A validated stable isotope dilution liquid chromatography tandem mass spectrometry assay for the trace analysis of cocaine and its major metabolites in plasma

Rapid Separation and Quantitation of Cocaine and its Metabolites in Human Serum by Differential Mobility Spectrometry-tandem Mass Spectrometry (DMS-MS-MS)

Cocaine continues to be one of the most widespread abused illicit drugs in the USA. Rapid methods are needed for the identification and quantitation of cocaine and its metabolites, benzoylecgonine (BE), ecgonine methyl ester (EME) and cocaethylene (CE), in biological specimens by clinical and forensic toxicology laboratories. Presented is a differential ion mobility spectrometry-tandem mass spectrometry (DMS-MS-MS) method for the analysis of cocaine and its major metabolites in human serum that requires minimal sample preparation and no column chromatography. A Shimadzu Nexera X2 ultra-high performance liquid chromatography system was used to infuse the samples into the DMS cell at a rate of 30 μL/min. Separation of cocaine and its metabolites were performed in a SelexION DMS component from Sciex coupled to a QTRAP 6500 with an IonDrive Turbo V source for TurbolonSpray® using acetonitrile as a chemical modifier. Analysis consisted of ramping the CoV from -35 V to -6 V while monitoring the multiple reaction monitoring (MRM) transitions of each analyte. The assay was evaluated for linearity, bias, precision, carryover, interferences and stability. Calibration curves ranged from 10 to 1,000 ng/mL with linear regression correlation coefficients (r2) of 0.9912 or greater for each analyte. The limit of quantitation was set at 10 ng/mL. Intra-day precision (%CV) ranged from 0% to 15% for cocaine, 1% to 19% for BE, 1% to 17% for EME and 0% to 18% for CE. Inter-day precision ranged from 9% to 14% for cocaine, 2% to 17% for BE, 5% to 11% for EME and 5% to 15% for CE. No carryover or interferences were detected. Bland-Altman analysis of previously analyzed specimens by UPLC-MS-MS showed variability of 30% or less. The method demonstrates the applicability of DMS-MS-MS for high throughout analysis of drugs and their metabolites in clinical and forensic toxicology laboratories.

Rapid and on-site analysis of illegal drugs on the nano-microscale using a deep ultraviolet-visible reflected optical fiber sensor

A deep ultraviolet-visible (DUV-Vis) reflected optical fiber sensor was developed for use in a simple spectrophotometric detection system to detect the absorption of various illegal drugs at wavelengths between 180 and 800 nm. Quantitative analyses performed using the sensor revealed a high specificity and sensitivity for drug detection at a wavelength of approximately 200 nm. Using a double-absorption optical path length, extremely small sample volumes were used (32 to 160 nL), which allowed the use of minimal amounts of samples. A portable spectrophotometric system was established based on our optical fiber sensor for the on-site determination and quantitative analysis of common illegal drugs, such as 3,4-methylenedioxymethamphetamine (MDMA), ketamine hydrochloride, cocaine hydrochloride, diazepam, phenobarbital, and barbital. By analyzing the absorbance spectra, six different drugs were quantified at concentrations that ranged from 0.1 to 1000 μg mL(-1) (16 pg-0.16 μg). A novel Matching Algorithm of Spectra Space (MASS) was used to accurately distinguish between each drug in a mixture. As an important supplement to traditional methods, such as mass spectrometry or chromatography, our optical fiber sensor offers rapid and low-cost on-site detection using trace amounts of sample. This rapid and accurate analytical method has wide-ranging applications in forensic science, law enforcement, and medicine.

Quantification of influenza virus hemagglutinins in complex mixtures using isotope dilution tandem mass spectrometry

Influenza vaccination is the primary method for preventing influenza and its severe complications. Licensed inactivated vaccines for seasonal or pandemic influenza are formulated to contain a preset amount of hemagglutinin (HA), the critical antigen to elicit protection. Current methods to establish the HA concentration of vaccines rely on indirect measurements that are subject to considerable experimental variability. We present a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for the absolute quantification of viral proteins in a complex mixture. Through use of an isotope dilution approach, HA from viral subtypes H1, H3, H5, and B was determined both directly and rapidly. This method can be applied to purified virus preparations, to monovalent bulk concentrates, or to trivalent inactivated influenza vaccines with improved speed, sensitivity, precision, and accuracy. This LC/MS/MS approach may substantially increase the reliability of methods used to quantitate the amount of antigen in seasonal and pandemic influenza vaccines and reduce the time and effort to deliver influenza vaccines for public health use during the next influenza pandemic.

Quantitative analysis of cocaine and its metabolites in whole blood and urine by high-performance liquid chromatography coupled with tandem mass spectrometry

AIM

In forensic toxicology it is important to have specific and sensitive analysis for quantification of illicit drugs in biological matrices. This paper describes a quantitative method for determination of cocaine and its major metabolites (ecgonine methyl ester, benzoylecgonine, norcocaine and ethylene cocaine) in whole blood and urine by liquid chromatography coupled with tandem mass spectrometry LC/MS/MS.

METHOD

The sample pre-treatment (0.20 g) consisted of acid precipitation, followed by centrifugation and solid phase extraction of supernatant using mixed mode sorbent columns (SPEC MP1 Ansys Diag. Inc.). Chromatographic separation was performed at 30 degrees C on a reverse phase Zorbax C18 column with a gradient system consisting of formic acid, water and acetonitrile. The analysis was performed by positive electrospray ionisation with a triple quadropole mass spectrometer operating in multiple reaction monitoring (MRM) mode. Two MRM transitions of each analyte were established and identification criteria were set up based on the retention time and the ion ratio. The quantification was performed using deuterated internal analytes of cocaine, benzoylecgonine and ecgonine methyl ester. The calibration curves of extracted standards were linear over a working range of 0.001-2.00 mg/kg whole blood for all analytes. The limit of quantification was 0.008 mg/kg; the interday precision (measured by relative standard deviation-%RSD) was less than 10% and the accuracy (BIAS) less than 12% for all analytes in whole blood. Urine samples were estimated semi-quantitatively at a cut-off level of 0.15 mg/kg with an interday precision of 15%.

CONCLUSION

A liquid chromatography mass spectrometric (LC/MS/MS) method has been developed for confirmation and quantification of cocaine and its metabolites (ecgonine methyl ester, benzoylecgonine, norcocaine and ethylene cocaine) in whole blood and semi-quantitative in urine. The method is specific and sensitive and offers thereby an excellent alternative to other methods such as GC-MS that involves derivatisation.

Using environmental analytical data to estimate levels of community consumption of illicit drugs and abused pharmaceuticals

A solid phase extraction (SPE) method has been developed and applied in conjunction with a previously reported liquid chromatography tandem mass spectrometry (LC-MS-MS) procedure for the determination of illicit drugs and abused pharmaceuticals in treated wastewater and surface water samples at the ng L(-1) level. A full method validation was also performed and determined levels of analytical sensitivity were found to lie in the 1-10 ng L(-1) range using river water as a test sample matrix and a sample size of 500 mL. The developed procedure was successfully applied for the determination of the chosen analytes in wastewater treatment plants in Dublin, Ireland and rapidly expanding commuter towns in the surrounding counties. Cocaine was detected in 70% of the collected samples in the range of 25-489 ng L(-1), its primary metabolite, benzoylecognine (BZE) was also detected in the range of 22-290 ng L(-1). Other substances detected included morphine, Tempazepam and the primary metabolite of methadone.

Determination of the platinum drug cis-amminedichloro(2-methylpyridine)platinum(II) in human urine by liquid chromatography-tandem mass spectrometry

A validated stable isotope dilution liquid chromatography-tandem mass spectrometry assay for the novel platinum drug cis-amminedichloro(2-methylpyridine)platinum(II) (ZD0473) in human urine has been developed. This method uses selected reaction monitoring on the transition of m/z 393 [M+NH(4)](+) to m/z 304 [M+NH(4)-NH(3)-2 x H(35)Cl](+) for ZD0473, and m/z 400 [M+NH(4)](+) to m/z 310 [M+NH(4)-NH(3)-H(35)Cl-(2)H(35)Cl](+) for the internal standard [(2)H(7)]ZD0473. Standard curves were prepared over the range from 0.15 to 50 microg/ml. The lower limit of quantitation was 0.2 microg/ml for 100 microl of urine. This simple, rapid, reliable, and sensitive method of quantitation displayed acceptable accuracy and precision over the 3 days of assay validation. A novel platinum adduct was formed during the storage of ZD0473 in human urine. The adduct did not correspond to any of the typical sulfhydryl adducts that have been identified previously for platinum drugs. Formation of the adduct was prevented by the addition of 50% (w/v) sodium chloride to the urine. The assay can be used to quantify intact ZD0473 in the urine of subjects dosed with this new platinum drug.

Radiometric solvent-partitioning assay for screening cocaine hydrolases and measuring cocaine levels in milligram tissue samples

To permit rapid screening and characterization of novel cocaine hydrolases, as well as accurate measurement of cocaine levels in small samples of tissue, a radiometric assay was developed. The assay is based on selective, organic solvent partition of [3H]benzene-labeled cocaine or of [3H]benzoic acid liberated during enzymatic hydrolysis. With dilute samples the assay can be conducted entirely in scintillation vials and quantitated by addition of appropriate aqueous buffer and toluene-based fluor, making phase separation unnecessary. In this way, several hundred samples can be assayed in an afternoon, nanogram quantities of enzyme can be characterized without prior purification, and cocaine concentrations can be accurately measured in milligram samples of tissue after administration of [3H]cocaine in vivo.

Cocaine metabolism accelerated by a re-engineered human butyrylcholinesterase

Plasma butyrylcholinesterase (BChE) is important in the metabolism of cocaine, but natural human BChE has limited therapeutic potential for detoxication because of low catalytic efficiency with cocaine. Here we report pharmacokinetics of cocaine in rats treated with A328W/Y332A BChE, an excellent cocaine hydrolase designed with the aid of molecular modeling. Compared with wild-type BChE, this enzyme hydrolyzes cocaine with 40-fold improved k(cat) (154 min(-1) versus 4.1 min(-1)) and only slightly increased K(M) (18 microM versus 4.5 microM). In rats given this hydrolase (3 mg/kg i.v.) 10 min before cocaine challenge (6.8 mg/kg i.v.), cocaine half-life was reduced from 52 min to 18 min. Mirroring the reductions of plasma cocaine were large increases in benzoic acid, a product of BChE-mediated cocaine hydrolysis. All other pharmacokinetic parameters confirmed a large, dose-dependent acceleration of cocaine removal by the injected cocaine hydrolase. These results show that A328W/Y332A, an efficient cocaine hydrolase in vivo as well as in vitro, might promote cocaine detoxication in a clinical setting.

Progress of liquid chromatography-mass spectrometry in clinical and forensic toxicology

The use of liquid chromatography-mass spectrometry (LC-MS) has recently exploded in various analytic fields, including toxicology and therapeutic drug monitoring (although still far behind pharmacokinetics). There is no doubt that LC-MS is currently competing with gas chromatography (GC)-MS for the status of the reference analytic technique in toxicology. This review presents, for the nonspecialist reader, the principles, advantages, and drawbacks of LC-MS systems using atmospheric pressure interfaces. It also gives an overview of the analytic methods for xenobiotics that could be set up with these instruments for clinical or forensic toxicology. In particular, as far as quantitative techniques are concerned, this review tries to underline the large number and variety of drugs or classes of drugs (drugs of abuse, therapeutic drugs) or toxic compounds (e.g., pesticides) that can be readily determined using such instruments, the respective merits of the different ionization sources, and the improvements brought about by tandem MS. It also discusses new applications of LC-MS in the field of toxicology, such as "general unknown" screening procedures and mass spectral libraries using LC-atmospheric pressure ionization (API)-MS or MS-MS, presenting the different solutions proposed to overcome the naturally low fragmentation power of API sources. Finally, the opportunities afforded by the most recent or proposed instrument designs are addressed.

A validated liquid chromatography/tandem mass spectrometry assay for cis-amminedichloro(2-methylpyridine)platinum(II) in human plasma ultrafiltrate

The clinical use of platinum drugs as anticancer agents has encountered problems when relating pharmacokinetic profiles with efficacy and toxicity is attempted. This has been mainly due to the lack of specific and sensitive analytical methodology to examine concentrations of the unbound drug in plasma. The presence of a carbocyclic ring on the new drug, cis-amminedichloro(2-methylpyridine)platinum(II) (ZD0473) suggested that it would be possible to develop the first stable isotope dilution LC/MS assay for a platinum drug in human plasma ultrafiltrate samples. The dichloro form of the drug exists in equilibrium with at least two aquated forms in plasma. The molecular form of the drug, therefore, depends on the length of time that the plasma sample is maintained at room temperature before freezing. Therefore, we have developed a method that quantitatively converts the aquated species back to the dichloro form of the parent drug so that a single molecular species can be analyzed. Selected reaction monitoring was performed on the transition of m/z 393 [M + NH4]+ to m/z 304 [M + NH4 -NH3 - 2 x HCl]- for ZD0473, and m/z 400 [M + NH4]+ to m/z 310 [M + NH4 - NH3 - HCl - 2HCl]+ for [2H7]ZD0473. The standard curves were fitted to a quadratic regression over the range from 10 to 5000 ng/mL in human plasma ultrafiltrate. The lower limit of quantitation for ZD0473 was 10 ng/mL for 100 microL of plasma ultrafiltrate. This simple, rapid, reliable, and sensitive method of quantitation had excellent accuracy and precision. The method provided adequate sensitivity for the analysis of plasma ultrafiltrate samples from a phase II study in which ZD0473 was administered to patients as an intravenous infusion at a dose of 150 mg/m2.

Analysis of peptides using partial (no discharge) atmospheric pressure chemical ionization conditions with ion trap mass spectrometry

A novel approach, based on the use of atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-ITMS) conditions, but without using corona discharge, was used to analyze peptides. The proposed method was applied to three standard peptides (bombesin, trityrosine and tyrosine-glycine-glycine) as well as peptides obtained through enzymatic digestion of two standard proteins (horse cytochrome c and horse myoglobin).

Analysis of protein ions in the range 3000-12000 Th under partial (no discharge) atmospheric pressure chemical ionization conditions using ion trap mass spectrometry

A new approach, based on the use of atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-ITMS), but without a corona discharge, was investigated for application to creating and monitoring protein ions. It must be emphasized that APCI is not usually used in protein analysis. In order to verify the applicability of the proposed method to the analysis of proteins, two standard proteins (horse cytochrome c and horse myoglobin) were analyzed. A mixture of the two proteins was also analyzed showing that this novel approach, based on the use of APCI, can be used in the analysis of protein mixtures.

Methodology for the development of a drug library based upon collision-induced fragmentation for the identification of toxicologically relevant drugs in plasma samples

The possibility of creating a robust mass spectral library with use of high-performance liquid chromatography-atmospheric pressure-electrospray ionization (HPLC-AP-ESI) for the identification of drugs misused in cases of clinical toxicology has been examined. Factors reported as influencing the fragmentation induced by "source transport region collision induced dissociation" (CID) have been tested in this study (i.e. solvent, pH, different acids or buffer salts and their concentration, different organic modifiers and the modifier concentration). The tests performed on a few "model drugs" were analysed with use of two different single quadrupole instruments. The large number of mass spectra obtained appears to be affected by the mobile phase conditions to only a minor extent. This also holds for the mass spectra obtained at two different instruments (laboratories). Subsequently breakdown curves have been measured for about 20 randomly chosen drugs by variation of the kinetic energy of their ions in the CID zone through changing the fragmenter voltage. These breakdown curves were used to optimize the fragmenter voltage for each drug. The optimized fragmenter voltages were then applied by use of a variably ramped fragmenter voltage to acquire mass spectra for the library. The chromatographic separations were run on a Zorbax Stable bond column using a 10-mM ammonium formate-acetonitrile gradient method. Spiked blank serum and patient samples with a total of 40 different drugs were extracted with use of a standard basic liquid-liquid extraction (LLE) method. A search of significant peaks in the chromatogram by application of the developed mass spectral library is shown to result in a more than 95% positive identification. reserved.

Direct determination of ecgonine methyl ester and cocaine in rat plasma, utilizing on-line sample extraction coupled with rapid chromatography/quadrupole orthogonal acceleration time-of-flight detection

Our current experiments assess the applicability of on-line sample extraction with coupled rapid chromatography systems to quadrupole orthogonal acceleration time-of-flight (Q-TOF) detection for the quantitative analysis of cocaine (COC), and ecgonine methyl ester (EME) in rat plasma. Experiments were performed on a Q-TOF instrument, operated in the MS/MS mode. Quantitation was achieved utilizing the most prominent parent-daughter transition and internal standard calibration techniques (COC-d3: IS). The calibration curves produced for EME and COC ranged from 5.0 to 10,000 and 0.5 to 10,000 ng/ml, respectively. Equations of regression line and correlation coefficients for the pseudo-multiple reaction monitoring (MRM) ion abundance ratio and the corresponding calibration concentrations (r2) were as follows: y = 0.0003 + 0.0703x (r2 = 0.9921) for EME and y = 0.0032 + 0.0035x (r2 = 0.9997) for COC. The system repeatability, given as percent coefficient of variation (% CV) of mean peak-area ratios, was assessed using 50 injections of a rat plasma sample from the pharmacokinetic study. The analyses were performed over the course of 5 days, rendering % CVs for EME and COC of 0.73 and 0.58, respectively. This method suggests that on-line sample extraction coupled with fast liquid chromatography/quadrupole orthogonal time-of-flight mass spectrometry may be a viable alternative for quantitative analysis of EME and COC in rat plasma.

Liquid chromatography--tandem mass spectrometry analysis of cocaine and its metabolites from blood, amniotic fluid, placental and fetal tissues: study of the metabolism and distribution of cocaine in pregnant rats

The ability to simultaneously quantitate cocaine and its 12 metabolites from pregnant rat blood, amniotic fluid, placental and fetal tissue homogenates aids in elucidating the metabolism and distribution of cocaine. An efficient extraction method was developed to simultaneously recover these 13 components using underivatized silica solid-phase extraction (SPE) cartridges. The overall recoveries for cocaine and its metabolites were studied from pregnant rat blood (47-100%), amniotic fluid (61-100%), placental homogenate (31-83%), and fetal homogenate (39-87%). Extraction of the samples using silica is not classical SPE, but rather allows for the concentration of the sample into a small volume prior to injection and the removal of the proteins due to their strong interaction with the active silica surface. A positive ion mode electrospray ionization liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was used and validated to simultaneously quantitate cocaine and 12 metabolites from these four biological matrices. A gradient elution method with a Zorbax XDB C8 reversed-phase column was used to separate the components. Multiple reaction monitoring (MRM) of a product ion arising from the corresponding precursor ion was used in order to enhance the selectivity and sensitivity of the method. Low background noise was observed from the complex biological matrices due to efficient SPE and the selectivity of the MRM mode. Linear calibration curves were generated from 0.01 to 2.50 ppm. The method also showed high intra-day (n =3) and inter-day (n=9) precision (% RSD) and accuracy (% error) for all components. The limits of detection (LODs) for the method ranged from 0.15 to 10 ppb. The LODs of cocaine and its major metabolites were less than 1 ppb from all four biological matrices. This method was applied to the study of the metabolism and distribution of cocaine in pregnant rats following intravenous infusion to a steady state plasma drug concentration. The following results were observed in the pregnant rat study: (1) the observations correlated strongly with the previous literature data on cocaine metabolism and distribution, (2) cocaine and norcocaine accumulated in the placenta, (3) arylhydroxylation of cocaine was a major metabolic pathway, (4) para-arylhydroxylation of cocaine was favored over meta-arylhydroxylation in rats and (5) accumulation of cocaine and its major metabolites was observed in the amniotic fluid.

Liquid chromatography/electron capture atmospheric pressure chemical ionization/mass spectrometry: analysis of pentafluorobenzyl derivatives of biomolecules and drugs in the attomole range

The corona discharge used to generate positive and negative ions under conventional atmospheric pressure chemical ionization conditions also provides a source of gas-phase electrons. This is thought to occur by displacement of electrons from the nitrogen sheath gas. Therefore, suitable analytes can undergo electron capture in the gas phase in a manner similar to that observed for gas chromatography/electron capture negative chemical ionization/mass spectrometry. This technique, which has been named electron capture atmospheric pressure chemical ionization/mass spectrometry, provided an increase in sensitivity of 2 orders of magnitude when compared with conventional atmospheric pressure chemical ionization methodology. It is a simple procedure to tag many biomolecules and drugs with an electron-capturing group such as the pentafluorobenzyl moiety before analysis. Pentafluorobenzyl derivatives have previously been used as electron capturing derivatives because they undergo dissociative electron capture in the gas phase to generate negative ions through the loss of a pentafluorobenzyl radical. A similar process was found to occur under electron capture atmospheric pressure chemical ionization conditions. By monitoring the negative ions that were formed, it was possible to obtain attomole sensitivity for pentafluorobenzyl derivatives of a representative steroid, steroid metabolite, prostaglandin, thromboxane, amino acid, and DNA-adduct.

Liquid chromatography-mass spectrometry in forensic toxicology

Liquid chromatography-mass spectrometry has evolved from a topic of mainly research interest into a routinely usable tool in various application fields. With the advent of new ionization approaches, especially atmospheric pressure, the technique has established itself firmly in many areas of research. Although many applications prove that LC-MS is a valuable complementary analytical tool to GC-MS and has the potential to largely extend the application field of mass spectrometry to hitherto "MS-phobic" molecules, we must recognize that the use of LC-MS in forensic toxicology remains relatively rare. This rarity is all the more surprising because forensic toxicologists find themselves often confronted with the daunting task of actually searching for evidence materials on a scientific basis without any indication of the direction in which to search. Through the years, mass spectrometry, mainly in the GC-MS form, has gained a leading role in the way such quandaries are tackled. The advent of robust, bioanalytically compatible combinations of liquid chromatographic separation with mass spectrometric detection really opens new perspectives in terms of mass spectrometric identification of difficult molecules (e.g., polar metabolites) or biopolymers with toxicological relevance, high throughput, and versatility. Of course, analytical toxicologists are generally mass spectrometry users rather than mass spectrometrists, and this difference certainly explains the slow start of LC-MS in this field. Nevertheless, some valuable applications have been published, and it seems that the introduction of the more universal atmospheric pressure ionization interfaces really has boosted interests. This review presents an overview of what has been realized in forensic toxicological LC-MS. After a short introduction into LC-MS interfacing operational characteristics (or limitations), it covers applications that range from illicit drugs to often abused prescription medicines and some natural poisons. As such, we hope it can act as an appetizer to those involved in forensic toxicology but still hesitating to invest in LC-MS.

Liquid chromatography-atmospheric pressure chemical ionization mass spectrometry as a tool for the characterization of anthraquinone derivatives from Chinese herbal medicine

We have examined the anthraquinone derivatives of a Chinese herb medicine 'Rhubarb' by using HPLC/MS/MS, equipped with an atmospheric pressure chemical ionization source. The simultaneous determination of five ingredients in the sample extracts by HPLC/MS/MS was demonstrated. Product ion spectra of these components in the extracts were obtained and matched against known standards. Concentrations of these active ingredients were estimated by multiple reaction monitoring in the negative ion mode using a single HPLC run.

Chronic continuous cocaine infusion in rats: effect on urine cocaine, ecgonine methylester and benzoylecgonine concentrations and bolus-dose cocaine pharmacokinetics

The aim of this study was to determine the effect of chronic cocaine infusion on urine cocaine, ecgonine methylester and benzoylecgonine concentrations to establish if they varied with dose and duration of cocaine administration. Male rats were continuously infused with cocaine at either 6 or 18 mg kg(-1) daily for 13 days. Three urine samples taken over the course of the infusion period showed that cocaine, ecgonine methylester and benzoylecgonine concentrations varied with the dose administered and the duration of administration. Cocaine, ecgonine methylester and benzoylecgonine concentrations were 2-3 times greater in the high-dose group than the low-dose group at each sampling time point. These decreased, respectively, from 7.0+/-1.1, 26.7+/-4.5 and 29.5+/-5.4 microg mL(-1) to 2.5+/-0.5, 10.5+/-1.8 and 11.8+/-1.5 microg mL(-1) in the high-dose group and from 1.0+/-0-2, 7.8+/-1.5 and 6.3+/-0.1 microg mL(-1) to 0.5+/-0.1, 4.0+/-0.6 and 3.1+/-0.4 microg mL(-1) in the low-dose group (P < 0.05) over the infusion period. We also studied the pharmacokinetic and metabolic profile of an intravenous bolus dose of 2.5 mg kg(-1) cocaine hydrochloride after a similar cocaine infusion in rats. Cocaine pharmacokinetics and the profile of ecgonine methylester, benzoylecgonine and norcocaine were no different from rats chronically infused with saline for the same period. Altered cocaine metabolism could not explain the effect of the duration of cocaine infusion on altered metabolite concentrations in urine. Ecgonine methylester/benzoylecgonine urine concentration ratios did not alter with duration of infusion (1.2+/-0.2 and 1.1+/-0.2 in the high-dose group at the first and last time point) and were not affected by the dose of cocaine (1.3+/-0.6 and 1.2+/-0.1 at corresponding times in the low-dose group (P > 0.05)). We conclude that chronic cocaine infusion does not alter cocaine metabolism. This was not reflected by absolute cocaine metabolite urine concentrations, which varied with time, but was represented by urine ecgonine methyl ester/benzoylecgonine concentration ratios.