Intracellular distribution of psychotropic drugs in the grey and white matter of the brain: the role of lysosomal trapping

1. Since the brain is not a homogenous organ (i.e. the phospholipid pattern and density of lysosomes may vary in its different regions), in the present study we examined the uptake of psychotropic drugs by vertically cut slices of whole brain, grey (cerebral cortex) and white (corpus callosum, internal capsule) matter of the brain and by neuronal and astroglial cell cultures. 2. Moreover, we assessed the contribution of lysosomal trapping to total drug uptake (total uptake=lysosomal trapping+phospholipid binding) by tissue slices or cells conducting experiments in the presence and absence of 'lysosomal inhibitors', i.e., the lysosomotropic compound ammonium chloride (20 mM) or the Na(+)/H(+)-ionophore monensin (10 microM), which elevated the internal pH of lysosomes. The initial concentration of psychotropic drug in the incubation medium was 5 microM. 3. Both total uptake and lysosomal trapping of the antidepressants investigated (imipramine, amitriptyline, fluoxetine, sertraline) and neuroleptics (promazine, perazine, thioridazine) were higher in the grey matter and neurones than in the white matter and astrocytes, respectively. Lysosomal trapping of the psychotropics occurred mainly in neurones where thioridazine sertraline and perazine showed the highest degree of lysosomotropism. 4. Distribution interactions between antidepressants and neuroleptics took place in neurones via mutual inhibition of lysosomal trapping of drugs. 5. A differential number of neuronal and glial cells in the brain may mask the lysosomal trapping and the distribution interactions of less potent lysosomotropic drugs in vertically cut brain slices. 6. A reduction (via a distribution interaction) in the concentration of psychotropics in lysosomes (depot), which leads to an increase in their level in membranes and tissue fluids, may intensify the pharmacological action of the combined drugs.

The effect of selective serotonin reuptake inhibitors (SSRIs) on the pharmacokinetics and metabolism of perazine in the rat

The aim of this study was to investigate the effect of three selective serotonin reuptake inhibitors (SSRIs), fluoxetine, fluvoxamine and sertraline, on the pharmacokinetics and metabolism of perazine in a steady state in rats. Perazine (10 mg kg(-1), i.p.) was administered twice daily for two weeks, alone or jointly with one of the SSRIs. Concentrations of perazine and its two main metabolites (N-desmethylperazine and 5-sulfoxide) in the plasma and brain were measured 30 min and 6 and 12 h after the last dose of the drugs. Of the investigated SSRIs, fluoxetine and fluvoxamine significantly increased plasma and brain concentrations of perazine (up to 900% and 760% of the control value, respectively), their effect being most pronounced after 30 min and 6 h. Moreover, simultaneous increases in perazine metabolites concentrations and in the perazine/metabolite concentration ratios were observed. Sertraline elevated plasma and brain concentrations of perazine after 30 min. In-vitro studies with liver microsomes of rats treated chronically with perazine, SSRIs ortheir combinations showed decreased concentrations of cytochrome P-450 after perazine and a combination of perazine and fluvoxamine (vs control), and increased concentration after a combination of perazine and fluoxetine (vs perazine-treated group). Prolonged treatment with perazine did not significantly change the rate of its own metabolism. Chronic administration of fluoxetine or sertraline, alone or in a combination with perazine, accelerated perazine N-demethylation (vs control or perazine group, respectively). Fluvoxamine had a similar effect. The 5-sulfoxidation of perazine was accelerated by fluvoxamine and sertraline treatment, but the process was inhibited by administration of a combination of perazine and fluoxetine or fluvoxamine (vs control). Kinetic studies using control liver microsomes, in the absence or presence of SSRIs added in-vitro, demonstrated competitive inhibition of both N-demethylation and sulfoxidation by the investigated SSRIs. Sertraline was the most potent inhibitor of perazine N-demethylation but the weakest inhibitor of sulfoxidation. Results of in-vivo and in-vitro studies indicate that the observed interaction between perazine and SSRIs mainly involves competition for an active site of perazine N-demethylase and sulfoxidase. Moreover, increases in the concentrations of both perazine and metabolites measured, produced by the investigated drug combinations in-vivo, suggest simultaneous inhibition of another, yet to be investigated, metabolic pathway of perazine (e.g. aromatic hydroxylation).

Different effects of amitriptyline and imipramine on the pharmacokinetics and metabolism of perazine in rats

The aim of this study was to search for possible effects of imipramine and amitriptyline on the pharmacokinetics and metabolism of perazine at steady state in rats. Perazine (10 mg kg(-1), i.p.) was administered to rats twice daily for two weeks, alone or jointly with imipramine or amitriptyline (10 mg kg(-1) i.p.). Concentrations of perazine and its two main metabolites (5-sulphoxide and N-desmethylperazine) in the plasma and brain were measured at 30 min (Cmax), 6h and 12h (slow disposition phase) after the last dose of the drugs. Liver microsomes were prepared 24 h after withdrawal of the drugs. Amitriptyline increased the plasma and brain concentrations of perazine (up to 300% of the control) and N-desmethylperazine, while not affecting those of 5-sulphoxide. Imipramine only tended to increase the neuroleptic concentration in the plasma and brain. Studies with control liver microsomes showed that amitriptyline and imipramine added to the incubation mixture in-vitro, competitively inhibited N-demethylation (Ki (inhibition constant) = 16 microM and 164 microM, respectively) and 5-sulphoxidation (Ki = 57 microM and 86 microM, respectively) of perazine, amitriptyline being a more potent inhibitor of perazine metabolism, especially with respect to N-demethylation. Studies with microsomes of rats treated chronically with perazine or tricyclic antidepressants, or both, did not show significant differences in the rate of perazine metabolism between perazine- and perazine+antidepressant-treated rats. The data obtained were compared with the results of analogous experiments with promazine and thioridazine. It was concluded that elevations of perazine concentration were caused by direct inhibition of the neuroleptic metabolism by the antidepressants. Similar interactions, possibly leading to exacerbation of the pharmacological action of perazine, may be expected in man. Since the interactions between phenothiazines and tricyclic antidepressants may proceed in two directions, reduced doses of both the neuroleptic and the antidepressant are recommended when the drugs are administered jointly.

Distribution interactions between perazine and antidepressant drugs. In vivo studies

Perazine belongs to the most frequently chosen neuroleptics for a combination with antidepressants in the therapy of complex or "treatment-resistant" psychiatric illnesses. The aim of the present study was to investigate the effect of the distribution interaction between perazine and antidepressants in vivo. Experiments were carried out on male Wistar rats. Animals received perazine and an antidepressant drug (imipramine or fluoxetine), separately or jointly, at a dose of 10 mg/kg ip. Concentrations of perazine, imipramine, fluoxetine and their metabolites in the blood plasma and tissues were measured at 1 h after administration of the drugs (HPLC). Effects of distribution interactions were estimated on the basis of the calculated tissue/plasma and lysosome-poor/lysosome-rich tissue concentration ratios, considering the heart and muscles as lysosome-poor and the lungs, liver and kidneys as lysosome-rich ones. Both imipramine and fluoxetine diminished the tissue/plasma concentration ratios of perazine for the lungs and kidneys (not for the liver), but elevated those ratios for the brain, muscles and heart. On the other hand, perazine lowered the lungs/plasma concentration ratio of both antidepressants and the liver/plasma concentration ratio of imipramine. Simultaneously, perazine elevated the brain/plasma and heart/plasma concentration ratios of both antidepressants. Consequently, the perazine concentration ratios of lysosome-poor/lysosome-rich tissue significantly increased in the presence of the investigated antidepressants, with an exception of the muscles/liver concentration ratio. At the same time, perazine raised the heart/lysosome-rich tissue concentration ratios of imipramine and fluoxetine, not changing significantly the muscles/lysosome-rich concentration ratios of the antidepressants. In conclusion, the presented results provide evidence that the observed in vitro distributive interactions between perazine and the antidepressants occur also in vivo, leading to a shift of the drugs from organs rich in lysosomes to those poor in these organella, in particular to the heart. Perazine and the antidepressants mutually increased the drug concentration ratios of heart/plasma and heart/lysosome-rich tissue, i.e. the heart/lung, heart/liver and heart/kidneys ratios. Similar results were obtained with lysosome-poor muscles in the case ofperazine. Moreover, the obtained results indicate that, apart from the lysosome density in the investigated tissues, the potential metabolic interactions in the liver and the order of drug circulation in a body have an important impact on the calculated drug concentration ratios.

Cytochrome P-450 enzymes and FMO3 contribute to the disposition of the antipsychotic drug perazine in vitro

RATIONALE

Perazine (PER) is a phenothiazine antipsychotic drug frequently used in Germany that undergoes extensive metabolism.

OBJECTIVES AND METHODS

To anticipate metabolic drug interactions and to explore the relevance of polymorphisms of metabolic enzymes, perazine-N-demethylation and perazine-N-oxidation were investigated in vitro using human liver microsomes and cDNA expressed enzymes.

RESULTS

CYP3A4 and CYP2C9 were identified as the major enzymes mediating PER-N-demethylation. At 10 microM PER, a concentration consistent with anticipated in vivo liver concentrations, CYP3A4 and CYP2C9 contributed 50% and 35%, respectively, to PER-N-demethylation. With increasing PER concentrations, contribution of CYP2C9 decreased and CYP3A4 became more important. In human liver microsomes, PER-N-demethylation was inhibited by ketoconazole (>40%) and sulfaphenazole (16%). Allelic variants of recombinant CYP2C9 showed differences in PER-N-demethylase activity. The wild type allele CYP2C9*1 was the most active variant. Maximal activities of CYP2C9*2 and CYP2C9*3 were 88% and 18%, respectively, compared to the wild type activity. Perazine-N-oxidation was mainly mediated by FMO3. In the absence of NADPH, heat treatment of microsomes abolished PER-N-oxidase activity. Methimazole inhibited PER-N-oxidation, while CYP specific inhibitors had no inhibitory effect. Perazine is a potent inhibitor of dextromethorphan-O-demethylase, S-mephenytoin-hydroxylase, alprazolam-4-hydroxylase, phenacetin-O-deethylase and tolbutamide-hydroxylase activity in human liver microsomes.

CONCLUSIONS

Alterations in the activity of CYP3A4, CYP2C9 and FMO3 through genetic polymorphisms, enzyme induction or inhibition bear the potential to cause clinically significant changes in perazine clearance. PER may alter the clearance of coadministered compounds metabolized by CYP2D6, CYP2C19, CYP2C9, CYP3A4 and CYP1A2.

[Poisoning by perazine--organ distribution and interpretation]

A fatal intoxication of a 22-year-old woman after intake of the phenothiazine perazine is described. In all of investigated organs e.g. in liver, lungs and kidneys high concentrations of the active agent could be found. The analytical results lead to the assumption that at least 14, most likely 30 tablets of Taxilan 100 have been taken. An unintended overdosage seems to be excluded just as an administration by another person.

Lysosomal trapping as an important mechanism involved in the cellular distribution of perazine and in pharmacokinetic interaction with antidepressants

Perazine, a piperazine-type phenothiazine neuroleptic, is the most frequently chosen drug for combination with antidepressants in the therapy of complex or 'treatment-resistant' psychiatric illnesses. The aim of the present study was to investigate the contribution of lysosomal trapping to the total tissue uptake of perazine, and the pharmacokinetic interaction between the neuroleptic and antidepressants. Experiments were carried out on slices of different rat organs regarded as a system with functional lysosomes. To distinguish between lysosomal trapping and tissue binding, the experiments were performed in the absence or presence of 'lysosomal inhibitors', i.e. the lysosomotropic compound ammonium chloride or [H+] ionophore monensin, which abolish the pH-gradient of lysosomes. Under steady-state conditions, the highest tissue uptake of perazine was observed for the adipose tissue, which descended in the following order: the adipose tissue>lungs>liver>heart=brain>kidneys>muscles. The contribution of lysosomal trapping to the total tissue uptake amounted to about 40% in the liver, brain and muscles, to 30% in the kidneys, and to 25% in the heart and lungs. In the adipose tissue, no lysosomotropism of perazine was observed. Of the psychotropics studied, perazine was the only drug showing such a high degree of lysosomal trapping in muscles and distinct lysosomotropic properties in the heart. Perazine and the antidepressants used, both tricyclic (imipramine, amitriptyline) and selective serotonin reuptake inhibitors (fluoxetine, sertraline), mutually decreased their tissue uptake. The potency of imipramine to decrease perazine uptake was similar to that of the 'lysosomal inhibitors'. Other antidepressants seemed to exert a somewhat weaker effect. The above interactions between perazine and antidepressants were not observed in the presence of ammonium chloride, which indicates that they proceeded at the level of lysosomal trapping. The adipose tissue in which the drug uptake was not affected by the 'lysosomal inhibitors' was not the site of such an interaction. Ammonium chloride did not affect the drug metabolism in liver slices; other tissues displayed only a negligible biotransformation of the psychotropics studied. A parallel metabolic interaction between perazine and tricyclic antidepressants took part in liver slices (i.e. perazine and antidepressants mutually inhibited their metabolic pathways), but the influence of such an interaction on the lysosomal uptake of the parent compounds in liver slices did not seem to be great. A substantial decrease in concentrations of the drugs in lysosomes (depot form) observed in vitro may lead to an increase in the concentration in vivo of the neuroleptic and antidepressants at the site of action, which, in turn, may increase the risk of cardiotoxic and anticholinergic side-effects of tricyclic antidepressants and sedative and extrapyramidal effects of the neuroleptic.

Pharmacokinetics of phenothiazine neuroleptics after chronic coadministration of carbamazepine

The aim of the present study was to assess the influence of carbamazepine on the pharmacokinetics of the two phenothiazine neuroleptics thioridazine and perazine in rats. The obtained results are compared with the results of analogical experiments concerning promazine. Thioridazine or perazine (10 mg/kg i.p.) were administered twice a day for two weeks alone or jointly with carbamazepine (15 mg/kg i.p. during the 1st week, and 20 mg/kg i.p. during the 2nd week of treatment). Concentrations of the neuroleptics and their main metabolites in the plasma and brain were measured at 30 min, 6 and 12 h after the last dose of the drugs. Carbamazepine decreased the concentrations of thioridazine and its metabolites (especially mesoridazine and sulforidazine) in plasma at 30 min and 6 h after the last dose of the drugs. Similar changes in the concentrations of thioridazine and its metabolites were observed at 6 h in the brain. Carbamazepine did not significantly influence the pharmacokinetics of perazine. In vitro studies with liver microsomes of control rats revealed that carbamazepine added to the incubation mixture inhibited N-demethylation of thioridazine via mixed mechanism, but it did not influence significantly 2- or 5-sulfoxidation of the neuroleptic. In the case of perazine, no distinct inhibition of its N-demethylation or sulfoxidation by carbamazepine was observed. Neither carbamazepine nor the neuroleptics, administered separately or jointly for two weeks, significantly influenced the concentrations of cytochromes P-450 and b-5 in the liver. Carbamazepine++ given chronically decreased the rate of N-demethylation and had a tendency to accelerate 2-sulfoxidation of thioridazine, both when given alone (as compared to the control) and when coadministered with thioridazine (as compared to the thioridazine-treated group). In contrast, chronic treatment with carbamazepine alone, significantly increased the rate of perazine N-demethylation. When carbamazepine was coadministered with perazine, the effect was less pronounced. In conclusion, carbamazepine given jointly with thioridazine or promazine at pharmacological doses to rats accelerates the metabolism of the neuroleptics, which is not the case with perazine. The observed induction proceeds by metabolic pathways other than N-demethylation or sulfoxidation. The different effect of carbamazepine on the N-demethylation of thioridazine and perazine in liver microsomes of control and carbamazepine-treated rats implicates that the two reactions are not catalyzed by the same enzyme. Such an induction of neuroleptic metabolism by carbamazepine in patients may worsen psychotic symptoms.

Suicide with moclobemide and perazine

A 51-year-old woman who was diagnosed as suffering from depression was found dead in her flat. The autopsy revealed no morphological changes sufficient to explain death. Toxicological analysis was performed and the drugs moclobemide (49.9 mg/l), perazine (1.27 mg/l) and some metabolites were identified in the blood. A combined drug intoxication resulting in synergistic effects to cardiovascular disorders was proposed as the cause of death.

[Analysis of combined phenothiazine-opiate poisoning]

Report about 2 death cases due to an overdosage of phenothiacine derivates. The EMIT-test showed positive results concerning opiates for both cases. But morphine only was detected in one case by a fluorimetric method. The EMIT-test for opiates can show positive results in error, if there exist phenothiacines in the specimen at the same time.

Early serum levels of neuroleptics do not predict therapeutic response in schizophrenia

Thirty-six acute schizophrenics were included in a 28-day open treatment study with the neuroleptic perazine. Peak serum levels of parent drug and its main inactive metabolite desmethyl-perazine were assessed 2 hours after an oral test dose given at the beginning of the study. Whereas peak levels of perazine were not significantly different in treatment responders and nonresponders, desmethyl-perazine was significantly higher in nonresponders. The ratio between desmethyl-perazine and perazine was not predictive of (non-) response to neuroleptic treatment in schizophrenia.

Pharmacokinetic interaction between imipramine and antidepressant neuroleptics in rats

Antidepressant neuroleptics, perazine (PZ), levomepromazine (LMZ) and flupenthixol (FPX) given to rats jointly with imipramine (IMI) for 2 weeks affected the plasma concentration of IMI only slightly but markedly elevated the concentration of its metabolite, desipramine (DMI). In the brain PZ significantly elevated both IMI and DMI concentrations while LMZ and FPX showed a tendency to increase the concentration of IMI and decrease the concentration of DMI. All three neuroleptics markedly decreased the DMI/IMI ratio in the brain and (except FPX) increased it in the plasma. Given alone for two weeks PZ, LMZ, FPX did not affect the levels of cytochromes P-450 and b-5 in liver microsomes. Chronic treatment with IMI significantly elevated the concentration of cytochrome P-450 in the liver and had a tendency to increase the concentration of cytochrome b-5. FPX, but not PZ or LMZ abolished this effect. Neuroleptics coadministered with IMI to rats did not affect the activity of the enzymes responsible for the IMI biotransformation as compared with IMI-treated animals. The neuroleptics added to the incubation mixture in vitro inhibited IMI hydroxylation noncompetitively. The demethylation was inhibited competitively by LMZ but noncompetitively by PZ and FPX. The inhibitory effect of neuroleptics on the hydroxylation was much more marked than that on the demethylation. FPX was the weakest inhibitor of IMI metabolism among the neuroleptics studied.

Single-dose kinetics of the neuroleptic drug perazine in psychotic patients

Eight male and two female unmedicated psychotic patients received 100 mg perazine orally and seven blood samples were taken within 25 h. Plasma levels of perazine and its demethylated metabolite were analyzed by HPLC with electrochemical detection. They exhibited large interindividual variations, with maximal concentrations as well as AUC values of perazine differing more than 10-fold. From the decay of plasma levels during the last 12-18 h half-lives were estimated to be between 7.5 and 10 h; they did not correlate with AUC. There was a significant positive correlation between AUC and age. Desmethylperazine was consistently present at lower concentrations than the parent drug during the first 12 h.

In vitro inhibition of human platelet monoamine oxidase by phenothiazine derivatives

Nineteen phenothiazines were tested for in vitro inhibition of human platelet type B monoamine oxidase (MAO). The inhibition potency was highly dependent on structures of their side chains. The inhibition was most potent for drugs with (hydroxyethyl-piperazinyl)propyl chains followed in decreasing order by those with (N-methylpiperazinyl)propyl, (2-dimethylamino-2-methyl)ethyl and 3-dimethylaminopropyl chains. Kinetic analyses were carried out for promazine, promethazine, perazine and perphenazine as representatives of each group; the four drugs showed competitive inhibition, and Ki values of 124, 31.4, 19.2 and 22.6 microM, respectively.