Influence of itraconazole on the pharmacokinetics and electrocardiographic effects of astemizole

Drug-drug interactions and QT prolongation as a commonly assessed cardiac effect - comprehensive overview of clinical trials

Background

Proarrhythmia assessment is one of the major concerns for regulatory bodies and pharmaceutical industry. ICH guidelines recommending preclinical tests have been established in attempt to eliminate the risk of drug-induced arrhythmias. However, in the clinic, arrhythmia occurrence is determined not only by the inherent property of a drug to block ion currents and disturb electrophysiological activity of cardiac myocytes, but also by many other factors modifying individual risk of QT prolongation and subsequent proarrhythmia propensity. One of those is drug-drug interactions. Since polypharmacy is a common practice in clinical settings, it can be anticipated that there is a relatively high risk that the patient will receive at least two drugs mutually modifying their proarrhythmic potential and resulting either in triggering the occurrence or mitigating the clinical symptoms. The mechanism can be observed either directly at the pharmacodynamic level by competing for the molecular targets, or indirectly by modifying the physiological parameters, or at the pharmacokinetic level by alteration of the active concentration of the victim drug.

Methods

This publication provides an overview of published clinical studies on pharmacokinetic and/or pharmacodynamic drug-drug interactions in humans and their electrophysiological consequences (QT interval modification). Databases of PubMed and Scopus were searched and combinations of the following keywords were used for Title, Abstract and Keywords fields: interaction, coadministration, combination, DDI and electrocardiographic, QTc interval, ECG. Only human studies were included. Over 4500 publications were retrieved and underwent preliminary assessment to identify papers accordant with the topic of this review. 76 papers reporting results for 96 drug combinations were found and analyzed.

Results

The results show the tremendous variability of drug-drug interaction effects, which makes one aware of complexity of the problem, and suggests the need for assessment of an additional risk factors and careful ECG monitoring before administration of drugs with anticipated QT prolongation.

Conclusions

DDIs can play significant roles in drugs’ cardiac safety, as evidenced by the provided examples. Assessment of the pharmacodynamic effects of the drug interactions is more challenging as compared to the pharmacokinetic due to the significant diversity in the endpoints which should be analyzed specifically for various clinical effects. Nevertheless, PD components of DDIs should be accounted for as PK changes alone do not allow to fully explain the electrophysiological effects in clinic situations.

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-016-0053-1) contains supplementary material, which is available to authorized users.

How to Choose In Vitro Systems to Predict In Vivo Drug Clearance: A System Pharmacology Perspective

The use of in vitro metabolism data to predict human clearance has become more significant in the current prediction of large scale drug clearance for all the drugs. The relevant information (in vitro metabolism data and in vivo human clearance values) of thirty-five drugs that satisfied the entry criteria of probe drugs was collated from the literature. Then the performance of different in vitro systems including Escherichia coli system, yeast system, lymphoblastoid system and baculovirus system is compared after in vitro-in vivo extrapolation. Baculovirus system, which can provide most of the data, has almost equal accuracy as the other systems in predicting clearance. And in most cases, baculovirus system has the smaller CV in scaling factors. Therefore, the baculovirus system can be recognized as the suitable system for the large scale drug clearance prediction.

Development, validation and utility of an in vitro technique for assessment of potential clinical drug-drug interactions involving P-glycoprotein

Regulatory interest is increasing for drug transporters generally and P-glycoprotein (Pgp) in particular, primarily in the area of drug-drug interactions. To aid in both identifying and discharging the potential liabilities associated with drug-transporter interactions, the pharmaceutical industry has a growing requirement for routine and robust non-clinical assays. An assay was designed, optimised and validated to determine the in vitro inhibitory potency of new chemical entities (NCEs) towards human Pgp-mediated transport. [3H]-Digoxin was established as a suitable probe substrate by investigating its characteristics in the in vitro system (MDCKII-MDR1 cells grown in 24-multiwell inserts). The inhibitory potencies (apparent IC50) of known Pgp inhibitors astemizole, GF120918, ketoconazole, itraconazole, quinidine, verapamil and quinine were determined over at least a 1000-fold concentration range. Validation was carried out using manual and automatic techniques. [3H]-Digoxin was found to be stable and have good mass balance in the system. In contrast to [A-->B] transport, [3H]-digoxin [B-->A] transport rates were readily measured with good reproducibility. There was no evidence of saturation of transport up to 10 microM digoxin and 30 nM digoxin was selected for routine assay use, reflecting clinical therapeutic concentrations. IC50 values ranged over approximately 100-fold with excellent reproducibility. Results from manual and automated versions were in close agreement. This method is suitable for routine use to assess the in vitro inhibitory potency of NCEs on Pgp-mediated digoxin transport. Comparison of IC50 values against clinical interaction profiles for the probe inhibitors indicated the in vitro assay is predictive of clinical digoxin-drug interactions mediated via Pgp.

Current use of anti-infectives in dermatology

Dermatologic diseases encompass a broad category of pathologic situations. Infection remains a significant aspect of the pathology faced in patient encounters, and it is natural to expect that anti-infectives play a major element in the armamentarium utilized by dermatologists. Aside from the treatment of the classic bacterial and fungal infections, there are now new uses for antiviral agents to help suppress recurrent disease, such as herpes simplex. There is also the novel approach of using anti-infectives, or agents that have been thought to have antimicrobial activity, to treat inflammatory diseases. This review describes anti-infectives, beginning with common antibiotics used to treat bacterial infections. The discussion will then cover the current use of antivirals. Finally, the description of antifungals will be separated, starting with the oral agents and ending with the topical antimycotics. The use of anti-infectives in tropical dermatology has been purposefully left out, and perhaps should be the subject of a separate review. Cutaneous bacterial infections consist chiefly of those microorganisms that colonize the skin, such as species of staphylococcus and streptococcus. Propionibacterium acnes and certain other anaerobes can be involved in folliculitis, pyodermas and in chronic conditions such as hidradenitis suppurativa.

Effect of trazodone on hERG channel current and QT-interval

Trazodone has been associated with prolonged QT-interval and increased risk of polymorphous ventricular tachycardias clinically and has demonstrated in vitro inhibition of hERG (human ether-á-go-go-related gene) channel current. This study attempts to put the effects of trazodone into perspective by comparing its hERG inhibition to that of three agents known to inhibit I(Kr), and comparing the effects of trazodone and cisapride on action potential duration and the QT-interval in the rabbit Langendorff heart preparation. Trazodone inhibited hERG channel current in a concentration-dependent manner with an IC50 of 0.69 microM. Like astemizole, terfenadine and cisapride, trazodone inhibits hERG channel current at clinically relevant concentrations. Like cisapride, trazodone increased both the QT-interval and APD90 in the Langendorff heart preparation in a reverse frequency-dependent manner at clinically relevant concentrations. These data strongly suggest that trazodone prolongs the QT-interval through inhibition of hERG channel current.

Drug-induced cardiac toxicity: emphasizing the role of electrocardiography in clinical research and drug development

This review describes the role of electrocardiography in clinical research and drug development, and addresses its utility in defining cardiac toxicity from noncardiac investigational drugs. Principles for designing electrocardiographic monitoring for cardiac safety in clinical trials are also reviewed.

Drug interactions in dentistry

BACKGROUND

The hepatic and intestinal cytochrome, or CY, P450 enzyme system is responsible for the biotransformation of a multitude of drugs. Certain medications used in dentistry can act as substrates, inducers or inhibitors of this system.

METHODS

The authors conducted a MEDLINE search of articles appearing between 1976 and the present using the keywords "drug interactions" and "cytochrome P450," and reviewed reports involving dental therapeutic agents using PubMed links from an Indiana University CYP450 drug interaction table on the World Wide Web.

RESULTS

The antibiotics erythromycin and clarithromycin are potent inhibitors of CYP3A4 and can increase blood levels and toxicity of CYP3A4 substrates. Likewise, quinolone antibiotics such as ciprofloxacin inhibit the metabolism of CYP1A2 substrates. Other dental therapeutic agents are substrates for CYP2C9 (celecoxib, ibuprofen and naproxen), CYP2D6 (codeine and tramadol), CYP3A4 (methylprednisolone) and CYP2E1 (acetaminophen). Because codeine and tramadol are prodrugs, inhibition of their metabolism can lead to a diminution of their analgesic effects. While inducers of acetaminophen metabolism, including alcohol, theoretically can increase the proportion of it that is biotransformed into a potentially hepatotoxic metabolite, recent research suggests that concomitant alcohol intake does not increase the hepatotoxic potential of therapeutic doses of acetaminophen.

CONCLUSIONS

A number of clinically significant drug interactions can arise with dental therapeutic agents that act as substrates or inhibitors of the CYP450 system. Clinical Implications. As polypharmacy continues to increase, the likelihood of adverse drug interactions in dentistry will increase as well. Ensuring that patients' medical histories are up to date and acquiring knowledge of the various substrates, inducers and inhibitors of the CYP450 system will help practitioners avoid potentially serious adverse drug interactions.

Antifungal agents of use in animal health--chemical, biochemical and pharmacological aspects

A limited number of antifungal agents is licensed for use in animals, however, many of those available for the treatment of mycoses in humans are used by veterinary practitioners. This review includes chemical aspects, spectra of activity, mechanisms of action and resistance, adverse reactions and drug interactions of the antifungals in current use.

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.

Studies on the mechanism of a fatal clarithromycin-pimozide interaction in a patient with Tourette syndrome

The authors report in detail the case of a 27-year-old man who experienced sudden cardiac death 2 days after coprescription of the neuroleptic pimozide and the macrolide antibiotic clarithromycin after the documentation of a prolonged QT interval. To determine the prevalence of this interaction, the authors referred to the Spontaneous Reporting System of the Food and Drug Administration and identified one similar case in which clarithromycin was coprescribed with pimozide and sudden cardiac death occurred shortly thereafter. In addition, the search identified 39 cases of cardiac arrhythmia associated with pimozide, 11 with pimozide alone, and 6 with clarithromycin alone, 1 of which had a positive rechallenge. The mechanism of the interaction between clarithromycin and pimozide seems to involve the inhibition of the hepatic metabolism of pimozide by the macrolide. The authors demonstrated that clarithromycin is able to inhibit the metabolism of pimozide in human liver microsomal preparations (K(i) = 7.65 +/- 1.18 microM) and that pimozide, but not clarithromycin or its primary metabolite, is able to prolong the electrocardiac QT interval in a dose-dependent manner in the isolated perfused rabbit heart. The increase was 9.6 +/- 1.1% in male hearts (N = 5) and 13.4 +/- 1.2% in female hearts (N = 4) (p < 0.05).

Effects of the antifungal agents on oxidative drug metabolism: clinical relevance

This article reviews the metabolic pharmacokinetic drug-drug interactions with the systemic antifungal agents: the azoles ketoconazole, miconazole, itraconazole and fluconazole, the allylamine terbinafine and the sulfonamide sulfamethoxazole. The majority of these interactions are metabolic and are caused by inhibition of cytochrome P450 (CYP)-mediated hepatic and/or small intestinal metabolism of coadministered drugs. Human liver microsomal studies in vitro, clinical case reports and controlled pharmacokinetic interaction studies in patients or healthy volunteers are reviewed. A brief overview of the CYP system and the contrasting effects of the antifungal agents on the different human drug-metabolising CYP isoforms is followed by discussion of the role of P-glycoprotein in presystemic extraction and the modulation of its function by the antifungal agents. Methods used for in vitro drug interaction studies and in vitro-in vivo scaling are then discussed, with specific emphasis on the azole antifungals. Ketoconazole and itraconazole are potent inhibitors of the major drug-metabolising CYP isoform in humans, CYP3A4. Coadministration of these drugs with CYP3A substrates such as cyclosporin, tacrolimus, alprazolam, triazolam, midazolam, nifedipine, felodipine, simvastatin, lovastatin, vincristine, terfenadine or astemizole can result in clinically significant drug interactions, some of which can be life-threatening. The interactions of ketoconazole with cyclosporin and tacrolimus have been applied for therapeutic purposes to allow a lower dosage and cost of the immunosuppressant and a reduced risk of fungal infections. The potency of fluconazole as a CYP3A4 inhibitor is much lower. Thus, clinical interactions of CYP3A substrates with this azole derivative are of lesser magnitude, and are generally observed only with fluconazole dosages of > or =200 mg/day. Fluconazole, miconazole and sulfamethoxazole are potent inhibitors of CYP2C9. Coadministration of phenytoin, warfarin, sulfamethoxazole and losartan with fluconazole results in clinically significant drug interactions. Fluconazole is a potent inhibitor of CYP2C19 in vitro, although the clinical significance of this has not been investigated. No clinically significant drug interactions have been predicted or documented between the azoles and drugs that are primarily metabolised by CYP1A2, 2D6 or 2E1. Terbinafine is a potent inhibitor of CYP2D6 and may cause clinically significant interactions with coadministered substrates of this isoform, such as nortriptyline, desipramine, perphenazine, metoprolol, encainide and propafenone. On the basis of the existing in vitro and in vivo data, drug interactions of terbinafine with substrates of other CYP isoforms are unlikely.

H1-receptor antagonists: safety issues

Histamine is an important neurotransmitter. Old (first-generation) H1-receptor antagonists such as chlorpheniramine, diphenhydramine, or triprolidine produce histamine blockade at H1-receptors in the central nervous system (CNS) and frequently cause somnolence or other CNS adverse effects. New (second generation) H1-antagonists such as cetirizine, fexofenadine, and loratadine represent an advance in therapeutics; in manufacturers' recommended doses, they enter the CNS in smaller amounts, produce relatively little somnolence or other CNS adverse effects, and do not exacerbate the adverse CNS effects of alcohol or other CNS-active chemicals. Two H1-antagonists, astemizole and terfenadine, have been found to prolong the QTc interval and, rarely, to cause cardiac dysrhythmias after overdose or under other specific conditions. This has led to withdrawal of regulatory approval for them. An H1-antagonist absolutely free from adverse effects under all circumstances is not yet available for use.

Drug interactions with itraconazole, fluconazole, and terbinafine and their management

A drug interaction develops when the effect of a drug is increased or decreased or when a new effect is produced by the prior, concurrent, or subsequent administration of the other. Before prescribing a drug, it is important to obtain a thorough drug history of the prescription and nonprescription medications taken by the patient. The nonprescription medications may include items such as nutritional supplements and herbal medications. The risk of side effects is an inevitable consequence of drug use. The frequency of adverse reactions is increased in those patients receiving multiple medications. Drug interactions reported in animal or in vitro studies may not necessarily develop in humans. When drug interactions are observed with a particular agent, it cannot be automatically assumed that all closely related drugs will necessarily produce the same interaction. However, caution is advised until sufficient experience accrues. The prescriber should not overestimate or underestimate the potential for a given drug interaction on the basis of personal experience alone. Drug interactions will not necessarily occur in every patient who is given a particular combination of drugs known to produce an interaction. For a clinically significant drug interaction to be manifest, several other factors may be relevant other than just using the two drugs. In many instances drug interactions can be predicted and therefore avoided if the pharmacodynamic effects, the pharmacokinetic properties, and the mechanisms of action of the 2 drugs in question are known. In the case of contraindicated drugs, it may be possible to use an alternative agent.

The metabolism of antihistamines and drug interactions: the role of cytochrome P450 enzymes

The non-sedating antihistamines show a diversity of fates in the body and the parent drugs and metabolites may differ in their biological properties. Clinically significant interactions with inhibitors of cytochrome P450 have been reported primarily for terfenadine, which has the potential for cardiac toxicity, and is metabolized to fexofenadine, an antihistamine without cardiac effects. Astemizole shares many of these characteristics and important safety-related interactions are likely. Loratadine undergoes extensive metabolism so that pharmacokinetic interactions could occur, but they would be of little clinical importance because of the lack of cardiac activity of the parent drug and its metabolites. Ebastine also undergoes pharmacokinetic interactions, the significance of which is dependent on clarification of the extent of any relevant cardiotoxicity of both ebastine and its metabolite. Interactions would not be clinically important for cetirizine and fexofenadine which do not show cardiac effects and are eliminated with little metabolism.

Clinical pharmacology of new histamine H1 receptor antagonists

The recently introduced H1 receptor antagonists ebastine, fexofenadine and mizolastine, and the relatively new H1 antagonists acrivastine, astemizole, azelastine, cetirizine, levocabastine and loratadine, are diverse in terms of chemical structure and clinical pharmacology, although they have similar efficacy in the treatment of patients with allergic disorders. Acrivastine is characterised by a short terminal elimination half-life (t1/2 beta) [1.7 hours] and an 8-hour duration of action. Astemizole and its metabolites, in contrast, have relatively long terminal t1/2 beta values; astemizole has a duration of action of at least 24 hours and is characterised by a long-lasting residual action after a short course of treatment. Azelastine, which has a half-life of approximately 22 hours, is primarily administered intranasally although an oral dosage formulation is used in some countries. Cetirizine is eliminated largely unchanged in the urine, has a terminal t1/2 beta of approximately 7 hours and a duration of action of at least 24 hours. Ebastine is extensively and rapidly metabolised to its active metabolite; carebastine, has a half-life of approximately 15 hours and duration of action of at least 24 hours. Fexofenadine, eliminated largely unchanged in the faeces and urine, has a terminal t1/2 beta of approximately 14 hours and duration of action of 24 hours, making it suitable for once or twice daily administration. Levocabastine has a terminal t1/2 beta of 35 to 40 hours regardless of the route of administration, but is only available as a topical application administered intranasally or ophthalmically in patients with allergic rhinoconjunctivitis. Loratadine is rapidly metabolised to an active metabolite descarboethoxyloratadine and has a 24-hour duration of action. Mizolastine has a terminal t1/2 beta of approximately 13 hours and duration of action of at least 24 hours. Most orally administered new H1 receptor antagonists are well absorbed and appear to be extensively distributed into body tissues; many are highly protein-bound. Most of the new H1 antagonists do not accumulate in tissues during repeated administration and have a residual action of less than 3 days after a short course has been completed. Tachyphylaxis, or loss of peripheral H1 receptor blocking activity during regular daily use, has not been found for any new H1 antagonist. Understanding the pharmacokinetics and pharmacodynamics of these new H1 antagonists provides the objective basis for selection of an appropriate dose and dosage interval and the rationale for modification in the dosage regimen that may be needed in special populations, including elderly patients, and those with hepatic dysfunction or renal dysfunction. The studies cited in this review provide the scientific foundation for using the new H1 antagonists with optimal effectiveness and safety.

Drug interactions and anti-infective therapies

Drug interactions are an important and often underappreciated cause of adverse clinical outcomes. This review considers the mechanisms for several clinically important drug interactions that involve the major classes of anti-infective agents. This approach is intended to complement the use of text-based references and computer databases so that physicians and pharmacists can avoid prescribing and dispensing drugs that have adverse interactions.

Update on drug interactions with azole antifungal agents

OBJECTIVE

To review and update the incidence, mechanism, and clinical relevance of drug interactions with itraconazole, ketoconazole, and fluconazole.

DATA SOURCES

Literature was identified by MEDLINE search (from January 1990 to May 1997) using the name of each antifungal and the term "interaction" as MeSH headings. Abstracts were identified by literature citation and by review of Interscience Conference on Antimicrobial Agents and Chemotherapy from 1995 to 1996.

STUDY SELECTION

Randomized, controlled, double-blind studies were emphasized; however, uncontrolled studies and case reports were also included. In vitro data were selected from literature review and citations.

DATA EXTRACTION

Data were evaluated with respect to study design, clinical relevance, magnitude of interaction, and recommendations provided.

DATA SYNTHESIS

The incidence of fungal infections and consequent azole antifungal usage continues to increase. By virtue of their antifungal mechanism (i.e., inhibition of cytochrome P450 fungal enzyme systems), azoles have been investigated and implicated in several drug interactions. The magnitude of interactions can vary from trivial to potentially fatal, and also vary with specific azole and interactant.

CONCLUSIONS

The azole antifungal agents represent a commonly used class of agents with a broad range of potential interactions. Recent data have increased our understanding of drug--drug interactions with azoles. Pharmacists are in a unique position to identify these interactions and to intervene to decrease their morbidity and improve patient care.

Systemic antifungal agents. Drug interactions of clinical significance

There are 3 main classes of systemic antifungals: the polyene macrolides (e.g. amphotericin B), the azoles (e.g. the imidazoles ketoconazole and miconazole and the triazoles itraconazole and fluconazole) and the allylamines (e.g. terbinafine). Other systemic antifungals include griseofulvin and flucytosine. Most drug-drug interactions involving systemic antifungals have negative consequences. The interactions of amphotericin B, flucytosine, griseofulvin, terbinafine and azole antifungals can be divided into the following categories: (i) additive dangerous interactions; (ii) modifications of antifungal kinetics by other drugs; and (iii) modifications of the kinetics of other drugs by antifungals. Amphotericin B and flucytosine mainly interact with other agents pharmacodynamically. Clinically important drug interactions with amphotericin B cause nephrotoxicity, hypokalaemia and blood dyscrasias. The most important drug interaction of flucytosine occurs with myelotoxic agents. Hypokalaemia can precipitate the long QT syndrome, as well as potentially lethal ventricular arrhythmias like torsade de pointes. Synergism is likely to occur when either QT interval-modifying drugs (e.g. terfenadine and astemizole) and drugs that induce hypokalaemia (e.g. amphotericin B) are coadministered. Induction and inhibition of cytochrome P450 enzymes at hepatic and extrahepatic sites are the mechanisms that underlie the most serious pharmacokinetic drug interactions of the azole antifungals. These agents have been shown to notably decrease the catabolism of numerous drugs: histamine H1 receptor antagonists, warfarin, cyclosporin, tacrolimus, digoxin, felodipine, lovastatin, midazolam, triazolam, methylprednisolone, glibenclamide (glyburide), phenytoin, rifabutin, ritonavir, saquinavir, nevirapine and nortriptyline. Non-antifungal drugs like carbamazepine, phenobarbital (phenobarbitone), phenytoin and rifampicin (rifampin) can induce the metabolism of azole antifungals. The bioavailability of ketoconazole and itraconazole is also reduced by drugs that increase gastric pH, such as H2 receptor antagonists, proton pump inhibitors, sucralfate and didanosine. Griseofulvin is an enzymatic inducer of coumarin-like drugs and estrogens, whereas terbinafine seems to have a low potential for drug interactions. Despite important advances in our understanding of the mechanisms underlying pharmacokinetic drug interactions during the 1990s, at this time they still remain difficult to predict in terms of magnitude in individual patients. This is because of the large interindividual and intraindividual variations in the catalytic activity of those metabolising enzymes that can either be induced or inhibited by various drugs. Notwithstanding these variations, increasing clinical experience is allowing pharmacokinetic interactions to be used to advantage in order to improve the tolerability of some drugs, as recently exemplified by the use of a fixed combination of ketoconazole and cyclosporin.