The Interaction of Heptakis (2,6-di-O-Methyl)-β-cyclodextrin with Mianserin Hydrochloride and Its Influence on the Drug Toxicity

One tetracyclic antidepressant, mianserin hydrochloride (MIA), has quite significant side effects on a patients’ health. Cyclodextrins, which are most commonly used to reduce the undesirable features of contained drugs within their hydrophobic interior, also have the potential to alter the toxic behavior of the drug. The present paper contains investigations and the characteristics of interaction mechanisms for MIA and the heptakis (2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) system, and evaluated the effects of the complexation on MIA cytotoxicity. In order to assess whether there was an interaction between MIA and DM-β-CD molecules, isothermal titration calorimetry (ITC) have been chosen. Electrospray ionization mass spectrometry (ESI-MS) helped to establish the complex stoichiometry, and circular dichroism spectroscopy was used to describe the process of complex formation. In order to make a wider interpretative perspective, the molecular docking results have been performed. The viability of Chinese hamster cells were investigated in the presence of DM-β-CD and its complexes with MIA in order to estimate the cytotoxicity of the drug and the conjugate with the chosen cyclodextrin. The viability of B14 cells treated with MIA+DM-β-CD is lower (the toxicity is higher) than with MIA alone, and no protective effects have been observed for complexes of MIA with DM-β-CD in any ratio.

Observed and modeled effects of pH on bioconcentration of diphenhydramine, a weakly basic pharmaceutical, in fathead minnows

A need exists to better understand the influence of pH on the uptake and accumulation of ionizable pharmaceuticals in fish. In the present study, fathead minnows were exposed to diphenhydramine (DPH; disassociation constant = 9.1) in water for up to 96 h at 3 nominal pH levels: 6.7, 7.7, and 8.7. In each case, an apparent steady state was reached by 24 h, allowing for direct determination of the bioconcentration factor (BCF), blood-water partitioning (PBW,TOT), and apparent volume of distribution (approximated from the whole-body-plasma concentration ratio). The BCFs and measured PBW,TOT values increased in a nonlinear manner with pH, whereas the volume of distribution remained constant, averaging 3.0 L/kg. The data were then simulated using a model that accounts for acidification of the gill surface caused by elimination of metabolically produced acid. Good agreement between model simulations and measured data was obtained for all tests by assuming that plasma binding of ionized DPH is 16% that of the neutral form. A simpler model, which ignores elimination of metabolically produced acid, performed less well. These findings suggest that pH effects on accumulation of ionizable compounds in fish are best described using a model that accounts for acidification of the gill surface. Moreover, measured plasma binding and volume of distribution data for humans, determined during drug development, may have considerable value for predicting chemical binding behavior in fish.

Prenatal and developmental toxicity study of meclizine and caffeine combination in female albino Wistar rats

Meclizine and caffeine combination is used for the treatment of morning sickness. Both compounds are teratogenic and caffeine is known to possess anti-fertility activity also. The present study was undertaken to evaluate the reproductive toxic effect of meclizine and caffeine combination. Three doses were taken for the study; low dose (LD; meclizine 3.7 mg/kg and caffeine 3 mg/kg) was selected from commercially available formulation, middle dose (MD; meclizine 37 mg/kg and caffeine 30 mg/kg) and high dose (HD; meclizine 370 mg/kg and caffeine 300 mg/kg). The mixture was administered 1-7 days and 8-14 days for fertility and embryotoxic studies respectively. Laparotomy was done on 10t day of gestation period. Number of implants and corpora lutea were counted, pre and post-implantation losses were determined. In embryo toxicity study fetuses were evaluated for external, skeletal and visceral examination. High dose was removed from both fertility and embryotoxicity studies due to its severe toxicity to the dam. Significant anti-fertility activity was observed at middle dose. Embryotoxicity study showed significant reduction in fetal body weight, body length and body mass index, dam body weight gain on gestation day 14. Absolute kidney weight in MD and absolute and relative spleen weight in both LD and MD were significantly reduced. There was no increase in external or internal congenital anomalies at both LD and MD. The, results suggest that prescription of meclizine and caffeine for morning sickness in early pregnancy should be reviewed carefully.

Acute and chronic effects of diphenhydramine and sertraline mixtures in Ceriodaphnia dubia

Ceriodaphnia dubia were tested to evaluate the acute and chronic interactive effects of diphenhydramine and sertraline. Observed effects were compared with 2 reference toxicity models, the concentration addition model and the independent action model. Results indicate that the 2 drugs exhibit additive toxicity in C. dubia. In some cases, individually sublethal concentrations of the chemicals resulted in 100% mortality when combined, demonstrating the potentially severe impact of trace environmental contaminants.

Necrosis caused by intra-arterial injection of promethazine: case report

Promethazine injections have led to necrosis and gangrene of the distal upper extremity when inadvertently injected into an artery. There have been few case reports of this alarming complication in the literature. We report on 2 cases of intra-arterial promethazine injection that led to amputation.

Blockade of HERG K+ channel by an antihistamine drug brompheniramine requires the channel binding within the S6 residue Y652 and F656

A number of clinically used drugs block delayed rectifier K+ channels and prolong the duration of cardiac action potentials associated with long QT syndrome. This study investigated the molecular mechanisms of voltage-dependent inhibition of human ether-a-go-go-related gene (HERG) delayed rectifier K+ channels expressed in HEK-293 cells by brompheniramine, an antihistamine. Brompheniramine inhibited HERG current in a concentration-dependent manner with the half-maximal inhibitory concentration (IC50) value of 1.7 microm at 0 mV. A block of HERG current by brompheniramine was enhanced by progressive membrane depolarization and showed significantly negative shift in voltage-dependence of channel activation. Inhibition of HERG current by brompheniramine showed time-dependence. The S6 residue HERG mutant Y652A and F656C largely reduced the blocking potency of HERG current. These results indicate that brompheniramine mainly inhibited the HERG potassium channel through the residue Y652 and F656 and these residues may be an obligatory determinant in inhibition of HERG current for brompheniramine.

Identification of genes implicated in methapyrilene-induced hepatotoxicity by comparing differential gene expression in target and nontarget tissue

BACKGROUND

Toxicogenomics experiments often reveal thousands of transcript alterations that are related to multiple processes, making it difficult to identify key gene changes that are related to the toxicity of interest.

OBJECTIVES

The objective of this study was to compare gene expression changes in a nontarget tissue to the target tissue for toxicity to help identify toxicity-related genes.

METHODS

Male rats were given the hepatotoxicant methapyrilene at two dose levels, with livers and kidneys removed 24 hr after one, three, and seven doses for gene expression analysis. To identify gene changes likely to be related to toxicity, we analyzed genes on the basis of their temporal pattern of change using a program developed at the National Institute of Environmental Health Sciences, termed "EPIG" (extracting gene expression patterns and identifying co-expressed genes).

RESULTS

High-dose methapyrilene elicited hepatic damage that increased in severity with the number of doses, whereas no treatment-related lesions were observed in the kidney. High-dose methapyrilene elicited thousands of gene changes in the liver at each time point, whereas many fewer gene changes were observed in the kidney. EPIG analysis identified patterns of gene expression correlated to the observed toxicity, including genes associated with endoplasmic reticulum stress and the unfolded protein response.

CONCLUSIONS

By factoring in dose level, number of doses, and tissue into the analysis of gene expression elicited by methapyrilene, we were able to identify genes likely to not be implicated in toxicity, thereby allowing us to focus on a subset of genes to identify toxicity-related processes.

Systems Toxicology: Integrated Genomic, Proteomic and Metabonomic Analysis of Methapyrilene Induced Hepatotoxicity in the Rat

Administration of high doses of the histamine antagonist methapyrilene to rats causes periportal liver necrosis. The mechanism of toxicity is ill-defined and here we have utilized an integrated systems approach to understanding the toxic mechanisms by combining proteomics, metabonomics by 1H NMR spectroscopy and genomics by microarray gene expression profiling. Male rats were dosed with methapyrilene for 3 days at 150 mg/kg/day, which was sufficient to induce liver necrosis, or a subtoxic dose of 50 mg/kg/day. Urine was collected over 24 h each day, while blood and liver tissues were obtained at 2 h after the final dose. The resulting data further define the changes that occur in signal transduction and metabolic pathways during methapyrilene hepatotoxicity, revealing modification of expression levels of genes and proteins associated with oxidative stress and a change in energy usage that is reflected in both gene/protein expression patterns and metabolites. The difficulties of combining and interpreting multiomic data are considered.

Drug-induced phospholipidosis: issues and future directions

Numerous drugs containing a cationic amphiphilic structure are capable of inducing phospholipidosis in cells under conditions of in vivo administration or ex vivo incubation. The principal characteristics of this condition include the reversible accumulation of polar phospholipids in association with the development of unicentric or multicentric lamellated bodies within cells. There is an abundance of data providing an understanding of potential mechanisms for the induction of phospholipidosis; however, the process is likely to be complex and may differ from one drug to another. The functional consequences of the presence of this condition on cellular or tissue function are not well understood. The general consensus is that the condition is an adaptive response rather than a toxicological manifestation; however, additional studies to examine this question are needed. Until this issue is resolved, concerns about phospholipidosis will continue to exist at regulatory agencies. Procedures for the screening of potential phospholipogenic candidate compounds are available. In contrast, a clear need exists for the identification of valid biomarkers to assess the development of phospholipidosis in preclinical and clinical studies.

Effects of cyamemazine on hERG, INa, ICa, Ito, Isus and IK1 channel currents, and on the QTc interval in guinea pigs

The antipsychotic and anxiolytic phenothiazine, cyamemazine, was investigated for its effects on the hERG (human ether-à-go-go related gene) channel expressed in HEK 293 cells and on native INa, ICa, Ito, Isus, or IK1 of human atrial myocytes. Moreover, cyamemazine and terfenadine were compared for their effects on the QT interval in anesthetized guinea pigs. Cyamemazine reduced hERG current amplitude with an IC50 value of 470 nM. Cyamemazine 1 microM failed to significantly affect INa, Ito, Isus, or IK1 amplitudes and slightly decreased ICa (18%). For comparison, haloperidol (30 nM) and olanzapine (300 nM) reduced hERG current amplitude by 44.2+/-3.9% and 49.7+/-4.2%, respectively. The cardiac safety ratio of cyamemazine, calculated from the IC50/receptor affinity ratios, is 81 and 313 against dopamine D2 receptors and 5-HT2A receptors, respectively. In guinea pigs, QT and QTcBazett were not significantly modified by intravenous cyamemazine when compared to the effects produced by the vehicle. Conversely, terfenadine (5 mg/kg iv) increased significantly QTcBazett (+58 ms), QTcFrediricia (+83 ms) and QTcVan de Water (+78 ms). In conclusion, cyamemazine concentrations required to inhibit hERG current exceed substantially those necessary to achieve therapeutic activity in humans. Moreover, cyamemazine, in contrast to terfenadine, does not delay cardiac repolarization in the anesthetized guinea pig. These non-clinical findings confirm the excellent cardiac safety records of cyamemazine during its 30 years of extensive therapeutic use.

A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation derived from the effects of terfenadine, cisapride and E-4031 in the conscious chronic av node—ablated, His bundle-paced dog

INTRODUCTION

Terfenadine, cisapride, and E-4031, three drugs that prolong ventricular repolarization, were selected to evaluate the sensitivity of the conscious chronic atrioventricular node--ablated, His bundle-paced Dog for defining drug induced cardiac repolarization prolongation. A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation was generated from these data.

METHODS

Three male beagle dogs underwent radiofrequency AV nodal ablation, and placement of a His bundle-pacing lead and programmable pacemaker under anesthesia. Each dog was restrained in a sling for a series of increasing dose infusions of each drug while maintained at a constant heart rate of 80 beats/min. RT interval, a surrogate for QT interval in His bundle-paced dogs, was recorded throughout the experiment.

RESULTS

E-4031 induced a statistically significant RT prolongation at the highest three doses. Cisapride resulted in a dose-dependent increase in RT interval, which was statistically significant at the two highest doses. Terfenadine induced a dose-dependent RT interval prolongation with a statistically significant change occurring only at the highest dose. The relationship between drug concentration and RT interval change was described by a sigmoid E(max) model with an effect site. Maximum RT change (E(max)), free drug concentration at half of the maximum effect (EC(50)), and free drug concentration associated with a 10 ms RT prolongation (EC(10 ms)) were estimated. A linear correlation between EC(10 ms) and HERG IC(50) values was identified.

DISCUSSION

The conscious dog with His bundle-pacing detects delayed cardiac repolarization related to I(Kr) inhibition, and detects repolarization change induced by drugs with activity at multiple ion channels. A clinically relevant sensitivity and a linear correlation with in vitro HERG data make the conscious His bundle-paced dog a valuable tool for detecting repolarization effect of new chemical entities.

Synthesis and Structure−Activity Relationships of Novel Histamine H1 Antagonists: Indolylpiperidinyl Benzoic Acid Derivatives

A series of indolylpiperidinyl derivatives were prepared and evaluated for their activity as histamine H(1) antagonists. Structure-activity relationship studies were directed toward improving in vivo activity and pharmacokinetic profile of our first lead (1). Substitution of fluorine in position 6 on the indolyl ring led to higher in vivo activity in the inhibition of histamine-induced cutaneous vascular permeability assay but lower selectivity toward 5HT(2) receptor. Extensive optimization was carried out within this series and a number of histamine H(1) antagonists showing potency and long duration of action in vivo and low brain penetration or cardiotoxic potential were identified. Within this novel series, indolylpiperidines 15, 20, 48,51 and 52 exhibited a long half-life in rat and have been selected for further preclinical evaluation.

Maternal exposure to diphenhydramine during the fetal period in rats: Effects on physical and neurobehavioral development and on neurochemical parameters

Previous research from our laboratory suggested that the administration of antihistaminics (H(1) receptor antagonists) to pregnant Wistar rats throughout pregnancy altered brain sexual differentiation and dopaminergic physiology of the offspring. In the present study, we assessed the effects of 20 mg/kg diphenhydramine (DPH) administration to pregnant rats during the fetal period of pregnancy [Gestation Days (GDs) 16-21], a critical period for brain sexual differentiation and central nervous system (CNS) maturation. Maternal body weight and water and food consumption were measured during pregnancy and offspring physical and behavioral development were evaluated during lactation. Offspring open-field behavior was assessed at 21 and 100 days of age. After the final open-field test, male and female sexual behavior, stereotypy following an apomorphine challenge, striatal content of dopamine (DA), the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA), serotonin (5-HT) and the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) were assessed. There were no significant treatment-related changes in maternal reproductive parameters, but DPH treatment decreased maternal body weight gain during the treatment period. Offspring physical parameters were not altered in the treated group, and no significant treatment-related changes were found in female open-field measures, sexual behavior or in striatal neurochemical measurements. However, delayed testis descent and altered patterns of sexual behavior occurred in male offspring accompanied by increased striatal DA, decreased striatal DOPAC as well as reduced DOPAC/DA, HVA/DA and 5-HIAA/5-HT ratios. Taken together, these data suggest that exposure to DPH during the fetal period of rat development altered postnatal CNS maturation and sexual development of male offspring via changes in striatal bioamine systems.

Effects of perinatal loratadine exposure on male rat reproductive organ development

Normal pre- and postnatal male reproductive development and function is dependent upon testicular androgen production and is sensitive to antiandrogenic perturbations. It was of interest to determine if the H(1) histamine antagonist loratadine had the potential to alter androgen-mediated reproductive development in the rat, a sensitive species for detecting antiandrogenic effects. Loratadine was administered orally by gavage to pregnant Sprague-Dawley rats at doses of 4, 12 or 24 mg/kg from gestation day 7 to postnatal day 4, encompassing the period of androgen-dependent male reproductive development. Vehicle control rats received 0.4% aqueous methylcellulose. Dams were allowed to deliver naturally and rear their offspring until postnatal day 21. On postnatal day 21 male offspring were retained for further evaluation of androgen-dependent endpoints and the female offspring were euthanized and their sex confirmed internally. Males were necropsied from postnatal day 72 to 85. Dams administered 24 mg/kg of loratadine exhibited a transient 45% decrement in maternal body weight gain at the initiation of dosing (gestation days 7-9). Mean pup body weight on postnatal days 1 and 4 were approximately 4% lower than controls. No other effects on offspring growth were observed. Anogenital distance on postnatal day 1 was unaffected by loratadine exposure. Loratadine exposure did not induce the retention of nipples in male rats, affect preputial separation, or induce external malformations, including hypospadias. Seminal vesicle and prostate weights were not decreased by loratadine exposure. These data clearly demonstrate that systemic loratadine exposure, in multiples up to 26 times clinical exposure levels, does not exhibit in vivo antiandrogen activity, as evidenced by the absence of alterations or malformations in androgen-dependent reproductive tissues in male rats exposed to loratadine during the critical period of androgen-dependent development.

RNA synthesis-dependent potentiation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor-mediated toxicity by antihistamine terfenadine in cultured rat cerebellar neurons

We have studied the effects of terfenadine on neurotoxicity and elevation of free cytoplasmic Ca2+ levels upon stimulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors in cultured cerebellar neurons. Pre-exposure to terfenadine (5 microM, 5 h) significantly increased neuronal death following specific stimulation of receptors by 100 microM AMPA or by subtoxic concentrations of domoate (8 microM), stimuli that are non-toxic when applied to terfenadine-untreated sister cultures. Terfenadine potentiation was prevented by the transcription inhibitor actinomycin D and was significantly ameliorated by histamine (1 mM). In terfenadine-treated neurons, AMPA increased [Ca2+](i) by approximately five fold, while AMPA induced no significant increase in [Ca2+](i) in the absence of terfenadine. Terfenadine reduced neuronal steady-state concentrations of [Ca2+](i) by approximately 75%. Our results suggest a role for histamine H1 receptors and intracellular calcium in the modulation of the excitotoxic response via AMPA receptors.

Labeling of diphenhydramine-containing drug products for over-the-counter human use. Final rule

The Food and Drug Administration (FDA) is issuing a final rule amending the final monographs for over-the-counter (OTC) antiemetic, antihistamine, antitussive, and nighttime sleep-aid drug products to add a warning statement for oral products containing diphenhydramine citrate or diphenhydramine hydrochloride. The warning advises consumers not to use oral OTC diphenhydramine products with any other product containing diphenhydramine, including products used topically. This final rule also includes the agency's conclusions on additional warning statements and a direction statement for OTC external analgesic drug products containing diphenhydramine hydrochloride. These conclusions will be incorporated into the final monograph for OTC external analgesic drug products in a future issue of the Federal Register. FDA is issuing this final rule after considering public comments on the agency's proposed regulation and all new data and information on drug products containing diphenhydramine that have come to the agency's attention

Methapyrilene toxicity: anchorage of pathologic observations to gene expression alterations

Methapyrilene (MP) exposure of animals can result in an array of adverse pathological responses including hepatotoxicity. This study investigates gene expression and histopathological alterations in response to MP treatment in order to 1) utilize computational approaches to classify samples derived from livers of MP treated rats based on severity of toxicity incurred in the corresponding tissue, 2) to phenotypically anchor gene expression pattems, and 3) to gain insight into mechanism(s) of methapyrilene hepatotoxicity. Large-scale differential gene expression levels associated with the exposure of male Sprague-Dawley rats to the rodent hepatic carcinogen MP for 1, 3, or 7 days after daily dosage with 10 or 100 mg/kg/day were monitored. Hierarchical clustering and principal component analysis were successful in classifying samples in agreement with microscopic observations and revealed low-dose effects that were not observed histopathologically. Data from cDNA microarray analysis corroborated observed histopathological alterations such as hepatocellular necrosis, bile duct hyperplasia, microvesicular vacuolization, and portal inflammation observed in the livers of MP exposed rats and provided insight into the role of specific genes in the studied toxicological processes.

Comparative effects of maternal prenatal and postnatal exposures to astemizole on reproductive parameters of rats

The prenatal and postnatal effects of administration of a nonsedative antihistamine H1, astemizole (ATZ), were compared. ATZ (10 mg/kg) was injected daily into female Wistar rats throughout pregnancy (prenatal treatment) or during the first 6 days of lactation (postnatal treatment). Neither treatment modified dam body weight. Prenatal exposure reduced offspring body weight and lead to a latter expression of the vaginal opening of female offspring. In addition, a long-term disruption of male reproductive behavior was observed, while female sexual behavior was not modified. The sexual activity index and the intromission frequency were increased in prenatally treated animals. Testes wet weight was reduced, but no modifications were detected in vas deferens or seminal vesicles. Postnatal treatment did not alter offspring body weight, open-field activity, sexual behavior and organ weight as well as did not delay testes descent but reduced the time until vaginal opening. Hypothalamic serotonin (5-HT), dopamine (DA) and noradrenaline (NA) as well as DA and NA metabolites were not modified by both prenatal and postnatal treatments. Increased striatal 3,4-dihydroxyphenylacetic acid (DOPAC) levels were observed after prenatal and postnatal treatments, while only postnatal 5-HT levels were increased. We propose that the present results indicate that prenatal ATZ exposure can have long-lasting organizational effects on reproductive behavior of male rats, while postnatal exposure to this drug did not alter mating behavior. In relation to female rats, prenatal and postnatal exposures to ATZ accelerated puberty but did not alter sexual behavior. Neurochemical data show that both treatments increased striatal dopaminergic system activity, suggesting a central ATZ effect after perinatal exposure.

Pharmacokinetic/pharmacodynamic assessment of the effects of E4031, cisapride, terfenadine and terodiline on monophasic action potential duration in dog

1. Torsades de pointes (TDP) is a potentially fatal ventricular tachycardia associated with increases in QT interval and monophasic action potential duration (MAPD). TDP is a side-effect that has led to withdrawal of several drugs from the market (e.g. terfenadine and terodiline). 2. The potential of compounds to cause TDP was evaluated by monitoring their effects on MAPD in dog. Four compounds known to increase QT interval and cause TDP were investigated: terfenadine, terodiline, cisapride and E4031. On the basis that only free drug in the systemic circulation will elicit a pharmacological response target, free concentrations in plasma were selected to mimic the free drug exposures in man. Infusion regimens were designed that rapidly achieved and maintained target-free concentrations of these drugs in plasma and data on the relationship between free concentration and changes in MAPD were obtained for these compounds. 3. These data indicate that the free ED50 in plasma for terfenadine (1.9 nM), terodiline (76 nM), cisapride (11 nM) and E4031 (1.9 nM) closely correlate with the free concentration in man causing QT effects. For compounds that have shown TDP in the clinic (terfenadine, terodiline, cisapride) there is little differentiation between the dog ED50 and the efficacious free plasma concentrations in man (< 10-fold) reflecting their limited safety margins. These data underline the need to maximize the therapeutic ratio with respect to TDP in potential development candidates and the importance of using free drug concentrations in pharmacokinetic/pharmacodynamic studies.

Antihistaminic and mast cell stabilizing activity of Striga orobanchioides

The ethanolic and aqueous extracts of the whole plant of S. orobanchioides were evaluated for antihistaminic and mast cell stabilizing activities. Both extracts inhibited histamine-induced contractions of the guinea-pig ileum at the concentration range of 2.5-25 microg/ml in a dose-related manner. At 25 microg/ml, both extracts inhibited the response of histamine (0.5 microg/ml) almost completely. The effect of these two extracts on the degranulation rate of sensitized peritoneal cells of albino rats when challenged with antigen (horse serum) was studied. Triple vaccine was used as adjuvant. Ketotifen and prednisolone were used for comparison. The ethanolic extract at 100 and 200 mg/kg body weight was found to significantly inhibit degranulation of mast cells to an extent of 52.14+/-3.24 and 67.96+/-3.70%, respectively. At the same doses, the aqueous extract showed 42.09+/-2.91 and 60.67+/-3.50% reduction in degranulation of mast cells, respectively. Hence, both extracts markedly protected the rats against antigen-induced challenge of mast cells.

Principal component analysis of mass spectra of peptides generated from the tryptic digestion of protein mixtures

Principal component analysis (PCA) has been used to analyse mass spectral peptide profiles obtained from the enzymatic digestion of standard protein mixtures. Scores and loadings plots clearly revealed peptide fragments that differentiated one protein mixture from another. Peptide map search results identified with a high degree of certainty any additional proteins in these mixtures. As a proof-of-concept this methodology was applied to hepatic protein mixtures obtained from rats treated with two hepatotoxic compounds: methapyriline and SB-219994. Liver proteins were extracted, pre-separated by one-dimensional polyacrylamide gel electrophoresis, subjected to tryptic digestion and analysed by mass spectrometry. Two up-regulated proteins, glutathione S-transferase with methapyrilene and peroxisomal bifunctional enzyme with SB-219994, were identified in this manner.

Screening for anti-HIV drugs that can combine virucidal and virustatic activities synergistically

Chlorcyclizine HCl and ciprofloxacin HCl were shown to have anti-HIV activity. They possess virustatic and virucidal activities against HIV, a murine retrovirus (RV) and several other RNA and DNA viruses. These drugs were screened from a large number of compounds on the basis of in vitro mutagenicity and antimetabolite detection tests. Subsequent studies were based on different exo vivo cell cultures. These two compounds were then tested on an animal model, following standard test protocols, using another retrovirus, maintained as Ehrlich's ascites cell tumour virus (EACTV). The animal mortality and protection tests corroborated the findings obtained in vitro, suggesting that these drugs acted synergistically against HIV, exhibiting both virucidal and virustatic properties.

Cicletanine prevents the excitation-conduction blocks induced by terfenadine in ischemic myocardium

Terfenadine, a histamine H(1) receptor antagonist, has been associated with clinical ventricular arrhythmias and in vitro excitation-conduction blocks, whereas anti-ischemic and antiarrhythmic effects have been shown with cicletanine, a prostacyclin generation stimulator. We aimed at determining in vitro if cicletanine can protect the ischemic myocardium from excitation-conduction blocks and specifically those induced by terfenadine. In a double-chamber bath, isolated guinea pig ventricular strips were partly exposed to normoxia and partly to ischemic, then reperfused, conditions, in the presence of 10 microM terfenadine, 10 microM indomethacin (prostacyclin generation blocker) or the solvent (dimethylsulfoxide 1:100, control) randomly allocated, and thus either in the absence (n=20) or presence (n=21) of 10 microM cicletanine during the total protocol duration. The multivariate Cox's model was used to predict the excitation-conduction block events and to assess the estimated survival of preparations (excitation-conduction block-free rate). Cicletanine protected the preparations (relative risk=0.08, t=-3.28) from the ischemia-induced excitation-conduction blocks (estimated survival=0.83 versus 0.30 in control), and this effect was abolished by indomethacin (estimated survival=0.35). Terfenadine enhanced 3. 58-fold the risk of occurrence of excitation-conduction blocks during ischemia (t=2.10) and this effect was inhibited by cicletanine pretreatment (estimated survival=0.40 versus 0.10 in untreated preparations). In conclusion, these in vitro findings have provided evidence for (1) protective effects of cicletanine against ischemia-induced excitation-conduction blocks, possibly related to its stimulating activity on local prostacyclin generation, and (2) efficacy of cicletanine to prevent excitation-conduction blocks induced by terfenadine in ischemic cardiac tissue.

Electrophysiological effects of cetirizine, astemizole and D-sotalol in a canine model of long QT syndrome

Observations of torsades de pointes during therapy with terfenadine and astemizole has raised concern about the cardiac safety of non-sedating H1-antagonist agents. We compared cetirizine, another compound of that class, to D-sotalol and to astemizole in a model of acquired long QT syndrome. Open-chest surgery was performed in adult beagle dogs anaesthetized with halothane and thiopental. Bradycardia was produced with beta-adrenergic blockade and sinus node crush. Four left ventricular intramyocardial unipolar monophasic action potentials (MAP) were recorded during atrial pacing at basic cycle lengths (BCL) 400-1500 msec, before and during three successive 1-h drug infusions (0.14, 0.45 and 1.4 mg/kg/h for astemizole and cetirizine and 1.1, 2.2 and 4.5 mg/kg/h for D-sotalol). Dose- and bradycardia-dependent prolongations of MAP duration (MAPD) were produced by D-sotalol (P < 0.001) and astemizole (P < 0.001) but not by cetirizine. At BCL 1500 ms, the three infusions of astemizole prolonged endocardial MAPD from 323 +/- 8 msec (mean +/- SE) at baseline to 343 +/- 10, 379 +/- 13 and 468 +/- 26 msec, respectively (n = 9). Sotalol prolonged that MAPD from 339 +/- 6 msec to 377 +/- 7, 444 +/- 15 and 485 +/- 24 msec (n = 7). In contrast, cetirizine did not prolong MAPD: 341 +/- 8 msec at baseline Vs 330 +/- 8, 324 +/- 9 and 323 +/- 11 msec (n = 9). Drug-induced increase in transmural dispersion reached +79 +/- 19 msec after astemizole, +59 +/- 21 msec after D-sotalol and only +7 +/- 11 msec after cetirizine. Runs of ventricular tachycardias and torsades de pointes occurred during dose three of astemizole (5/9 dogs) and D-sotalol (4/7 dogs) but never during cetirizine. In the present model, astemizole and D-sotalol but not cetirizine prolonged MAPD and transmural dispersions of repolarization and produced torsades de pointes. These results suggest that the halothane-anaesthetized bradycardic dog could be a valuable model to discriminate drugs for their class III effects and proarrhythmic potencies.

Terfenadine induces toxicity in cultured cerebellar neurons: a role for glutamate receptors

Exposure of cultured cerebellar neurons to the histamine H1 receptor antagonist terfenadine resulted in neuronal degeneration and death. Terfenadine neurotoxicity was dependent upon concentration and time of exposure. After 2 h exposure, 20 microM terfenadine reduced the number of surviving neurons by 75%, and as low as 10 nM terfenadine induced significant neurotoxicity after 5 days of exposure. Neuronal sensitivity to terfenadine changed with age in culture, and at 25 days in culture neurons appeared to be much less sensitive than at 5 or 9-17 days in culture. Neurotoxicity by terfenadine could not be prevented by high concentrations of histamine (5 mM), but it was significantly delayed by blocking NMDA or non-NMDA glutamate receptors with MK-801 or CNQX respectively, suggesting the involvement of excitatory transmission mediated by glutamate in the neurotoxicity induced by terfenadine in these neurons. We also found that the presence of terfenadine (5 microM) unveiled the potential excitotoxity of the non-NMDA receptor agonist AMPA (100 microM), and reduced the concentration of glutamate necessary to induce excitotoxicity, compared to untreated cultures. These results suggest a role for terfenadine in the modulation of the excitotoxic response mediated in cerebellar neurons through ionotropic glutamate receptors.

Pharmacokinetic-pharmacodynamic analysis of the arrhythmogenic potency of a novel antiallergic agent, ebastine, in rats

Ebastine (EBS), a novel nonsedative antiallergic agent, is similar to terfenadine in its chemical structure. However, clinical arrhythmogenicity of EBS remains controversial. In this study, we evaluated the possible arrhythmogenic potency of EBS as assessed by QT prolongation from a pharmacokinetic-pharmacodynamic viewpoint in comparison with that of terfenadine. EBS was intravenously infused into anesthetized rats at a rate of 3.0 or 10 mg/kg/h for 60 min, and electrocardiographic effects were continuously monitored from lead II. The plasma concentrations of EBS and its major metabolite, carebastine, were also measured under the same conditions. When intravenously administered, EBS exhibited QT prolongation in an infusion rate-dependent manner, with a lag time. Pharmacokinetic-pharmacodynamic analysis of EBS based on the effect-compartment model revealed values of EC50, Emax and EC(10 ms), (where 10 ms of QT prolongation was evoked) of 0.73 microg/mL, 12.5 ms and 2.90 microg/mL, respectively. The EC(10 ms) value of EBS was five times higher than that of terfenadine reported previously (Ohtani et al., J. Pharm. Pharmacol., 49, 458-462 (1997)). In conclusion, EBS was suggested to be less arrhythmogenic than terfenadine.

Effects of induction and inhibition of cytochromes P450 on the hepatotoxicity of methapyrilene

The mechanisms by which the antihistamine drug methapyrilene causes acute periportal hepatotoxicity in rats are not yet elucidated. This study investigated the effects of modulators of cytochrome P450 (CYP) activity on the hepatotoxicity of methapyrilene and also the effect of methapyrilene on hepatic CYP. Pretreatment of male Han Wistar rats with beta-naphthoflavone, phenobarbitone, butylated hydroxytoluene, piperonyl butoxide, Aroclor 1254, or cobalt protoporphyrin IX, agents known to modify hepatic CYP, all afforded some degree of protection against a hepatotoxic dose of methapyrilene (150 mg/kg x 3 days p.o.), as assessed by clinical chemistry and histology. Total hepatic CYP depletion by cobalt protoporphyrin IX treatment indicated CYP-mediated bioactivation was a prerequisite for methapyrilene-induced hepatotoxicity. Protection against hepatic damage was strongly associated with beta-naphthoflavone induction of CYP1A and phenobarbitone-associated CYP2B induction. However, the role of CYP3A, which is constitutively expressed in the liver and induced by piperonyl butoxide, butylated hydroxytoluene, or Aroclor 1254, was unclear. Modulation of FAD monooxgenase activity by methimazole pretreatment was not associated with increased methapyrilene-induced hepatotoxicity. Methapyrilene treatment alone specifically decreased microsomal enzyme activity markers for CYP2C11, CYP3A, and CYP2A and pretreatment with all the hepatic enzyme-inducing agents specifically prevented the loss of CYP2C11. Together this suggested that CYP2C11 was responsible for the suicide substrate bioactivation of methapyrilene and the toxicologic outcome largely relied upon an abundance of detoxifying enzymes present in the liver.

A review and investigation into the mechanistic basis of the genotoxicity of antihistamines

The genotoxicity of twenty one clinically used (or discontinued) antihistamines is reviewed. New results are also presented from an evaluation of selected antihistamines in the V79 in vitro micronucleus assay. For two antihistamines, no genotoxicity data is available. Of the remaining nineteen, nine have been reported as positive and one equivocal in at least one genotoxicity assay despite the fact that none possess structural alerts for genotoxicity. Ethidium displacement and bleomycin amplification studies in V79 cells indicate that nine of these ten antihistamines are capable of intercalative DNA binding. Further, nine of the ten positive compounds, but none of the tested compounds which also intercalate but are reported to be negative in gene-tox assays (e.g. triprolidine, chlorcyclizine, clemastine), possess a dimethylamino substituent suggesting the requirement for this cationic function in the genotoxicity. It is proposed that the apparent genotoxicity of antihistamines and possibly many other pharmaceuticals derives from a hitherto unappreciated propensity of these drugs for stabilized intercalative DNA binding. It is further proposed that the bleomycin amplification assay may provide a widely applicable means for assessing functional intercalative drug/DNA interaction in intact mammalian cells.

Methapyrilene hepatotoxicity is associated with oxidative stress, mitochondrial disfunction and is prevented by the Ca2+ channel blocker verapamil

Methapyrilene (MP) is an unusual hepatotoxin in that it causes periportal necrosis in rats. The mechanism of acute methapyrilene hepatotoxicity has, therefore, been investigated in cultured male rat hepatocytes. Addition of methapyrilene to rat hepatocytes resulted in a time- and dose-dependent loss in cell viability between 4 and 8 h of incubation as judged by cellular enzyme leakage. The cytochrome P450 (CYP) inhibitor metyrapone protected against methapyrilene-mediated toxicity suggesting that MP is metabolised by CYP for toxicity. The concentration-dependent protection from methapyrilene toxicity afforded by metyrapone correlated with an inhibition of microsomal CYP2C11-associated androstenedione 16alpha hydroxylase activity, and hepatocytes prepared from hypophysectomised rats (containing reduced levels of microsomal immunodetectable CYP2C11 and associated androstenedione 16alpha hydroxylase activity) showed resistance to the toxic effects of methapyrilene. These data suggest that the toxicity of methapyrilene is predominantly dependent on the CYP2C11 isoform. Treatment of hepatocytes with a toxic concentration of MP caused oxidative stress as indicated by increases in NADP+ levels within 2 h and cellular thiol oxidation as evidenced by a reduction--but not complete loss--in glutathione levels. Methapyrilene hepatotoxicity was associated with an early loss in mitochondrial function, as indicated by mitochondrial swelling and significant losses in cellular ATP within 2 h. Co-incubation of methapyrilene-treated hepatocytes with inhibitors of inner mitochondrial transition permeability pore opening--cyclosporin A or the thiol reductant dithiothreitol--abrogated cell death suggesting that pore opening and loss of mitochondrial Ca2+ homeostasis play a significant role in methapyrilene-mediated cell death. Co-incubation of methapyrilene-treated hepatocytes with the phenylalkylamine calcium channel blocker verapamil--but not by treating cells in a nominally calcium-free medium--also abrogated cell death, suggesting that if Ca2+ is involved in cell killing then it is dependent on an intracellular Ca2+ pool. Pre-treatment of hepatocytes for 1 h with verapamil--to inhibit intracellular Ca2+ pool filling--increased the potency of verapamil protection against methapyrilene toxicity by approximately 100-fold. Taken together, these data indicate that methapyrilene intoxication leads to mitochondrial disfunction and suggest a critical role for a loss of mitochondrial Ca2+ homeostasis in this model of hepatocyte death.

Effect of pertussis toxin on baclofen- and diphenhydramine-induced amnesia

The effect of pretreatment with pertussis toxin at the doses of 0.25 and 0.50 microg per mouse ICV on the amnesic effect produced by baclofen (0.1 4 mg kg(-1) i.p.), diphenhydramine (15-30 mg kg(-1) i.p.) and scopolamine (0.5-5 mg kg(-1) i.p.) was investigated in the mouse passive avoidance test. Ten days after a single injection of pertussis toxin, baclofen (2 4 mg kg(-1) i.p.) amnesia was prevented. By contrast, pertussis toxin had no effect on diphenhydramine- and scopolamine-induced amnesia. Pretreatment with pertussis toxin at both doses used did not impair motor coordination of the mice, as revealed by the rota-rod test. The present results indicate that the activation of pertussis toxin-sensitive G-proteins represents an important transduction step in memory impairment induced by GABA(B) (gamma-aminobutyric acid B) agonists, but not by antihistaminic and antimuscarinic drugs.

Prenatal exposure of rats to diphenhydramine: effects on physical development, open field, and gonadal hormone levels in adults

Diphenhydramine (DPH), a classical H1 receptor antagonist, has been used in pregnancy for the treatment of allergies, nausea, and vomiting. It has been reported that 10-20% of pregnant women take antihistamine-containing preparations at some point during pregnancy. The present study analyzed the influence of prenatal exposure to DPH of rats on: 1) maternal behavior and milk production of dams; 2) physical and reflexologic development of offspring; and 3) long-term effects on open field behaviors and gonadal hormone levels in offspring. Female pregnant rats were injected s.c., daily, with 20 mg/kg DPH or saline from embryonic day (E) 0 to 21. After delivery, maternal behavior was assessed and offspring physical and reflexologic development was examined. Open field activity of male and female rats was measured at 21 and 75 days of age and plasma hormone levels were evaluated in both sexes at 120 days of age. Neither maternal behavior nor milk production was affected by DPH treatment. Treated offspring showed an accelerated pinna unfolding, eye opening, and a delay of testes descent and vaginal opening. Both righting reflex and negative geotaxis development were accelerated, but prenatal exposure to DPH did not modify offspring locomotor activity. When tested as adults, a lack of sexual dimorphism in the open field activity of males and females was observed. No differences were observed between gonadal hormone levels of control and experimental groups of either sex. The findings suggest that prenatal DPH exposure influences physical and reflex development of rat pups.

Therapeutic doses of theophylline exert proconvulsant effects in developing mice

We studied the effect of therapeutic doses of theophylline on electrically-induced convulsions in developing mice. A theophylline dose as small as 3 mg/kg increased seizure susceptibility of 21-day-old mice, but not of 42-day-old mice. These findings were consistent with clinical reports that theophylline at the therapeutic blood concentrations occasionally induced convulsions in children. The age-dependent proconvulsant effect of theophylline was well inhibited by phenobarbital (PB), dose-dependently, but not by other well-established antiepileptic drugs (AEDs). PB may be a good choice of AED in patients with bronchial asthma and seizure disorders, if PB is indicative for their seizure types. The proconvulsant effect of theophylline in 21-day-old mice was counteracted by not only an adenosine A1 agonist, but also an NMDA antagonist and a histamine H3 antagonist. Several studies have established that the proconvulsant effect of theophylline intoxication is mainly due to the blockade of adenosine A1 receptors. The present findings suggested that the proconvulsant properties of therapeutic doses of theophylline in developing period were different from those of theophylline intoxication. Combination of therapeutic doses of theophylline and centrally-acting histamine H1 antagonists showed proconvulsant effects even in 42-day-old mice, suggesting that peripherally acting histamine H1 antagonists, such as astemizole, evastine and epinastine, were much safer than centrally acting histamine H1 antagonists for patients with both allergy and seizure history.

Photo hen's egg test: a model for phototoxicity

The aim of this investigation was to establish a new model for phototoxicity which is more advanced than the widely used cultures of yeasts, bacteria or cells of various origin, and at the same time to avoid animal testing. We studied the extraembryonal vasculature of the incubated hen's egg. This model was originally introduced by toxicologists as an alternative to the rabbit's eye irritation test (Draize test). In the photo hen's egg test, substances are applied to the embryo's yolk-sac blood vessel system at a non-toxic concentration and are irradiated with 5 J/cm2 ultraviolet A (UVA) (320-400 nm). Promethazine, haematoporphyrin, ciprofloxacin and 8-methoxypsoralen were tested in this system. Death of the embryo, membrane discoloration and haemorrhage are parameters for phototoxic damage, which were recorded during an observation period of 24 h. These well-known phototoxic substances induced pronounced damage of the yolk-sac membrane and blood vessels which was not found in the controls (test substance alone, UVA alone or untreated) using a 2 x 2 factorial test design. The photo hen's egg test serves as a valid screening model for substances supposed to be photosensitizers owing to a phototoxic mechanism.

Effects of nonsedating antihistamine, astemizole, on the in situ canine heart assessed by cardiohemodynamic and monophasic action potential monitoring

The possible mechanisms of cardiac adverse effects of astemizole were studied using a halothane-anesthetized in vivo canine model under the cardiohemodynamic and monophasic action potential monitoring. A dose of 0.3 mg/kg of iv astemizole (n = 7), which is close to the recommended dose for clinical use, showed a bradycardic effect and a reversed use-dependent lengthening of repolarization. The increase in the repolarization was greater than in the effective refractory period. These effects persisted even when the plasma drug concentration became undetectable. Additional administration of 3.0 mg/kg of iv astemizole (n = 7) decreased the mean blood pressure, suppressed the cardiac contraction and conduction, and induced early after depolarization-like potential in addition to the qualitatively similar effects compared to those observed by the lower dose. The decrease of the plasma concentration of astemizole followed the pattern predicted by the two-compartment theory of pharmacokinetics, but the drug concentration in the cardiac muscle was estimated to be more than 100 times greater than that in plasma. Our study emphasizes that each cardiac consequence of astemizole overdose may be related to proarrhythmic effects and the monitoring of plasma drug concentration will be less helpful in predicting the cardiac adverse effects of astemizole. The results provide some insights into the clinical cardiotoxicity of astemizole. Drugs or interventions inducing positive chronotropic, inotropic, and dromotropic effects can become good candidates for the treatment of astemizole intoxication, which may attenuate the cardiac effects of astemizole including the lengthening of repolarization.

Effects of doxylamine succinate on thyroid hormone balance and enzyme induction in mice

The effects of doxylamine (as the succinate salt) on microsomal enzyme activity and serum thyroid hormone levels were examined in B6C3F1 mice following dietary exposure for 7 or 15 days (0, 40, 375, 750, or 1500 ppm in diet, expressed as free base doxylamine). In addition, the hepatic P450 enzyme inducer sodium phenobarbital (375 ppm, expressed as free acid phenobarbital) was used as a positive control for CYP2B induction. Exposure of mice to doxylamine produced dose-related increases in liver weight at both time points. Liver weights were also increased in the phenobarbital-treated mice. Doxylamine treatment caused a dose-dependent increase (up to 2.6-fold) in liver microsomal cytochrome P450 in both male and female mice, at both time points. Analyses of the activities of various hepatic microsomal cytochromes P450 indicated that doxylamine caused a marked induction of CYP2B enzymes. This was demonstrated by a large increase in the O-dealkylation of 7-pentoxyresorufin (up to 38-fold) and the 16beta-hydroxylation of testosterone (up to 6.9-fold), both of which are indicative of CYP2B induction. In addition, like phenobarbital, doxylamine treatment resulted in a modest induction of CYP3A and CYP2A enzymes and approximately a 50% increase in thyroxine-glucuronosyltransferase activity. Doxylamine did not appear to induce P450 enzymes in the CYP1A, CYP2E, or CYP4A enzyme subfamilies. None of the enzyme-inducing effects of doxylamine could be distinguished from those of phenobarbital. These results suggest that doxylamine is a phenobarbital-type inducer of liver microsomal cytochrome P450 in B6C3F1 mice. Exposure to either doxylamine or phenobarbital also resulted in decreases in serum thyroxine (T4) levels (approximately 80% of control) with compensatory increases in serum thyroid-stimulating hormone levels (approximately 4-fold). No clear changes in serum triiodothyronine levels were apparent. These findings are consistent with the hypothesis that doxylamine increases the activity of those hepatic enzymes involved in T4 metabolism.

Enhancement of tumor growth by drugs with some common molecular actions

A group of structurally related drugs representing diverse therapeutic classes share, among a number of pharmacological properties, enhancement of tumor growth in several rodent models of malignancy. One common action, the inhibition of histamine binding to and catalytic activity of cytochrome P450 monooxygenases, is highly correlated with potency to enhance tumor growth. Among members of this drug ensemble, the antiestrogen tamoxifen has been shown in controlled clinical studies to increase the incidence of uterine and gastrointestinal cancer and to accelerate the course of gastric cancer, and the tamoxifen analogue clomiphene has been linked to neuroblastoma and the tricyclic group of antidepressants to ovarian cancer. The determination of drug affinities for protein modulators of cell growth, proliferation, and transformation suggests a strategy for identifying at least some classes of chemicals that impart oncologic risks to humans.

Preclinical skin sensitization testing of antihistamines: guinea pig and local lymph node assay responses

Preclinical test methods for allergic contact sensitivity have been widely used for sensitization hazard identification and, with consideration of human exposure conditions, have also been valuable tools for sensitization risk assessment. For many years, the guinea pig has been the test species of choice with a variety of test methods developed to assess the sensitization response. More recently the local lymph node assay (LLNA) in mice has been developed to provide a more objective index of sensitization potential. The standardized methods have proven to be very well suited to most situations in which potential skin sensitization of a chemical needs to be assessed before human exposure. A potential difficulty with all these relatively limited exposure preclinical test methods, however, is in the ability to detect weak contact allergens that prove to be significant clinical allergens due to chronic topical exposure, exposure to compromised skin, and/or highly exaggerated exposure through transdermal delivery. This has been shown with the transdermal drug clonidine and might also be the case for topical antihistamines. The latter are considered significant clinical contact allergens, although predictive preclinical test data are minimal or lacking. A series of guinea pig (modified Buehler) tests with two common antihistamine compounds (triprolidine and diphenhydramine) and LLNA on these and two other compounds (chlorpheniramine and promethazine) was conducted. Positive Buehler test results required use of penetrating vehicle systems and a modified nine-induction patch regimen. Positive LLNA responses were obtained with all four materials (to varying degrees) only if the application site was pre-abraded or a penetrating vehicle (dimethylformamide) was used. These data support the notion that preclinical sensitization test methods can be modified to increase sensitivity. This may be critical for preclinical assessment of topical/transdermal drugs or other materials with chronic or high-concentration exposures in man.

Inhibition of terfenadine metabolism in vitro by azole antifungal agents and by selective serotonin reuptake inhibitor antidepressants: relation to pharmacokinetic interactions in vivo

Biotransformation of the H-1 antagonist terfenadine to its desalkyl and hydroxy metabolites was studied in vitro using microsomal preparations of human liver. These metabolic reactions are presumed to be mediated by Cytochrome P450-3A isoforms. The azole antifungal agent ketoconazole was a highly potent inhibitor of both reactions, having mean inhibition constants (Ki) of 0.037 and 0.34 microM for desalkyl- and hydroxy-terfenadine formation, respectively. Itraconazole also was a potent inhibitor, with Ki values of 0.28 and 2.05 microM, respectively. Fluconazole, on the other hand, was a weak inhibitor. Six selective serotonin reuptake inhibitor antidepressants tested in this system were at least 20 times less potent inhibitors of terfenadine metabolism than was ketoconazole. An in vitro-in vivo scaling model used in vitro Ki values, typical clinically relevant plasma concentrations of inhibitors, and presumed liver:plasma partition ratios to predict the degree of terfenadine clearance impairment during coadministration of terfenadine with these inhibitors in humans. The model predicted a large and potentially hazardous impairment of terfenadine clearance by ketoconazole and, to a slightly lesser extent, by itraconazole. However, fluconazole and the six selective serotonin reuptake inhibitors (SSRIs) at usual clinical doses were not predicted to impair terfenadine clearance to a degree that would be of clinical importance. Caution is nonetheless warranted with the coadministration of SSRIs and terfenadine when high doses of SSRIs (particularly fluoxetine) are administered. Also, some individuals may be unusually susceptible to metabolic inhibition for a variety of reasons.

Comparative analysis of the cardiotoxicity proclivities of second generation antihistamines in an experimental model predictive of adverse clinical ECG effects

Terfenadine and astemizole belong to the second generation histamine H1 antagonists and are widely prescribed for allergic and upper respiratory diseases. The popularity of the newer H1 antihistamines is due to their ability to provide relief from allergic symptoms without the undesirable side effect of sedation commonly associated with first generation H1 receptor antagonists such as diphenhydramine and promethazine. Recent clinical evidence that the second generation histamine H1 antagonists terfenadine and astemizole have the potential for inducing life threatening ventricular arrhythmias has raised questions as to whether other drugs in this class have similar cardiotoxic potential. The objective of this study was to evaluate and compare the arrhythmogenic potential of a series of second generation antihistamines in a quantitative experimental model predictive of adverse ECG effects in man. Antihistamines were given intravenously and electrocardiographic (ECG) and cardiovascular parameters (blood pressure and heart rate) were measured. The ECG wave form was analyzed to determine QTc interval, PR interval, QRS interval and heart rate. To determine the relative cardiotoxic potential of the antihistamines, the lowest dose producing significant prolongation of the QTc interval was compared with the dose required to inhibit by 50% the peripheral bronchospasm elicited by histamine at 10 micrograms/kg i.v. (antihistamine ED50). The second generation antihistamines studied were astemizole (CAS 68844-77-9), carebastine (CAS 90729-42-3), cetirizine hydrochloride (CAS 83881-52-1), ebastine (CAS 90729-43-4), norastemizole (CAS 75970-99-9), terfenadine (CAS 50679-08-8) and terfenadine carboxylate (CAS 83799-24-0). The second generation antihistamines astemizole, ebastine and terfenadine produced pronounced dose-dependent QTc interval prolongation effects. These arrhythmogenic effects occurred at doses that were between 1 and 4 times their respective peripheral antihistamine doses. These drugs produced significant disruption of the ECG wave form including large amplitude, morphologically aberrant T-waves and, in some cases, torsades de pointes-type arrhythmias. In contrast, terfenadine carboxylate (100 mg/kg i.v.), norastemizole (20 mg/kg, i.v.) and carebastine (50 mg/kg, i.v.), the major metabolites of terfenadine, astemizole and ebastine, were largely devoid of adverse ECG effects. Similarly, cetirizine (20 mg/kg, i.v.) was also found to not alter ECG or cardiovascular function. These findings demonstrate that terfenadine, astemizole and ebastine exhibit significant arrhythmogenic effects including QTc interval prolongation, bradycardia and distortion of the ECG morphology in the guinea pig. The relative cardiotoxicity of these antihistamines based on the separation of antihistamine activity and adverse ECG effects was similar for terfenadine and astemizole, but slightly less for ebastine. In this model carebastine, cetirizine, loratadine, norastemizole and terfenadine carboxylate are devoid of QTc prolongation effects. Given the structural similarity of terfenadine and ebastine it is not surprising that these drugs produce significant cardiotoxicity in this animal model. Taken together, these results indicate that the ability to cause QTc interval prolongation and the proclivity for producing arrhythmias is not a class effect and is seen only with some second generation nonsedating antihistamines.

Cardiotoxic and drug interaction profile of the second generation antihistamines ebastine and terfenadine in an experimental animal model of torsade de pointes

Second generation antihistamines are widely used because of their efficacy in treating allergic disorders without significant sedative side effects. Recent clinical evidence shows that some of the early prototypes in this class, namely terfenadine and astemizole, have the potential for producing torsade de pointes, a rare form of ventricular arrhythmia that is life-threatening. Important questions have been raised as to whether this is a property shared by newer, recently-introduced second generation antihistamines. The objective of this study was to characterize and compare the ECG and cardiovascular effects of terfenadine (CAS 50679-08-8) and ebastine (CAS 90729-43-4), a new second generation antihistamine, in an experimental animal model predictive of the cardiotoxic proclivity of these agents. Also, the drug interaction effect of the antifungal drug ketoconazole (CAS 65277-42-1) was evaluated, which blocks hepatic first-pass biotransformation of ebastine and terfenadine leading to increased cardiotoxity of terfenadine in man, on the ECG effects of terfenadine and ebastine in this animal model. Terfenadine (10 mg/kg) and ebastine (50 mg/kg) were administered intravenously to anesthetized guinea pigs. Electrocardiographic (ECG) and cardiovascular parameters (blood pressure and heart rate) were measured during the course of the experiment. The ECG wave form was analyzed to determine QTc interval, PR interval, QRS interval and heart rate. In separate studies in conscious guinea pigs, the effect of oral ketoconazole (200 mg) on the ECG effects of oral terfenadine (60 mg) and ebastine (10 mg) was studied. Terfenadine (10 mg/kg) and ebastine (50 mg/kg) produced significant prolongation of the QTc interval and disruption of the ECG signal when given intravenously to anesthetized guinea pigs. The ECG effects were characterized by large amplitude, morphologically aberrant T-waves, and instances of arrhythmogenic activity. Both drugs produced pronounced bradycardia and hypotension. In conscious animals, pretreatment with oral ketoconazole significantly enhanced the QTc interval prolongation effects of terfenadine and ebastine. Oral terfenadine and ebastine, when given alone at the doses tested, were devoid of adverse QTc interval prolongation effects in the conscious guinea pig. In separate studies in conscious guinea pigs, oral loratadine (10 mg; CAS 79794-75-5) given alone or in animals pretreated with ketoconazole did not affect ECG parameters. The present studies show that terfenadine and ebastine share similar cardiotoxic properties characterized by QTc interval prolongation, bradycardia, hypotension and proarrhythmogenic activity in the anesthetized guinea pig. In addition, pretreatment with ketoconazole enhances the QTc interval effect of both drugs, most likely due to the accumulation of parent compound that occurs after blockade of hepatic metabolism by CYP3A4. In conclusion, our findings indicate that ebastine and terfenadine display similarities in their inherent potential for cardiotoxic and adverse drug interaction effects. In contrast, loratadine is devoid of adverse ECG and drug interaction effects.

Dose-dependent induction of GST-P+ staining foci by the rat hepatocarcinogen methapyrilene in the medium-term bioassay

Previous studies have demonstrated that methapyrilene hydrochloride (MP) is a rat-specific nongenotoxic carcinogen which induces liver tumors in a dose-dependent manner following chronic exposure in the diet. This study was conducted to determine the dose response of MP in the medium-term bioassay and to compare the response to tumor incidence. Two weeks following a single initiating dose of diethylnitrosamine (DEN), male F344 rats were administered MP at doses of 0, 62.5, 125, 250, or 1000 ppm in the diet for 6 weeks. A 2/3 partial hepatectomy was performed 3 weeks post-DEN. At termination, sections from the remaining three lobes were stained with GST-P antibody. Number and size of foci were measured using an image analysis system with a digitizing board. MP induced a dose-dependent increase in the number of GST-P+ foci/cm2 (0 ppm = 0.85 foci/cm2; 62.5 ppm = 1.29 foci/cm2; 125 ppm = 1.59 foci/cm2; 250 ppm = 6.55 foci/cm2; 1000 ppm = 28.23 foci/cm2). A significantly greater number of foci were observed in the caudate lobe than in the anterior and posterior lobes. The size of individual foci was largely unaffected. This study demonstrates a strong correlation between foci induction and tumor incidence and suggests that this assay may have utility in predicting dose responses for the chronic bioassay.

Carcinogenicity studies of astemizole in mice and rats

The histamine H1 antagonist astemizole (Hismanal) was tested for carcinogenicity in Swiss mice and Wistar rats. Astemizole was administered with the food to mice for 18 and to rats for 24 consecutive months. The doses given--approximately 5, 20, and 80 mg/kg body weight.day--were equivalent to 25, 100, and 400 times, respectively, the recommended human dose of 10 mg/day. Survival of both mice and rats was comparable between groups. Peto's age-adjusted, dose-related trend analysis for the tumor-bearing rats did not reveal a statistically significant difference for males or females. There was no evidence that astemizole led to an increased incidence of spontaneously or unusually occurring neoplastic lesions in either mice or rats. Special attention was given to the effect of astemizole on the progression of spontaneously occurring mammary gland adenomas and fibroadenomas. Peto's analysis applied to the number of female rats bearing these benign mammary gland tumors disclosed no statistically significant dose-related trend. There was no positive trend for the onset of this tumor type, and the median size of the tumor over time per rat was also not statistically significantly different in a comparison of the control group with each of the dosed groups. The findings from these carcinogenicity studies suggest that astemizole is not tumorigenic and that it does not promote tumor growth.

Triprolidine: 104-week feeding study in rats

The antihistamine triprolidine hydrochloride, was fed at dietary concentrations of 0, 250, 1000, or 2000 ppm (as the free base) to groups of 60 Fischer 344 (F344) rats of each sex for up to 2 years to evaluate its potential carcinogenicity. Up to 12 per sex from each group were killed at 65 weeks, and hematology, clinical chemistry, and histopathology were evaluated. A complete histopathological evaluation was performed on all other animals; survivors were killed at 2 years. Survival was significantly extended in triprolidine-treated males and females, particularly at the high dose. At the close of the study high-dose males and females had gained significantly less body weight than controls. Among rats killed at 65 weeks females in the mid- and high-dose groups weighed significantly less than controls, but weights of control and dosed males were not significantly different. The incidences of numerous lesions tended to decrease with increasing triprolidine dose. In females, clitoral gland adenomas, thyroid c-cell hyperplasia and neoplasia, mammary gland hyperplasia and fibroadenomas, and uterine stromal polyps, and in males, anterior pituitary gland adenomas, preputial gland neoplasia, thyroid c-cell pancreatic islet neoplasia, mononuclear cell leukemia, and the combination of lymphocytic, histiocytic, and undifferentiated cell malignant lymphomas and mononuclear leukemia, all exhibited negative dose trends. Cytoplasmic alterations of the parotid gland and numerous liver lesions tended to be more frequent in treated than in control animals. Liver lesions that exhibited positive dose trends include chronic inflammation and centrilobular fatty change in both sexes, mixed cell foci, and the combination of mixed cell foci and eosinophilic foci in females, and in males, basophilic foci and eosinophilic foci. Triprolidine was not carcinogenic in F344 rats.