Confirming urinary excretion of mephentermine and phentermine following the ingestion of oxethazaine by gas chromatography-mass spectrometry analysis.

Mephentermine and phentermine, substances prohibited in sports by the World Anti-Doping Agency, were found for the first time in urine specimens following the administration of a therapeutic medication, oxethazaine. In a recent sporting event, a urine specimen donor who tested positive for mephentermine and phentermine claimed consumption of Mucaine((R)) for treating stomach pain was the reason for testing positive. Five volunteers were administrated oxethazaine (a topical anesthetic found in the multi-ingredient medication Mucaine and its generic equivalent, Stoin, both of which are available in Taiwan), mephentermine, and phentermine. Excretion profiles of mephentermine and phentermine following the administration of these drugs were found to be similar. However, the mephentermine/phentermine ratios found in urine specimens collected at different time points following the administration of oxethazine and mephentermine were found to be characteristically different.

Dopamine/serotonin releasers as medications for stimulant addictions.

The use of 'agonist therapy' for cocaine and methamphetamine addiction involves administration of stimulant-like medications (e.g. monoamine releasers) to reduce withdrawal symptoms and prevent relapse. A significant problem with this strategy is that many candidate medications possess abuse liability due to activation of mesolimbic dopamine (DA) neurons in the brain. One way to reduce DA-mediated abuse liability of candidate drugs might be to add in serotonin (5-HT)-releasing properties, since substantial evidence shows that 5-HT neurons provide an inhibitory influence over mesolimbic DA neurons. This chapter addresses several key issues related to the development of dual DA/5-HT releasers for the treatment of substance use disorders. First, we briefly summarize the evidence supporting a dual deficit in DA and 5-HT function during withdrawal from chronic cocaine or alcohol abuse. Second, we discuss data demonstrating that 5-HT release can dampen DA-mediated stimulant effects, and the 'anti-stimulant' role of 5-HT(2C) receptors is considered. Next, the mechanisms underlying potential adverse effects of 5-HT releasers are described. Finally, we discuss recently published data with PAL-287, a novel non-amphetamine DA/5-HT-releasing agent that suppresses cocaine self-administration but lacks positive reinforcing properties. It is concluded that DA/5-HT releasers could be useful therapeutic adjuncts for the treatment of cocaine and alcohol addictions as well as for obesity, attention deficit disorder and depression.

Fluoxetine increases the anorectic and long-term dopamine-depleting effects of phentermine.

The anorectic drug phentermine produces dose-related toxic effects on brain dopamine (DA) neurons in animals. Until recently, phentermine was widely used in combination with fenfluramine for purposes of appetite suppression and weight loss. With the recent withdrawal of fenfluramine from the market, many people have begun combining phentermine with fluoxetine, a serotonin reuptake inhibitor which also produces mild anorectic effects. Fluoxetine, in addition to inhibiting serotonin reuptake, inhibits hepatic mixed function oxidase, which plays an important role in the metabolic degradation of amphetamines. The purpose of the present study was to assess the effects of fluoxetine on the anorectic and DA neurotoxic effects of phentermine in mice. Phentermine, in combination with fluoxetine, produced greater reductions in food intake and body weight than phentermine alone. The phentermine/fluoxetine combination also produced greater long-term reductions in brain DA levels than phentermine alone, likely reflecting greater DA neurotoxicity of the drug combination. Brain concentrations of phentermine were also found to be higher in animals pretreated with fluoxetine. These findings indicate that fluoxetine potentiates both the anorectic and DA neurotoxic effects of phentermine, probably by increasing phentermine brain levels. The clinical significance of these findings remains to be ascertained.

Metabolism of mephentermine and its derivatives by the microsomal fraction from male Wistar rat livers.

1. The N-demethylation of mephentermine (MP), p-hydroxymephentermine (p-hydroxy-MP) and N-hydroxymephentermine (N-hydroxy-MP), to produce phentermine (Ph), p-hydroxyphentermine (p-hydroxy-Ph) and N-hydroxyphentermine (N-hydroxy-Ph), and the p-hydroxylation of MP and Ph, to produce p-hydroxy-MP and p-hydroxy-Ph, were examined using rat liver microsomal preparations containing NADPH. Microsomal reduction of N-hydroxy-Ph to Ph was also examined using various cofactors. In addition, enzymic system for the N-demethylation and p-hydroxylation were examined using various inhibitors. 2. N-Hydroxy-MP demethylation to N-hydroxy-Ph proceeded at a rate almost 10-fold faster than other reactions. MP demethylation to Ph, MP oxidation to P-hydroxy-MP, Ph oxidation to p-hydroxy-Ph proceeded at similar rates, whilst p-hydroxy-MP demethylation to p-hydroxy-Ph was catalysed at the slowest rate. Microsomal reduction of N-hydroxy-Ph to Ph required NADH, and the activity was similar to that of MP oxidation to p-hydroxy-MP. 3. N-Demethylation of MP, p-hydroxy-MP and N-hydroxy-MP were inhibited not only by inhibitors of cytochrome P450, but also by methimazole, an inhibitor of the FAD-monooxygenase system. p-Hydroxylations of MP and Ph were inhibited only by inhibitors of cytochrome P450.

Intestinal metabolism of mephentermine and its biliary metabolites in male Wistar rats.

1. Intestinal metabolites produced in the incubation (0-24 h) of mephentermine (MP), phentermine (Ph), N-hydroxymephentermine (N-hydroxy-MP), N-hydroxyphentermine (N-hydroxy-Ph), p-hydroxymephentermine (p-hydroxy-MP) and p-hydroxyphentermine (p-hydroxy-Ph) with male Wistar rat intestinal contents under N2 were examined by g.l.c. and g.l.c.-electron impact (EI) mass spectrometry. Metabolites produced in the anaerobic incubation of bile from rats given MP, with the intestinal contents were also examined. In addition, urinary and biliary metabolites of p-hydroxy-MP and p-hydroxy-Ph dosed orally to rat were examined. 2. Metabolites in the anaerobic incubation of N-hydroxy-MP and N-hydroxy-Ph were MP and Ph, and Ph, respectively. No metabolites were detected in the incubation of MP, Ph, p-hydroxy-MP and p-hydroxy-Ph. 3. p-Hydroxy-MP and p-hydroxy-Ph (major), and MP and Ph (minor) were detected when bile from rats given MP was incubated with intestinal contents. 4. Unchanged p-hydroxy-MP, and conjugates of p-hydroxy-MP and p-hydroxy-Ph, were detected in the 24-h urine of rats dosed with p-hydroxy-MP, which accounted for about 3, 72 and 1% dose, respectively. Unchanged p-hydroxy-Ph and conjugated p-hydroxy-Ph were detected in the 24-h urine of rats dosed with p-hydroxy-Ph, which accounted for about 4 and 68% dose, respectively. 5. Conjugated p-hydroxy-MP and conjugated p-hydroxy-Ph, which accounted for about 3% doses, were detected in the 24-h bile of rats dosed with p-hydroxy-MP and p-hydroxy-Ph.(ABSTRACT TRUNCATED AT 250 WORDS)

The formation of metabolites of mephentermine by microsomal and cytosolic preparations of male Wistar rat livers.

1. Metabolites of mephentermine (MP), phentermine (Ph), p-hydroxy-MP, p-hydroxy-Ph, N-hydroxy-MP and N-hydroxy-Ph on incubation with rat liver microsomal and cytosolic preparations were identified by g.l.c. and g.l.c.-mass spectrometry. 2. Identification of the metabolites indicated the following new metabolic routes of MP: NADPH-dependent microsomal formation of p-hydroxy-MP from MP, of p-hydroxy-Ph from p-hydroxy-MP, and the NADH-dependent microsomal formation of Ph from N-hydroxy-Ph.

Mechanism of oxidation of N-hydroxyphentermine by superoxide.

Cytochrome P-450 oxidizes N-hydroxyphentermine (MPPNHOH) by an indirect pathway involving superoxide. The chemical details of this oxidation, in which N-hydroxyphentermine is converted to 2-methyl-2-nitro-1-phenylpropane (MPPNO2), have been elucidated by examining the interaction of MPPNHOH with superoxide in aqueous and organic solvents. The role of peroxide, hydroperoxy radicals, and oxygen in the reaction was also examined. The results indicate that superoxide itself is oxidizing MPPNHOH to a nitroxide that disproportionates to MPPNHOH and 2-methyl-2-nitroso-1-phenylpropane (MPPNO). MPPNO is then oxidized to MPPNO2 by O2 or hydroperoxide. Two possible mechanisms for the superoxide oxidation were considered, a proton abstraction and a hydrogen atom abstraction. Stoichiometric and oxygen evolution studies favor the hydrogen abstraction pathway.

Role of superoxide in the N-oxidation of N-(2-methyl-1-phenyl-2-propyl)hydroxylamine by the rat liver cytochrome P-450 system.

The N-oxidation of N-(2-methyl-1-phenyl-2-propyl)hydroxylamine (N-hydroxyphentermine, MPPNHOH) and the N-hydroxylation of 2-methyl-1-phenyl-2-propylamine (phentermine) by reconstituted systems that contained cytochromes P-450 purified from rat liver microsomes were demonstrated. The oxidation of MPPNHOH, but not of phentermine, could also be mediated by a superoxide and hydrogen peroxide generating system that contained xanthine and xanthine oxidase. Superoxide dismutase completely inhibited the oxidation of MPPNHOH by the xanthine/xanthine oxidase system and inhibited by 70% the oxidation mediated by a reconstituted cytochrome P-450 oxidase system. The majority of the microsomal oxidation was inhibited by an antibody raised against the major isozyme of cytochrome P-450 purified from livers of phenobarbital-pretreated rats. 2-Methyl-2-nitroso-1-phenylpropane (MPPNO) was found to be an intermediate in the overall oxidation of MPPNHOH to 2-methyl-2-nitro-1-phenylpropane (MPPNO2). Superoxide dismutase appeared to inhibit the first step, the conversion of MPPNHOH to MPPNO. These observations are accounted for by a sequence of two mechanistically distinct P-450-mediated oxidations. In the first reaction, N-hydroxylation of phentermine occurs by a normal cytochrome P-450 pathway. The formed hydroxylamine then uncouples the cytochrome P-450 system to generate superoxide and hydrogen peroxide. The superoxide oxidizes MPPNHOH to MPPNO which is then oxidized to MPPNO2, the ultimate product. This superoxide-mediated oxidation represents another pathway for N-oxidation by cytochrome P-450.

A fatality involving phentermine.

A case is presented where phentermine, a sympathomimetic amine used as an anorectic drug, is believed to have significantly contributed to the death of an individual in whom other drugs were also found. Blood, urine, and tissue concentrations of phentermine are reported and compared to other cases in the literature.

Effects of chlorphentermine and phentermine on the pulmonary disposition of 5-hydroxytryptamine in the rat in vivo.

This study was designed to examine whether chlorphentermine (CP) affects pulmonary disposition of 5-hydroxytryptamine (5-HT) in rat in vivo. Further, the effects of CP were compared with those of phentermine (P), the nonchlorinated congener. The right jugular vein and left carotid artery of male Sprague-Dawley rats were cannulated to the level of the superior caval vein and ascending aorta, respectively. After 10 min of stabilization, 0.3 ml fresh saline solution containing 150 micrograms indocyanine green and a mixture of labeled and unlabeled 5-HT was injected into the jugular vein, and arterial blood samples were collected for 20 s. Pulmonary extraction of 5-HT during a single pass was inversely proportional to the injected dose, ranging from 67% cf injected dose for a 2.6 nmol dose to 30% for a 130 nmol dose, indicating a saturable pulmonary uptake for 5-HT. In order to compare the effect of CP and P on pulmonary disposition of 5-HT, 2.6 nmol [14C]-5-HT was employed for in vivo single-pass experiments. Each animal was used for 2 in vivo single-pass experiments. After the first experiment, which served as a control, animals received an indicated dose of CP or P, to commence the second "drug-treated" in vivo experiment. Pulmonary clearance of 5-HT was inhibited by prior administration of CP (1 mg/kg) by 42%, whereas at the highest dose (20 mg/kg) P inhibited 5-HT clearance by only 25%. Pulmonary accumulation of CP was greater than P at higher doses, and the inhibition of 5-HT clearance correlated with the pulmonary accumulation of these drugs. In addition to the in vivo demonstration of the CP inhibition of pulmonary clearance of 5-HT in the rat, these studies also demonstrate a higher affinity of the lung tissue for CP than for P and a greater propensity for the impairment of pulmonary 5-HT clearance.

Plasma phentermine levels, weight loss and side-effects.

Fifty women with refractory obesity received phentermine resinate. Seven were withdrawn because of side-effects: three developed severe headaches, one each hypertension, depressive symptoms, breathlessness and palpitations with irritability. The mean weight loss in the 34 who completed the 20-week study was 6.4 kg. Nine lost 10 kg or more. Sustained appetite suppression was related to weight loss. Plasma phentermine concentrations did not correlate with the severity of the obesity problem, the degree of subjective anorexia or with weight loss. Poor initial response to standard dosage of phentermine is unlikely to improve with higher dosage. The individual's response to phentermine is unpredictable and appears to relate to factors other than the plasma drug concentration.

N-oxidation of phentermine to N-hydroxyphentermine by a reconstituted cytochrome P-450 oxidase system from rabbit liver.

Previous studies in our laboratory have indicated that the cytochrome P-450 system is involved in the oxidation of phentermine (2-methyl-1-phenyl-2-aminopropane) to N-hydroxyphentermine by liver microsomal preparations. In the present study, a reconstituted system which consisted of cytochrome P-450 and NADPH cytochrome P-450 reductase purified from liver microsomes of phenobarbital-induced rabbits was found to oxidize phentermine to N-hydroxyphentermine. The reaction was NADPH-dependent and required the presence of both the cytochrome P-450 and reductase preparations. N-Hydroxyphentermine was formed 3 times more rapidly in incubation mixtures which contained dilauroyl phosphatidylcholine than in those without added phospholipid. The reaction was inhibited several-fold by octylamine. It is concluded that the cytochrome P-450 system is able to catalyze the oxidation of phentermine to N-hydroxyphentermine.

Kinetic isotope effects in cytochrome P-450-catalyzed oxidation reactions. Intermolecular and intramolecular deuterium isotope effects during the N-demethylation of N,N-dimethylphentermine.

Two N,N-dimethylphentermine (N,N-dimethyl-2-amino-2-methyl-3-phenylpropane) substrates differing in deuterium substitution have been used to determine the intermolecular and intramolecular isotope effects associated with the cytochrome P-450-dependent N-demethylation of this substrate. No intermolecular isotope effect was observed in Vmax or Vmax/Km when the reaction rates for this substrate were compared to those for the substrate in which both N-methyl groups contained deuterium. In contrast, identical isotope effects of 1.6 to 2.0 were observed in both Vmax and Vmax/Km when this reaction was studied with a substrate in which only one of the two N-methyl groups was substituted with deuterium. Furthermore, both the intermolecular and intramolecular isotope effects were independent of the cytochrome P-450/NADPH-cytochrome P-450 reductase mole ratio. From these data, it is concluded that: 1) the carbon-hydrogen bond cleavage step does not contribute significantly to Vmax; 2) the contribution of the carbon-hydrogen bond cleavage step to Vmax is not detectably increased through changes in the cytochrome P-450/NADPH-cytochrome P-450 reductase mole ratio; 3) the N-methyl groups are free to exchange at the enzyme active site. The basis for these conclusions is the proposal of a new kinetic model for interpretation of intramolecular isotope effects which shows that intramolecular isotope effects are not necessarily equal to intrinsic isotope effects and, in fact, may be much smaller.

Studies on the persistence of basic amines in the rabbit lung.

We have investigated the time-course of the pulmonary deposition of imipramine (IMIP) following a single iv injection into rabbits. A pool of IMIP and its demethylated metabolites, which exhibited considerable persistence (half-life of decay = 4 hr), was formed in the lung. This pool, now called the slowly effluxable pool (SEP), appears to be synonymous with the noneffluxable pool (NEP), which we have previously shown to be formed with IMIP in the isolated perfused lung (PL). Furthermore, this pool appears to be responsible for the pulmonary persistence of IMIP, inasmuch as 24 hr after an iv injection it contributes greater than 90% of the total lung concentration. Chlorphentermine and methadone formed SEP's in the IPL of comparable size to that formed with IMIP, whereas phentermine formed a considerably smaller SEP. These results suggest that the degree of hydrophobicity of the amine is an important determinant of the size of the SEP formed. This further supported by the lack of an SEP with the relatively polar amines, 5-hydroxytryptamine and amphetamine. The 10-fold difference in the size of the SEP for compounds known to induce pulmonary phospholipidosis (chlorphentermine and IMIP) and known not to induce lipidosis (phentermine and amphetamine) may suggest a possible involvement of the SEP in the onset of phospholipidosis; this possibility is discussed.

The metabolism of N-hydroxyphentermine by rat liver microsomes.

N-Hydroxyphentermine is oxidized to 2-methyl-2-nitro-1-phenylpropane by rat liver microsome preparations. This oxidation accounts for differences noted in levels of N-hydroxyphentermine formed from phentermine in washed and unwashed microsome preparations. The reaction is inhibited by hemoglobin and catalase, whose presence in unwashed microsomes could terminate the N-oxidation of phentermine at the hydroxylamine level. The hydroxylamine-nitro-oxidation appears to be dependent on cytochrome P-450, as the reaction was induced by phenobarbital pretreatment and inhibited by carbon monoxide and 2,4-dichloro-6-phenylphenoxyethylamine.