Levo-alpha-acetylmethadol (LAAM) induced QTc-prolongation - results from a controlled clinical trial.

BACKGROUND: Due to potential proarrhythmic side-effects levo-alpha-Acetylmethadol (LAAM) is currently not available in EU countries as maintenance drug in the treatment of opiate addiction. However, recent studies and meta-analyses underline the clinical advantages of LAAM with respect to the reduction of heroin use. Thus a reappraisal of LAAM has been demanded. The aim of the present study was to evaluate the relative impact of LAAM on QTc-interval, as a measure of pro-arrhythmic risk, in comparison to methadone, the current standard in substitution therapy. METHODS: ECG recordings were analysed within a randomized, controlled clinical trial evaluating the efficacy and tolerability of maintenance treatment with LAAM compared with racemic methadone. Recordings were done at two points: 1) during a run-in period with all patients on methadone and 2) 24 weeks after randomisation into methadone or LAAM treatment group. These ECG recordings were analysed with respect to QTc-values and QTc-dispersion. Mean values as well as individual changes compared to baseline parameters were evaluated. QTc-intervals were classified according to CPMP-guidelines. RESULTS: Complete ECG data sets could be obtained in 53 patients (31 LAAM-group, 22 methadone-group). No clinical cardiac complications were observed in either group. After 24 weeks, patients receiving LAAM showed a significant increase in QTc-interval (0.409s +/- 0.022s versus 0.418s +/- 0.028s, p = 0.046), whereas no significant changes could be observed in patients remaining on methadone. There was no statistically significant change in QTc-dispersion in either group. More patients with borderline prolonged and prolonged QTc-intervals were observed in the LAAM than in the methadone treatment group (n = 7 vs. n = 1; p = 0.1). CONCLUSIONS: In this controlled trial LAAM induced QTc-prolongation in a higher degree than methadone. Given reports of severe arrhythmic events, careful ECG-monitoring is recommended under LAAM medication.

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.

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.

Detection of methadone, LAAM, and their metabolites by methadone immunoassays.

l-Alpha-acetylmethadol (LAAM) was recently approved as a substitute for methadone. LAAM, methadone, and their common metabolite, methadol, are extensively N-demethylated. The structural similarities of LAAM and its metabolites to methadone suggest that they may cross-react in methadone immunoassays. To test this hypothesis, drug-free urine was fortified with LAAM, norLAAM, dinorLAAM, methadol, normethadol, dinormethadol, methadone, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), or 2-ethyl-5-methyl-3,3-diphenylpyrroline (EMDP) at 12 concentrations (0.03 to 100 microg/mL). Samples were analyzed using two enzyme immunoassays (Behring Diagnostics, EIA-b; Diagnostic Reagents, EIA-d); a fluorescent polarization immunoassay (Abbott, FPIA); two enzyme-linked immunosorbant immunoassays (Diagnostix, ELISA-d; STC Technologies, ELISA-s); a kinetic microparticles in solution immunoassay (Roche Diagnostic Systems, KIMS); and a radioimmunoassay (Diagnostic Products, RIA). LAAM had high cross-reactivity with ELISA-d (318.3%), RIA (249.5%), EIA-d (100.8%), KIMS (91.1%), and ELISA-s (75.3%). Methadol also displayed relatively high cross-reactivity as follows: EIA-d (97.8%), KIMS (85.4%), ELISA-d (70.3%), and FPIA (37.7%). Successive N-demethylations of LAAM and methadol were associated with loss of cross-reactivity. The methadone metabolites EDDP and EMDP showed little cross-reactivity. These findings suggest that LAAM use could result in positive immunoassay test results when using many of the commercially available methadone immunoassay kits and that confirmation of LAAM and its metabolites should be considered.

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.

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%.

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.

Mass fragmentographic determination of methadyl acetate in urine using stable isotope labeled analog as internal standard.

A quantitative GLC-mass spectrometric assay was developed for the determination of methadyl acetate in urine. The assay utilized selective ion focusing to monitor, in a GLC effluent, the M--15 ion generated by electron-impact ionization of methadyl acetate. Methadyl acetate-d4 was used as an internal standard. The assay can measure 10 ng of drug/ml with about 6% precision. The curve relating the amounts of drug added to control urine versus the amounts experimentally found over a large concentration range is a straight line with a slope of 0.98 +/- 0.02 and a nearly zero intercept. Assay specificity was confirmed by complete identity of the mass spectrum of methadyl acetate in the biological extract with that of the authentic material. The method was used for the urinary analysis of methadyl acetate in a rabbit given a single intravenous dose. The animal excreted less than 1% of the intact drug with a half-life of approximately 15 hr. Consequently, the long-acting characteristic of methadyl acetate must be attributed to its metabolism into active metabolites.

The effect of ethanol on the metabolism of chronically-administered l-alpha-acetylmethadol (LAAM) in the rhesus monkey.

The metabolism of 3H-LAAM was studied in monkeys treated acutely and chronically with 2 mg/kg LAAM via intragastric catheter three times weekly. From the 15th week, 250 mg/kg ethanol every 2 hours (3g/kg/day) was also administered. This dose of ethanol did not impair the metabolism of LAAM in monkeys.

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.

Metabolism and probable active metabolite of alpha-l-acetylmethadol in rat.

alpha-l-Acetylmethadol is being currently evaluated as a substitute for methadone in the treatment of heroin addicts. The metabolites, isolated from urine, liver, and serum, were identified by gas-liquid chromatography. Methadone and its metabolites were found to be present in urine, liver and serum of rats treated with alpha-l-acetylmethadol. The presence of methadone was confirmed by gas-chromatography-mass spectometry. The purpose of this study was to determine whether alpha-l-acetylmethadol is metabolized to methadone, which might explain in part the longer duration of action of alpha-l-acetylmethadol.

Comparative study on the derivatization of l-alpha-acetyl-methadol metabolites for electron capture gas-liquid chromatography.

Six reagents-trichloroacetyl chloride, trichloroacetic anhydride, pentafluorobenzoyl chloride, heptafluorobutyryl chloride, heptafluorobutyric anhydride, and trifluoroacetic anhydride- were evaluated as potential derivatizing reagents for quantitating the metabolites of l-alpha-acetylmethadol (LAAM) -noracetylmethadol, dinoracetylmethadol, methadol, and normethadol-by electron capture gas-liquid chromatography. All of the reagents studied reacted quantitatively with all of the metabolites except methadol; however, trichloroacetyl chloride was found to be the most satisfactory general reagent for analyzing these metabolites in biological fluids. A gas-liquid chromatographic method is presented which combines both flame ionization and electron capture detection for quantitating plasma and urine levels of methadone, l-alpha-acetylmethadol and its metabolites.

Extraction method and thin-layer chromatographic system for the determination of alpha-l-acetylmethadol and metabolites in biological fluids.

An extraction method and thin-layer chromatographic (TLC) system for the determination of alpha-l-acetylmethadol and its known metabolites (methadol, noracetylmethadol, dinoracetylmethadol, normethadol, 6-acetamide-4,4-diphenyl-3-heptanol, and N-methyl-6-acetamido-4,4-diphenyl-3-heptanol) are described. The parent drug and metabolites are extracted from biological fluids with ethyl acetate and separated by TLC using silica gel plates and a developing system of ethyl acetate-methanol-water-ammonia (85:10:1:1). This system may be used to quantitatively determine levels of radiolabeled drug and metabolites by scraping the TLC plates into 3-mm zonal fractions and measuring the amount of radioactivity by scintillation counting. A representative radiochromatogram obtained from an extract of monkey urine is shown.

Simultaneous determination of acetylmethadol and its active riotransformation products in human biofluids.

A method employing solvent extraction and gas-liquid chromatography has been developed for the quantitative determination of acetylmethadol simultaneously with its two major biotransformation products, noracetylmethadol and dinoracetylmethadol. Noracetylmethadol and dinoracetylmethadol are analyzed following their conversion to the corresponding amides. The amide structure is confirmed by the use of chemical ionization mass spectroscopy and infrared spectroscopy. The method can be used to determine the concentration of acetylmethadol and these compounds in plasma samples from acetylmethadol maintenance subjects. Methadol and normethadol do not attain neasurable plasma levels. Urine contains predominantly noracetylmethadol and dinoracetylmethadol. Evidence was also obtained for the urinary excretion of acetylmethadol, methadol and normethadol. A mean quantity equal to 28% of the administered dose was excreted in the urine of a 48-h dosing interval as acetylmethadol and metabolites.