Forensic Drug Profile: Cocaethylene

Abstract

Introduction

Drug profiles represent a useful source of information when forensic toxicologists write expert opinions or prepare affidavits in various drug-related crimes and overdose deaths. A good drug profile should provide information about the pharmacokinetic and pharmacodynamic properties of the drug. It should also report the concentrations of active substance in blood after therapeutic, recreational doses and in fatalities. However, reading a drug profile should not substitute for retrieval of original articles from peer reviewed journals that give additional information about disposition and fate in the body of the drug of interest.

Drug-related crimes are a worldwide problem, including drunk and drugged driving (1), drug facilitated sexual assaults (2) and drug poisoning deaths (3). My involvement in a recent criminal trial involving the co-ingestion of large doses of ethanol and cocaine led me to look at a number of reference books in forensic toxicology. These included Disposition of Toxic Drugs and Chemicals in Man (11th edition), which contains a wealth of information about cocaine, although a drug profile or monograph dedicated to CE was lacking (4).

Another widely used reference source, Clarke’s Analysis of Drugs and Poisons (fourth edition) did not contain any information about CE (5). The chapter devoted to cocaine in the fourth edition of the book Principles of Forensic Toxicology mentions formation of CE, but there were no references given to articles published in scientific journals (6). Likewise, a drug fact sheet about the behavioral effects of cocaine was included in a book published by the US National Highway Traffic Safety Administration, although this contained little useful information about CE (7). This lack of easily available information about CE, which is a pharmacologically active and toxic metabolite of cocaine, prompted me to write this forensic toxicology drug profile.

What is cocaethylene?

Cocaine was extracted from Erythroxylum coca in 1860 (8) by Albert Niemann (1834–1861) and its chemical structure was elucidated by Richard Willstätter (1872–1942) as part of his doctoral thesis on tropane alkaloids done at the University of Munich in 1894 (9, 10). According to the MERCK index (13th edition) cocaethylene was first prepared in 1885, but its pharmacological properties were probably not thoroughly investigated, because cocaine was available in large quantities from coca leaves. Soon after the extraction and purification of cocaine, its local anesthetic and stimulant properties were discovered and this natural product became a major recreational drug of abuse worldwide (11).

Cocaine is often identified in blood and other biological specimens from impaired drivers (12), poisoned patients (13) and medical examiner cases (14). The principal metabolites of cocaine of most interest in forensic toxicology are benzoylecgonine (BZE) and ecgonine methyl ester (EME), which are determined in blood (15) and excreted in urine, BZE being the target analyte for screening analysis (16). Another minor and pharmacologically active metabolite of cocaine is formed by the action of hepatic P450 enzymes causing N-demethylation of the tertiary amine group to give norcocaine (6).

A targeted analysis of CE should be considered whenever forensic blood samples are positive for both cocaine and ethanol. CE is a novel metabolite formed in a transesterification reaction between ethanol and cocaine and catalyzed by the action of hepatic carboxyl-estrase enzymes (17, 18). Hence, the methyl carboxylic ester of BZE (cocaine) is converted into the ethyl carboxylic ester of BZE, which is cocaethylene (19).

The chemical structures of cocaine (mol. wt. 303.4) and CE (mol. wt. 317.4) and the biosynthesis of CE are shown in Figure 1. CE is not a drug of abuse per se, but is formed in the liver when a person drinks alcohol and also ingests cocaine (20, 21).

Figure 1.

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Formation of cocaethylene in transesterification reaction between ethanol and cocaine catalyzed by liver carboxylesterases.

Figure 1.

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Formation of cocaethylene in transesterification reaction between ethanol and cocaine catalyzed by liver carboxylesterases.

Discovery of cocaethylene

A search of PUBMED for cocaethylene shows the first reference appeared in 1990 to a news item entitled Miami vice metabolite published in the journal SCIENCE (22). This focused on investigations of cocaine-related deaths done at the Dade County Medical Examiner’s Office in Miami. During gas chromatographic-mass spectrometric (GC–MS) analysis, forensic toxicologist Lee Hearn PhD saw a prominent peak on the mass chromatograms with molecular ion m/z 317, which eluted from the GC column shortly after cocaine m/z 303 (20). This unexpected mass fragment (m/z 317) twigged Hearn’s interest, especially when he noticed that it was more prevalent when the deceased also had elevated blood ethanol concentration (23). Further investigation of the fragmentation pattern of the unknown peak suggested it was CE and this was later confirmed by synthesis from ecgonine and comparing the full spectrum with authentic CE standard provided by the US Drug Enforcement Agency.

The same investigators from Miami showed that CE was rapidly formed when liver homogenates were incubated with ethanol and cocaine (20). This line of research was extended by Jatlow et al. (24), who confirmed that CE was not an artifact produced during the work-up of specimens. To drug-free blood they added both ethanol and cocaine and no CE was formed when the mixture was incubated 37°C. Neither was CE produced when the incubation mixture were acidified (pH 1–2) to simulate conditions existing in the stomach.

Since these first reports, the pharmacology and toxicology of CE have been studied extensively including its cardiovascular effects and stimulant properties (25, 26). It appears that CE and cocaine are equipotent in blocking the reuptake of dopamine at synapses, which is the mechanism mainly responsible for the pleasurable, addictive and reinforcing effects of the two drugs (27).

Analytical methods

The close similarity in chemical structure and physicochemical properties of cocaine and CE (see Figure 1) means that the two drugs are co-extracted from biological media, either by shaking with organic solvents or the use of solid-phase extraction columns (28). Both drugs have been identified and quantified in a wide variety of biological specimen types, including blood, oral fluid, meconium, plasma, urine and hair strands (29).

The GC and MS methods currently available in forensic toxicology laboratories are applicable to the analysis of CE, cocaine and their metabolites (30). Neither cocaine nor CE require any prior derivatization before GC or GC–MS analysis, although this is necessary for BZE and EME to ensure sharp chromatographic peaks without appreciable tailing (31). Deuterium labeled analogs are available as internal standards when mass spectrometry is used for analysis of cocaine, CE and their metabolites.

GC with NPD detection, GC–MS and LC–MS methods have all been used for the analysis of cocaine and CE in biological specimens (32). More popular today are LC–MS methods or some hyphenated technique, such as LC–MS-MS, because derivatization is unnecessary (29). A recent article reported a GC ion-trap mass spectrometric method for analysis of cocaine, CE and their metabolites (33).

Pharmacokinetics

Cocaine can be administered in various ways, but for recreational purposes the drug is mostly taken by snorting or sniffing into a nostril (insufflation), which facilitates absorption into the bloodstream through the mucous membranes of the nasal cavity (34). Compared with most drugs encountered in forensic toxicology, cocaine has a short plasma elimination half-life (t½) of ~1 h (35). Accordingly, after six x t½ (6 h) only trace amounts of the parent drug should be detectable in forensic blood samples (36). Like cocaine, CE is metabolized to BZE and it also undergoes N-demethylation to the normetabolite, norcocaethylene (37).

After intravenous (i.v.) administration of CE (0.25 mg/kg) the mean (±SE) plasma elimination half-life was 1.68 ± 0.11 h compared with 1.07 ± 0.09 h for the same dose of cocaine (38). In the same study, the difference in mean ± SE peak concentration of cocaine in plasma (0.170 ± 0.024 mg/L) and CE (0.159 ± 0.030 mg/L) was not statistically significant (P > 0.05). Areas under the concentration (AUC) time profiles of cocaine and CE (0–60 min post-dosing) were also similar; AUC for cocaine was 6.2 ± 0.953 mg x h/L compared with 6.8 ± 0.792 mg x h/L for CE (P > 0.05).

In another human study, 0.25 mg/kg of cocaine or CE were given intravenously and the resulting peak concentrations in plasma were 0.195 mg/L and 0.160 mg/L, respectively (P > 0.05) (39). After doubling the doses of each drug to 0.50 mg/kg, the corresponding C_max in plasma was 0.444 mg/L for cocaine and 0.329 mg/L for CE (P > 0.05). After these two doses, mean elimination half-lives of CE from plasma were 2.48 h (0.25 mg/kg) and 2.43 h (0.50 mg/kg) compared with a mean of 1.51 h and 1.45 h for cocaine.

When deuterated-cocaine (d₅) was given orally (2.0 mg/kg), i.v. (1.0 mg/kg) or by smoking (0.2 mg/kg) to six volunteers, who also drank ethanol (1.0 g/kg), the elimination half-lives of cocaine (CE) were 1.8 h (2.3 h), 1.5 h (2.7 h) and 1.0 h (2.5 h), respectively (40). The amount of cocaine converted to CE depended on the route of administration, being 34 ± 20% (oral), 24 ± 11% (i.v.) and 18 ± 11% (smoking).

In a double-blind crossover design study 10 volunteer subjects drank ethanol (1.0 g/kg) and one hour later received either 0.30, 0.60 or 1.2 mg/kg d₅-cocaine by constant rate i.v. infusion over 15 min (41). As expected, the peak plasma concentrations of cocaine and CE and AUCs increased proportionally with increasing dose of cocaine. The plasma elimination half-lives of CE and cocaine were independent of the dose, but were ~1 h longer for CE. Furthermore, plasma peak C_max for CE was about 15 times lower than C_max for cocaine for each dose administered. This study found that 17 ± 6% of the dose of cocaine was converted into CE. It was also observed that ingestion of ethanol prior to cocaine administration decreased urine BZE levels by 48% and increased urinary CE and EME levels.

The longer elimination half-life of CE means that it is detectable in blood or plasma for a few hours longer than the parent drug cocaine, but not as long as BZE (t½ ~5 h) (42). BZE is the target analyte for drug screening in routine casework and when proof of cocaine intake is required (15, 30). However, it is not possible to draw conclusions about the impairment effects of drugs or time of last use from the concentrations determined in urine. Unlike CE, BZE is not a psychoactive metabolite of cocaine and should therefore not contribute to pharmacological or toxic manifestations of cocaine misuse (42).

Pharmacodynamics

There is general agreement that the psychoactive stimulant effects of cocaine and CE are mediated via dopaminergic neurons in the nucleus accumbens (11, 43). Both drugs work by blocking the reuptake of dopamine and thereby increasing post-synaptic neuronal activity (25). This stimulates brain activity making people more energetic, mentally alert, excited, and gives feelings of ‘being high’. And in this respect, CE and cocaine appear to be equipotent as central stimulants (44). Because the plasma elimination half-life of CE is longer than cocaine, this helps to prolong the pleasurable dopaminergic effects, which might explain why cocaine addicts often consume alcohol when they misuse cocaine (45). One study found that CE was a more potent blocker of cardiac sodium channels than cocaine, which might exacerbate the adverse cardiovascular effects of cocaine (46).

After six volunteer subjects snorted cocaine (2 mg/kg) and immediately afterwards drank ethanol (1 g/kg), the cocaine-induced euphoria was more enhanced and prolonged compared with the same dose of cocaine and placebo (47). Furthermore, heartbeat was significantly faster in the ethanol and cocaine arm of the study.

Feelings of ‘high’ and effects on cardiovascular parameters were measured in six male subjects who received either cocaine (0.25 mg/kg) or CE (0.25 mg/kg) as an intravenous bolus injection (38). For the first two hours post-dosing, both the cocaine ‘high’ as well drug-induced effects on heart rate and blood pressure were lower after CE compared with an equivalent dose of cocaine.

Cocaine exerts powerfully reinforcing effects after chronic use, which leads to physiological and psychological dependence. Many people exhibit drug-seeking behavior and accordingly they tend to relapse after a period of abstinence (43). There is no effective pharmacotherapy for treatment of cocaine addiction, although this is an active and ongoing area of research (48).

Blood concentrations of CE

The concentrations of CE in blood after the co-ingestion of alcohol and cocaine are difficult to predict, because much depends on amount of precursor drugs ingested and the order and timing of administration. Without drinking any alcohol there should be no measurable CE in blood after use of cocaine. However, there are situations when CE might be measurable in blood after the concentration of ethanol has dropped below the usual analytical cut-off of 0.01 g% used in many laboratories.

The order of administration of the precursor drugs is also an important consideration, for example if ethanol was consumed several hours before or after ingestion of cocaine. The formation of CE is probably more favorable with a pre-existing high blood–ethanol concentration when the person starts to take cocaine. This follows because of cocaine’s relatively short elimination half-life from plasma of ~1 h, so that concentrations might be insignificant when a person drinks ethanol. With low concentrations of cocaine in blood there should not be much CE produced, regardless of the amount of alcohol consumed (49). This makes it difficult to predict, in any individual case, the concentration of CE in biological specimens analyzed in clinical and forensic cases.

The roughly one hour longer plasma elimination half-life of CE compared with cocaine means that the latter could be reported as ‘negative’ or ‘not detected’ when CE was still measurable in body fluids. This would nevertheless verify that a person had earlier ingested both ethanol and cocaine.

CE was first identified in autopsy blood at concentrations ranging from 0.05 mg/L to 0.31 mg/L when co-existing cocaine concentrations were from < LLOQ to 4.03 mg/L and blood-ethanol cases was 0.03–0.46 g% (20). In a later report, from the same laboratory, the concentrations of CE in postmortem bloods (N = 6) ranged from 0.03 mg/L to 0.55 mg/L when cocaine ranged from 0.03 mg/L to 1.4 mg/L and blood–ethanol was 0.01–0.10 g% (32).

In 62 medical examiner cases, the mean concentrations of cocaine, CE and ethanol in blood and vitreous humor (VH) were not significantly different (50). However, the concentrations of CE in both blood and VH were about 20 times lower than the concentrations of cocaine. In another report of seven cocaine-related deaths, the mean (range) of CE concentrations were 0.348 mg/L (0.073–1.45), compared with 0.758 mg/L (0.034–4.37) for cocaine and 0.12 g% (0.02–0.24) for blood–ethanol (24).

In 41 hospital admissions, mainly trauma patients, with elevated blood–ethanol (mean 0.168 g%) the mean cocaine and CE concentrations in blood were 0.117 mg/L and 0.112 mg/L, respectively (51). In drug-positive emergency patients, 28 individuals had cocaine, CE and ethanol in plasma at mean concentrations (range) of 0.0862 mg/L(0–0.335) for cocaine, 0.0584 mg/L(0–0.250) for CE and 0.12 g% (0.005–0.31) for ethanol (52). In this same study, cocaine and CE concentrations were highly correlated (r = 69), but no correlation was found between CE and ethanol (r = −0.078).

In 68 urban trauma patients CE was identified in plasma at mean ± SE (range) of concentrations of 0.041 ± 0.027 mg/L (0.003–0.213 mg/L). All patients were also positive for cocaine at a mean (range) of concentration in plasma of 0.093 ± 0.052 mg/L (0.004–0.699 mg/L). Ethanol was reported positive in 56% of the patients at a mean (range) of concentrations of 0.175 ± 0.085 g% (0.012–0.37 g%). The correlation of cocaine and CE levels in plasma in this study was low and insignificant (53).

The concentration–time profiles of CE and cocaine were determined after six healthy men drank ethanol (1.0 g/kg) before they snorted cocaine (2 mg/kg) (54). In the ethanol–cocaine arm of the study, the mean concentration of cocaine in plasma was 0.366 mg/L, being appreciable higher than CE, which reached a maximum of 0.062 mg/L and plasma ethanol averaged 0.113 g%.

After eight volunteers snorted 100 mg cocaine and also drank ethanol (0.8 g/kg), the mean peak plasma CE concentration was 0.049 mg/L compared with 0.331 mg/L for cocaine. In this same study, the average concentration of ethanol in plasma was 0.1 g% (55).

After taking single recreational doses of cocaine and ethanol, the concentration of CE in blood or plasma is considerably lower than cocaine (55). But in real world situations, much will depend on the order, timing and the doses of the two precursor drugs. After repetitive binge use of cocaine, the concentration of CE in blood will tend to accumulate, owing to its longer plasma elimination half-life. Under these circumstances one can expect higher CE concentrations when a person ingests a new dose of cocaine, depending on the amount taken (56).

Toxicity

Because both CE and cocaine are pharmacologically active substances, a strong case can be made for adding together the blood or plasma concentrations of the two substances when toxicological results are interpreted in routine casework. The sum of the cocaine and CE concentrations should provide a more reliable indication of intensity of drug-effects on human performance and behavior and the risk of toxicity and overdose death (57).

Studies in mice showed that lethality of CE, as determined by its LD50, surpassed cocaine and both drugs were more toxic than ethanol (58). The LD50 of CE in Long-Evans rats was 96 mg/kg for females compared with 70 mg/kg for males (59). However, the LD50 also depended on the particular strain of rats tested. The general finding from animal studies indicates that CE is potentially more dangerous than cocaine in mediating lethality (lower LD50), In Swiss-Webster mice the LD50 was 62 mg/kg for CE compared with 93 mg/kg for cocaine (23).

Both cocaine and CE are powerful stimulants of the central nervous system (CNS) acting via dopaminergic neurons, leading to hypertension, increased heartbeat and an elevated body temperature, which probably exaggerates the risk for cardiotoxicity (60). Anecdotal evidence suggests that chronic cocaine users can manifest in excited delirium and drug-induced convulsions (61).

The findings at autopsy in cocaine intoxication deaths are generally similar to other CNS stimulants, such as amphetamine or methamphetamine (62, 63). This includes cerebral hemorrhage, stroke or other adverse cardiovascular events (64, 65). Misuse of cocaine also disrupts the body’s thermoregulation, which can lead to fatalities from hyperthermia, especially when the drug is misused in a hot climate and at higher environmental temperature (66).

Concluding remarks

CE is a pharmacologically active metabolite of cocaine formed in the body when a person drinks alcohol and also ingests cocaine. The concentration of CE produced is difficult to predict, because it will depended on the dose of each precursor drug and the timing of administration of each (40). Both cocaine and CE stimulate the CNS and augment the feelings of high elicited by cocaine. Because acute toxicity of cocaine is enhanced in the presence of CE, the concentrations of the two drugs should be added together when effects on performance and behavior and risk of intoxication and death are considered. The role played by CE in acute poisonings associated with cocaine misuse should not be underestimated. Whenever forensic blood samples are positive for both ethanol and cocaine a dedicated quantitative determination of the amount of CE present is recommended and the concentration reported alongside other drugs to aid in making a correct interpretation.

References