Why do patients taking hydrocodone sometimes show negative oral fluid analysis?
The time-course of appearance and disappearance of hydrocodone in oral fluid after dosing in controlled laboratory settings has not been studied. Since the parent drug is quantitated in oral fluid, if that drug is metabolized or eliminated very quickly in a particular patient, it may not reach sufficient concentrations in oral fluid for detection. Yet the drug metabolites would end up concentrated in urine. Whereas oral fluid windows of detection more closely parallel windows of detection in blood, the concentrations achieved can be quite different. Oral fluid concentrations of some drugs are considerably lower than those found in serum. The factors underlying this are unclear. We have observed that in a few patients, hydrocodone windows of detection are small.. Analysis of a urine sample will always demonstrate the drug if it is present.
