Most dogs with epilepsy don't have problems with heartworm preventatives. However, a few patients seem to be more likely to suffer seizures soon after the administration of a particular preventative. In these cases, it is recommended that they switch to a different product. There isn't one heartworm preventative that's better or worse for dogs with epilepsy and the incidence of seizures is low for all of them. (Please see note on Proheart 6).
The exception to this may be with collies because some collies (not all) have a genetic deficiency in a protein associated with the blood-brain barrier. This allows Ivermectin to enter the brain from the blood. Sensitivity to Ivermectin has also been noted in other herding breeds.
Proheart 6 Injectable: Since this drug is still very new, I would avoid using it on an epileptic dog. The following excerpt is from Fort Dodge's website:
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Last Updated August 2009