Torsade de pointes associated with long-term antiretroviral drugs in a patient with HIV: a case report

With the improving life expectancy of patients with human immunodeficiency virus (HIV), there is an increasing health concern of potential toxicity and drug interactions of long-term antiretroviral therapies. We describe a female patient with HIV, who was admitted to the emergency department following an unexplained loss of consciousness. This patient had been on antiretroviral therapy comprising tenofovir disoproxil fumarate, lamivudine, and lopinavir/ritonavir for 12 years. Coincidentally, she had been prescribed terfenadine for urticaria recently. After 3 days on this medication, she suddenly lost her consciousness, with a distinctive electrocardiogram alteration characterized by QT prolongation and torsade de pointes. This symptom recurred several times over a span of 2 days. We postulate that the primary instigator was an elevated concentration of terfenadine, which can be traced back to her antiretroviral therapy regimen comprising lopinavir/ritonavir. This drug is known to impede the metabolism of cytochrome P450 3A4 substrates and consequently elevate terfenadine concentrations.

Repurposing Terfenadine as a Novel Antigiardial Compound

Giardia lamblia is a highly infectious protozoan that causes giardiasis, a gastrointestinal disease with short-term and long-lasting symptoms. The currently available drugs for giardiasis treatment have limitations such as side effects and drug resistance, requiring the search for new antigiardial compounds. Drug repurposing has emerged as a promising strategy to expedite the drug development process. In this study, we evaluated the cytotoxic effect of terfenadine on Giardia lamblia trophozoites. Our results showed that terfenadine inhibited the growth and cell viability of Giardia trophozoites in a time-dose-dependent manner. In addition, using scanning electron microscopy, we identified morphological damage; interestingly, an increased number of protrusions on membranes and tubulin dysregulation with concomitant dysregulation of Giardia GiK were observed. Importantly, terfenadine showed low toxicity for Caco-2 cells, a human intestinal cell line. These findings highlight the potential of terfenadine as a repurposed drug for the treatment of giardiasis and warrant further investigation to elucidate its precise mechanism of action and evaluate its efficacy in future research.

Terfenadine resensitizes doxorubicin activity in drug-resistant ovarian cancer cells via an inhibition of CaMKII/CREB1 mediated ABCB1 expression

Ovarian cancer is one of the most lethal gynecological malignancies. Recurrence or acquired chemoresistance is the leading cause of ovarian cancer therapy failure. Overexpression of ATP-binding cassette subfamily B member 1 (ABCB1), commonly known as P-glycoprotein, correlates closely with multidrug resistance (MDR). However, the mechanism underlying aberrant ABCB1 expression remains unknown. Using a quantitative high-throughput combinational screen, we identified that terfenadine restored doxorubicin sensitivity in an MDR ovarian cancer cell line. In addition, RNA-seq data revealed that the Ca2+-mediated signaling pathway in the MDR cells was abnormally regulated. Moreover, our research demonstrated that terfenadine directly bound to CAMKIID to prevent its autophosphorylation and inhibit the activation of the cAMP-responsive element-binding protein 1 (CREB1)-mediated pathway. Direct inhibition of CAMKII or CREB1 had the same phenotypic effects as terfenadine in the combined treatment, including lower expression of ABCB1 and baculoviral IAP repeat-containing 5 (BIRC5, also known as survivin) and increased doxorubicin-induced apoptosis. In this study, we demonstrate that aberrant regulation of the Ca2+-mediated CAMKIID/CREB1 pathway contributes to ABCB1 over-expression and MDR creation and that CAMKIID and CREB1 are attractive targets for restoring doxorubicin efficacy in ABCB1-mediated MDR ovarian cancer.

Inhibitory effect of terfenadine on Kir2.1 and Kir2.3 channels

Terfenadine is a second-generation H1-antihistamine that despite potentially can produce severe side effects it has recently gained attention due to its anticancer properties. Lately, the subfamily 2 of inward rectifier potassium channels (Kir2) has been implicated in the progression of some tumoral processes. Hence, we characterized the effects of terfenadine on Kir2.x channels expressed in HEK-293 cells. Terfenadine inhibited Kir2.3 channels with a strikingly greater potency (IC50 = 1.06 ± 0.11 μmol L-1) compared to Kir2.1 channels (IC50 = 27.8 ± 4.8 μmol L-1). The Kir2.3(I213L) mutant, possessing a larger affinity for phosphatidylinositol 4,5-bisphosphate (PIP2) than the wild-type Kir2.3, was less sensitive to terfenadine inhibition (IC50 = 13.0 ± 2.9 μmol L-1). Additionally, the PIP2 intracellular application had largely reduced the inhibition of Kir2.1 channels by terfenadine. Our data support that Kir2.x channels are targets of terfena-dine by affecting their interaction with PIP2, which could be regarded as a mechanism of the antitumor properties of terfenadine.

Molecular Mobility of Terfenadine: Investigation by Dielectric Relaxation Spectroscopy and Molecular Dynamics Simulation

The molecular mobility of an amorphous active pharmaceutical ingredient, terfenadine, was carefully investigated by dielectric relaxation spectroscopy and molecular dynamics simulation for the first time. Comprehensive characterization on a wide frequency (10^-2 to 10⁹ Hz) and temperature (300 K) range highlights the fragile nature of this good glass-former (m = 112) and the relatively large nonexponentiality of the main relaxation (β_KWW = 0.53 ± 0.01). In the glassy state, a particularly broad secondary relaxation of intramolecular origin is evidenced. Terfenadine is a flexible molecule, and from molecular dynamics simulation, a clear link is established between the flexibility of the central part of the molecule (carrying, on the one side, the nitrogen group, and on the other side, the OH group) and the distribution of dipole moments, which explains that broadness. Terfenadine is one of the very few cases for which the molecular mobility of the glass obtained by the quench of the melt or by milling can be compared. From the present study, no major difference in terms of molecular mobility is found between these two glasses. However, terfenadine amorphized by milling (for 1-20 h) clearly shows a lower stability than the quenched liquid as we observed its recrystallization upon heating. Interestingly, it is shown that this recrystallization upon heating is not complete and that the 1-2% of the remaining amorphous phase has an original behavior. Indeed, it exhibits an enhanced main mobility induced by an autoconfinement effect created by the surrounding crystalline phase.

The exploration of effect of terfenadine on Ca2+ signaling in renal tubular cells

Terfenadine, an antihistamine used for the treatment of allergic conditions, affected Ca²⁺-related physiological responses in various models. However, the effect of terfenadine on cytosolic free Ca²⁺ levels ([Ca²⁺]_i) and its related physiology in renal tubular cells is unknown. This study examined whether terfenadine altered Ca²⁺ signaling and caused cytotoxicity in Madin-Darby canine kidney (MDCK) renal tubular cells. The Ca²⁺-sensitive fluorescent dye fura-2 was used to measure [Ca²⁺]_i. Cell viability was measured by the fluorescent reagent 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay. Terfenadine at concentrations of 100-1000 μM induced [Ca²⁺]_i rises concentration dependently. The response was reduced by approximately 35% by removing extracellular Ca²⁺. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) partly inhibited terfenadine-evoked [Ca²⁺]_i rises. Conversely, treatment with terfenadine abolished BHQ-evoked [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) with U73122 inhibited 95% of terfenadine-induced Ca²⁺ release. Terfenadine-induced Ca²⁺ entry was supported by Mn²⁺-caused quenching of fura-2 fluorescence. Terfenadine-induced Ca²⁺ entry was partly inhibited by an activator of protein kinase C (PKC), phorbol 12-myristate 13 acetate (PMA) and by three modulators of store-operated Ca²⁺ channels (nifedipine, econazole, and SKF96365). Terfenadine at 200-300 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in MDCK cells, terfenadine induced [Ca²⁺]_i rises by evoking PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. Furthermore, terfenadine caused cell death that was not triggered by preceding [Ca²⁺]_i rises.

Virtual Clinical Trial Toward Polytherapy Safety Assessment: Combination of Physiologically Based Pharmacokinetic/Pharmacodynamic-Based Modeling and Simulation Approach With Drug-Drug Interactions Involving Terfenadine as an Example

A Quantitative Systems Pharmacology approach was utilized to predict the cardiac consequences of drug-drug interaction (DDI) at the population level. The Simcyp in vitro-in vivo correlation and physiologically based pharmacokinetic platform was used to predict the pharmacokinetic profile of terfenadine following co-administration of the drug. Electrophysiological effects were simulated using the Cardiac Safety Simulator. The modulation of ion channel activity was dependent on the inhibitory potential of drugs on the main cardiac ion channels and a simulated free heart tissue concentration. ten Tusscher's human ventricular cardiomyocyte model was used to simulate the pseudo-ECG traces and further predict the pharmacodynamic consequences of DDI. Consistent with clinical observations, predicted plasma concentration profiles of terfenadine show considerable intra-subject variability with recorded C_max values below 5 ng/mL for most virtual subjects. The pharmacokinetic and pharmacodynamic effects of inhibitors were predicted with reasonable accuracy. In all cases, a combination of the physiologically based pharmacokinetic and physiology-based pharmacodynamic models was able to differentiate between the terfenadine alone and terfenadine + inhibitor scenario. The range of QT prolongation was comparable in the clinical and virtual studies. The results indicate that mechanistic in vitro-in vivo correlation can be applied to predict the clinical effects of DDI even without comprehensive knowledge on all mechanisms contributing to the interaction.

Observations on conducting whole-cell patch clamping of the hERG cardiac K+ channel in pure human serum

Inhibition of the human ether-a-go-go-related gene (hERG) K⁺ channel by drugs leads to QT prolongation on the electrocardiogram and can result in serious cardiac arrhythmia. For this reason, screening of drugs on hERG is mandatory during the drug development process. Patch clamp electrophysiology in a defined physiological saline solution (PSS) represents the standard method for assaying drug effects on the channel. To make the assay more translatable to clinical studies, we have conducted whole-cell patch clamping of hERG using pure human serum as the extracellular medium. Pure human serum had little effect on the hERG channel waveform or the current-voltage relationship when compared to PSS. hERG current recordings were highly stable in serum at room temperature, but prolonged recordings at the physiological temperature required prior heat inactivation of the serum. Compared to PSS, the IC₅₀ values, conducted at room temperature, of the classic hERG blocking drugs cisapride, moxifloxacin, and terfenadine were shifted to the right by an extent predicted by their known plasma protein binding, but we did not detect any differences in IC₅₀ s between male and female serum. Total plasma levels of these drugs associated with clinical QT prolongation corresponded to small (<15%) inhibition of hERG current in pure serum suggesting that minor inhibition of the channel leads to observable pharmacodynamic effects. Conducting whole-cell patch clamping of hERG in human serum has the potential to make the assay more translatable to clinical studies and improve its predictive value for safety testing. Copyright © 2016 John Wiley & Sons, Ltd.

The effects of topical (gel) astemizole and terfenadine on wound healing

Objective:

To develop topical gel preparations of astemizole and terfenadine and to investigate the actions of the gels on the healing of incision and excision wounds in male albino rats.

Materials and Methods:

Gels containing 1% astemizole, with varying concentrations of carbopol 934 (polymer), were prepared. Similarly, 1% terfenadine gels were made. The formulations were evaluated for release rate and stability. Incision and excision wounds were inflicted on male albino rats under ketamine anesthesia, taking aseptic precautions. The animals were divided into two groups. They were given a topical application of either astemizole or terfenadine gel, at a dose of 100 mg per wound, once daily, for 10 days in the case of incision wounds and till the time of complete closure in the case of excision wounds. On the 11^th day, breaking strength of the incision wound was measured. In the excision wound model, wound closure rate, epithelization time, scar features and hydroxyproline content of scar tissue were studied from the day of wounding till the day of the scab falling off, with no residual raw area.

Results:

Gels prepared using 0.8% carbopol 934 and 1% of drug in gel base were found to be stable. The gels of astemizole and terfenadine significantly (P < 0.05) promoted the phases of healing such as collagenation (in incision wounds), wound contraction and epithelization (in excision wounds).

Conclusion:

The gels of astemizole and terfenadine might play an important role in wound management program.

Proarrhythmic potential of halofantrine, terfenadine and clofilium in a modified in vivo model of torsade de pointes

1. This study was designed to compare the proarrhythmic activity of the antimalarial drug, halofantrine and the antihistamine, terfenadine, with that of clofilium a K(+) channel blocking drug that can induce torsade de pointes. 2. Experiments were performed in pentobarbitone-anaesthetized, open-chest rabbits. Each rabbit received intermittent, rising dose i.v. infusions of the alpha-adrenoceptor agonist phenylephrine. During these infusions rabbits also received increasing i.v. doses of clofilium (20, 60 and 200 nmol kg(-1) min(-1)), terfenadine (75, 250 and 750 nmol kg(-1) min(-1)), halofantrine (6, 20 and 60 micromol kg(-1)) or vehicle. 3. Clofilium and halofantrine caused dose-dependent increases in the rate-corrected QT interval (QTc), whereas terfenadine prolonged PR and QRS intervals rather than prolonging cardiac repolarization. Progressive bradycardia occurred in all groups. After administration of the highest dose of each drug halofantrine caused a modest decrease in blood pressure, but terfenadine had profound hypotensive effects resulting in death of most rabbits. 4. The total number of ventricular premature beats was highest in the clofilium group. Torsade de pointes occurred in 6 out of 8 clofilium-treated rabbits and 4 out of 6 of those which received halofantrine, but was not seen in any of the seven terfenadine-treated rabbits. 5. These results show that, like clofilium, halofantrine can cause torsade de pointes in a modified anaesthetized rabbit model whereas the primary adverse effect of terfenadine was cardiac contractile failure.

Effects of supratherapeutic doses of ebastine and terfenadine on the QT interval

AIMS

The objective of this study was to compare the effects of high doses of ebastine with terfenadine and placebo on QTc.

METHODS

Thirty-two subjects were randomly assigned to four treatments (ebastine 60 mg x day(-1), ebastine 100 mg x day(-1), terfenadine 360 mg x day(-1), placebo) administered for 7 days. Serial ECGs were performed at baseline and day 7 of each period. QT interval was analysed using both Bazett (QTcB) and Fridericia (QTcF) corrections.

RESULTS

Ebastine 60 mg (+ 3.7 ms) did not cause a statistically significant change in QTcB compared with placebo (+ 1.4 ms). The mean QTcB for ebastine 100 mg was increased by + 10.3 ms which was significantly greater than placebo but was significantly less (P < 0.05) than with terfenadine 360 mg (+ 18.0 ms). There were no statistically significant differences in QTcF between ebastine 60 mg (-3.2 ms) or ebastine 100 mg (1.5 ms) and placebo (-2.1 ms); although terfenadine caused a 14.1 ms increase which was significantly different from the other three treatments. The increase in QTcB with ebastine most likely resulted from overcorrection of the small drug-induced increase in heart rate.

CONCLUSIONS

Ebastine at doses up to five times the recommended therapeutic dose did not cause clinically relevant changes in QTc interval.

Involvement of multiple human cytochromes P450 in the liver microsomal metabolism of astemizole and a comparison with terfenadine

AIMS

The aims of the present study were to investigate the metabolism of astemizole in human liver microsomes, to assess possible pharmacokinetic drug-interactions with astemizole and to compare its metabolism with terfenadine, a typical H1 receptor antagonist known to be metabolized predominantly by CYP3A4.

METHODS

Astemizole or terfenadine were incubated with human liver microsomes or recombinant cytochromes P450 in the absence or presence of chemical inhibitors and antibodies.

RESULTS

Troleandomycin, a CYP3A4 inhibitor, markedly reduced the oxidation of terfenadine (26% of controls) in human liver microsomes, but showed only a marginal inhibition on the oxidation of astemizole (81% of controls). Three metabolites of astemizole were detected in a liver microsomal system, i.e. desmethylastemizole (DES-AST), 6-hydroxyastemizole (6OH-AST) and norastemizole (NOR-AST) at the ratio of 7.4 : 2.8 : 1. Experiments with recombinant P450s and antibodies indicate a negligible role for CYP3A4 on the main metabolic route of astemizole, i.e. formation of DES-AST, although CYP3A4 may mediate the relatively minor metabolic routes to 6OH-AST and NOR-AST. Recombinant CYP2D6 catalysed the formation of 6OH-AST and DES-AST. Studies with human liver microsomes, however, suggest a major role for a mono P450 in DES-AST formation.

CONCLUSIONS

In contrast to terfenadine, a minor role for CYP3A4 and involvement of multiple P450 isozymes are suggested in the metabolism of astemizole. These differences in P450 isozymes involved in the metabolism of astemizole and terfenadine may associate with distinct pharmacokinetic influences observed with coadministration of drugs metabolized by CYP3A4.

Mechanism of terfenadine block of ATP-sensitive K(+) channels

The ATP-sensitive K(+) (K(ATP)) channel is a complex of a pore-forming inwardly rectifying K(+) channel (Kir6.2) and a sulphonylurea receptor (SUR). The aim of the present study was to gain further insight into the mechanism of block of K(ATP) channels by terfenadine. Channel activity was recorded both from native K(ATP) channels from the clonal insulinoma cell line RINm5F and from a C-terminal truncated form of Kir6.2 (Kir6.2Delta26), which - in contrast to Kir6.2 - expresses independently of SUR. Kir6.2Delta26 channels were expressed in COS-7 cells, and enhanced green fluorescent protein (EGFP) cDNA was used as a reporter gene. EGFP fluorescence was visualized by a laser scanning confocal microscope. Terfenadine applied to the cytoplasmic side of inside-out membrane patches concentration-dependently blocked both native K(ATP) channel and Kir6.2Delta26 channel activity, and the following values were calculated for IC(50) (the terfenadine concentration causing half-maximal inhibition) and n (the Hill coefficient): 1.2 microM and 0.7 for native K(ATP) channels, 3.0 microM and 1.0 for Kir6. 2Delta26 channels. Terfenadine had no effect on slope conductance of either native K(ATP) channels or Kir6.2Delta26 channels. Intraburst kinetics of Kir6.2Delta26 channels were not markedly affected by terfenadine and, therefore, terfenadine acts as a slow channel blocker on Kir6.2Delta26 channels. Terfenadine-induced block of Kir6. 2Delta26 channels demonstrated no marked voltage dependence, and lowering the intracellular pH to 6.5 potentiated the inhibition of Kir6.2Delta26 channels by terfenadine. These observations indicate that terfenadine blocks pancreatic B-cell K(ATP) channels via binding to the cytoplasmic side of the pore-forming subunit. The presence of the pancreatic SUR1 has a small, but significant enhancing effect on the potency of terfenadine.

Terfenadine and risk of acute liver disease

AIMS

To estimate the risk of idiopathic acute liver disease among users of terfenadine.

METHODS

We conducted a population-based cohort study based on the General Practice Research Database (GPRD) in the U.K. All persons who received at least one prescription for terfenadine during the period 1991 through 1995 were eligible for the study. Among these patients we identified all those with a diagnosis of a liver disorder requiring hospitalization or referral to a consultant within 60 days of a prior prescription for terfenadine. We obtained clinical records, including hospital discharge summaries, consultant reports and relevant laboratory results in order to identify a potentially drug-inducible liver illness.

RESULTS

From a cohort of 210683 recipients of terfenadine, we found only three cases of acute liver disease where a causal connection to terfenadine could not be ruled out, yielding a risk estimate of 1.4/100000 users (95% CI 0.5, 4.2) and 0.5/100000 prescriptions (95% CI 0.2, 1.4). All cases were receiving a concomitant hepatotoxic drug and all had a full recovery.

CONCLUSION

The use of terfenadine is rarely associated with idiopathic acute liver disease.

Effects of cetirizine on the delayed K+ currents in cardiac cells: comparison with terfenadine

1. The aim of the present experiments was to analyse the effect of the H1-histamine antagonist, cetirizine, on the delayed K+ currents in cardiac cells and to compare its effects with another H1-histamine antagonist terfenadine, known to possess proarrhythmic effects. 2. Whole cell currents were measured by use of the single electrode patch-clamp technique in rabbit and guinea-pig myocytes. 3. The activation relationship for the IKr current in rabbit ventricular myocytes was depressed and its voltage-dependence shifted in the negative direction with a V1/2 value -13.4+/-2.4 mV under control conditions which changed to -19.1+/-1.9 mV (n=4) in the presence of 0.1 mM cetirizine. 4 In rabbit ventricular myocytes the IC50 for block of IKr was 108+/-8 microM (n=5); in guinea-pig ventricular myocytes this concentration of cetirizine reduced the rapidly activating component IKr to 49+/-4.5% (n=5), while the slowly activating IKs was less affected and only inhibited to 79+/-2.3% (n=5). 5 The block of IKr did not show use-dependence and the time course of the tail current was not changed, suggesting rested-state block or fast activated-state block and no rapid recovery on deactivation. No important difference was found in the activity of the two enantiomers of cetirizine. 6 Terfenadine in comparison was more potent in blocking IKr, the IC50 being 96+/-15 nM (n=6). 7 Based on the present results and information in the literature on binding, it was concluded that cetirizine is a relatively selective H1-histamine receptor antagonist, with minor effects on K+ currents. The IC50 concentration for IKr block in heart cells was 1.000 times higher than the concentrations needed to block H1 histamine receptors. The occurrence of cardiac arrhythmias due to K+ current blockade is therefore unlikely with this drug.

Terfenadine-antidepressant interactions: an in vitro inhibition study using human liver microsomes

AIMS

Inhibition of the metabolism of terfenadine has been associated with torsades de pointes ventricular arrhythmias. The aim of this study was to assess in vitro the potency of the antidepressants nefazodone, sertraline and fluoxetine in inhibiting terfenadine biotransformation.

METHODS

Human liver microsomes were incubated with terfenadine and the antidepressants at various concentrations. Formation of the two major metabolites of terfenadine was determined by h.p.l.c.

RESULTS

The apparent Km for microsomes from four human livers was 11+/-5 and 18+/-3 microM (mean +/-s.e.mean) for the N-dealkylation and C-hydroxylation pathways, respectively. Nefazodone, sertraline and fluoxetine inhibited terfenadine N-dealkylation with K(i) values of 10+/-4, 10+/-3 and 68+/-15 microM respectively. Inhibition of the C-hydroxylation pathway yielded noncompetitive K(i) values of 41+/-4, 67+/-13 and 310+/-40 microM respectively.

CONCLUSIONS

Nefazodone and sertraline were moderately weak in vitro inhibitors of terfenadine metabolism while fluoxetine was a very weak inhibitor. Clinically significant interaction of terfenadine is more likely with nefazodone than sertraline or fluoxetine since therapeutic plasma levels of nefazodone are comparatively higher.