Impaired psychomotor function and plasma methadone and levo-alpha-acetylmethadol (LAAM) concentrations in opioid-substitution patients.

Tolerance to the psychomotor impairing effects of opioid drugs is expected to develop with repeated dosing, but may be incomplete. The relationship between plasma opioid concentration and psychomotor function in opioid-dependent patients was examined to determine whether impairment was more likely at the time of highest plasma drug concentration. Sixteen patients participating in a cross-over trial comparing methadone and LAAM completed a tracking task (OSPAT) 11 times over the dosing-interval for methadone (24-hrs) and LAAM (48-hrs). Venous blood was collected for the quantification of plasma (R)-(-)-methadone, LAAM, and nor-LAAM concentrations. The Digit Symbol Substitution Test (DSST) and Trail-Making Test were administered at the time of peak plasma concentration. Ten healthy controls (HCs) also participated. OSPAT scores (obtained for 15 patients) fluctuated significantly across the dosing-interval for both drugs and were lower in patients than HCs at the times of peak concentrations of (R)-(-)-methadone (1 hr: (mean difference; 95% CI) (2.13; 0.18-4.08); 2 hrs: (2.38; 0.48-4.28) postdosing) and LAAM (2 hrs: (1.81; 0.09-3.53), and 4 hrs (1.90: 0.9-3.71) postdosing). Within-participant analysis of the peak-change from baseline for OSPAT scores found that 10 of the 15 patients could be categorized as impaired on methadone and 9 on LAAM. No HCs were impaired. Patients performed worse on the DSST and Trails-A than HCs, but not on Trails-B. Results suggest that some patients receiving opioids long term may exhibit impairment at the time of highest plasma drug concentration. These patients should be made aware that their ability to undertake complex tasks may be affected. (PsycINFO Database Record

Paradoxical role of cytochrome P450 3A in the bioactivation and clinical effects of levo-alpha-acetylmethadol: importance of clinical investigations to validate in vitro drug metabolism studies.

OBJECTIVE: Levo-alpha-acetylmethadol (LAAM, levacetylmethadol) is a long-acting opioid agonist used for the prevention of opioid withdrawal. LAAM undergoes sequential N-demethylation to norLAAM and dinorLAAM, which are more potent and longer-acting than LAAM. Hepatic and intestinal microsomal N-demethylation in vitro is catalysed mainly by cytochrome P450 (CYP) 3A4; however, the role of CYP3A in LAAM disposition in humans in vivo is unknown. This investigation tested the hypothesis that CYP3A induction (or inhibition) would increase (or decrease) LAAM metabolism and bioactivation and, thus, clinical effects. It also related changes in LAAM disposition during enzyme inhibition or induction to any changes in pharmacological effect. METHODS: Healthy volunteers (n = 13) completed the three-way, randomised, balanced crossover study. Subjects received oral LAAM (0.25 mg/kg) after CYP3A induction (rifampicin [rifampin]), inhibition (troleandomycin) or nothing (controls). Plasma and urine LAAM, norLAAM and dinorLAAM were determined by electrospray high-performance liquid chromatography/mass spectrometry (HPLC/MS). Dark-adapted pupil diameter change from baseline (miosis) was the LAAM effect measure. Results were analysed by noncompartmental methods and by a combined pharmacokinetic/pharmacodynamic model. RESULTS: Compared with controls, CYP3A induction (or inhibition) decreased (or increased) plasma LAAM concentrations and mean area under the plasma concentration-time curve from time zero to infinity (AUC(infinity) 199 +/- 91 [control] versus 11.3 +/- 4.0 [rifampicin] and 731 +/- 229 ng . h/mL [troleandomycin]; p < 0.05), and increased (or decreased) median formation clearances of norLAAM (1740 versus 14 100 and 302 mL/h/kg; p < 0.05) and dinorLAAM (636 versus 7840 and 173 mL/h/kg; p < 0.05). Surprisingly, however, CYP3A induction (or inhibition) decreased (or increased) mean plasma metabolite AUC from 0 to 96 hours (AUC(96)) [norLAAM + dinorLAAM] (859 +/- 241 versus 107 +/- 48 and 1185 +/- 179 ng . h/mL; p < 0.05) and clinical effects (mean miosis AUC(96) 128 +/- 40 versus 22.5 +/- 14.9 and 178 +/- 81 mm . h; p < 0.05). Clinical effects were best correlated with plasma norLAAM concentrations. CONCLUSION: CYP3A mediates human LAAM N-demethylation and bioactivation to norLAAM and dinorLAAM in vivo. Paradoxically, however, CYP3A induction decreased and inhibition increased LAAM active metabolite concentrations and clinical effects. This suggests a CYP3A-mediated metabolic pathway leading to inactive metabolites, which predominates over CYP3A-dependent bioactivation. These results highlight the need for clinical investigations to validate in vitro drug metabolism studies.

Determination of human plasma levels of levo-alpha-acetylmethadol and its metabolites by gas chromatography-mass spectrometry.

A gas chromatography-mass spectrometry (GC-MS) method is presented which allows the simultaneous determination of the plasma concentrations of the levo-alpha-acetylmethadol (LAAM) and of its active metabolites (NorLAAM and DiNorLAAM), after derivatization with the reagent trifluoroacetic anhydride (TFAA). No interferences from endogenous compounds were observed following the extraction of plasma samples from 11 different human subjects. The standard curves were linear over a working range of 5-200ng/ml for the three compounds. Recoveries measured at three concentrations ranged from 47 to 67% for LAAM, from 50 to 69% for NorLAAM and from 28 to 50% for DiNorLAAM. Intra- and interday coefficients of variation determined at three concentrations ranged from 5 to 13% for LAAM, from 3 to 9% for NorLAAM and from 5 to 13% for DiNorLAAM. The limits of quantitation of the method were found to be 4ng/ml for the three compounds. No interference was noted from methadone. This sensitive and specific analytical method could be useful for assessing the in vivo relationship between LAAM's blood levels, clinical efficacy and/or cardiotoxicity

Toxicologic aspects of heroin substitution treatment.

Heroin abuse is an international problem with which all countries must continually cope. Many countries have implemented heroin substitution therapy as an effective means of decreasing illicit heroin use, crime, HIV risk, and death, and in improving employment and social adjustment. Although methadone is the most commonly used medication for heroin substitution, other agonists in current use include levomethadyl acetate (LAAM), buprenorphine, and pharmaceutical-grade heroin. This report reviews toxicologic issues that arise in these programs. A broad array of testing methodologies are available that allow selection of on-site testing or laboratory-based methodology. Urine specimens may be monitored for nonprescribed drugs on a qualitative or semiquantitative basis. Methods for differentiating opiate sources by urinalysis have been proposed to distinguish poppy seed consumption from heroin abuse and for distinguishing pharmaceutical-grade heroin from illicit heroin. Therapeutic drug monitoring for methadone in plasma continues to be evaluated for use in establishing adequate dosing and detecting diversion, and new methods have been devised for measurement of the optical isomers of methadone in plasma. Biologic specimens, in addition to plasma and urine, have been evaluated for use in drug monitoring, including sweat, hair, and oral fluid, with promising results. Overall, the many recent developments in testing methodology provide more effective means to assess patients in heroin substitution programs and should contribute to improvements in public health.

Intravenous and oral l-alpha-acetylmethadol: pharmacodynamics and pharmacokinetics in humans.

Levo-alpha-acetylmethadol (LAAM) is a long-acting opioid agonist approved for use as a maintenance treatment for opioid dependence. Previous clinical studies report that the onset of the effects of LAAM is slower after parenteral administration than oral administration; however, preclinical studies suggest otherwise. This study examined the pharmacodynamic and pharmacokinetic profile of LAAM when given orally and intravenously to humans. Opioid-experienced volunteers (n = 6), who were not physically dependent on opioids, received LAAM (20 and 40 mg/70 kg i.v. and p.o.) and placebo under double-blind, double-dummy conditions during five weekly experimental sessions. Behavioral, physiological, subjective and pharmacokinetic measures were collected before and for 96 hr after drug administration. Intravenous LAAM produced significant subjective and physiological effects that appeared within 5 min, whereas the effects of oral LAAM appeared more slowly within 1 to 2 hr after drug administration. Pharmacokinetic data indicate that the immediate effects of intravenous LAAM are largely attributable to the parent drug rather than the active metabolites, nor-LAAM and dinor-LAAM. LAAM produced prototypic opioid agonist effects (i.e., miosis, subjective ratings of high, nodding) that were of equal magnitude across routes, dose-related and of long duration (up to 60 hr). These data are in contrast to previous clinical reports and indicate that LAAM produces effects of immediate onset when administered parenterally, which suggests that intravenous LAAM possesses greater abuse potential than previously believed.

Determination of l-alpha-acetylmethadol, l-alpha-noracetylmethadol and l-alpha-dinoracetylmethadol in plasma by gas chromatography-mass spectrometry.

A method is described for the simultaneous determination of l-alpha-acetylmethadol (LAAM) and its N-demethylated metabolites, l-alpha-noracetylmethadol (norLAAM) and l-alpha-dinoracetylmethadol (dinorLAAM), in plasma by gas chromatography-chemical ionization mass spectrometry. Deuterated internal standards for each analyte serve as carriers and control for recovery during sample purification on a solid-phase extraction column (C18), and subsequent separation and analysis on a DB-17 capillary column. With this method, we have determined levels of LAAM, norLAAM, and dinorLAAM in small volumes of plasma (100 microliters). The limit of quantitation for all analytes was approximately 1.0 ng/g plasma and the limit of detection was approximately 0.5 ng/g plasma. An experimental application is also described where these analytes are quantitated in plasma obtained from rats before, during, and after chronic administration of LAAM-HCl. Since this technique affords a selective and sensitive means of detection of LAAM and its active, N-demethylated metabolites in small samples of blood, it may enable patient compliance to be more easily assessed by allowing samples to be collected by a simple finger-prick technique.

Quantitation of l-alpha-acetylmethadol and its metabolites in human serum by capillary gas-liquid chromatography and nitrogen detection.

A procedure is described for the simultaneous measurement of l-alpha-acetylmethadol and its two pharmacologically active metabolites: noracetylmethadol and dinoracetylmethadol. In the method an intramolecular conversion reaction of the two metabolites to their amide configuration is utilized. The reaction is performed while the metabolites are still in the serum. Following solvent extraction the samples are analyzed by capillary gas-liquid chromatography coupled with nitrogen detection. Quantitation is achieved by internal standardization. The lower limit of sensitivity is 5 ng/ml in serum. Absolute sensitivity is 0.1 ng for all three compounds. The advantages over other procedures are: speed due to the single extraction step; increased recovery of noracetylmethadol and dinoracetylmethadol due to decreased polarity of the amides; greater stability of the metabolites in the amide configuration; better chromatographic quantitation and separation because detector response for the amides is greater than it is for the original configuration of the metabolites and the area of the chromatographic tracing is free of interfering substances.

Effect of phenobarbital pretreatment on the plasma and urinary levels of (-)-alpha-acetylmethadol and its metabolites.

The effect of phenobarbital (PB), an inducer of the hepatic microsomal enzyme system, on the plasma levels and urinary elimination of (-)-alpha-acetylmethadol 1 and its metabolites have been examined in the rat. [3H]1 was administered to saline control and PB-pretreated rats at doses of 5 mg/kg ip (55 muCi/kg). The concentration of 1 and its metabolites noracetylmethadol 2, dinoracetylmethadol 3, methadol 4, normethadol 5, and N-acetylnormethadol 6 were quantitated in plasma and urine over 48 h by TLC and liquid scintillation counting. PB pretreatment significantly decreased the plasma total radioactivity and the levels of 1 and its five metabolites over the 48-h period investigated. Urinary total radioactivity and elimination of 1 and its five metabolites were also reduced in PB-pretreated rats. The results indicated that PB pretreatment markedly affects the in vivo transformation and elimination of 1 and its metabolites. The decrease in the levels observed for 1 and its metabolites in the plasma and urine can be due either to an increase in the metabolism of 1 via a different pathway than the formation of the biologically active metabolites 2, 3, 4, and 5, or it may be that PB is enhancing the further metabolism of these compounds to more polar water-soluble products which are mainly excreted through the bile.

Variability in simian motor and social behavior with alternating-day acetylmethadol.

Monkeys receiving acetylmethadol thrice weekly were more active on dosing days, and less active on between-dose days, than while drug-free. Aggressive social behaviours increased significantly on drug-dosing days, while quiescent resting behaviors were much more common on between-dose days. Tolerance to these effects was modest, and the effects were not blocked by naltrexone. These subtle but potentially disruptive behavioral effects appear to parallel many of the actions of acetylmethadol in man.

Methadyl acetate (LAAM) in the treatment of heroin addicts. II. Double-blind comparison of gradual and abrupt detoxification.

One hundred nineteen patients were admitted to a six-month (26-week) prenaltrexone detoxification program comparing abrupt and gradual withdrawal from methadyl acetate (LAAM) therapy. All patients were brought to a maintenance level of 50, 50, and 65 mg (Monday, Wednesday, and Friday). Patients randomly assigned to the gradual group (group G) began 4-mg/wk reduction the Monday of week 9 and reached zero dosage (placebo) the Monday of week 23; patients in the abrupt group (group A) continued to receive 50, 50, and 65 mg until the Monday of week 23, when their dosage was dropped to zero (placebo). All patients were given placebo for four weeks. This study showed the superiority of abrupt withdrawal over this gradual-withdrawal schedule. Forty-six percent of group P compared with 28% of group G made the transition to naltrexone treatment. Severity of withdrawal problems was in no case significantly greater in group A.

Plasma and urine disposition of 1-alpha-acetylmethadol and its principal metabolites in man.

The disposition of 1-alpha-acetylmethadol (LAAM) in plasma and urine was monitored by GC/CIMS following oral administration of 10 doses (0.73-1.5 mg/kg) over 42 days, to twelve human subjects. Plasma concentration-time course profiles fitted a two-compartment, first order kinetic model. Mean plasma t1/2 alpha for LAAM was 2.4 hours; t1/2 beta was 37.5 hours for the first dose and 46.8 hours for the last dose. The mean terminal half-life for nor-LAAM was 38.2 hours for first and 64.6 for last dose; for dinor-LAAM t1/2 beta was 168 hours, last dose. Drug accumulation occurred in some subjects, but within the study range, dosage was not related to maximum plasma levels nor to accumulation. In urine, the sum of LAAM, nor-LAAM, and dinor-LAAM represented 25% of the dose, and unconjugated methadol metabolites, 1.6-1.7%.

Enterohepatic circulation of l-alpha-acetylmethadol in the rat.

The enterohepatic circulation of the biliary metabolites of l-alpha[3H]acetylmethadol ([3H]LAAM) was studied in rats. Bile was collected for 48 hr from a biliary-cannulated donor rat after s.c. administration of [3H]LAAM. This bile containing tritium-labeled LAAM metabolites was then infused into the small intestine of a recipient rat for 48 hr and the appearance of radioactivity in bile formed in the liver of the recipient rat was monitored. Forty-eight hours after the start of infusion, 40% of the infused radioactivity had been excreted into the bile of the recipient rat, indicating extensive enterohepatic circulation of the biliary metabolites of LAAM. The data indicated that only a small percentage of the infused [3H]LAAM metabolites were present in the systemic circulation at any one time. This was further investigated by comparing the plasma levels of tritium with time and the tissue concentrations at 24 and 48 h after s.c. [3H]LAAM administration in biliary-cannulated and sham-operated control rats. Complete diversion of the bile did not significantly decrease the levels of [3H]LAAM or its metabolites in the systemic pool. These findings tend to minimize the contribution of enterohepatic circulation in the recirculation of active metabolites of LAAM and ultimately in its long duration of opiate-like action.

Pharmacokinetics of acetylmethadols I: gas-liquid chromatographic determination of L-alpha-acetylmethadol and its major metabolites in plasma.

A gas chromatographic method is reported for simultaneously determining acetylmethadol, noracetylmethadol, and dinoracetylmethadol in plasma. Minimum detectable concentrations are 10 ng ml-1 for acetylmethadol using a flame ionization detector, and 5 and 25 ng ml-1 for noracetylmethadol and dinoracetylmethadol respectively using electron capture detection. Extraction efficiency is quantitative for acetylmethadol but lower for the metabolites. The method is useful for monitoring drug levels following therapeutic doses of acetylmethadol.

The quantitative analysis of 1-alpha-acetylmethadol and its principal metabolites in biological specimens by gas chromatography-chemical ionization-multiple ion monitoring mass spectrometry.

1-alpha-acetylmethadol (LAAM) is a new drug under development for the treatment of heroin dependence. A new analytical method applicable to the accurate biodispositional study of the drug and its metabolities is described and critically discussed in this report. The procedure involves sample preparation and direct organic solvent extraction using eta-butyl chloride, amide derivatization by molecular rearrangement, and gas chromatography-chemical ionization mass spectrometry-selected ion monitoring, with methane as the carrier and ammonia as reagent gases. Deuterated (d3 stable isotopes of LAAM and its metabolites are used as internal standards. The method is free from qualitative interferences and has quantitative sensitivity to 5 ng/ml for 2.0 ml samples with 10-15% accuracy and precision in the range 5-100 ng/ml; and 2-5% at concentrations up to 750 ng/ml. Specimens of plasma, whole blood, urine, bile, brain, liver, and other visceral samples have been successfully analyzed, as well as in vitro preparations such as hepatic microsomes. By appropriate data processing, the method lends itself to routine analysis and high volume work; even manually the method is capable of at least 50 samples per week. A simplified procedure for the analysis of LAAM and its metabolites in urine only is also presented and discuet up and use the methods.

Metabolism and disposition of l-alpha-acetylmethadol in the rat.

The metabolism and disposition of the long-acting narcotic analygesic l-alpha-acetylmethadol (LAAM) were studied in the rat. 3H-LAAM was administered to male and female rats at doses of 5 mg/kg po and iv, and 10 mg/kg po. LAAM was rapidly absorbed and extensively metabolized. Five metabolites-noracetylmethadol, dinoracetylmethadol, methadol, normethadol, and N-acetylnormethadol-were identified in plasma and urine. Feces were the major route of elimination for the parent drug and metabolites. Less than 20% of the administered dose was excreted in the urine and, of this, greater than 90% was in the form of conjugates or polar metabolites. There is an apparent sex-related difference in LAAM disposition in the rat. LAAM and metabolites tended to persist in higher levels in female rats as compared with male rats. Similarly, male rats tended to excrete the drug at a faster rate than did females.

Time-action and behavioral effects of amphetamine, ethanol, and acetylmethadol.

As time increased between drug administration and the start of experimental sessions, effects of drugs on food-maintained responding in rhesus monkeys increased to a maximum and then decreased. d-Amphetamine, ethanol, and alpha-l-acetylmethadol (LAAM) generally decreased high response rates in one component of a chain schedule, while very low response rates in another component were increased reliably only by ethanol. The time of peak LAAM and ethanol concentrations in blood or plasma corresponded with or overlapped the time of maximal behavioral effect, while the time of maximal behavioral effect with d-amphetamine occurred somewhat prior to the time of peak plasma-amphetamine concentration. With d-amphetamine and perhaps with ethanol, effects on operant responding were greater after 30-min pretreatment intervals than after six-hr pretreatment intervals despite higher plasma or blood concentrations at six hours than at 30 min.