Urine retention on fluoxetine — where do we go next?

My cat, Bean, struggles from severe generalized anxiety, noise phobia, and panic. She was doing great on fluoxetine for about a year until I finally noticed that she was having trouble urinating. She would skip from box to box and lay down for long periods of time, only ending up urinating a massive amount once a day (while laying down).

We are in the process of taking her off fluoxetine and even going from 4mg daily to 2.5mg every other day now, she still has similar urinary habits, though I think things are slightly improved. My vet is on board and we’re planning to do a 2 week reset after weaning and before starting anything else to make sure nothing else is going on unrelated to the meds.

My vet is not very experienced in prescribing different behavior meds and has never seen urine retention from fluoxetine before, so we’re struggling with the decision of where to go next. I am a professional behavior consultant and we have been researching together but this is not either of our strong points.

Is it likely that another SSRI will give her similar side effects? The fluoxetine was working so well for her behavior. Would it be best to switch to another class entirely? Are there any behavior meds that don’t carry that risk as a side effect at all?

Thank you!

Note — I am a certified cat behavior consultant through IAABC