Standards of laboratory practice: analgesic drug monitoring

¹ Departments of Pediatrics and Emergency Medicine, Wayne State University School of Medicine, Detroit, MI 48201.

² Department of Pathology, Medical College of Wisconsin and Milwaukee County Medical Examiner's Office, Milwaukee, WI 53226.
^a Address correspondence to this author at: Medical College of Wisconsin, 8700 Wisconsin Ave., Milwaukee, WI 53226. Fax 414-456-6305; e-mail shwong{at}mcw.edu.

Analgesics are the most commonly consumed over-the-counter preparations in the United States. They are used in the treatment of various pain syndromes and other medical conditions. Although analgesics are generally perceived to be safe agents, serious toxicity may occur in the setting of acute overdose, chronic abuse, or overuse. The indications for therapeutic drug monitoring in patients using these medications appropriately is as yet not well defined. The emphasis of this discussion, therefore, is on recommendations for monitoring in situations where toxicity is suspected. Preanalytical, analytical, and practice issues including drug interactions, frequency of monitoring, pertinent ancillary tests, reporting, and special patient groups at risk for toxicity are reviewed. Recent information from a major manufacturer of evacuated tubes arguing against the use of gel tubes for blood collection for drug monitoring is included. Colorimetric/enzymatic/immunoassays for the routine/stat monitoring of acetaminophen and salicylate and diflunisal cross-reactivity with most of the currently used salicylate assays are presented. Achiral and chiral chromatographic assays and newly introduced columns such as restricted access media and/or automated chromatographic systems are reviewed for the analysis of ibuprofen, naproxen, and the recently introduced tramadol. Finally, concepts regarding future directions including drug chirality and chiral analysis are presented.