I was covering for Dr. Kim the other day. A 60-something diabetic who had started taking insulin a few months ago had left a message that she wanted to change from Novolog (insulin aspart) to Humalog (insulin lispro) because she had just had her second UTI (urinary tract infection). And she had just read that UTI is listed as a side effect of Novolog but not of Humalog.
I’d never heard of insulin causing UTIs, but if that were the case, wouldn’t all insulin do the same thing, I thought. I opened epocrates, the drug app 60% of doctors use (created by the CEO of Galileo, where I work). Sure enough, UTI is listed as number 5 of common side effects for Novolog, but it is not on the list for Humalog, where URI (upper respiratory infection) is included as number 8.
My trusted, much younger colleague, Dr. Google, quickly produced the most interesting answer to my query “UTI from insulin”.
Here are two quotes from the article Google delivered to me:
What Is Insulin’s Role in Diabetes-Related Urinary Tract Infections?
“…reduced insulin receptor activity….led to a weakened response to bacterial infections, lower antimicrobial peptide production, and compromised immunity.”
“suppressed insulin receptor signaling lowered antimicrobial peptide production and increased susceptibility to “leaky bladders” and infections caused by….Escherichia coli.”
I’ll say it again, just as I did in my story about the woman with precipitous drop in albumin:
You can’t know everything and you’re never too old to learn.
The Case of the Dropping Albumin
A Country Doctor Writes: 
I find it amazing that you listened to her research on the matter. Too many doctors would just roll their eyes and never look into it themselves.