Interaction between ethanol and opioids in a protozoan assay

The Effects of Two New Amphetamine-like Derivatives on the Phagocytic Ability of the Protozoan, Tetrahymena pyriformis

Six new amphetamine-like molecules (2-[2,3-dihydro-4 H-1,4-benzoxazine-4-yl]-1-methyl-2-[l-methyl-2-phenylethylamino] ethanamines) were synthesised and their physico-chemical behaviour was studied. The log P values (index of lipophilicity) of the derivatives were calculated according to Rekker's fragmental system. One derivative representative of each series (C-5508 and C-5512) was selected, and their biological effects on the phagocytic ability of the protozoan, Tetrahymena pyriformis, were studied as a basic functional test for an amphetamine-like action. Furthermore, the action of both derivatives when administered concomitantly with haloperidol was also investigated. The data indicate that both derivatives significantly increased the phagocytic ability of the protozoan (p < 0.001), presumably via an alternative pathway to that of one of the dopamine monoaminergic pools. The administration of haloperidol significantly suppressed phagocytosis (p < 0.001). However, cultures exposed to the derivatives and to haloperidol indicated quantitatively different reactions. The lipophilic behaviours of the derivatives provide & possible explanation for such distinct effects.

Interindividual variability of the clinical pharmacokinetics of methadone: implications for the treatment of opioid dependence

Methadone is widely used for the treatment of opioid dependence. Although in most countries the drug is administered as a racemic mixture of (R)- and (S)- methadone, (R)-methadone accounts for most, if not all, of the opioid effects. Methadone can be detected in the blood 15-45 minutes after oral administration, with peak plasma concentration at 2.5-4 hours. Methadone has a mean bioavailability of around 75% (range 36-100%). Methadone is highly bound to plasma proteins, in particular to alpha(1)-acid glycoprotein. Its mean free fraction is around 13%, with a 4-fold interindividual variation. Its volume of distribution is about 4 L/kg (range 2-13 L/kg). The elimination of methadone is mediated by biotransformation, followed by renal and faecal excretion. Total body clearance is about 0.095 L/min, with wide interindividual variation (range 0.02-2 L/min). Plasma concentrations of methadone decrease in a biexponential manner, with a mean value of around 22 hours (range 5-130 hours) for elimination half-life. For the active (R)-enantiomer, mean values of around 40 hours have been determined. Cytochrome P450 (CYP) 3A4 and to a lesser extent 2D6 are probably the main isoforms involved in methadone metabolism. Rifampicin (rifampin), phenobarbital, phenytoin, carbamazepine, nevirapine, and efavirenz decrease methadone blood concentrations, probably by induction of CYP3A4 activity, which can result in severe withdrawal symptoms. Inhibitors of CYP3A4, such as fluconazole, and of CYP2D6, such as paroxetine, increase methadone blood concentrations. There is an up to 17-fold interindividual variation of methadone blood concentration for a given dosage, and interindividual variability of CYP enzymes accounts for a large part of this variation. Since methadone probably also displays large interindividual variability in its pharmacodynamics, methadone treatment must be individually adapted to each patient. Because of the high morbidity and mortality associated with opioid dependence, it is of major importance that methadone is used at an effective dosage in maintenance treatment: at least 60 mg/day, but typically 80-100 mg/day. Recent studies also show that a subset of patients might benefit from methadone dosages larger than 100 mg/day, many of them because of high clearance. In clinical management, medical evaluation of objective signs and subjective symptoms is sufficient for dosage titration in most patients. However, therapeutic drug monitoring can be useful in particular situations. In the case of non-response trough plasma concentrations of 400 microg/L for (R,S)-methadone or 250 microg/L for (R)-methadone might be used as target values.

Interaction of alcohol and drugs in fatal poisonings

In Finnish data from 1995-2000, 1006 fatal poisonings due to alcohol (ethanol), a single drug or both were statistically analysed in retrospect to evaluate the interaction between alcohol and drugs. In 53% of these cases, low concentrations of some common benzodiazepines were present. The median postmortem blood alcohol concentration (BAC) was 3.3 percent per thousand (w/w) in the 615 alcohol poisonings, but significantly lower, ranging from 1.3 to 1.7 percent per thousand, when promazine, doxepin, amitriptyline or propoxyphene were found together with alcohol. When levomepromazine, temazepam or zopiclone were present, the median BAC was also significantly lower, 2.5-2.7 percent per thousand. Citalopram and diltiazem did not exhibit a significant effect. The median BAC was significantly lower in cases with high concentrations than in those with low concentrations of a drug (excluding citalopram), suggesting a positive concentration-effect relationship. Fatal toxicity indices (FTIs) were calculated by relating the number of deaths caused by a drug to the corresponding sales figures. Promazine had an extremely high FTI, followed by levomepromazine, propoxyphene, doxepin and amitriptyline. The other drugs had relatively low FTIs. The results reflect not only the acute toxicity of a given drug-alcohol combination but also the manners of use and abuse of these drugs.

Characterization of methadone overdose: clinical considerations and the scientific evidence

Overdosing with methadone is a growing phenomenon in Britain and other countries due to the increase in prescription and the availability of this compound. Little is known of the circumstances surrounding methadone death due to some extent to the difficulty of defining drug-related death and also the difficulty of collecting clinical and biographical data in a predominantly illegal and marginal milieu. However, the evidence points to highest risk at night (to this end manifestations of its toxicity often go unrecognized) in those whose usual tolerance has been reduced and occurring some considerable time after ingestion. Further investigations are needed to elucidate fully the mechanism and spectrum of methadone overdose. Death from methadone is eminently preventable more so because of the long-term nature of the clinical sequelae. Indeed the key issue with methadone that sets it apart from other opioids is its potential for delayed toxicity. Consequently steps should be taken to disseminate the salient facts to all those who come into contact with the drug.

The effect of lofepramine and other related agents on the motility of Tetrahymena pyriformis

Tricyclic antidepressants (TCAs) were introduced almost 50 years ago. Whilst there is no doubt that TCAs are effective in treating depression, they are also more cardiotoxic when taken in overdose than other antidepressant groups. Lofepramine is a more recently introduced modified TCA, which in animals and man has low toxicity when compared to older TCAs. Paradoxically, lofepramine is extensively metabolised to desipramine, which has considerable toxicity, both experimentally and in overdose. The toxicity of such compounds is attributed, in part, to a membrane stabilising effect (MSA) on cell membranes. This MSA causes gross effects to the cell structure and in turn, normal cell activity. The aim of this study was to compare the MSA of lofepramine with that of desipramine and amitriptyline in order to see if this might help to explain the low toxicity of lofepramine. The local anaesthetic agent lignocaine was also studied for comparison. Each compound was enclosed in a beta-cyclodextrin to increase its solubility in aqueous medium. The extent of MSA was determined as a measure of the effect on the swimming speed of the protozoan Tetrahymena pyriformis using a video image analysis system. The IC50s for the various drugs were then correlated with their respective octanol-water partition coefficient values (Pow). Amitriptyline had an IC50 of 1.26+/-0.29 mM, desipramine 75.99+/-14.40 mM, while lofepramine had an IC50 of 357.40+/-25.00 mM. Lignocaine had an IC50 of 85.73+/-18.30 mM. There was also a significant correlation between the IC50 values and the Pow values.

DNA toxicity of cocaine hydrochloride and cocaine freebase by means of DNA image analysis on Tetrahymena pyriformis

An assay for computerized scoring of the DNA content of the protozoan Tetrahymena pyriformis has been used for the detection of toxic responses to cocaine, since DNA is responsible for the replication of the genetic material and also reflects closely the number of chromosomes in the nucleus. Thus, doubling of the number of chromosomes in a cell will also correspond to doubling of the DNA content and of the nuclear volume. Two chemical forms of cocaine were used, cocaine hydrochloride and cocaine freebase (crack), at two doses of 1 and 2 mg per 100 ml of protozoan culture, respectively. Image analysis of the protozoan nucleus patterns revealed a rapid stimulating effect on the DNA content for both cocaine hydrochloride and freebase after 1 h of incubation. However, after 2 h of treatment a reduction, although not statistically significant, of the DNA content of the protozoan was observed. These observations were further correlated with the phagocytic activity of the protozoan cultures. This paper provides some possible explanations of the toxic effects of cocaine on this particular cell model.

Tetrahymena pyriformis: a tool for toxicological studies. A review

Among protozoa, Tetrahymena pyriformis is the most commonly ciliated model used for laboratory research. After a brief description of the morphology and biology of Tetrahymena pyriformis, this article focuses on the most important and recent investigations performed with this species in toxicology and ecotoxicology. The methodological features of its culture, and main tests, based on cell growth rate, biochemical markers, behavioral changes and motility, are discussed. Examples of xenobiotics (organic and inorganic substances, pharmaceutical drugs, water pollutants) tested with Tetrahymena pyriformis are also given.

Membrane toxicity of opioids measured by protozoan motility

The acute toxicity of some opioid drugs cannot solely be explained by a specific interaction with the opioid receptor. The anaesthetic-like membrane effect of 10 opioid agents and the antagonist naloxone was determined and correlated with their hydrophobicity. The inhibitory effect of drugs on protozoan motility was used as a measure of their membrane toxicity, measured by the reduction in swimming speed of Tetrahymena pyriformis using an image analysis system. Hydrophobicity was determined as the n-octanol/water partition coefficient, at pH 7.4, 37 degrees C. Opioid agents dose-dependently reduced the swimming speed of Tetrahymena pyriformis with a wide range of IC50 values. Some weak opioid agents were shown to have high protozoan immobilising potency comparable to quinidine, an agent with known membrane stabilising activity. Norpropoxyphene, the metabolite of dextropropoxyphene, with little affinity for the opioid receptor, also had a high potency. The inhibition of protozoan motility by these opioid agents was not antagonised by the opioid receptor antagonist naloxone; moreover an additive inhibitory action was demonstrated when opioid agents were combined with naloxone. The effect of opioid agents on protozoan motility was closely correlated with their partition coefficient but not with their known affinity for opioid receptors. These results suggest that opioid agents possess differing degrees of membrane depressant action independent from their interaction with the opioid receptor, and have a potential for causing depressant effects on excitable tissues.

Modulation by alcohol and methadone of 2-deoxyglucose-stimulated pancreatic secretion in the rat

Alcohol intake is a major problem in drug addicts, and it is not clear whether the effects of alcohol and opiates are additive or potentiating. Vagally stimulated pancreatic secretion in rats is potently inhibited by opiates acting centrally at mu-receptors. In the present experiments, we determined the effects of methadone on 2-deoxyglucose (2DG)-stimulated pancreatic secretion in rats treated with acute (1.9 g/kg.3 h, intravenously) or chronic (1 or 3 month drinking) ethanol. In both acute and 1 month chronic alcoholic rats, methadone administered at its 50% inhibitory dose (ID50) reduced by about 50% 2DG-stimulated pancreatic secretion of sodium, bicarbonate and protein, and ethanol had only faint, nonsignificant inhibitory effects. In 3 month chronic alcoholic rats, similar results were obtained, but methadone inhibited 2DG-stimulated pancreatic secretion by 60 to 90% in these older rats. No significant interaction was found in any condition between ethanol and methadone, suggesting that they had only additive, but not potentiating effects in this method.

Endogenous opiates: 1994

This article is the 17th installment of our annual review of research concerning the opiate system. It includes papers published during 1994 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics covered this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.