Pantothenic acid does work to an extent. It helps accelerate the metabolism of lipids and on a relevant note, our skin is comprised of lipids. Essentially it reduces the collection of sebum and reduces the sebaceous glands daily excretions. It'll treat an immediate issue, but a combination of multiple synergistic nutrients will really stop the severity of future breakouts.
B-Complex and more specifically cobalamin analogues (B12) under uncommon, but specific circumstances aid in the development of bacterial acne vulgaris if you unfortunately possess a genetic marker for the predisposition. Here is a little study I recently found.
http://www.ncbi.nlm.nih.gov/pubmed/26109103
Androgen related acne development is honestly pretty hard to mitigate unless you remove the sole denominator, which is your supraphysiological androgen supplementation. Best thing is to avoid using excessively harsh washes, no touching, and maintain optimal hygiene practices that involve what your face touches. For the back I'd try a 10% benzoyl peroxide wash and a thick bristled brush as the texture, density, and sensitivity on our back is hardly a comparison to the feeble nature of our skin.