved”.
The dose of this drug would be approximately 200 mg three times a day for a dogs this size for 7-14 days, with food to avoid stomach upset.
Side effects which might be seen include: gastrointestinal disturbances (primarily vomiting), peripheral neuropathies or nerve issues (reversible) and liver issues. Chronic active hepatitis, hemolytic anemia, and pneumonitis have been described in humans, but are believed to occur very rarely in animals.
This drug would be contraindicated in patients with kidney issues.
I should point out that it would be illegal for me to suggest or advise the use of a drug for whom it wasn't prescribed (human or pet) but I can provide the dosage information which is what I have done.
I hope this helps although, again, my apologies for the delayed reply. Deb