Heartworm prevention with Portal atresia

My 12 year old corgi mix has portal atresia, diagnosed when she was about 5 years old, and has been on liver supplements ever since (milk thistle, hepato support, denamarin). Her liver is very sensitive and her ALT and post bile acid levels spike if given antibiotics, certain supplements, etc.  Because of this, she has been on revolution for heartworm for years since it is easier on the liver. However, in October, she had a bought of what the vet thinks was geriatric vestibular syndrome (complete with nystagmus) for about 3 days. This happened the same day I gave her the revolution. Two questions: 1) could the revolution have caused this? 2) If so, and maybe more urgent a question, since I’m scared to use revolution, what can/should I use for heartworm prevention? My vet has suggested interceptor every two months and to test her liver more frequently, but due to her liver issues I am concerned and feel uncomfortable giving her something I know will inflame the liver. Any advice would be most appreciated! (Her latest ALT level this friday was elevated at 250). Im in florida, so mosquitos and heartworm are a real concern and I also take her paddling and hiking with me.  I also understand that heartworm treatment would be difficult for her considering her liver issues, so I want to make sure I find a suitable prevention. Thanks in advance and thank you for all you do!

Hello.  It sounds as thpugh you have a balance to strike. I didn't see why the drug you mentioned would cause a head tilt, so I checked the data sheets.    Ataxia (inbalance) and other neurological signs have been reported as potential side effects, but Im unclear as to how / why. I wonder if the manufacturerer has any more data about this that they could share with your vet?  In general, an MRI scan could help to rule out some of the more common causes of a head-tilt and vestibular signs eg internal lumps and bumps, but of course these scans have a price tag associated with them.  It sounds to me as though there is a judgement call to be made - and given that your vet has examined your dog and will understand the associated risks of parasites in your area and the likely causes / outcome of your dogs' vestibular syndrome, they may be the best person to guide you in the making of it.  Wishing you and your golden oldie all the very best from here and please do let us know what is decided.  A good question for your vet is, 'if this were your dog, what would you do next about the anti-parasiticide?'