Taken from internet library article, see link at bottom of post:

Pantothenic acid (PA), a B-complex vitamin (also known as vitamin B5), is essential for humans and animals for growth, reproduction, and normal physiological functions. It is a precursor of the coenzymes, CoA and acyl carrier protein of fatty acid synthase, which are involved in more than 100 different metabolic pathways including energy metabolism of carbohydrates, proteins and lipids, and the synthesis of lipids, neurotransmitters, steroid hormones, porphyrins and hemoglobin.

Toxicity: In humans, the only reported symptom after intakes of 10 to 20 g calcium pantothenic acid was diarrhea.

To avoid a deficiency a person only needs like 5 milligrams a day or some small amount. That is the minimum a person needs. B5 deficiency is pretty rare these days. However, because it is a WATER-SOLUBLE VITAMIN (like vit. C) it is very difficult to experience toxicity or OD. Extra that is not utilized by the body is excreted in the urine. High doses like the 10 to 20 grams mentioned above may cause diarrhea.
However, for Acne you never take even 10 grams a day. If a person takes 3 grams 3 times a day that's 9 grams. There is no cause to be concerned with this dosage and no reason not to try this therapy.

Another reference - Linus Pauling Institute B5 Information:
http://lpi.oregonstate.edu/infocenter/vitamins/pa/

Info on PANTOTHENIC ACID (excerpts above)