I had bilateral compression of the lateral femoral cutaneous nerve for YEARS and after oral opioids didn't provide relief, a neurologist prescribed a fentanyl patch.

It worked great in treating the pain, which, luckily, resolved on its own (after YEARS).

BUT, over the years I was on the patch, my creatinine levels were elevated.

An endocrinologist later told me that the patch was impairing my kidney function. So I got off it. Ironically, I had seen a nephrologist for the elevated creatinine and didn't think it was the cause.

Botton line -- as it was for me, within months of getting off the patch my creatinine went down from 1.4 to .85 (which is great) and my EGFR went from 88 to 112 (which is great). In hindsight, I got very lucky. My good friend - an ER doctor -- told me as such, since once the kidneys go, there's no coming back. Kidneys - -unlike the liver -- don't regenerate. And kidney impairment is one of the LESS know risks of chronic opiod use. Pain sucks for sure, there's no doubt about it -- and most treatment for chronic pain failed me (including Gabapentin--which made me gain weight and increased the pressure on my nerves) -- but living with pain, I suppose, beats living with chronic kidney disease.