If you are treating hypovitaminosis A, I found a treatment protocol that uses 1 unit of vitamin a per gram of weight your toad is. Since the gel caps are so concentrated compared to a ~50 gram or less toad, they recommended diluting in vegetable oil. This was given once daily for 14 days and reversed signs of hypo vit A in one referenced article by a herp vet that I found. I have actually started this protocol in my 2 American Toads that I suspect hypo A in. I am at day 4 now, and I will say they are more alert and active, I haven't seen a change in their ability to catch prey well with the tongue yet.

In terms of how often you should supplement, the Repashy vit A recommends daily dusting, although I have read most people recommending alternating the multi vitamin with a calcium supplement and that is what I plan to do (prior I was only using calcium with D). There is another study looking at vitamin A in amphibians that found dusting vitamin A supplementation did not significantly increase vitamin A content of the liver post mortem after 30 days compared to topical administration with a product called Aquasol A which I have found a hard time finding on the internet. It was comparable to the amphibians that didn't get dusting, so I think an alternate day approach to dusting is probably safe at avoiding hyper vitaminosis, but hopefully enough to prevent a deficiency from occurring.

I think gut loading is a smart thing to do, as well as varying the diet as much as possible.

Hope your toad is doing well!

here is the article along with some quotes from it: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685470/

Specifically, the whole-body vitamin A level of deficient African foam-nesting frogs (C. xeramplina) was not significantly increased by providing these animals with crickets powdered with a nutritional supplement understood to contain high amounts of vitamin A [Sim et al., 2010]. On the other hand, topical administration of a water-soluble emulsion of retinyl palmitate increased whole-body vitamin A levels by approximately four-fold [Sim et al., 2010].

Importantly, the occurrence of short tongue syndrome has been linked to low tissues levels of vitamin A in Wyoming toads (B. baxteri), and an enriched diet containing high levels of vitamin A has been shown to resolve the feeding problems associated with short tongue syndrome in deficient frogs [Li et al., 2009; Pessier, 2013). Similarly, treatment with vitamin A was able to resolve swellings on the lower eyelids of vitamin A deficient frogs [Wright, 2006; Pessier, 2013].