Streetman DS, Ellis RE, Nafziger AN, Leeder JS, Gaedigk A, Gotschall R, Kearns GL, Bertino JS. Dose dependency of dextromethorphan for cytochrome P450 2D6 (CYP2D6) phenotyping. Clin Pharmacol Ther. 1999 Nov; 66(5):535-41.