How to cite and build on the work of another paper that is still under peer review? I've written a paper which I submitted to journal ~5 months ago and is still in peer review. I have a follow up piece of work that is similar, but uses a different formulation of a problem (so I can show the results are similar and draw attention to the positive/negatives of using one formulation or the other). 

How can I cite this in my new paper? I have published the first paper on arXiv, but it hasn't even got to the first round of reviews. I also have a need to publish as soon as possible as my Ph.D. funding runs out in 6 months - so I'd like to complete before then!
Cite your arXiv preprint, just like you would cite any other prior work.  Peer review is not a prerequisite for something to be citeable.