Our patient is on a fentanyl patch and the drug test came back negative. Why did this happen?
In part this is due to the low dose of fentanyl given to patients and the fact that only 26 to 55% is recovered in urine as the metabolic product norfentanyl. Very little of the parent drug fentanyl is recovered. Considering a 12 microgram per hour patch given over 72 hours and an average urine output of 1.5 liters, we would expect to find about 24ng/mL of norfentanyl in the urine. This is near our cut-off. Patches with higher doses would be more easily detectable. The 26-55% recovery in urine is only an estimate. We know that people vary considerably in their metabolism, so that negative results at higher doses will occur in some patients.
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- Our patient is on a fentanyl patch and the drug test came back negative. Why did this happen?
