Opossums and Urinary Tract Infections

I am a wildlife rehabber in the southern USA. I have 3 non releasable opossums with a male approximately 2 years old who has a urinary tract infection. I have him on an antibiotic at the moment and will start a different antibiotic in 2 days. He gets his medicines with yogurt as well. I have been told that Birch Bark tea is good for this. Could you suggest other remedies?

Living in Canada, I have not had any experience with opossums. However, the first question in chronic conditions is always, "What is the cause of this problem?" Are opossums prone to urinary tract infections (UTIs) in the wild or does this happen once in captivity? If the latter, what can rehabilitation centres do about this? Is the diet implicated or is there another reason to do with the environment at the rehabilitation centre? In most species diet is often a culprit in UTIs. In addition, it is important to determine whether the infection is solely in the bladder or if there is any kidney involvement. If the latter, many herbs normally employed in UTIs would be contra-indicated. Further questions also need to be answered: Is there any blood? Does there appear to be pain on urination? How often/much urine is expelled? Is the opossum drinking more or less water? Etc.
In general then, some of the possible herbs used in bladder infections include: Arcstaphylos uva-ursi (Bearberry), Althaea officinalis (Marshmallow), Berberis aquifolium (Oregon grape), Echinacea purpurea (Echinacea), Zea mays (Corn silk), Agropyren repens (Couchgrass) and Plantago major (Plantain). As for your question regarding Birch Bark, it is not a herb I use in daily practice so cannot comment other than to say it contains, amongst other constituents, salicylates. Many animals do not metabolise salicylates well and can have severe reactions. I would recommend you look at opossum physiology and metabolism as well as the constituent profile of the above herbs before making your choice.