Hi -
I did a quick search re the use of terbanifine, and found several results that indicated its use in the treatment of Paracoccidioidomycosis, or South American Blastomycosis, but the results are from back in 1999, and it seems to have been utilized due to the lower cost. In ideal conditions, they'd most likely use the newer, more effective antifungal group.
It does seem to be most useful in the treatment of cutaneous skin/nail conditions.
The thing about South American Blastomycosis (which is not the same as Blastomycosis Dermatitides) is that most of the time the patients affected develop lesions in their mouths and noses first.
Usually it's because they've been picking their teeth with splinters of wood or tree bark, which harbors these types of fungi. (Thanks to Dr. Friedlander: pathguy.com)
Couldn't comment on testing for steroid levels. Some dogs do have seizure/shaking spells while being treated.
I did see that someone mentioned a mulch pile? If you search back, you'll see that many of us have the common factor of landscaping and mulch in our animals' disease history. For myself and 2 other families that I did some landscaping work for, 2 tons of mulch equalled 4 dead dogs and 1 that survived. Enough evidence for me.
Since then we've developed a fear of it and have eradicated it from our property.
Here's more on the use of terbanifine vs. the newer azoles:
http://emedicine.medscape.com/article/1092860-treatmentExcerpt:
"Historically, the sulfonamides have been the most widely used medications for the treatment of P braziliensis; their advantage is their low cost. However, relapses are more common with the sulfonamides than with other mediations, and longer courses of therapy are required. The percentage of patients who have a relapse after receiving sulfonamides is 20-30%, whereas with itraconazole it is 3.5-10%, and with ketoconazole it is 7-11%. Further, 3-5 years of sulfonamide therapy may be required, whereas 6-10 months and 6-12 months are recommended with itraconazole and ketoconazole, respectively."