Naltrexone: disposition, metabolism, and effects after acute and chronic dosing.

The disposition of naltrexone during acute and chronic administration of 100-mg oral dose was studied in 4 subjects. Following an acute dose the mean (X) peak naltrexone plasma level was 43.6 +/- 29.9 ng/ml at 1 hr and for the major biotransformation product, beta-naltrexol, was 87.2 +/- 25.0 ng/ml at 2 hr. Twenty-four hours after the dose the X levels of naltrexone and beta-naltrexol declined to 2.1 +/- 0.47 and 17.6 +/- 5.0 ng/ml, respectively. Following chronic administration and X peak plasma levels of naltrexone and beta-naltrexol rose to 46.4 +/- 18.5 and 158.4 +/- 89.9 ng/ml at 1 hr, but by 24 hr both compounds declined to levels of the same order as in the acute state at 24 hr. Plasma levels of naltrexone and beta-naltrexol measured 24 hr after the daily doses of naltrexone throughout the study indicated that steady-state equilibrium was rapidly attained and that there was no accumulation of naltrexone and beta naltrexol in the plasma after chronic treatment on 100 mg oral doses. Biexponential kinetics were observed for naltrexone and beta-naltrexol in the first 24 hr. The half-life of naltrexone and beta-naltrexol decreased slightly from the acute to thechronic study from 10.3 +/- 3.3 to 9.7 +/- 1.1 hr and from 12.7 +/- 2.6 to 11.4 +/- 2.0 hr. The plasma levels of naltrexone declined slowly from 24 through 72 hr from 2.4 to 1.7 ng/ml, with an apparent half-life of 96 hr. The renal clearance data indicate that naltrexone is partially reabsorbed while beta naltrexol is actively secreted by the kidney. During acute and chronic naltrexone administration the mean fecal excretion was 2.1% and 3.6% while urinary excretion was 38% and 70% of the dose in a 24-hr period. Opiate antagonism to 25 mg heroin challenges was nearly complete through 48 hr after naltrexone. At 72 hr the objective responses reappeared to a greater extent than the subjective ones. Correlation coefficient (r) between naltrexone plasma levels and opiate antagonism was 0.91 and between individual half-life of naltrexone and opiate antagonism it was 0.99.

Phencyclidine-induced stereotype in rats: effects of methadone, apomorphine, and naloxone.

Phencyclidine (PCP) given to male Wistar rats produced hyperactivity and various stereotypic motor behaviors. Methadone, apomorphine, and naloxone were tested for their effects on PCP-induced stereotypy. Methadone (0.5 mg/kg) had no effect on the hyperactivity produced by PCP, but significantly attenuated PCP-induced stereotypy when given both before and after PCP. Low doses of apomorphine were equally effective as methadone in attenuating PCP-induced stereotypy. However, when naloxone was given after methadone or apomorphine to PCP-treated rats, the full PCP-induced stereotypy was again observed. Naloxone pretreatment on doses up to 20 mg/kg was not effective in antagonizing PCP-induced behavioral effects. Methadone and apomorphine antagonism of PCP-induced stereotypy may be mediated by opiate receptors. The results of this study and observations from human studies collectively suggest the possible effectiveness of opiates in treating PCP-induced and functional psychoses.

Comparative effects of cocaine and pseudococaine on EEG activities, cardiorespiratory functions, and self-administration behavior in the rhesus monkey.

The effects of cocaine and pseudococaine on the EEGs, heart and respiratory rates, and self-administration behavior were studied in rhesus monkeys. An intravenous injection of cocaine (2.5 and 4.0 mg/kg) in the monkey produced low-voltage fast waves (LVFWs) in the EEGs and behavioral hyperexcitation accompanied by marked increases in the heart and respiratory rates with mydriasis and excessive salivation. In contrast, pseudococaine produced high-voltage slow waves (HVSWs) in the EEGs and behavioral depression accompanied by the same symptoms of the autonomic functions as those produced by cocaine. Both isomers were self-administered by the monkeys. During cocaine self-administration sessions, the animals showed hyperexcitation in their overall behavior, while with pseudococaine they showed almost normal behavioral responses. These results suggest that cocaine produced excitatory effects and pseudococaine inhibitory effects on the EEGs and behavior. Both isomers stimulate the heart and respiratory rates, and were self-administered by the monkeys.

Confirmation and quantitation of cocaine, benzoylecgonine, ecgonine methyl ester in human urine by GC/MS.

A rapid, sensitive, reliable quantitative GC/MS method using 0.2 mL of urine was developed for the confirmation of cocaine use. After a simple organic solvent extraction and derivatization with pentafluoropropionic anhydride, cocaine, benzoylecgonine, and ecgonine methyl ester were identified by GC/MS through the retention time for the total ion current and selected ion monitoring (SIM) for each analyte. Quantitation was achieved by obtaining the calibration curves for the molecular ion ratios of the analyte/ketamine (IS) over a range of 12.5-250 ng/mL (0.1-2 ng total). The extraction efficiency for these analytes ranged from 70 to 82%. The sensitivity limit of detection for each analyte was 12.5 ng/mL (0.1 ng) at p less than 0.01. Intra- and interday precision for these analytes ranged between 14.7 and 29.5% CV. This method is in routine use in our laboratory for the GC/MS confirmation of enzyme immunoassay cocaine-positive urine samples.

Confirmation of marijuana, cocaine, morphine, codeine, amphetamine, methamphetamine, phencyclidine by GC/MS in urine following immunoassay screening.

Rapid, reliable, sensitive, qualitative, and quantitative methods using small urine volumes (0.2-0.5 mL) were developed primarily for confirmation of marijuana, cocaine, benzoylecgonine, ecgonine methyl ester, morphine, codeine, amphetamine, methamphetamine, and phencyclidine. Using capillary gas chromatography/mass spectrometry (GC/MS) and selected ion monitoring (SIM), mass spectra were obtained for each analyte. Samples were prepared by hydrolysis where applicable, organic solvent extraction, and derivatization where necessary. Confirmation was achieved by comparing abundance of major ions and retention time of the total ion current (TIC) of an analyte with those of the appropriate analytical standard. Quantitation was achieved and calibration curves derived by obtaining the molecular ion ratios of that analyte/internal standard (IS) over a concentration range of 10-300 ng/mL (0.16-4.0 ng total injected into GC/MS). The overall extraction efficiency for these analytes ranged from 53% to 96%. Statistically significant cut-off values (p less than 0.01) were obtained for each analyte. The slope, y-intercept, and coefficient of determination (r2) were calculated for each analyte. All of the GC/MS methods were extensively tested against urine samples determined positive or negative by immunoassay (IA) and are now used in our laboratory.

Confirmation and quantitation of barbiturates in human urine by gas chromatography/mass spectrometry.

A sensitive, reliable, rapid quantitative method was developed for the N,N'-dimethyl derivatives of the 5,5'-disubstituted barbiturates (NNDM-barbiturates) after liquid-liquid extraction of 0.5-mL urine volumes. Each barbiturate was identified by GC/MS through the retention time for the total ion current and selected ion monitoring of four ion currents for each analyte. Quantitation was achieved through the base peak ion ratios for each NNDM-barbiturate/tolylbarbiturate (IS) over the concentration range 20-250 ng/mL (0.4 to 5 ng injected into the GC/MS). The limit of detection for all the barbiturates (p less than 0.01) was 20 ng/mL (0.4 ng total). The extraction efficiency ranged from 75 to 84% for all the barbiturates. The coefficient of variation of the barbiturates for the within-day run was 2.5 to 4.8% and between days was 6.7 to 8.6%. The percentage abundances of the ion current ratios for each NNDM-barbiturate was determined and found to be fully stable over a one-week period. This method is currently in routine use in our laboratory for the GC/MS confirmation of presumably positive barbiturate urine samples.

Quantitation and confirmation of the diazolo- and triazolobenzodiazepines in human urine by gas chromatography/mass spectrometry.

We report a reliable, rapid, sensitive, and quantitative method for the N- and O-trimethylsilyl (TMS) derivatives of the diazolo- and triazolobenzodiazepines after enzymatic incubation (2 h) and liquid-liquid extraction of 0.5-mL urine volumes. Each analyte was identified by gas chromatography/mass spectrometry through the retention time for the total ion current (TIC) and selected ion monitoring (SIM) of four ion currents. Quantitation of the diazolobenzodiazepines was obtained by the ratio of the base peak ion of the TMS analyte to that of the internal standard bromazepam in the concentration range 50-500 ng/mL (1-10 ng injected into the GC/MS). The limit of detection (LOD) at p less than 0.01 was 50 ng/mL for all the diazolobenzodiazepines. The assay was not quite as sensitive for triazolobenzodiazepines (5-20 ng injected in the GC/MS). The extraction efficiency of the assay ranged from 75 to 92% for all the analytes. The coefficient of variation (CV) for the diazolobenzodiazepines ranged from 5.4 to 9.4% for within-day runs and from 11.1 to 13.9% for between-day runs. For the triazolobenzodiazepines the values were 3.8 to 18.9% for a single day and 3.4 to 19.9% between days. The selected ion current ratio for each analyte was determined for a single day and over a one-week period. There was no statistical difference in the ratios during this time. The confirmation of diazolobenzodiazepines in urine by this method was relatively easy after screening by the immunoassay technique. Identification of triazolobenzodiazepines appeared to be more difficult by both the screening technique and the GC/EI/MS analysis.

Active and realistic passive marijuana exposure tested by three immunoassays and GC/MS in urine.

Human urine samples obtained before and after active and passive exposure to marijuana were analyzed by immune kits (Roche, Amersham, and Syva) and gas chromatography/mass spectrometry (GC/MS). Seven of eight subjects were positive for the entire five-day test period with one immune kit. The latter correlated with GC/MS in 98% of the samples. Passive inhalation experiments under conditions likely to reflect realistic exposure resulted consistently in less than 10 ng/mL of cannabinoids. The 10-100-ng/mL cannabinoid concentration range essential for detection of occasional and moderate marijuana users is thus unaffected by realistic passive inhalation.

Evaluation of the TRI 'dipstick' test for the detection of drugs of abuse in urine.

An evaluation of Technology Resources Inc. (TRI) Amphetamine, Barbiturate, Narcotic (G) and Narcotic (S) "Dipsticks" for drugs of abuse in urine was made. The results obtained by six individuals reading the "Dipstick" papers was compared with the analysis of the same urine samples, by a combination of TLC, EMIT, RIA and GLC. The data obtained with "Dipstick" papers, regardless of the drug tested, were clearly unreliable (high percentage of false negatives, low percentage of true positives) and the assay was unsuitable as a technique for screening urines for drugs of abuse.

Confirmation of EMIT benzodiazepine assay with GLC/NPD.

A simple, rapid, and reliable gas-liquid chromatographic (GLC) confirmation procedure was developed for urine samples found positive by the EMIT-dau benzodiazepine metabolite assay. The procedure involves acid hydrolysis, organic extraction, and identification using GLC-nitrogen-phosphorus detection (NPD). The method was validated in three subjects who took 10 mg diazepam daily for five days. Urinary excretion of the diazepam related substances was monitored quantitatively for 12 days. Considerable differences in diazepam metabolism was observed, despite the small number of subjects used. The data further indicated that both the physical characteristics and the metabolic profile of each individual may determine whether or not their occasional benzodiazepine use would be detected by the EMIT procedure. In some individuals taking daily diazepam, 48 to 72 hours may be required before sufficient metabolites accumulate in the urine to give a positive EMIT reaction.

A rapid, quantitative GLC method for the simultaneous determination of nicotine and cotinine.

Published gas-liquid chromatographic (GLC) methods for the determination of nicotine and cotinine have proved impractical for the analysis of a large number of clinical samples. Significant improvements over other methods have been achieved, being low sample volume (0.5 mL plasma), rapid two-step extraction from plasma, no evaporation step, and good separation. The lower limits of sensitivity for nicotine and cotinine were 1 and 5 ng/mL, respectively. The method was validated by the analysis of plasma samples from cigarette-smoking volunteers. The method described permits the quick, routine determination of nicotine and cotinine in a large number of samples.

Quantitative determination of 2-hydroxy-3-methoxy-6 beta-naltrexol (HMN), naltrexone, and 6 beta-naltrexol in human plasma, red blood cells, saliva, and urine by gas liquid chromatography.

Two gas liquid chromatographic methods differing mainly in sensitivity are described for the quantitative determination of 2-hydroxy-3-methoxy-6 beta-naltrexol (HMN), a minor metabolite of naltrexone (NT), in human body-fluids. The methods also incorporate simultaneous determinations of naltrexone and its major human metabolite, 6 beta-naltrexol (beta-OL), in urine, serum (or plasma), red blood cells (RBC), and saliva. Flame ionization detection of the bis-(trimethylsylil) trifluoroacetamide (BSTFA) derivatives provided sufficient sensitivity for quantitation of the bases in urine. However, lower levels in serum, RBC and saliva necessitated the use of more sensitive electron capture detection of the pentafluoropropionate (PFPA) derivatives of the bases. Because HMN and 6 beta-naltrexol PFPA derivatives have nearly identical gas chromatographic retention times, their separation was achieved by differential extraction, based on their different partition characteristics between aqueous and organic solvents. In the plasma of 4 subjects, 16 and 24 hrs. after 2 X 200 mg NT doses, the relative percentages were 23.1% HMN, 3.4% NT and 73.5% beta-OL. In urine samples collected at the same time as the blood samples the relative percentages were 14.4% HMN, 9.0% NT and 76.6% beta-OL. The nonpolar nature of HMN and the greater polarity of beta-OL may have influenced their differential distribution into RBCs and saliva. In the RBCs, 96.1% HMN and no significant amount of beta-OL was found, in saliva, 92.3% of beta-OL and no HMN was found.

Simultaneous determination of nicotine and cotinine in human plasma by nitrogen detection gas-liquid chromatography.

Human plasma levels of nicotine and its principal metabolite, cotinine, were simultaneously quantitated by gas-liquid chromatography combined with nitrogen selective detection. Nicotine, cotinine, and the added internal standard ketamine are extracted from plasma at basic pH into methylene chloride, back-extracted into acid, and then re-extracted into methylene chloride. Analysis is carried out on a packed glass column of 3% SE-30 while column temperature is programmed from 150 to 200 degrees C. Detector response is linea over the range of 2 to 50 ng/mL nicotine and 50 to 500 ng/mL cotinine. The method was validated on 150 plasma samples obtained from habitual smokers. Mean levels of 19.5 and 219 ng/mL were found for nicotine and cotinine, respectively. Both the mean and the range of the levels were in agreement with previously reported plasma levels for nicotine and cotinine.