Combined Dextromethorphan and Chlorpheniramine Intoxication in Impaired Drivers.

This report describes a series of eight drivers arrested for driving under the influence of the combined effects of dextromethorphan and chlorpheniramine, and a further four drivers under the influence of dextromethorphan alone. In the combined dextromethorphan/chlorpheniramine cases, blood dextromethorphan concentrations ranged from 150 to 1220 ng/mL (n = 8; mean 676 ng/mL, median 670 ng/mL), and chlorpheniramine concentrations ranged from 70 to 270 ng/mL (n = 8; mean 200 ng/mL, median 180 ng/mL). The four cases without chlorpheniramine present had blood dextromethorphan concentrations between 190 and 1000 ng/mL (mean 570 ng/mL, median 545 ng/mL). Some drivers had therapeutic concentrations of other drugs present. Drivers generally displayed symptoms of central nervous system (CNS) depres...