Determining zolpidem compliance: urinary metabolite detection and prevalence in chronic pain patients.

Zolpidem (Ambien(®)) is the most prescribed insomnia treatment in the USA; however, little is known about zolpidem metabolite excretion in chronic pain patients. As zolpidem is extensively metabolized in vivo to zolpidem 4-phenyl carboxylic acid (ZCA), metabolite detection may provide improved accuracy for compliance determinations, thereby improving clinical decisions. Zolpidem and ZCA were extracted from 1 mL human urine by mixed-mode solid-phase extraction. Samples were analyzed by LC-MS-MS using positive electrospray ionization with multiple reaction monitoring mode employed for detection and quantification. Gradient chromatographic separation was achieved with a reversed-phase column in a rapid 1.8 min analysis. The assay was linear from 4 to 1,000 µg/L for zolpidem and 4 to 10,000 µg/L for ZCA. Interday recovery (bias) and imprecision (n = 20) were 100-107% of target and 2.4-3.7% relative standard deviation, respectively. Extraction efficiencies were 78-90%. Pain compliance samples (n = 3,142) were de-identified and analyzed for zolpidem and ZCA. Zolpidem was detected greater than limit of quantification in 720 specimens (22.9%), while ZCA was detected in 1,579 specimens (50.3%). Only five specimens contained zolpidem alone. ZCA was observed without parent zolpidem in 864 specimens, thereby increasing population detection rates by 27.5%. Addition of a zolpidem metabolite to compliance determinations substantially improved detection for zolpidem intake and also should prove useful in clinical and forensic settings.

Prevalence of heroin markers in urine for pain management patients.

Surveys of current trends indicate heroin abuse is associated with nonmedical use of pain relievers. Consequently, there is an interest in evaluating the presence of heroin-specific markers in chronic pain patients who are prescribed controlled substances. A total of 926,084 urine specimens from chronic pain patients were tested for heroin/diacetylmorphine (DAM), 6-acetylmorphine (6AM), 6-acetylcodeine (6AC), codeine (COD), and morphine (MOR). Heroin and markers were analyzed using liquid chromatography tandem mass spectrometry (LC-MS-MS). Opiates were analyzed following hydrolysis using LC-MS-MS. The prevalence of heroin use was 0.31%, as 2871 were positive for one or more heroin-specific markers including DAM, 6AM, or 6AC (a known contaminant of illicit heroin). Of these, 1884 were additionally tested for the following markers of illicit drug use: 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA), methamphetamine (MAMP), 11-nor-9-carboxy-Δ(9)-tetracannabinol (THCCOOH), and benzoylecgonine (BZE); 654 (34.7%) had positive findings for one or more of these analytes. The overall prevalence of heroin markers were as follows: DAM 1203 (41.9%), 6AM 2570 (89.5%), 6AC 1082 (37.7%). MOR was present in 2194 (76.4%) and absent (

Urine drug testing of chronic pain patients. V. Prevalence of propoxyphene following its withdrawal from the United States market.

Propoxyphene is an opioid analgesic that was surrounded by controversy concerning its safety and efficacy during its lifespan in the US market. Propoxyphene was withdrawn in November of 2010 from the US market and is still being detected one year post-withdrawal in urine specimens from the pain management population. In this study, the prevalence of propoxyphene was determined in a total of 417,914 urine specimens collected from 630 clinics involved in pain management located in 24 states during the period of January 1, 2010, through December 31, 2011. Propoxyphene and norpropoxyphene were measured in urine by a validated liquid chromatography-tandem mass spectrometry procedure with a lower limit of quantitation of 50 ng/mL. The positivity rate for propoxyphene prevalence declined sharply between November and December of 2010 and further declined at a gradual rate, ending in a prevalence of 0.27% (one out of every 370 specimens, n = 25,658) for the month of December 2011. The presented data provide evidence of the dramatic decline in the use of propoxyphene products since their removal from the medical market, and may be beneficial to US urine drug testing programs determining the need for continual monitoring of propoxyphene levels.

Oral fluid drug testing of chronic pain patients. II. Comparison of paired oral fluid and urine specimens.

A clinical study was conducted to compare the use of oral fluid to urine for compliance monitoring of pain patients. Patients (n = 133) undergoing treatment for chronic pain at four clinics participated in the study and provided paired oral fluid and urine specimens. Oral fluid specimens were collected with Quantisal(TM) saliva collection devices immediately following urine collection. Oral fluid specimens were analyzed for 42 drugs and/or metabolites by validated liquid chromatography-tandem mass spectrometry procedures. Accompanying urine specimens were initially screened by immunoassay and non-negative results were confirmed. Of the 1544 paired tests, 329 (21.3%) drug analytes were positive, and 984 (63.7%) were negative for both specimens resulting in an overall agreement of 85%. There were 83 (5.4%) analyte results that were positive in oral fluid and negative in urine, and 148 (9.6%) were negative in oral fluid and positive in urine for an overall disagreement of 15%. Cohen's Kappa value was 0.64, indicating "substantial" agreement. The primary exceptions to agreement were the lower detection rates for hydromorphone, oxymorphone, and benzodiazepines in oral fluid compared to urine. The authors conclude that, overall, oral fluid tests produced comparable results to urine tests with some minor differences in detection rates for different drug classes.

Oral fluid drug testing of chronic pain patients. I. Positive prevalence rates of licit and illicit drugs.

Oral fluid compliance monitoring of chronic pain patients is an analytical challenge because of the limited specimen volume and the number of drugs that require detection. This study evaluated oral fluid for monitoring pain patients and compared results to urine studies of similar populations. Oral fluid specimens were analyzed from 6441 pain patients from 231 pain clinics in 20 states. Specimens were screened with 14 ELISA assays and non-negative specimens were confirmed by LC-MS-MS for 40 licit and illicit drugs and metabolites. There was an 83.9% positive screening rate (n=5401) of which 98.7% (n=5329) were confirmed at ≥ LOQ concentrations for at least one analyte. The prevalence of confirmed positive drug groups was as follows: opiates > oxycodone > benzodiazepines > methadone ≈ carisoprodol > fentanyl > cannabinoids ≈ tramadol > cocaine > amphetamines ≈ propoxyphene ≈ buprenorphine > barbiturates > methamphetamine. Approximately 11.5% of the study population of pain patients apparently used one or more illicit drugs (cannabis, cocaine, methamphetamine and/or MDMA). Overall, the pattern of licit and illicit drugs and metabolites observed in oral fluid paralleled results reported earlier for urine, indicating that oral fluid is a viable option for use in compliance monitoring programs of chronic pain patients.

Urine drug testing of chronic pain patients. IV. prevalence of gabapentin and pregabalin.

Gabapentin and pregabalin are well established for the treatment of seizures and neuropathic pain. Both drugs are eliminated primarily unchanged by renal excretion. As part of an ongoing research program to improve and expand drug testing methods for compliance monitoring of pain patients, the prevalence and concentrations of gabapentin and pregabalin in urine specimens from chronic pain patients were determined by a validated liquid chromatography-tandem mass spectrometry assay. The study was approved by an Institutional Review Board. A total of 57,542 urine specimens from 231 pain clinics located in 19 states were analyzed over the period of November 24, 2009, through May 2010. The limit of quantitation (LOQ) and upper LOQ of the assays for both drugs were 2.5 and 1000 µg/mL, respectively. Gabapentin was identified in 7013 specimens (12.2% prevalence), and pregabalin was identified in 4799 patients (8.3% prevalence). Generally, gabapentin concentrations were more than twofold higher than pregabalin, consistent with their relative potencies. Interestingly, both drugs were found in specimens from 249 patients, likely representing switching of prescriptions by the prescriber.

Urine drug testing of chronic pain patients. II. Prevalence patterns of prescription opiates and metabolites.

This study of 20,089 urine specimens from chronic pain patients provided a unique opportunity to evaluate the prevalence of prescription opiates and metabolites, assess the usefulness of inclusion of normetabolites in the test panel, and compare opiate and oxycodone screening results to liquid chromatography with tandem mass spectrometry (LC-MS-MS) results. All specimens were screened by an opiate [enzyme-linked immunosorbent assay (ELISA), 100 ng/mL] and oxycodone assay [ELISA, 100 ng/mL or enzyme immunoassay (EIA), 50 ng/mL] and simultaneously tested by LC-MS-MS [limit of quantitation (LOQ) = 50 ng/mL] for 10 opiate analytes (codeine, norcodeine, morphine, hydrocodone, dihydrocodeine, norhydrocodone, hydromorphone, oxycodone, noroxycodone, and oxymorphone). Approximately two-thirds of the specimens were positive for one or more opiate analytes. The number of analytes detected in each specimen varied from 1 to 8 with 3 (34.8%) being most prevalent. Hydrocodone and oxycodone (in combination with metabolites) were most prevalent followed by morphine. Norcodeine was only infrequently detected whereas the prevalence of norhydrocodone and noroxycodone was approximately equal to the prevalence of the parent drug. A substantial number of specimens were identified that contained norhydrocodone (n = 943) or noroxycodone (n = 702) but not the parent drug, thereby establishing their interpretative value as biomarkers of parent drug use. Comparison of the two oxycodone screening assays revealed that the oxycodone ELISA had broader cross-reactivity with opiate analytes, and the oxycodone EIA was more specific for oxycodone. Specimens containing only norhydrocodone were best detected with the opiate ELISA whereas noroxycodone (only) specimens were best detected by the oxycodone EIA.

Urine drug testing of chronic pain patients. III. Normetabolites as biomarkers of synthetic opioid use.

Opioids are important therapeutic agents available to patients with moderate to severe pain. The synthetic opioids, buprenorphine, fentanyl, meperidine, methadone, and propoxyphene have been utilized for decades as analgesics. One of the major biotransformation pathways of these drugs occurs through N-demethylation leading to the formation and excretion of normetabolites. Normetabolites generally exhibit longer half-lives than the parent drug leading to accumulation with prolonged use. As part of continuing research efforts to improve monitoring programs of chronic pain patients undergoing opioid treatment, we evaluated the prevalence and relative abundance of normetabolites of buprenorphine, fentanyl, meperidine, methadone, and propoxyphene in patients? urine specimens. Selected sets of specimens were analyzed without prior immunoassay screening by liquid chromatography-tandem mass spectrometry for buprenorphine, fentanyl, meperidine, methadone, propoxyphene, and their respective normetabolites. Limits of quantitation (LOQ) were as follows: buprenorphine, 1 ng/mL; fentanyl, 0.5 ng/mL; meperidine, 50 ng/mL; methadone, 50 ng/mL; and propoxyphene, 50 ng/mL. LOQs for normetabolites were equal to the parent drug with the exception of norbuprenorphine (2.5 ng/mL). The percentage of positive specimens that contained normetabolite (only) ranged from 8.0% for EDDP (2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine) to 53.1% for norpropoxyphene. Inclusion of the five normetabolites in the test panel produced an increase in detection rates for parent drug use as follows: buprenorphine, 10.0%; fentanyl, 42.1%; meperidine, 98.7%; methadone, 8.7%; and propoxyphene, 113.2%. The authors conclude that testing for synthetic opioid normetabolites enhances the effectiveness of monitoring programs for pain patients.

Urine testing for norcodeine, norhydrocodone, and noroxycodone facilitates interpretation and reduces false negatives.

Urine drug testing of pain patients provides objective information to health specialists regarding patient compliance, diversion, and concurrent illicit drug use. Interpretation of urine test results for semi-synthetic opiates can be difficult because of complex biotransformations of parent drug to metabolites that are also available commercially and may be abused. Normetabolites such as norcodeine, norhydrocodone and noroxycodone are unique metabolites that are not available commercially. Consequently, detection of normetabolite in specimens not containing parent drug, provides conclusive evidence that the parent drug was consumed. The goal of this study was to evaluate the prevalence and patterns of the three normetabolites, norcodeine, norhydrocodone and noroxycodone, in urine specimens of pain patients treated with opiates. Urine specimens were hydrolyzed with beta-glucuronidase and analyzed by a validated liquid chromatography tandem mass spectrometry (LC/MS/MS) assay for the presence of codeine, norcodeine, morphine, hydrocodone, norhydrocodone, hydromorphone, dihydrocodeine, oxycodone, noroxycodone, and oxymorphone. The limit of quantitation (LOQ) for these analytes was 50ng/mL. The study was approved by an Institutional Review Board. Of the total specimens (N=2654) tested, 71.4% (N=1895) were positive (>or=LOQ) for one or more of the analytes. The prevalence (%) of positive results for codeine, hydrocodone and oxycodone was 1.2%, 26.1%, and 36.2%, respectively, and the prevalence of norcodeine, norhydrocodone and noroxycodone was 0.5%, 22.1%, and 31.3%, respectively. For specimens containing normetabolite, the prevalence of norcodeine, norhydrocodone and noroxycodone in the absence of parent drug was 8.6%, 7.8% and 9.4%, respectively. From one-third to two-thirds of these specimens also did not contain other metabolites that could have originated from the parent drug. Consequently, the authors conclude that inclusion of norcodeine, norhydrocodone and noroxycodone is useful in interpretation of opiate drug source and reduces potential false negatives that would occur without tests for these unique metabolites.

Urine toxicology testing in chronic pain management.

Treatment guidelines for chronic noncancer pain recommend opioids for carefully selected, closely monitored patients. However, many primary care physicians have a limited understanding of urine toxicology testing, which is the standard for monitoring opioid therapy. This article describes the technical aspects of urine toxicology testing and provides recommendations for monitoring patients to maximize the safety of opioid therapy. Articles were identified in PubMed, Medline, and EMBASE (January 1980-November 2008) using the search term opioid in combination with the terms urine toxicology, compliance monitoring, abuse, and diversion. Articles characterizing the pharmacology of individual opioids and practice guidelines for the management of chronic pain were also identified. Articles selected for inclusion discussed technical aspects of urine toxicology testing, clinical aspects of monitoring, and issues related to abuse and diversion. Urine tests can detect prescribed and illicit substances that are present above a specific threshold, but they provide limited data about the source, dose, or route of administration of substances detected. Effective monitoring requires careful test selection, an understanding of pharmacologic and metabolic factors influencing test results, and awareness of methods by which patients who are substance abusers may tamper with test specimens to escape detection. All patients prescribed opioids, not just those considered at risk for abuse, should undergo urine toxicology testing. Given its inherent complexities, effective urine testing requires close collaboration between the primary care physician and a reliable laboratory to develop an appropriate test protocol for each patient and to interpret test results.

Multiple drug ingestion by ecstasy abusers in the United States.

The abuse of ecstasy-type drugs such as 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) is generally associated with young adults attending "Rave" parties. Little toxicological information has been reported regarding ecstasy usage by individuals undergoing monitoring in other settings in the United States. The goal of this study was to determine the prevalence and patterns of licit and illicit drugs in urine specimens of ecstasy users. A survey of laboratory data over the years 2005-2007 revealed that 198 urine specimens were confirmed positive (cutoff concentration 100 ng/mL) for MDMA and/or MDA from the following types of donors ( positive specimens): Correctional (159); Sports (19); Workplace (9); Pain Patients (8); and Special Test Requests (3). Of these, 122 (61.6%) were positive for MDMA and MDA, 70 (35.4%) were positive for MDMA, and 6 (3.0%) were positive for MDA. A majority (84.3%) of the specimens contained multiple drugs and/or metabolites in addition to MDMA and MDA. The median number of drugs/metabolites reported for these ecstasy users was 5 (range, 1-9). In addition to MDMA/MDA, the most commonly identified drug groups (%) were cannabis (THCCOOH) (61.6%); amphetamine/ methamphetamine (38.4%); benzoylecgonine (30.8%); diazepam-related (9.6%); opiates (7.1%); alprazolam (5.6%); and others (5.6%). Although multidrug ingestion appears to be common amongst ecstasy users, caution is recommended in interpretation. Illicit ecstasy in the United States and Canada frequently contains methamphetamine and other active substances, and multidrug use may not have been intentional.

Normalization of urinary drug concentrations with specific gravity and creatinine.

Excessive fluid intake can substantially dilute urinary drug concentrations and result in false-negative reports for drug users. Methods for correction ("normalization") of drug/metabolite concentrations in urine have been utilized by anti-doping laboratories, pain monitoring programs, and in environmental monitoring programs to compensate for excessive hydration, but such procedures have not been used routinely in workplace, legal, and treatment settings. We evaluated two drug normalization procedures based on specific gravity and creatinine. These corrections were applied to urine specimens collected from three distinct groups (pain patients, heroin users, and marijuana/ cocaine users). Each group was unique in characteristics, study design, and dosing conditions. The results of the two normalization procedures were highly correlated (r=0.94; range, 0.78-0.99). Increases in percent positives by specific gravity and creatinine normalization were small (0.3% and -1.0%, respectively) for heroin users (normally hydrated subjects), modest (4.2-9.8%) for pain patients (unknown hydration state), and substantial (2- to 38-fold increases) for marijuana/cocaine users (excessively hydrated subjects). Despite some limitations, these normalization procedures provide alternative means of dealing with highly dilute, dilute, and concentrated urine specimens. Drug/metabolite concentration normalization by these procedures is recommended for urine testing programs, especially as a means of coping with dilute specimens.

Urine drug testing of chronic pain patients: licit and illicit drug patterns.

Chronic pain patients are frequently maintained on one or more powerful opioid medications in combination with other psychoactive medications. Urine tests provide objective information regarding patient compliance status. Little information is available on testing this unique population. The goal of this study was to characterize drug disposition patterns in urine specimens collected from a large population of pain patients. Confirmation data for 10,922 positive specimens were collated into 11 drug Classes. The number of drug/metabolites tested (#) and number of confirmed positive specimens were as follows: amphetamines (7), 160; barbiturates (5), 308; benzodiazepines (6), 2397; cannabinoids (1), 967; carisoprodol (2), 611; cocaine (1), 310; fentanyl (1), 458; meperidine (2), 58; methadone (2), 1209; opiates (7), 8996; and propoxyphene (2), 385. Subdivision into 19 distinct drug Groups allowed characterization of drug use patterns. Of the 10,922 positive specimens, 15,859 results were reported as positive in various drug Classes, and 27,197 drug/metabolites were measured by gas chromatography-mass spectrometry. The frequency of illicit drug use (cannabis, cocaine, ecstasy) was 10.8%. Being the first study of this type, these data present a large array of information on licit and illicit drug use, drug detection frequencies, drug/metabolite patterns, and multi-drug use combinations in pain patients.

Evidence that morphine is metabolized to hydromorphone but not to oxymorphone.

A minor pathway for the biotransformation of morphine to hydromorphone has been identified in humans. Recently, an unsubstantiated claim that morphine is metabolized to hydromorphone and then to oxymorphone was published. The goal of this study was to determine if credible evidence that oxymorphone is a metabolite of either morphine or hydromorphone exists. Urine specimens from pain patients who were treated exclusively with high daily doses of morphine (N = 34) or hydromorphone (N = 26) were analyzed by liquid chromatography-tandem mass spectrometry for oxymorphone, hydromorphone, and morphine (LOD = 25 ng/mL). Specimens were also tested for a variety of other medications. Criteria for inclusion of patients' specimens were as follows: 1. patients were undergoing exclusive dosing with either morphine or hydromorphone; 2. non-prescribed medications were not detected; and 3. urine concentrations of morphine were > 100,000 ng/mL for the high-dose morphine group and > 1,000 ng/mL of hydromorphone for the high-dose hydromorphone group. Consistent with earlier reports, hydromorphone was detected in patients treated with high-dose morphine. The ratio of hydromorphone to morphine ranged from 0.2 to 2.2%. Oxymorphone was not detected in any specimen from high-dose morphine or high-dose hydromorphone patients. The authors conclude, based on these data, that oxymorphone is not a metabolite of morphine or hydromorphone.

Urine pH: the effects of time and temperature after collection.

The Mandatory Guidelines for Federal Workplace Drug Testing Programs provide criteria for specimen validity testing, including urine pH cut-offs, to report a urine specimen as adulterated or invalid. Since the urine pH criteria for invalid classifications, > or = 3 and < 4.5 or > or = 9 and < 11, became effective in November 2004, a number of specimens with results within the upper invalid limits, typically in the range of 9.1 to 9.3, have been reported with no evidence of adulteration. This study evaluated the hypothesis that these pH findings were the result of exposure to increased environmental temperatures during specimen standing and transport. Indeed, increased storage temperatures were associated with increased urine pH, with the magnitude of the change related to both storage time and temperature. The pH values of specimens stored at -20 degrees C are relatively stable, whereas pH results > 9 are achieved at storage temperatures of room temperature or higher. It is noteworthy that no condition(s) produced a specimen with a pH > 9.5. Degradation of nitrogenous urine analytes is most likely responsible for the noted increases in pH. These findings are intended to supplement information used by the Medical Review Officers who are responsible for interpreting such marginally invalid pH results.

Evidence of morphine metabolism to hydromorphone in pain patients chronically treated with morphine.

Minor metabolic pathways in human subjects have been shown to exist for the conversion of codeine to hydrocodone but have not been reported for the metabolic conversion of morphine to hydromorphone. In this study, urine specimens were collected in an out-patient setting from 13 pain patients who were chronically treated with morphine and other opioids (methadone, oxycodone, and fentanyl). The chronic pain patients were chosen for study because they were treated with high-dose morphine and had no personal or family history of addiction. Results of the initial evaluation and follow up of these patients with random urine tests did not indicate opioid misuse. The specimens were analyzed by GC-MS for the presence of hydromorphone. The reporting limit for hydromorphone was 100 ng/mL. Ten of the 13 morphine-treated patients excreted hydromorphone in minor amounts ranging 120 to 1400 ng/mL. Concurrent morphine concentrations were exceedingly high in these 10 patients and frequently exceeded the upper limit of linearity (> 10,000 ng/mL) of the assay. The ratio of hydromorphone to morphine ranged from 0.015 to 0.024. Morphine concentrations in the three patients in which hydromorphone was not detected tended to be lower than those observed in other patients. For comparison, one additional patient was included in the study, who was prescribed both morphine and hydromorphone. Concentrations of hydromorphone in this patient were in the range of 3400-13,000 ng/mL, while concurrent morphine concentrations were in the range of 3200-6600 ng/mL. These data are highly suggestive that hydromorphone can be produced as a minor metabolite of morphine in humans. Although additional studies in more restricted settings are needed, it is recommended that interpretation of low urinary concentrations of hydromorphone in combination with high concentrations of morphine in morphine-treated pain patients should not be considered as conclusive evidence of hydromorphone misuse.

Oxycodone involvement in drug abuse deaths. II. Evidence for toxic multiple drug-drug interactions.

Recent surveys suggest that the abuse of drugs, often in combination, is pervasive throughout society. Adverse consequences of drug abuse tend to be attributed to the single drug "most likely" to be responsible. This is frequently seen in fatality cases, particularly those involving opioids. However, it is difficult to determine the specific cause of death when multiple drugs are involved. Although enhanced toxicity of alcohol and other centrally acting drugs with opioids has been well established in animal studies, there is a paucity of data in well-controlled human studies. We evaluated 1014 fatality cases involving oxycodone (OXC) for evidence of enhanced toxicity associated with multiple drug-drug interactions. We previously reported on these cases, and we classified them by a standardized method into groups that distinguished cases unrelated to drug abuse from those related to drug abuse, cases that involved only OXC from cases involving multiple drugs, drug-induced fatalities from drug-related fatalities, and cases in which the specific drug product OxyContin (oxycodone HCl controlled-release) Tablets were identified from cases where OxyContin was not identified. Our working hypothesis was that OXC in combination with other centrally acting drugs is more toxic than OXC alone, evidenced by the finding of lower mean blood concentrations of OXC in multiple-drug-induced deaths compared to single (OXC only)-drug-induced deaths. Assessment of blood levels determined by specific assay methodology (primarily gas chromatography-mass spectrometry) in these cases provided the following mean postmortem concentrations of OXC: multiple-drug-induced deaths, OxyContin identified, 0.93 microg/mL (N = 167); multiple-drug-induced deaths, OxyContin not identified, 0.73 microg/mL (N = 579); single (OXC)-drug-induced deaths, OxyContin identified, 1.55 microg/mL (N = 12); and single (OXC)-drug-induced deaths, OxyContin not identified, 1.70 microg/mL (N = 15). Overall, mean OXC concentration trends were as follows: single (OXC)-drug-induced, drug-abuse deaths > multiple-drug-induced drug-abuse deaths > drug-related drug-abuse deaths approximately deaths unrelated to drug abuse; and deaths in which OxyContin was identified approximately deaths in which OxyContin was not identified, whether the deaths involved oxycodone alone or multiple drugs. Drug abuse patterns in the multiple-drug-induced cases were complex. Over 135 drugs that were considered to be plausibly contributory to enhanced toxicity were identified in body fluids and tissues. Evaluation of mean OXC blood concentrations in cases that contained one, two, three, four, five, and six or more contributory drugs in combination demonstrated consistently lower mean OXC concentrations than those cases in which OXC was the only drug identified. A smaller number of cases were evaluated in the multiple-drug-induced groups in which OXC was paired with a single other contributory drug. The overall mean OXC concentration for these cases was 0.71 microg/mL (N = 90) as compared to 1.64 microg/mL (N = 27) for the cases in the single drug-induced groups. The consistent finding of lower mean OXC blood levels associated with multiple-drug-induced fatalities supports the stated hypothesis that OXC in combination with other centrally active drugs is more toxic than when OXC was the only drug involved. It was concluded that in cases of multiple-drug fatalities, cause of death (COD) should not be attributed to any single drug. Rather, the unique combination of drugs, the pattern of drug use/abuse, and individual factors, such as tolerance to the respiratory depressant effects of opioids, must be taken into account in arriving at a valid COD statement.