Up to 20% of dogs taking AEDs may have a drug reaction that manifests as a dermatologic reaction.
Wow! That number is higher than I remember from residency; what's your experience?? I dug into this statistic this week after consulting on a case about a possible dermatologic drug reaction in a dog receiving an anti-epileptic drug (AED).
What signs are seen?
During a prospective study, 15 dogs (of 137 dogs) were identified as having a dermatologic condition after starting an AED. However, three may have had signs before starting the AED. All 15 were treated with phenobarbital!
9 dogs were seen by a dermatologist and the following signs were documented:
Extensive erosions or epidermal necrosis leading to skin detachment (4 dogs)
Papules, pustules, erythema, crusty lesions (8 dogs)
Pruritus and/or alopecia (3 dogs)
How do they *know* it is related to the drug?
They utilized an index based assessment, which is used for drugs in which withdrawal or drug challenges may be unethical (AEDs!). The index is called the Naranjo intext. I'm not terribly familiar with the nuances of using this index, so forgive my lack of a more detailed explanation. When they applied this, they considered 6 dogs to have probable cutaneous drug reactions, possible drug reactions in 8 dogs and doubtful in 1 dog. We all know these indexes can be wrong, but those numbers sound pretty compelling, and concerning.
How was it managed?
The AED therapy was withdrawn in 7 cases and 5 subsequently resolved completely with 2 weeks. Another dog had partial improvement after withdrawal of the drug and the rest received supportive or directed treatment such as anti-inflammatory, antimicrobial topicals, ant parasitic agents, or systemic prednisolone. All dogs had resolution of signs with the above treatments, but improvement wasn't complete and appeared temporary.
Key Point: Do a thorough physical examination on your patients before starting any AED and document new dermatologic changes if they arise. Can they still be coincidental? Yes. But, maybe we're are missing some that are not.
Do you need help with an epileptic patient? I am especially fond of helping with seizure management so I'd love to help! Call, text or email. Please note that I respond to emails at night (most days) so if you have an urgent question please call or text.
*Reference: Koch T, Mueller BD, et al. Cutaneous adverse drug reactions in dogs treated with antiepileptic drugs. Frontiers in Veterinary Science 2016: 3: 1-10.