On the dermal absorption of cocaine.

A 5-mg dose of cocaine free base applied to the volar forearm skin surface of a volunteer resulted in a maximal urinary benzoylecgonine concentration of 55 ng/mL at 48 h, using discrete urine specimens. A total of 58 micrograms of benzoylecgonine, representing 1.2% of the dose, was excreted in the 96-h urine. An identical trial using 5 mg of cocaine hydrochloride resulted in a maximal urinary benzoylecgonine concentration of 15 ng/mL at 24 h. We conclude that dermal absorption of cocaine represents a minor, but significant route of exposure to this drug that needs to be considered when interpreting low-level urine drug testing results.