Investigation of morphine and morphine glucuronide levels and cytochrome P450 isoenzyme 2D6 genotype in codeine-related deaths Joachim Frost a,b,1, *, Arne Helland b,1 , Ivar S. Nordrum a,c , Lars Slørdal a,b a Department of Laboratory Medicine, Children’s and Women’s Health, Norwegian University of Science and Technology (NTNU), Trondheim, Norway b Department of Clinical Pharmacology, St. Olav University Hospital, Trondheim, Norway c Department of Pathology and Medical Genetics, St. Olav University Hospital, Trondheim, Norway 1. Introduction Codeine is an opiate analgesic that is widely used, often in combination formulations with paracetamol (acetaminophen). Combinations with other analgesics or miscellaneous drugs such as acetylsalicylic acid, ibuprofen, carisoprodol, caffeine, barbitu- rates and sedative antihistamines are available in some countries. Codeine is also used as a cough suppressant, either alone or in combination with other antitussive drugs. Codeine is mainly metabolized in the liver, although some intestinal and CNS metabolism occurs. The principal pathways are outlined in Fig. 1. A major part (50–70%) of a codeine dose is glucuronidated to codeine-6-glucuronide (C6G), while 10–15% is N-demethylated to norcodeine via the cytochrome P450 isoen- zyme 3A4 (CYP3A4) [1]. Norcodeine is in turn glucuronidated to norcodeine-6-glucuronide (N6G), and a minor part is O-demethy- lated to normorphine [2,3]. Of an ingested codeine dose, 0–15% is O-demethylated to morphine by the polymorphic cytochrome P450 isoenzyme 2D6 (CYP2D6), and further glucuronidated to the inactive metabolite morphine-3-glucuronide (M3G; approximate- ly 60% of morphine formed) and the active metabolite morphine-6- glucuronide (M6G; 5–10% of morphine formed) [1]. A minor part of morphine is N-demethylated to normorphine [2,3]. Compared to morphine and M6G, codeine and its main metabolites C6G and norcodeine/N6G have weak affinity to opioid m-receptors [4–6]. Normorphine has about four times weaker opioid m-receptor affinity than morphine [4] and is produced in small amounts [3]. Accordingly, the analgesic effects of codeine are largely dependent on metabolic conversion to morphine by CYP2D6. Approximately 7–10% of the European population lack func- tional CYP2D6 enzyme due to a genetic polymorphism (‘‘poor metabolizers’’) [7], and are thus unable to convert codeine to morphine. It has been demonstrated in several studies that such individuals do not obtain pain relief from codeine [8–11]. Diminished O-demethylation of codeine to morphine has also Forensic Science International 220 (2012) 6–11 A R T I C L E I N F O Article history: Received 21 October 2011 Received in revised form 3 January 2012 Accepted 6 January 2012 Available online 28 January 2012 Keywords: Forensic science Forensic toxicology Codeine Morphine Toxicity Death Postmortem Blood concentration A B S T R A C T Compared to morphine and morphine-6-glucuronide (M6G), codeine and its other major metabolites codeine-6-glucuronide and norcodeine have weak affinity to opioid m-receptors. Analgesic effects of codeine are thus largely dependent on metabolic conversion to morphine by the polymorphic cytochrome P450 isoenzyme 2D6 (CYP2D6). How this relates to toxicity and post-mortem whole blood levels is not known. This paper presents a case series of codeine-related deaths where concentrations of morphine, M6G and morphine-3-glucuronide (M3G), as well as CYP2D6 genotype, are taken into account. Post-mortem toxicological specimens from a total of 1444 consecutive forensic autopsy cases in Central Norway were analyzed. Among these, 111 cases with detectable amounts of codeine in femoral blood were identified, of which 34 had femoral blood concentrations exceeding the TIAFT toxicity threshold of 0.3 mg/L. Autopsy records of these 34 cases were retrieved and reviewed. In the 34 reviewed cases, there was a large variability in individual morphine to codeine concentration ratios (M/C ratios), and morphine levels could not be predicted from codeine concentrations, even when CYP2D6 genotype was known. 13 cases had codeine concentrations exceeding the TIAFT threshold for possibly lethal serum concentrations (1.6 mg/L). Among these, 8 individuals had morphine concentrations below the toxic threshold according to TIAFT (0.15 mg/L). In one case, morphine as well as M6G and M3G concentrations were below the limit of detection. A comprehensive investigation of codeine-related fatalities should, in addition to a detailed case history, include quantification of morphine and morphine metabolites. CYP2D6 genotyping may be of interest in cases with unexpectedly high or low M/C ratios. ß 2012 Elsevier Ireland Ltd. All rights reserved. * Corresponding author at: Department of Clinical Pharmacology, St. Olav University Hospital, NO-7006 Trondheim, Norway. Tel.: +47 72 82 91 05; fax: +47 72 82 91 10. E-mail address: joachim.frost@stolav.no (J. Frost). 1 These two authors contributed equally to this work. Contents lists available at SciVerse ScienceDirect Forensic Science International jou r nal h o mep age: w ww.els evier .co m/lo c ate/fo r sc iin t 0379-0738/$ – see front matter ß 2012 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2012.01.019