Quantitation of cocaine and cocaethylene in canine serum by high-performance liquid chromatography

The effect of ethanol on oral cocaine pharmacokinetics reveals an unrecognized class of ethanol-mediated drug interactions

Ethanol decreases the clearance of cocaine by inhibiting the hydrolysis of cocaine to benzoylecgonine and ecgonine methyl ester by carboxylesterases, and there is a large body of literature describing this interaction as it relates to the abuse of cocaine. In this study, we describe the effect of intravenous ethanol on the pharmacokinetics of cocaine after intravenous and oral administration in the dog. The intent is to determine the effect ethanol has on metabolic hydrolysis using cocaine metabolism as a surrogate marker of carboxylesterase activity. Five dogs were administered intravenous cocaine alone, intravenous cocaine after ethanol, oral cocaine alone, and oral cocaine after ethanol on separate study days. Cocaine, benzoylecgonine, and cocaethylene concentrations were determined by high-performance liquid chromatography. Cocaine had poor systemic bioavailability with an area under the plasma concentration-time curve that was approximately 4-fold higher after intravenous than after oral administration. The coadministration of ethanol and cocaine resulted in a 23% decrease in the clearance of intravenous cocaine and a 300% increase in the bioavailability of oral cocaine. Cocaine behaves as a high extraction drug, which undergoes first-pass metabolism in the intestines and liver that is profoundly inhibited by ethanol. We infer from these results that ethanol could inhibit the hydrolysis of other drug compounds subject to hydrolysis by carboxylesterases. Indeed, there are numerous commonly prescribed drugs with significant carboxylesterase-mediated metabolism such as enalapril, lovastatin, irinotecan, clopidogrel, prasugrel, methylphenidate, meperidine, and oseltamivir that may interact with ethanol. The clinical significance of the interaction of ethanol with specific drugs subject to carboxylesterase hydrolysis is not well recognized and has not been adequately studied.

Pharmacodynamic evaluation of the cardiovascular effects after the coadministration of cocaine and ethanol

One of the most common drug dependencies occurring with alcoholism is cocaine dependence. This combination is particularly worrisome because of the increased risk of cardiovascular events associated with their coabuse. Although it is well known that ethanol increases the cardiovascular effects of cocaine by inhibiting cocaine clearance and the formation of cocaethylene, it has also been postulated that ethanol enhances the cardiovascular effects of cocaine independent of the two latter mechanisms. In this study, we investigated the cardiovascular pharmacodynamics of the cocaine-ethanol interaction to determine whether ethanol directly enhanced the cardiovascular effects of cocaine. Dogs (n = 6) were administered cocaine alone (3 mg/kg i.v.) and in combination with ethanol (1 g/kg i.v.) on separate study days. Blood pressure, heart rate, and the electrocardiogram were monitored continuously, and blood samples were collected periodically after drug administration. Concentration-time data were fitted to a two-compartment model, and concentration-effect data were fitted to a simple E(max) model using WinNonlin software. Pharmacokinetic and pharmacodynamic parameters were compared between the two treatment phases by a paired t test. The administration of ethanol before cocaine resulted in a decrease in cocaine clearance, but there were no differences in any of the other pharmacokinetic or pharmacodynamic parameter values between the cocaine alone and cocaine plus ethanol phases. As has been demonstrated in previous animal and human studies, the clearance of cocaine was decreased by prior administration of ethanol. However, ethanol did not change the concentration-effect relationship of the cardiovascular response to cocaine administration. It is concluded from this study that ethanol does not directly enhance the cardiovascular effects of cocaine.

Separation of cocaine stereoisomers by capillary electrophoresis using sulfated cyclodextrins

A capillary electrophoretic method for the separation of cocaine and its stereoisomers was developed. In this study, the effect of organic modifier was also investigated. The separation was achieved using 1% sulfated cyclodextrin, 10 mmol L(-1) phosphate buffer, 10% methanol at pH 3. The method provides good reproducibility and easy application.

Recovery, enrichment and selectivity in liquid-phase microextraction comparison with conventional liquid-liquid extraction

Mathematical descriptions for extraction recovery and enrichment were applied for liquid-phase microextraction (LPME) and comparison with conventional two- and three-phase liquid-liquid extraction techniques (LLE) was made. The LPME theoretical calculations were verified by experimental determination of actual partition coefficients and by data obtained with LPME in a robust hollow fibre formate. With hollow fibre LPME operated in the two-phase mode, analytes were extracted from 1 to 4 ml aqueous samples into 25-50 microl of an organic solvent present in the pores and in the lumen of the porous hollow fibres. Compared with conventional two-phase LLE, two-phase LPME provided substantially higher enrichments for compounds with relatively large partition coefficients (K(org)/d>500). In contrast, because of the large volume of organic solvent relative to the sample volume, LLE provided high recovery and moderate enrichment even for compounds with relatively low partition coefficients (K(org)/d>5). Thus, two-phase LPME may be used for substantially enhanced extraction selectivity and enrichment of relatively hydrophobic analytes as compared with LLE whereas conventional two-phase LLE is superior for more hydrophilic analytes. Similar results were found for three-phase LPME where analytes where extracted from 1 to 4 ml aqueous samples through approximately 20 microl organic solvent immobilized within the pores of the hollow fibre and into 25 microl of an aqueous acceptor solution inside the lumen of the hollow fibre. The fundamental differences of LPME and LLE were further demonstrated with practical experiments on extraction of the basic drugs promethazine, methadone, and haloperidol from human plasma and urine.

High-performance liquid chromatographic determination of cocaine and its metabolites in serum microsamples with fluorimetric detection and its application to pharmacokinetics in rats

A sensitive, selective and simple HPLC method with fluorimetric detection is described for quantitating cocaine and its three metabolites in rat serum microsamples (50 microl). Chromatographic separation is achieved on a Hypersil BDS C18 column (100X2.1 mm, 5 microm) with an isocratic mobile phase consisting of methanol-acetonitrile-25.8 mM sodium acetate buffer, pH 2.6, containing 1.0 x 10(-4) M tetrabutylammonium phosphate (14:10:76, v/v/v). The detection limit (0.5 ng/ml) for all the compounds, using direct fluorometric detection operated at excitation and emission wavelengths of 230 and 315 nm, respectively, was approximately five-times lower than that of using a UV detector operated at 235 nm. The effects of ratio of 2-propanol to chloroform in extraction solvents on the recovery and precision for cocaine and its metabolites were systematically examined. The method was used to study the pharmacokinetics of cocaine after administration of intravenous 2 mg/kg and oral 20 mg/kg doses.

Cocaethylene formation in rat, dog, and human hepatic microsomes

The dog and rat are important animal models for studying the role of cocaethylene in the pharmacodynamic interaction between cocaine and ethanol. In a previous study in our laboratory it was found that a cocaine dose of 3 mg/kg IV and ethanol 1 g/kg IV failed to produce detectable concentrations of cocaethylene in the plasma of dogs. In follow up to this result, the pharmacokinetic disposition of cocaine and cocaethylene in the dog were determined to be similar. These results suggested significant differences between animal and human cocaethylene formation may occur. To test this possibility the in vitro formation of cocaethylene was determined in rat, dog and human hepatic microsomal preparations containing cocaine (0-7 mM) and ethanol (50 mM). Nonlinear least-squares regression was used to estimate Km and Vmax and the results were compared statistically. The mean +/- standard deviation for Km and Vmax in the rat, dog and human were 0.53 +/- 0.04, 0.97 +/- 0.07, and 0.56 +/- 0.08 mM, and 390 +/- 9, 233 +/- 6, and 60 +/- 3 pmol/minute/mg protein, respectively. The Km in the dog was significantly greater (p<0.05) than the Km in the rat and human. The Vmax was statistically different among all three species (rat>dog>human; p<0.05). These results demonstrate that cocaethylene formation is greater in dog than human hepatic microsomes, which is in contrast to in vivo studies that appear to show that humans produce more cocaethylene than dogs. It is suggested by the authors that route of cocaine administration may be an important factor in the formation of cocaethylene when cocaine and ethanol are co-administered.

Evaluation of dose-dependent pharmacokinetics of cocaethylene and cocaine in conscious dogs

Cocaine use continues to be widespread in the United States. Most cocaine users co-ingest ethanol resulting in decreased elimination of cocaine and formation of the active cocaine metabolite, cocaethylene, by hepatic carboxylesterases. In a recent study from our laboratory in dogs to evaluate the cocaine-ethanol interaction, we demonstrated a similar ethanol-induced reduction in cocaine metabolism, although we were unable to detect cocaethylene when the two drugs were given together. This unexpected finding could be explained by ethanol-induced inhibition of cocaine metabolism via a pathway that does not involve hepatic carboxylesterases or formation of cocaethylene that inhibits cocaine metabolism and is then rapidly cleared. The purpose of the present study is to determine which of these mechanisms best explain our data by characterizing the pharmacokinetics of cocaine and cocaethylene over a range of doses in conscious dogs. Seven adult mongrel dogs received 1, 3, and 5 mg/kg cocaine and cocaethylene HCl base with each drug dose administered i.v. on a separate study day. Arterial blood samples were collected at various times after each dose and analyzed for cocaine and cocaethylene by HPLC. Cocaine clearance was dose-dependent with clearance decreasing from 1.53 +/- 0.31 to 1.09 +/- 0.11 l/min as the dose was increased from 1 to 5 mg/kg (p<0.05). Vmax x Vss and Km for cocaine were 0.95 +/- 0.40 l/min/kg and 11.2 +/- 6.2 mg/kg, respectively. Cocaethylene pharmacokinetics were similar to those of cocaine, but were not dose-dependent over the dose range of 1-5 mg/kg. These results suggest that cocaethylene is not formed and rapidly cleared after co-administration of cocaine and ethanol to the dog, but rather suggests that cocaethylene is not formed in appreciable quantities in the dog. Therefore, we conclude that the decrease in cocaine elimination in the dog associated with ethanol administration is due to ethanol-mediated inhibition cocaine metabolism, rather than inhibition by cocaethylene.

Sensitive and specific high-performance liquid chromatographic assay with ultraviolet detection for the determination of cocaine and its metabolites in rat plasma

A sensitive, specific and precise HPLC-UV assay was developed to quantitate cocaine (COC) and its metabolites benzoylecgonine (BE), norcocaine (NC) and cocaethylene (CE) in rat plasma. After adding 50 microl of the internal standard solution (bupivacaine, 8 microg/ml) and 500 microl of Sørensen's buffer (pH 6) to 100 microl of rat plasma sample, the mixture was extracted with 10 ml of chloroform. The organic layer was transferred to a clean test tube and was evaporated under nitrogen. The residue was reconstituted in 100 microl of mobile phase and 35 microl was injected onto the HPLC column. The mobile phase consisted of methanol-acetonitrile-50 mM monobasic ammonium phosphate (5:7:63, v/v/v) and was maintained at a flow-rate of 0.4 ml/min. Separation of COC and its metabolites was achieved using a Supelcosil ABZ+plus deactivated reversed-phase column (250x2.1 mm I.D., 5 microm). Calibration curves were linear over the range of 25-5000 ng/ml for COC and its three metabolites. The absolute extraction efficiencies for BE, COC, NC, CE and bupivacaine were 56.6%, 78.6%, 61.1%, 76.4% and 67.0%, respectively. COC and its metabolites were stable in mobile phase for 24 h at room temperature and in rat plasma for 2 weeks at -20degrees C. The limits of detection for BE, COC, NC and CE were 20, 24, 15 and 12.9 ng/ml, respectively. These values correspond to 0.70, 0.84, 0.525 and 0.452 ng of the according compound being injected on column. The within-day coefficient of variation for the four compounds ranged from 3.0% to 9.9% while the between-day precision varied from 3.6% to 14%. This method was used to analyze rat plasma samples after administration of COC alone and in combination with alcohol. The pharmacokinetic profiles of COC and its metabolites in these rats are also described.