Ecoli how much convenia needed

Both of my senior cats have uti ecoli infection. Rigby level is 10^3.   Izzy is 10^5. They each had once convenia injection.  Is a 2nd injection necessary for this level of infection? My vet is advising yes without asking for another urine test after the first dose.  I’m wondering why would one injection not be enough to resolve the infection.

Hello! -  It is very common for no bacteria to be found and cystitis to be sterile, but in this case I understand that a UTI has actually been diagnosed.  E-coli are thought to be the amongst the commonest UTIs in cats, but reliable diagnosis obviously depends on getting an uncontaminated sample of urine that cannot have come into contact with any faeces or feacally-contaminated surfaces such as the cats' perineum (which often have e-coli from poo).  Best practice would be to grow this for Culture and Sensitivity against different antibiotics but obviously this takes time, so a lot of clinicians treat with a 'common,' first-line antibiotic that is effective against e-coli, pending treatment.  Convenia is a Cephalosporin antibiotic is generally not given first-line but kept back for difficult cases.  However, what makes it attractive to clinicians is that it can be injected, once, and thereafter the clinician knows that it "is in the cat" unlike the situation with tablets.  What I can't tell you is for how long convenia remains at an appropriate concentration in the bladder to treat a urine infection, which is probably what you need to know here - you would probably get your answer from speaking to Pfizer, who make it.   However, to my understanding, it may be best practise to repeat culture and sensitivity at this point. This article is about cystitis rather than UTIs:   https://vethelpdirect.com/vetblog/2021/03/02/cystitis-in-cats-causes-symptoms-treatment/ And this an outline about antibiotics: https://vethelpdirect.com/vetblog/2020/08/28/why-did-the-vet-prescribe-antibiotics/ I'm afraid that I haven't really answered your question and the best way would be to ask your vet.

Your vet should be able to clearly explain their thinking about drug choices that have been made.