I agree. In retrospect I'd edit that out if I could now, as there are too many variables, general lack of scientific knowledge, and common math mistakes could easily hurt your pet.
However just to play devil's advocate for a minute, there are cases where people are using common products in place of over-priced pet pharmecuticals.
Lets take Fipronil, one of the common anti-flea topicals made by BASF.
The Fipronil in BASF Termidor is at 9.1%, w/90.9% inerts
The Fipronil in Frontline Topspot is at 9.7% w/90.3% inerts
Someone noticed this, and decided to try it on their dog, seeing as it is a slightly weaker form of Fipronil on a ml to ml basis. According to the other forums I visit, many of those which are geared towards actual hunting dogs, coonhounds, bluenoses, etc, this is rather old news, and accepted practice.
There have been no reports of adverse health issues, which makes sense as Fipronil is a water-soluble product which would most likely mean that the 'inert ingredients' is all/mostly water.
Again, I'm not trying to push anyone into doing likewise, just pointing whats going on outside the Sheltie world as I come across it.
From an economics POV, it is certainly enticing.
On a cost basis, per 1800petmeds,for a 23-44# dog:
Per 1.34 ml applicator Topspot Fipronil 9.7% is ~$12/dose
BASF Termidor is ~$65 for 20 oz or 591ml
591/1.34 = 441 doses or $0.14/dose
Costs aside though, no/limited adverse reactions in hunting dogs does not mean there would likewise be the same results with a Sheltie. Not sure I'd consider it unless there was some real financial hardship.
A totally useful drug with a bad rap years and years later. No thanks here, I would rather go without if I couldn't afford it. Or since the patent is off Fontline look into the generic forms ie Pet Armor 3 dose for a 1/3 of the cost. I have used it this summer and it works great.