Great post.

Regarding Nitrofuratonin; I think that we can probably use it in patients with UTI with moderately impaired renal function. To my knowledge, the risk of subtherapeutic concentrations in the urine is more theoretical secondary to known poor tissue penetration by nitrofuratonin. In fact, previously, the nitrofuratonin product information said that the CrCl cut-off was 40; but somewhere along the way they changed this to 60.

A recent review by Oplinger and Andrews published in Annals of Pharmacotherapy suggests that maybe the evidence isn't that great that we should draw the line at CrCl of 60. They suggest that the limited data available would support considering using Nitrofuratonin in patients with a CrCl of 40 mL/min or higher rather than 60 mL/min.

And I think that this is a legitimate point that needs to be discussed and looked into further because a lot of our options don't work so well against common UTI bugs. But nitrofuratonin does and we maybe limiting ourselves a bit by not using it on a patients who may benefit from it.

References:
M. Oplinger, and C.O. Andrews, "Nitrofurantoin contraindication in patients with a creatinine clearance below 60 mL/min: looking for the evidence.", The Annals of pharmacotherapy, 2013. http://www.ncbi.nlm.nih.gov/pubmed/23341159