Potential therapy of multidrug-resistant and extremely drug-resistant tuberculosis with thioridazine

Multidrug-resistant tuberculosis (MDRTB) infections that continue to increase in frequency globally have progressed to become extremely drug-resistant tuberculosis (XDRTB). The therapeutic problems associated with MDRTB pale in comparison to those for XDRTB where mortality is high. This mini-review highlights the evidence that supports the use of the phenothiazine neuroleptic thioridazine for the therapy of XDRTB. Although thioridazine does produce some serious side-effects, the poor prognosis associated with an XDRTB infection of a patient that presents with AIDS merits that the use of thioridazine for therapy of XDRTB is seriously considered. A recommended protocol is presented.

Postmortem redistribution of two antipsychotic drugs, haloperidol and thioridazine, in the rat

Antipsychotic drugs may be associated with arrhythmia, ventricular fibrillation, or torsades de pointes, which can result in sudden death. These drugs could therefore be found in postmortem toxicological analyses of autopsy specimens following unexplained sudden death. The drug concentrations in tissues and body fluids change between the death and postmortem specimens collection because of postmortem redistribution. For this reason, it is often difficult to interpret the postmortem analysis. The aim of this study was to investigate postmortem redistribution of the two cardiotoxic antipsychotic drugs, haloperidol and thioridazine, in order to interpret the postmortem analysis. We have chosen the rat as an animal model. The rats received 1 mg/kg of haloperidol and 5 mg/kg of thioridazine by intraperitoneal injection. They were sacrificed and left at room temperature for 2, 6, 12, 24, or 48 h, at which times blood and tissue samples were taken. The drug analyses in tissues and blood were done using a liquid chromatography- tandem mass spectrometry method. Our results show that there is a redistribution of the two drugs from the lung to the cardiac blood. The concentration of the antipsychotic drugs in the lung decreased rapidly, whereas in the cardiac blood, this concentration increased within the first 2 h postmortem. By 48 h after death, the concentrations of the antipsychotic drugs were about twice as high as the initial concentrations in the cardiac blood. For the lungs, a decrease of 50% was observed between 0 and 48 h. Only myocardium and muscle concentrations did not change with the postmortem delay.

Comparative metabolic capabilities and inhibitory profiles of CYP2D6.1, CYP2D6.10, and CYP2D6.17

Polymorphisms in the cytochrome P450 2D6 (CYP2D6) gene are a major cause of pharmacokinetic variability in human. Although the poor metabolizer phenotype is known to be caused by two null alleles leading to absence of functional CYP2D6 protein, the large variability among individuals with functional alleles remains mostly unexplained. Thus, the goal of this study was to examine the intrinsic enzymatic differences that exist among the several active CYP2D6 allelic variants. The relative catalytic activities (enzyme kinetics) of three functionally active human CYP2D6 allelic variants, CYP2D6.1, CYP2D6.10, and CYP2D6.17, were systematically investigated for their ability to metabolize a structurally diverse set of clinically important CYP2D6-metabolized drugs [atomoxetine, bufuralol, codeine, debrisoquine, dextromethorphan, (S)-fluoxetine, nortriptyline, and tramadol] and the effects of various CYP2D6-inhibitors [cocaine, (S)-fluoxetine, (S)-norfluoxetine, imipramine, quinidine, and thioridazine] on these three variants. The most significant difference observed was a consistent but substrate-dependent decease in the catalytic efficiencies of cDNA-expressed CYP2D6.10 and CYP2D6.17 compared with CYP2D6.1, yielding 1.32 to 27.9 and 7.33 to 80.4% of the efficiency of CYP2D6.1, respectively. The most important finding from this study is that there are mixed effects on the functionally reduced allelic variants in enzyme-substrate affinity or enzyme-inhibitor affinity, which is lower, higher, or comparable to that for CYP2D6.1. Considering the rather high frequencies of CYP2D6*10 and CYP2D6*17 alleles for Asians and African Americans, respectively, these data provide further insight into ethnic differences in CYP2D6-mediated drug metabolism. However, as with all in vitro to in vivo extrapolations, caution should be applied to the clinical consequences.

Factors affecting drug concentrations and QT interval during thioridazine therapy

The objective of this study was to investigate factors affecting steady-state plasma concentrations of thioridazine. A cross-sectional study of patients receiving chronic thioridazine was employed. Common allelic variants of CYP2D6 and CYP2C19, as well as thioridazine and metabolite concentrations and QTc intervals, were determined. In 97 patients, dose-corrected plasma concentrations (C/Ds) of thioridazine and metabolites were correlated with age but not sex or CYP2C19 genotype. Patients with no functional CYP2D6 alleles (n=9) had significantly higher C/D for thioridazine (P=0.017) and the ring sulfoxide metabolite and a significantly higher thioridazine/mesoridazine ratio compared with those with >/=1 functional CYP2D6 allele (n=82). Smokers had significantly lower C/D for thioridazine, mesoridazine, and sulforidazine and significantly lower thioridazine/ring sulfoxide ratios than non-smokers. QTc interval was not significantly affected by CYP2D6 or CYP2C19 genotypes. Plasma concentrations of thioridazine are influenced by age, smoking, and CYP2D6 genotype, but CYP2D6 genotype does not appear to influence on-treatment QTc interval.

Comparison of the Effects of Thioridazine and Mesoridazine on the QT Interval in Healthy Adults After Single Oral Doses

We compared the effects of single doses of thioridazine and mesoridazine on the heart rate-corrected QT (QTc) interval in healthy adult volunteers. QTc intervals and plasma concentrations of thioridazine, mesoridazine, and metabolites were measured after single oral doses of thioridazine hydrochloride 50 mg, mesoridazine besylate 50 mg, or placebo in a double-blind, crossover study. Mean maximum increases in the QTc interval following thioridazine (37.3+/-4.1 ms, P=0.023) and mesoridazine (46.6+/-7.4 ms, P=0.021) were similar and significantly greater than following placebo (12.9+/-8.1 ms). The area under the effect-time curve over 8 h following drug administration was similar between the two drugs (129.3+/-22.1 vs 148.3+/-43.0 ms h). In conclusion, thioridazine and mesoridazine are associated with similar effects on the QTc interval.

Practical application of guinea pig telemetry system for QT evaluation

The purpose of this study was to evaluate a telemetry system for examining QT evaluation in the conscious free-moving guinea pig using 10 reference compounds whose effects on human QT interval are well established: 8 positive references (bepridil, terfenadine, cisapride, haloperidol, pimozide, quinidine, E-4031 and thioridazine), and 2 negative references (propranolol and nifedipine). Pharmacokinetic experiments were also performed for the 8 positive references. Telemetry transmitters were implanted subcutaneously in male Hartley guinea pigs, and the RR and QT intervals were measured. All 8 positive references prolonged QTc (QTc = k x QT/RR(1/2)) 10% or more during the 60 min observation period. When the values of the QTc changes were plotted against the serum concentrations, the resulting curves exhibited an anticlockwise hysteresis loop for all 8 references. In guinea pigs treated with haloperidol, changes of the T-wave shape from positive to flat were observed. The 2 negative references did not prolong the QTc. These findings suggest that the present telemetry guinea pig model is useful for QT evaluation in the early stages of drug development, because of the small body size of guinea pigs and their action potential configuration, which is similar to that of humans.

Prediction of drug-drug interactions for AUCoral of high clearance drug from in vitro data: utilization of a microtiter plate assay and a dispersion model

The purpose of this study was to propose a new method to predict in vivo drug-drug interactions (DDIs) for a high clearance drug from in vitro data. As the high clearance drug, NE-100 (N, N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride) was used. First, approach based on I(u)/K(i) value was used for the prediction of DDIs between NE-100 and concomitant drugs. When the K(i) values (K(i-cal)) obtained from the microtiter plate (MTP) assay and the reported K(i) values (K(i-rep)) for these drugs were used to predict increases at levels of NE-100 AUC(oral) (AUC(oral) ratio), the AUC(oral) ratios from the I(u)/K(i-cal) correlated with those from the I(u)/K(i-rep). This result suggests that the K(i-cal) from the MTP assay can be used for prediction of DDIs instead of the K(i-rep) value. Second, a new approach combining the inhibition rate (R) calculated from the MTP assay and two physiological models was used to predict DDIs. When the AUC(oral) ratios of NE-100 by various drugs were predicted using the R value and the well-stirred model, the ratios were similar to those predicted using the I(u)/K(i). However, after co-administration of drugs such as quinidine, propafenone and thioridazine (potent inhibitors of CYP2D6), the NE-100 AUC(oral) ratios predicted from the dispersion model was much greater than those from well-stirred model. This result shows that application of the dispersion model to the prediction method using the R value might sensitively and precisely predict the increased levels of AUC(oral) by DDIs for high clearance drug, compared with the prediction method using I(u)/K(i) value.

CHARACTERIZATION OF HUMAN CYTOCHROME P450 ENZYMES INVOLVED IN THE METABOLISM OF THE PIPERIDINE-TYPE PHENOTHIAZINE NEUROLEPTIC THIORIDAZINE

The aim of the present study was to identify human cytochrome P450 enzymes (P450s) involved in mono-2-, di-2-, and 5-sulfoxidation, and N-demethylation of the piperidine-type phenothiazine neuroleptic thioridazine in the human liver. The experiments were performed in vitro using cDNA-expressed human P450s (Supersomes 1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4), liver microsomes from different donors, and P450-selective inhibitors. The results indicate that CYP1A2 and CYP3A4 are the main enzymes responsible for 5-sulfoxidation and N-demethylation (34-52%), whereas CYP2D6 is the basic enzyme that catalyzes mono-2- and di-2-sulfoxidation of thioridazine in human liver (49 and 64%, respectively). Besides CYP2D6, CYP3A4 contributes to a noticeable degree to thioridazine mono-2-sulfoxidation (22%). Therefore, the sulforidazine/mesoridazine ratio may be an additional and more specific marker than the mesoridazine/thioridazine ratio for assessing the activity of CYP2D6. In contrast to promazine and perazine, CYP2C19 insignificantly contributes to the N-demethylation of thioridazine. Considering serious side-effects of thioridazine and its 5-sulfoxide (cardiotoxicity), as well as strong dopaminergic D2 and noradrenergic alpha1 receptor-blocking properties of mono-2- and di-2-sulfoxides, the obtained results are of pharmacological and clinical importance, in particular, in a combined therapy. Knowledge of the catalysis of thioridazine metabolism helps to choose optimum conditions (a proper coadministered drug and dosage) to avoid undesirable drug interactions.

Repeated dosing with donepezil does not affect the safety, tolerability or pharmacokinetics of single-dose thioridazine in young volunteers

AIM

To investigate the effects of donepezil at steady state on the safety, tolerability and pharmacokinetics of a single dose of thioridazine, in healthy subjects.

METHODS

An open, two-way, balanced crossover study, in 12 subjects (six men and six women) aged 19-41 years. During both treatment periods, subjects received a single oral dose of 50 mg thioridazine; in one period the thioridazine was given alone, and in the other period it was given together with the last of 15 daily, oral doses of donepezil 5 mg. The 'washout' periods were 1 week when thioridazine was given first, and 2 weeks when thioridazine was given last. Plasma concentrations of thioridazine were measured after each dose, and pharmacokinetic parameters were determined. Interactions were tested by using an equivalence analysis in which thioridazine was the 'Reference' and thioridazine + donepezil the 'Test' regimen. Safety and tolerability were monitored.

RESULTS

Donepezil had no marked effect on the pharmacokinetics of thioridazine, as judged by the equivalence analysis of AUC(0-tn), AUC(0-infinity), t((1/2)) and t(max). C(max) was very similar in the 'Test' and 'Reference' regimens, but the confidence intervals were too wide to confirm equivalence. Donepezil was well tolerated, whereas thioridazine was associated with light-headedness, tiredness and postural hypotension, irrespective of whether or not donepezil was given concurrently.

CONCLUSIONS

Repeated dosing with donepezil, 5 mg daily for 2 weeks, had no significant effect on the safety, tolerability or pharmacokinetics of thioridazine. Thioridazine was poorly tolerated.

QTc interval lengthening is related to CYP2D6 hydroxylation capacity and plasma concentration of thioridazine in patients

Thioridazine cardiotoxicity has been associated with a prolonged heart-rate corrected QT (QTc) interval. However, no systematic studies have been performed on patients at therapeutic doses. The present study aimed to evaluate the influence of dose and plasma concentration of thioridazine and CYP2D6 enzyme status on the QTc interval in psychiatric patients. Sixty-five Spanish European psychiatric patients receiving thioridazine antipsychotic monotherapy were studied. The plasma levels of thioridazine and its metabolites were determined by high-performance liquid chromatography. All patients were phenotyped for CYP2D6 activity with debrisoquine during treatment. Thirty-five patients (54%) had a QTc interval over 420 ms. The lengthening of QTc interval was correlated with plasma concentration (p < 0.05) and daily dose (p < 0.05) of thioridazine. CYP2D6 enzyme hydroxylation capacity, evaluated by debrisoquine metabolic ratio (MR) (p < 0.05) and thioridazine/mesoridazine ratio (p < 0.05), was also correlated with QTc intervals. The present study shows the relationship between QTc interval lengthening among psychiatric patients treated at therapeutical doses with the dose and the plasma concentration of thioridazine. Since debrisoquine MR has been shown to be correlated with the QTc intervals, CYP2D6 enzyme hydroxylation capacity might be relevant in determining the risk for QTc interval lengthening. Patients with impaired CYP2D6 enzyme activity due to enzyme inhibition by thioridazine might be more prone to increased risk of sudden death due to torsade de pointes type cardiac dysrhythmia.

Enantiomers' potential in psychopharmacology--a critical analysis with special emphasis on the antidepressant escitalopram

Stereochemistry is now influencing most areas of pharmacotherapy, with a growing awareness in the field of psychiatry and, more specifically, depression. This is due to the fact that the enantiomers of many chiral drugs may have distinct pharmacological, pharmacokinetic and/or pharmacogenetic profiles. Consequently, in some instances there may be an advantage in using a single enantiomer over the racemic form-thus providing a basis for the development of new therapeutic agents, as well as the potential to improve current treatments. This review highlights some of the potential advantages and disadvantages that using single enantiomers might offer. The principles are exemplified through reference to the stereoselective properties of several established chiral psychotropic drugs, including thioridazine, methadone, trimipramine, mianserin, mirtazapine, fluoxetine and citalopram. Emphasis is given to the treatment of depression and how the potential of one pure enantiomer-escitalopram, the S-enantiomer of the selective serotonin reuptake inhibitor citalopram-appears to be fulfilling its preclinical promise in the clinic.

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.

Pharmacokinetics and metabolism of thioridazine during co-administration of tricyclic antidepressants

1. Because of serious side-effects of thioridazine and tricyclic antidepressants (cardiotoxicity), a possible influence of imipramine and amitriptyline on the pharmacokinetics and metabolism of thioridazine was investigated in a steady state (2-week treatment) in rats. 2. Imipramine and amitriptyline (5 and 10 mg kg(-1) i.p., respectively) elevated 30 and 20 fold, respectively, the concentration of thioridazine (10 mg kg(-1) i.p.) and its metabolites (N-desmethylthioridazine, 2-sulphoxide, 2-sulphone, 5-sulphoxide) in blood plasma. Similar, yet weaker increases in the thioridazine concentration were found in the brain. Moreover, an elevation of thioridazine/metabolite ratios was observed. 3. Imipramine and amitriptyline added to control liver microsomes in vitro inhibited the metabolism of thioridazine via N-demethylation (an increase in K(m)), mono-2-sulphoxidation (an increase in K(m) and a decrease in V(max)) and 5-sulphoxidation (mainly a decrease in V(max)). Amitriptyline was a more potent inhibitor than imipramine of the thioridazine metabolism. 4. The varying concentration ratios of antidepressant/thioridazine in vivo appear to be more important to the final result of the pharmacokinetic interactions than are relative direct inhibitory effects of the antidepressants on thioridazine metabolism observed in vitro. 5. Besides direct inhibition of the thioridazine metabolism, the decreased activity of cytochrome P-450 towards 5-sulphoxidation, produced by chronic joint administration of thioridazine and the antidepressants, seems to be relevant to the observed in vivo interaction. 6. The obtained results may also point to inhibition of another, not yet investigated, metabolic pathway of thioridazine, which may be inferred from the simultaneous elevation of concentrations of both thioridazine and the measured metabolites.

Psychomotor effects of zaleplon and thioridazine coadministration

OBJECTIVE

To assess the potential pharmacokinetic and pharmacodynamic interaction of zaleplon and thioridazine administered concomitantly in healthy volunteers.

METHODS

A three-period, double-blind, randomized crossover study of the psychomotor effects of single oral doses of zaleplon 20 mg alone, thioridazine 50 mg alone, or the two drugs administered concomitantly was performed in 12 healthy subjects. Pharmacodynamic testing was performed before, and at 1, 2, 4, and 8 h after drug administration. Critical flicker fusion (CFF), tapping rate (TR), reaction time (RT) with dominant and nondominant hands, and digit symbol substitution test (DSST) were used to assess psychomotor performance.

RESULTS

Pharmacokinetic results showed that coadministration of zaleplon and thioridazine did not alter the pharmacokinetic profile of either drug. In both CFF and TR tests, values for change from baseline with combined treatment were not significantly different from those with thioridazine at any time point, indicating no pharmacodynamic interaction. RT test values with coadministered treatment were significantly different from those with thioridazine alone at 1 h after administration, indicating additivity. Supra-additivity was observed in DSST results at 1, 2, and 4 h. There was no interaction at 8 h.

CONCLUSION

The results of single-dose administration showed an additive pharmacodynamic interaction between zaleplon and thioridazine at 1 h in one of four tests and supra-additivity for 4 h in another test. This interaction is relatively short in duration due to the short half-life of zaleplon.

Pharmacokinetic interaction of fluvoxamine and thioridazine in schizophrenic patients

This study investigated to what extent fluvoxamine affects the pharmacokinetics of thioridazine (THD) in schizophrenic patients under steady-state conditions. Concentrations of THD, mesoridazine, and sulforidazine were measured in plasma samples obtained from 10 male inpatients, aged 36 to 78 years, at three different time points: A, during habitual monotherapy with THD at 88 +/-54 mg/day; B, after addition of a low dosage of fluvoxamine (25 mg twice a day) for 1 week; and C, 2 weeks after fluvoxamine discontinuation. After the addition of fluvoxamine, THD concentrations relative to time point A significantly increased approximately threefold from 0.40 to 1.21 micromol/L (225%) (p < 0.002), mesoridazine concentrations increased from 0.65 to 2.0 micromol/L (219%) (p < 0.004), and sulforidazine levels increased from 0.21 to 0.56 micromol/L (258%) (p < 0.004). The THD-mesoridazine and THD-sulforidazine ratios remained unchanged during the study. Mean plasma THD, mesoridazine, and sulforidazine levels decreased at time point C, but despite fluvoxamine discontinuation for 2 weeks, three patients continued to exhibit elevated concentrations of THD and its metabolites. In conclusion, fluvoxamine markedly interferes with the metabolism of THD, probably at the CYP2C19 and/or CYP1A2 enzyme level. Therefore, clinicians should be aware of the potential for a clinical drug interaction between both compounds, and careful monitoring of THD levels is valuable to prevent the accumulation of the drug and resulting toxicity.

Adsorption of drugs onto a poly(acrylic acid) grafted cation-exchange membrane

The influence of pH, ionic strength and the concentration of albumin in the adsorption medium as well as the charge and lipophilicity of a model drug on their adsorption onto poly(acrylic acid) grafted poly(vinylidene fluoride) (PAA-PVDF) membranes was evaluated. The PAA-PVDF membrane is a responsive porous polymer membrane that we have studied for controlled drug delivery. Sodium salicylate (anionic), flunitrazepam (neutral), primidone (neutral), desipramine (cationic) and thioridazine (cationic) were used as model drugs. The extent of drug adsorption was dependent on pH. Drug adsorption was enhanced by the dissociation of the grafted PAA chains and by a positive charge and a high lipophilicity of the drug. Increasing the ionic strength of the medium retarded the adsorption of the cationic drugs. Interestingly, the present results showing that drugs are adsorbed onto the membrane while albumin is not adsorbed onto the membrane suggest that the PAA-PVDF membrane may be suitable for separating drugs from proteinaceous substances for subsequent monitoring and evaluation.

Single dose pharmacodynamics of thioridazine and remoxipride in healthy younger and older volunteers

Phenothiazines are widely used in older patients, but little experimental work has been carried out in this age group. Two groups of healthy volunteers, a younger group (Y: six males and six females, aged 20-42 years) and an older group (O: six males and eight females, aged 65-77 years) took part in a randomized double-blind three-period crossover study in which they received by mouth single doses of thioridazine (Y: 50 mg; O: 25 mg) remoxipride (Y: 100 mg; O: 50 mg) or placebo. Measures of central nervous system (CNS) and haemodynamic function were carried out before drug administration and at 1.5-h intervals up to 9 h post-dose, and blood samples were collected over a 24-h period. No significant differences in dose-corrected pharmacokinetic variables were found between the two groups. There was evidence of marked CNS depressant effects of thioridazine from both objective and subjective measures. The effects for remoxipride were similar, though generally less marked. After allowance was made for dose, there was little indication of any difference in degree of CNS depression between the two age groups. Haemodynamic measures showed orthostatic reductions in blood pressure with thioridazine which were particularly marked in the older group, who also showed lower compensatory increases in pulse rate. These results indicate potential problems with orthostatic hypotension with thioridazine in older patients. CNS depression may also be a problem, especially in patients with compromised cholinergic function.

The role of lysosomes in the cellular distribution of thioridazine and potential drug interactions

The purpose of the present study was to investigate the contribution of lysosomal trapping to the total tissue uptake of thioridazine and to potential drug distribution interactions between thioridazine and tricyclic antidepressants (imipramine, amitriptyline) or selective serotonin reuptake inhibitors (SSRIs; fluoxetine, sertraline). The experiment was carried out on slices of various rat tissues as a system with intact lysosomes. Thioridazine and antidepressants (5 microM) were incubated separately or jointly with the tissue slices in the absence or presence of "lysosomal inhibitors," i.e., ammonium chloride or monensin. The results show that the contribution of lysosomal trapping to the total tissue uptake of thioridazine is as important as phospholipid binding. A high degree of dependence of thioridazine tissue uptake on the lysosomal trapping is the cause of substantial distributive interactions between thioridazine and the investigated antidepressants at the level of cellular distribution. Thioridazine and the antidepressants, both tricyclic and SSRIs, mutually decreased their tissue uptake. The potency of antidepressants to decrease thioridazine uptake was similar to that of lysosomal inhibitors. In general, the observed interactions between thioridazine and antidepressants occurred only in those tissues in which thioridazine showed lysosomotropism (the lungs, liver, kidneys, brain, and muscles) but were not observed in the presence of ammonium chloride. The above finding provides evidence that the interactions proceeded at the level of lysosomal trapping. In the adipose tissue and heart no lysosomal trapping of thioridazine was detected and those tissues were not the site of such an interaction. Since the organs and tissues involved in the distributive interactions constitute a major part of the organism and take up most of the total drug in the body, the interactions occurring in them may cause a substantial shift of the drugs to organs and tissues poor in lysosomes, e.g. the heart and muscles. An in vivo study into the thioridazine-imipramine interaction showed that joint administration of the drugs under study (10 mg/kg ip) increased drug concentration ratios of lysosome-poor tissue/plasma and lysosome-poor/lysosome-rich tissue. Considering serious side effects of thioridazine and tricyclic antidepressants (cardiotoxicity, anticholinergic activity), the thioridazine-antidepressant combinations studied should be approached with respect to the appropriate dose adjustment.

The influence of selective serotonin reuptake inhibitors (SSRIs) on the pharmacokinetics of thioridazine and its metabolites: in vivo and in vitro studies

Due to its psychotropic profile, thioridazine is a neuroleptic suitable for a combination with antidepressants in a number of complex psychiatric illnesses. However, because of its serious side-effects, such a combination with selective serotonin reuptake inhibitors (SSRIs) which inhibit cytochrome P-450 may be dangerous. The aim of the present study was to investigate a possible impact of SSRIs on the pharmacokinetics and metabolism of thioridazine in a steady state in rats. Thioridazine (10 mg/kg) was injected intraperitoneally, twice a day, for two weeks, alone or jointly with one of the antidepressants (fluoxetine, fluvoxamine or sertraline). Concentrations of thioridazine and its main metabolites (2-sulfoxide = mesoridazine; 2-sulfone = sulforidazine; 5-sulfoxide = ring sulfoxide and N-desmethylthiorid-azine) were assessed in the blood plasma and brain at 30 min, 6 and 12 h after the last dose of the drugs using an HPLC method. Fluoxetine potently increased (up to 13 times!) the concentrations of thioridazine and its metabolites in the plasma, especially after 6 and 12 h. Moreover, an increase in the sum of concentrations of tioridazine + metabolites and thioridazine/metabolite ratios was observed. In vitro studies with control liver microsomes, as well as with microsomes of rats treated chronically with fluoxetine show that the changes in the thioridazine pharmacokinetics may be attributed to the competitive (N-demethylation, Ki = 23 microM) and mixed inhibition (2- and 5-sulfoxidation, Ki = 60 microM and 34 microM, respectively) of thioridazine metabolism by fluoxetine, and to the adaptive changes produced by chronic administration of fluoxetine, as reflected by inhibition of N-demethylation and formation of sulforidazine. Sertraline seemed to have a tendency to decrease thioridazine concentration in vivo, though in vitro studies showed that - like fluoxetine - it competitively or via mixed mechanism inhibited the three metabolic pathways of thioridazine (Ki = 41 microM, 64 microM and 47 microM, respectively). Chronic treatment with sertraline stimulated thioridazine 2- and 5-sulfoxidation, which may be responsible for the observed tendency of sertraline to decrease concentrations of the neuroleptic. In the case of fluvoxamine, a tendency to increase the thioridazine level was observed, which may be connected with the competitive or mixed inhibition of thioridazine N-demethylation and 2-sulfoxidation by the antidepressant (Ki = 17 microM and 167 microM, respectively). Repeated administration of fluvoxamine did not produce any changes in the activity of thioridazine-metabolizing enzymes. In conclusion, of the SSRIs studied, only fluoxetine produces a substantial increase in the thioridazine level in the plasma and brain. In the case of fluvoxamine, a tendency to increase the thioridazine level should be considered. Coadministration of thioridazine and sertraline seems to be safe, though a tendency to decrease the thioridazine level may be expected.

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.

Pharmacokinetics of thioridazine and its metabolites in blood plasma and the brain of rats after acute and chronic treatment

This study was aimed at investigation of the pharmacokinetics of thioridazine and its metabolites after a single and repeated administrations. Male Wistar rats received thioridazine as a single dose (10 mg/kg i.p.) or they were treated chronically with the neuroleptic (10 mg/kg i.p., twice a day for two weeks). Plasma and brain concentrations of thioridazine and its metabolites (N-desmethylthioridazine, mesoridazine, sulforidazine, and the ring sulfoxide) were determined using the HPLC method. The obtained data showed that sulfoxidation in position 2 of the thiomethyl substituent and in the thiazine ring are main metabolic pathways of thioridazine, and showed that, in contrast to humans, in the rat N-desmethylthioridazine is formed in appreciable amount. The biotransformation of thioridazine was rather fast yielding plasma peak concentrations of metabolites lower than that of the parent compound. The maximum concentrations of thioridazine and its metabolites in the brain appeared later than in plasma. The peak concentrations and AUC values of thioridazine and its metabolites were higher in the brain than in plasma and this corresponded well with their longer half-lives in the brain as compared to plasma. The drug was not taken up by the brain as efficiently as other phenothiazines. Chronic treatment with thioridazine produced significant increases (with the exception of thioridazine ring sulfoxide) in the plasma concentrations of the parent compound and its metabolites which was accompanied with the prolongation of their plasma half-lives. The observed plasma levels of thioridazine were within 'therapeutic range' while the concentrations of its metabolites were relatively lower as compared to those observed in psychiatric patients. The increased plasma concentrations of thioridazine and its metabolites observed in plasma after chronic treatment were not followed by parallel changes in the brain.

Concentration-related pharmacodynamic effects of thioridazine and its metabolites in humans

OBJECTIVE

To measure cardiac and other effects of thioridazine and relate these to the plasma concentration of the parent drug and its principal metabolites.

METHODS

A double-blind, randomized-order crossover study involving nine healthy male subjects compared the effects of single doses of thioridazine (10 mg and 50 mg) with placebo. Plasma concentrations of thioridazine and its ring sulfoxide, side-chain sulfoxide, and side-chain sulfone metabolites were measured, together with effects on the ECG, blood pressure, salivary flow, and a batch of psychomotor tests for 72 hours after administration.

RESULTS

Thioridazine, 50 mg, reduced standing systolic blood pressure (mean peak changes from baseline [95% CI] -32 mm Hg [-55, 10 mm Hg]; p < 0.01 versus placebo) and diastolic blood pressure (-14 mm Hg [-26, -2 mm Hg]; p < 0.05), increased standing heart rate (7 beats/min [-1, 16 beats/min]; p < 0.05), impaired psychomotor function, and prolonged the JT (20 ms1/2 [7, 34 ms1/2]; p < 0.05), QTa (22 ms1/2 [8, 36 ms1/2]; p < 0.05), and QTc (22 ms1/2 [11, 33 ms1/2]; p < 0.01) intervals, but had no effect on QT dispersion (-12 ms1/2 [-31, 6 ms1/2]). Thioridazine, 1.0 mg, also significantly increased QTc, but the effect was less marked (9 ms1/2 [-1, 19 ms1/2]; p < 0.05). Plasma thioridazine and metabolite concentrations did not correlate significantly with these effects. Maximum effects on QTc occurred after peak concentrations of thioridazine but before peak concentrations of the ring sulfoxide and side-chain sulfone metabolites.

CONCLUSIONS

These data suggest that thioridazine has dose-related effects on ventricular repolarization and that the parent drug causes an important proportion of these effects, although its metabolites may also contribute.

Identification of lactams as in vitro metabolites of piperidine-type phenothiazine antipsychotic drugs

The metabolism of the piperidine-type phenothiazine antipsychotic agents thioridazine, mesoridazine and sulforidazine was studied in vitro with 10,000 g liver supernatants obtained from rats and dogs. After incubations at 37 degrees C for different time intervals, the incubates were extracted with dichloromethane and the isolated compounds analyzed by HPLC, direct probe MS and on-line HPLC-MS. Five lactam metabolites of these three drugs were unequivocally identified in the rat in vitro system, but none was found in dog preparations; at least one lactam metabolite was identified for each drug in the rat. The lactams of thioridazine and thioridazine ring sulfoxide were characterized as metabolites of thioridazine for the first time in any system. The other three lactam metabolites, namely the lactams of mesoridazine, sulforidazine and mesoridazine ring sulfoxide, were found in vitro for the first time, although they have been previously reported as in vivo metabolites of these drugs. The results indicate that rat would be a more suitable animal model than dog for further studies on the formation of lactam metabolites of these drugs.

Absorption of surfactants by membranes: erythrocytes versus synthetic vesicles

Three surfactants (chlorpromazine hydrochloride, thioridazine hydrochloride, and sodium deoxycholate) are found to absorb just as strongly into the protein-containing membranes of erythrocytes as into the phospholipid bilayers of synthetic vesicles. In the concentration region where hemolysis occurs and the Langmuir adsorption isotherm is no longer valid, one may use a phase partition model in which the erythrocyte membrane is one of the phases. The partition coefficients, expressed as the ratio of mole fraction surfactant in the membrane lipid phase to concentration of surfactant in the aqueous phase, have been calculated at the point of saturation in the erythrocyte membrane. These values are Ky = 430 M-1 (chlorpromazine, pH 5.9), 550 M-1 (deoxycholate, pH 7.6), and 640 M-1 (thioridazine, pH 5.9), in isotonic buffer at 27 degrees C. Corresponding values for synthetic vesicles made from dimyristoylphosphatidylcholine are Kx = 230 M-1 (chlorpromazine, 0.12 M buffer/KCl pH 5.9), 440 M-1 (deoxycholate, 0.20 M buffer/NaCl pH 8.0) and 510 M-1 (thioridazine, 0.12 M buffer/KCl pH 5.9), at 27 degrees C. It appears that the surfactants become an integral part of the bilayer in both vesicles and natural membranes and that the absorption is not of a peripheral nature. There is no evidence that the presence of proteins in the natural membrane inhibits the absorption of these surfactants in any way.

Metabolism of phenothiazine and butyrophenone antipsychotic drugs. A review of some recent research findings and clinical implications

Whereas some metabolites of antipsychotic drugs are psychoactive and contribute to clinical improvement, recent studies have provided evidence that certain metabolites contribute to side-effects which can be disabling enough to negate clinical improvement as regards the psychosis. The route of administration of the drug can determine the amount of metabolite produced in the body and affect how the patient feels in response to the treatment.

Plasma levels of thioridazine and metabolites are influenced by the debrisoquin hydroxylation phenotype

The pharmacokinetics of thioridazine and its metabolites were studied in 19 healthy male subjects: 6 slow and 13 rapid hydroxylators of debrisoquin. The subjects received a single 25 mg oral dose of thioridazine, and blood samples were collected during 48 hours. Concentrations of thioridazine and metabolites in serum were measured by HPLC. Slow hydroxylators of debrisoquin obtained higher serum levels of thioridazine with a 2.4-fold higher Cmax and a 4.5-fold larger AUC(0-infinity) associated with a twofold longer half-life compared with that of rapid hydroxylators. The side-chain sulphoxide (mesoridazine) and sulphone (sulphoridazine), which are active metabolites, appeared more slowly in serum and had lower Cmax values, but comparable AUC. The thioridazine ring-sulphoxide attained higher Cmax and 3.3-fold higher AUC in slow hydroxylators than in rapid hydroxylators of debrisoquin. Thus the formation of mesoridazine from thioridazine and the 4-hydroxylation of debrisoquin seem to be catalyzed by the same enzyme, whereas the formation of thioridazine ring-sulphoxide is probably formed mainly by another enzyme.

Single dose kinetics of thioridazine and its two psychoactive metabolites in healthy humans: a dose proportionality study

Dose proportionality in some pharmacokinetic parameters for thioridazine and its two active metabolites (mesoridazine and sulforidazine) was investigated in 11 healthy human subjects following oral administration of three single doses (25, 50, and 100 mg) of thioridazine hydrochloride separated in each case by an interval of two weeks. Also, after a further two weeks, another 100-mg dose of thioridazine (divided as 5 mg every 0.5 h) was administered to all the volunteers to investigate the effect of a slow rate of dosage input on the pharmacokinetic parameters of this drug. An HPLC method was used to measure concentrations of thioridazine, mesoridazine, and sulforidazine in plasma samples collected up to 72 h following each dose. Dose proportionality for the three single doses of thioridazine was observed for all three analytes in the area under the plasma concentration versus time curves (AUC infinity 0 or AUCt0) and the maximum plasma concentration (Cmax) in that the relationships between the dose and these parameters were each describable by an equation for a straight line (r2 greater than or equal to 0.8). However, the mean apparent distribution and elimination rate constants for thioridazine and mesoridazine and the mean apparent oral clearance for thioridazine decreased significantly with increasing dose. This suggests nonlinear trends in the elimination kinetics at high doses of thioridazine. When a 100-mg divided oral dose of thioridazine was administered, no statistically significant differences between single and divided doses were observed in the mean AUC infinity 0 or AUCt0 for thioridazine or sulforidazine. A significant decrease in the mean AUC infinity 0 or AUCt0 was observed for mesoridazine after the administration of the divided dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Correction of serum neuroleptic activity for blood-to-brain distribution: a method that may render radioreceptor assay results comparable between neuroleptics

Serum neuroleptic activity by radioreceptor assay and prolactin concentration were measured every 6 months for 2 years in 105 male schizophrenic outpatients. The patients took a variety of neuroleptics at clinically determined doses. As expected, when four dissimilar neuroleptics were examined together, there was no significant correlation between serum neuroleptic activity and either equivalent neuroleptic dose or serum prolactin concentration. Moderate correlations were seen, however, when neuroleptic activity was standardized between neuroleptic drugs. Similar moderate correlations were seen when neuroleptic activity was corrected for the blood-to-brain distribution of each neuroleptic. These two correction techniques ranked corrected neuroleptic activity in very similar orders. Correction for blood-to-brain distribution may be a practical way to compare serum neuroleptic activity from different neuroleptics.

Limiting solubilities and ionization constants of sparingly soluble compounds: determination from aqueous potentiometric titration data only

A new method is described for the concomitant determination of limiting solubilities and ionization constants of sparingly soluble compounds, i.e., drugs. Aqueous potentiometric titration data were recorded both before and after precipitation of the compound and subjected to computer-assisted analysis. Limiting solubilities and ionization constants were obtained for nucleoside transport inhibitors, viz., dilazep, soluflazine, and hexobendine. The method was validated by comparison of titration results for known antidepressants with data from the literature. The procedure was found to be rapid and reliable for compounds with limiting solubilities as low as 30 microM, and it circumvents problems of direct methods for measuring limiting solubilities.

Radioreceptor assay and high-performance liquid chromatography yield similar results for serum thioridazine and its major metabolites

Thioridazine and its major metabolites were quantified in serum of thioridazine-treated psychiatric patients by radioreceptor assay and high performance liquid chromatography (HPLC) every second day during 3 weeks of drug administration. Serum neuroleptic levels measured by radioreceptor assay and serum concentrations of thioridazine and its active metabolites estimated by HPLC correlated (r = 0.82, n = 60); the intra- and interassay coefficients of variation of both assays were low (less than 7%). Thus, serum thioridazine can be adequately monitored by radioreceptor assay as well as by HPLC.

S-oxidation of thioridazine to psychoactive metabolites: an oral dose-proportionality study in healthy volunteers

Thioridazine has two major active metabolites, which are formed from S-oxidation of its 2-methylthio group; the sulphoxide, mesoridazine, and the sulphone, sulforidazine. Dose proportionality of the three compounds was investigated for the first time in 11 males after administration of three single oral doses (25, 50, and 100 mg) of thioridazine hydrochloride separated in each case by two weeks. Based on the plasma concentrations of the three analytes over 72 h following each dose, large intersubject variabilities in such parameters as AUCot and Cmax were observed for each of the three compounds. The relationships between dose and parameters such as AUCot and Cmax for each analyte were described by an equation for a straight line (r2 greater than or equal to 0.8). However, the mean apparent distribution and elimination rate constants for thioridazine and mesoridazine and the mean apparent oral clearance for thioridazine decreased significantly with increasing dose, suggesting non-linearity in the elimination of thioridazine at high dose.

Concentration and distribution of thioridazine and metabolites in schizophrenic post-mortem brain tissue

Thioridazine (THD) and its major metabolites, mesoridazine (MES), sulforidazine (SULF), and northioridazine (norTHD) accumulate at a predictable rate in human brain tissue after chronic medication. Although the concentration of THD is normally lower than or the same as its major metabolite, MES, in the plasma, it was found to be up to five times as concentrated in the brain tissue of treated patients. THD and its metabolites were evenly distributed throughout all regions of the brain in chronically medicated patients. Brain concentrations of THD were also compared with those of chlorpromazine (CPZ) when both drugs had been given at the same dose before death, and were shown to be up to 10 times more concentrated in brain at doses greater than 300 mg/day. Because some of the metabolites of THD are pharmacologically active, it is important to know how they accumulate in the brain in relation to the parent compound to understand how this drug mediates its clinical effect.

Absorption and excretion of thioridazine and mesoridazine in man

Tritium labeled thioridazine and mesoridazine were given to four schizophrenic subjects to determine if differences in reported clinical potency of these two drugs could be explained by different rates of absorption and excretion. Mesoridazine was found to have earlier peak blood levels and lower fecal excretion. However, the blood and fecal differences were too small to be an adequate explanation for the differences in clinical potency suggesting that the rate of metabolic degradation is a more likely explanation for the potency difference. Thioridazine differs from other phenothiazines by containing two sulfur atoms. Thioridazine is metabolized by oxidative demethylation, oxidation at both sulfur atoms to sulfoxides and sulfones and by hydroxylation in the ring followed by glucuronide formation. Monosufoxides, disulfoxide and disufone have been found in the urine and bile of rats after thioridazine administration by inverse isotope dilution analysis. Neither the ring sulfoxide nor the disulfone show significant pharmacological activity, but activity is shown by the side chain monosulfoxide, mesoridazine. In fact it has been postulated that mesoridazine is the active form of thioridazine. Mesoridazine when compared on an equal dose basis to thioridazine is more potent in anti-emotional and hypotensive effects and produces more extrapyramidal symptoms. Since oxidation of the ring sulfur would be expected to decrease potency, it has been theorized that a portion of thioridazine is oxidized within the ring prior to the oxidation of the side chain sulfur atom thus effectively decreasing the potential activity of thioridazine. Thioridazine studies in rats have shown greater excretion in the urine and bile of the side chain sulfoxide than of the ring sulfoxide or of unchanged thioridazine. The difference in potency of these two compounds could alternatively be a result of differences in absorption, reabsorption after biliary excretion or the rate of urinary excretion. The metabolic pathways of mesoridazine in the human are essentially unknown. Because of this, we thought it worthwhile to determine if the difference in potency between thioridazine and mesoridazine is also related to differences in the rate of excretion and absorption. Because phenothiazines are found in extremely low plasma concentrations, we used radioactive compounds to perform this study.