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

Pharmacokinetic Evaluation of the Drug Interaction between Intravenous Itraconazole and Intravenous Tacrolimus or Intravenous Cyclosporin A in Allogeneic Hematopoietic Stem Cell Transplant Recipients

A single-institution, open-label prospective pharmacokinetic evaluation of the interaction between intravenous itraconazole and intravenous cyclosporin A and tacrolimus was conducted in allogeneic hematopoietic stem cell transplant recipients. The study was conducted in 2 phases, with patients acting as their own controls. In phase 1, steady-state concentrations and clearance of cyclosporin A and tacrolimus administered alone were evaluated. Phase 2 evaluated serum concentrations and clearance of cyclosporin A and tacrolimus under the influence of itraconazole therapy. Among 17 patients who completed both phases of the study, the mean increase in the serum tacrolimus concentration was 83% (P<.0001), and the mean increase in the serum cyclosporin A concentration was 80% (P=.0001). There was no correlation between serum itraconazole concentrations and the serum concentrations of tacrolimus or cyclosporin A. The drug interaction between itraconazole and calcineurin inhibitors is predictable and occurs within 48 hours of concomitant drug administration. The data suggest that dose reductions of tacrolimus and cyclosporin A in the range of 50% to 100% are necessary when itraconazole therapy is initiated and that subsequent close monitoring of serum concentrations is necessary to guide further dose modifications.

Association between plasma interleukin-18 levels and liver injury in chronic hepatitis C virus infection and non-alcoholic fatty liver disease

There is significant upregulation of interleukin-18 (IL-18) expression in viral infectious diseases and in some chronic hepatic diseases, especially (i) hepatitis C virus (HCV) infection, (ii) HCV infection with persistently normal ALT levels (PNAL), and (iii) non-alcoholic fatty liver disease (NAFLD). The aim of this study was a better understanding of the implications of plasma IL-18 levels in the above-mentioned liver diseases. Thirty-four patients with HCV infection, 13 with NAFLD, and 10 controls were enrolled. The HCV-RNA and HCV-genotypes and the serum or plasma levels of IL-18, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyltranspeptidase (gamma-GT), alkaline phosphatase, total cholesterol, triglycerides, alpha(1)-fetoprotein, and ferritin were evaluated. Patients with HCV showed higher levels of IL-18 than the NAFLD patients (p <0.01) and the controls (p <0.005). Patients with NAFLD showed higher values of body mass index and liver disease parameters, compared to HCV-infected subjects or controls. These data confirm previous reports of enhanced expression of IL-18 in patients with HCV and NAFLD, compared to healthy subjects, and suggest that IL-18 is important as a marker of liver diseases.

Effects of Itraconazole and Tandospirone on the Pharmacokinetics of Perospirone

Perospirone is an atypical antipsychotic agent originated and clinically used in Japan. Based on an in vitro study, it is reported that perospirone is mainly metabolized to ID-15036 by cytochrome P450 (CYP) 3A4. In this study, the authors investigated the effects of itraconazole, which is a specific inhibitor of CYP3A4, or tandospirone, which is mainly metabolized by CYP3A4 and is expected to competitively inhibit the activity of this enzyme, on single oral dose pharmacokinetics of perospirone. After pretreatment with 200 mg daily of itraconazole or 10 mg daily of tandospirone for 5 days, 9 healthy male subjects received 8 mg of perospirone. Plasma concentrations of perospirone and ID-15036 up to 10 hours after perospirone dosing were measured by high-performance liquid chromatography (HPLC). The metabolism of perospirone was significantly inhibited by treatment with itraconazole but not by tandospirone. The present study suggests that CYP3A4 is significantly involved in metabolism of perospirone in humans.

Coadministration of gemfibrozil and itraconazole has only a minor effect on the pharmacokinetics of the CYP2C9 and CYP3A4 substrate nateglinide

BACKGROUND AND AIMS

Gemfibrozil, and particularly its combination with itraconazole, greatly increases the area under the plasma concentration-time curve [AUC(0, infinity)] and response to the cytochrome P450 (CYP) 2C8 and 3A4 substrate repaglinide. In vitro, gemfibrozil is a more potent inhibitor of CYP2C9 than of CYP2C8. Our aim was to investigate the effects of the gemfibrozil-itraconazole combination on the pharmacokinetics and pharmacodynamics of another meglitinide analogue, nateglinide, which is metabolized by CYP2C9 and CYP3A4.

METHODS

In a randomized crossover study with two phases, nine healthy subjects took 600 mg gemfibrozil and 100 mg itraconazole (first dose 200 mg) twice daily or placebo for 3 days. On day 3, they ingested a single 30-mg dose of nateglinide. Plasma nateglinide and blood glucose concentrations were measured for up to 12 h.

RESULTS

During the gemfibrozil-itraconazole phase, the AUC(0, infinity) and C(max) of nateglinide were 47% (range 23-74%; P < 0.0001) and 30% (range - 8% to 104%; P = 0.0146) higher than during the placebo phase, respectively, but the t(max) and t1/2 of nateglinide remained unchanged. The combination of gemfibrozil and itraconazole had no effect on the formation of the M7 metabolite of nateglinide but impaired its elimination. The blood glucose response to nateglinide was not significantly changed by coadministration of gemfibrozil and itraconazole.

CONCLUSIONS

The combination of gemfibrozil and itraconazole has only a limited influence on the pharmacokinetics of nateglinide. This is in marked contrast to the substantial effect of this combination on the pharmacokinetics of repaglinide. The findings suggest that in vivo gemfibrozil, probably due to its metabolites, is a much more potent inhibitor of CYP2C8 than of CYP2C9.

Effect of Simultaneous Insertion of Oleaginous Base on the Absorption and on the Anticonvulsant Effect of Diazepam Suppository

To clarify the drug-base interaction between diazepam (DZP) suppository and oleaginous base, we investigated the effect of simultaneous combination of oleaginous base on the absorption and on the anticonvulsant effect of DZP Suppository in rats. Simultaneous insertion of DZP suppository and oleaginous base significantly decreased maximum concentration (C(max)) and area under the blood concentration-time curve (AUC) of plasma DZP concentrations. Administration of DZP suppositories (2.5, 5 mg/kg) dose-dependently suppressed the pentylenetetrazol (PTZ)-induced seizures, and the anticonvulsant effect of DZP suppository (5 mg/kg) was reduced by simultaneous insertion of oleaginous base. In an in vitro study using a suppository release apparatus, simultaneous combination of DZP suppository and oleaginous base (1.5-98 mg) significantly decreased the accumulative release of DZP in a dose-dependent manner. These results suggested that when DZP suppository and oleaginous base are inserted simultaneously, the released DZP distributes partially to the oleaginous base, and this phenomenon is related to the decreases in the plasma concentration and the anticonvulsant effect of DZP.

CYP3A4 activity in four different animal species liver microsomes using 7-benzyloxyquinoline and HPLC/spectrofluorometric determination

Some microplate-based direct assays with different fluorometric substrates have been developed, among which 7-benzyloxyquinoline (BOQ) has demonstrated the highest degree of selectivity for CYP3A subfamily. In our study, we firstly developed and validated an efficient, fast and cheap HPLC/spectrofluorometric analytical method to quantify 7-hydroxyquinoline (BOQ metabolite). Secondly, BOQ oxidation rate (1.95 +/- 0.24 microM/mg protein/min) was compared to that of midazolam (MDZ) (1.4 +/- 0.21 microM/mg protein/min), an other specific CYP3A probe. However, the difference did not reach statistically significance (test of Sign; p = 0.125, two tailed). Thirdly, the potential use of BOQ in other species than the rat (mouse, dog and monkey) was studied. The highest BOQ activity was observed in rat microsomes (3.75 micromol/mg protein/min) with lower P450 content (0.3 nmol/mg protein) compared to other species. Finally, the effect of CYP3A enzymes-selective inhibitor ketoconazole on the dealkylation of BOQ in control and dexamethasone (DM)-treated rat microsomes was studied. Ketoconazole inhibition potency was greater in control (IC(50) approximately 21.6 microM) compared to DM induced (IC(50) approximately 32.3 microM) microsomes. At concentrations greater than that considered to be enzyme-selective (e.g., 10-30 microM), ketoconazole inhibitory activity did not rise significantly, and at the maximal concentration tested (1,000 microM) a nearly similar inhibition (76%) was observed than that at 50 microM concentration (68.2%).

Sequence diversity and haplotype structure at the human CYP3A cluster

The four members of the human CYP3A subfamily play important roles in the clearance of xenobiotics, hormones, and environmental compounds. Many SNPs at the CYP3A locus have been characterized, with several showing large allele frequency differences across populations. In addition to the effects of CYP3A SNPs on drug metabolism, recent studies have highlighted the potential for CYP3A variation in susceptibility to several common phenotypes, including hypertension and cancer. We previously showed that the CYP3A4 and CYP3A5 genes have a strong haplotype structure at varying frequencies across ethnic groups. Here, we extend our re-sequencing survey to the remaining CYP3A genes in the same cluster, CYP3A7 and CYP3A43. Our study identified a large number of SNPs in coding and conserved noncoding sequences, several of which are common. The combined data set allows us to investigate patterns of sequence variation and linkage disequilibrium at the entire CYP3A locus for use in future association studies.

Undesirable effects of citrus juice on the pharmacokinetics of drugs: focus on recent studies

It is well known that intake of grapefruit juice affects the pharmacokinetics of various kinds of drugs. It has been reported that other citrus juices also interact with certain drugs. To re-evaluate citrus juice-drug interactions based on currently available evidence, a literature search was conducted for new and updated information since the grapefruit juice-drug interaction was last reviewed in 1998. MEDLINE (1998-October 2004) was accessed and more than 200 reports were found. The effects of grapefruit juice ingestion on the pharmacokinetics of orally administered drugs have been reported for 40 drugs since the reviews published in 1998. Increases in either area under the concentration-time curve (AUC) or maximum plasma concentration (C(max)) were found with 34 of these, the major mechanism being considered to be inactivation of intestinal cytochrome P450 3A4, a so-called mechanism-based inhibition. Although recent reports point to the inhibitory effects of grapefruit juice on the function of P-glycoprotein, which transports substrates from enterocytes back into the lumen, the contribution to the bioavailability of drugs that are substrates of P-glycoprotein has not been established yet. Dramatic decreases in AUC and C(max) for two drugs in association with grapefruit juice ingestion has been reported and, in these cases, inhibitory effects on organic anion transporting polypeptide, which mediates absorption from the intestinal lumen to enterocytes, might be involved. Other citrus juices such as Seville (sour) orange juice and commonly ingested varieties of orange juice also showed significant effects on the AUC and C(max) of some drugs. Although the situation is complex and uncertainties remain, we recommend that patients avoid citrus juice intake while taking medications and that healthcare providers advise against citrus juice intake in this setting until any interactions with subject drugs can be clarified in clinical studies.

Drug-Drug Interaction of Antifungal Drugs

This article reviews the in vitro metabolic and the in vivo pharmacokinetic drug-drug interactions with antifungal drugs, including fluconazole, itraconazole, micafungin, miconazole, and voriconazole. In the in vitro interaction studies, the effects of antifungal drugs on specific activities of cytochrome P450s (CYPs), including CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4, in human liver microsomes are compared to predict the possibility of drug interactions in vivo. Fluconazole, micafungin, and voriconazole have lower inhibitory effects on CYP3A4 activities than itraconazole and miconazole, and IC(50) and/or K(i) values against CYP2C9 and CYP2C19 activities are the lowest for miconazole, followed by voriconazole and fluconazole. In in vivo pharmacokinetic studies, it is well known that itraconazole is a potent clinically important inhibitor of the clearance of CYP3A4 substrates, and fluconazole and voriconazole are reported to increase the blood or plasma concentrations of not only midazolam and cyclosporine (CYP3A4 substrates) but also of phenytoin (CYP2C9 substrate) and/or omeprazole (CYP2C19/CYP3A4 substrate). On the other hand, no inhibition of CYP activities except for CYP3A4 activity by micafungin is observed in vitro, and the blood concentrations of cyclosporine and tacrolimus are not affected by coadministration of micafungin in vivo, suggesting that micafungin would not cause clinically significant interactions with drugs that are metabolized by CYPs via the inhibition of metabolism. Miconazole is a potent inhibitor of all CYPs investigated in vitro, although there are few detailed studies on the clinical significance of this except for CYP2C9. Therefore the differential effects of these antifungal drugs on CYP activities must be considered in the choice of antifungal drugs in patients receiving other drugs.

The role of CYP2C and CYP3A in the disposition of 3-keto-desogestrel after administration of desogestrel

AIMS

Our objective was to study in vivo the role of CYP2C and CYP3A4 in the disposition of 3-keto-desogestrel after administration of desogestrel, by using the selective inhibitors fluconazole (CYP2C) and itraconazole (CYP3A4).

METHODS

This study had a three-way crossover design and included 12 healthy females, the data from 11 of whom were analyzed. In the first (control) phase all subjects received a single 150 microg oral dose of desogestrel alone. In the second and third phases subjects received a 4 day pretreatment with either 200 mg fluconazole or 200 mg itraconazole once daily in a randomized balanced order. Desogestrel was given 1 h after the last dose of the CYP inhibitor. Plasma 3-keto-desogestrel concentrations were determined for up to 72 h post dose.

RESULTS

Pretreatment with itraconazole for 4 days significantly increased the area under the plasma concentration-time curve (AUC) of 3-keto-desogestrel by 72.4% (95% confidence interval on the difference 12%, 133%; P = 0.024) compared with the control phase, whereas fluconazole pretreatment had no significant effect (95% CI on the difference -42%, 34%). Neither enzyme inhibitor affected significantly the maximum concentration (95% CI on the difference 14%, 124% for itraconazole and -23%, 40% for fluconazole) or elimination half-life (95% CI on the difference -42%, 120% for itraconazole and -24%, 61% for fluconazole) of 3-keto-desogestrel.

CONCLUSIONS

According to the present study, the biotransformation of desogestrel to 3-keto-desogestrel did not appear to be mediated by CYP2C9 and CYP2C19 as suggested earlier. However, the further metabolism of 3-keto-desogestrel seems to be catalyzed by CYP3A4.

Lack of effect of ketoconazole-mediated CYP3A inhibition on sorafenib clinical pharmacokinetics

Sorafenib is a novel, small-molecule anticancer compound that inhibits tumor cell proliferation by targeting Raf in the Raf/MEK/ERK signalling pathway, and inhibits angiogenesis by targeting tyrosine kinases such as vascular-endothelial growth factor receptor (VEGFR-2 and VEGFR-3) and platelet-derived growth factor receptor (PDGFR). In vitro microsomal data indicate that sorafenib is metabolized by two pathways: phase I oxidation mediated by cytochrome P450 (CYP) 3A4; and phase II conjugation mediated by UGT1A9. Approximately 50% of an orally administered dose is recovered as unchanged drug in the feces, due to either biliary excretion or lack of absorption. The aim of this study was to evaluate the effect of CYP3A inhibition by ketoconazole on sorafenib pharmacokinetics. This was an open-label, non-randomized, 2-period, one-way crossover study in sixteen healthy male subjects. A single 50 mg dose of sorafenib was administered alone (period 1) and in combination with ketoconazole 400 mg once daily (period 2) (ketoconazole was given for 7 days, and a single 50 mg sorafenib dose was administered concomitantly on day 4). No clinically relevant change in pharmacokinetics of sorafenib and no clinically relevant adverse events or laboratory abnormalities were observed in this study upon co-administration of the two drugs. Plasma concentrations of the main CYP3A4 generated metabolite, sorafenib N-oxide, decreased considerably upon ketoconazole co-administration. This effect is in accordance with the in vitro finding that CYP3A4 is the primary enzyme for sorafenib N-oxide formation. Further, these data indicate that blocking sorafenib metabolism by the CYP3A4 pathway will not lead to an increase in sorafenib exposure. This is consistent with data from a clinical mass-balance study that showed 15% of the administered dose was eliminated by glucuronidation, compared to less than 5% eliminated as oxidative metabolites. Since there was no increase in sorafenib exposure following concomitant administration of the highly potent CYP3A4 inhibitor ketoconazole with low dose sorafenib, it is postulated that higher therapeutic doses of sorafenib may be safely co-administered with ketoconazole, as well as with other inhibitors of CYP3A.

Ketoconazole increases plasma concentrations of antimalarial mefloquine in healthy human volunteers

BACKGROUND

Antimalarial mefloquine has a structure related to quinine. The major metabolite of quinine is 3-hydroxyquinine formed by cytochrome P450 3A4 (CYP3A4). Ketoconazole, a potent inhibitor of CYP3A4, is known to markedly increase plasma concentrations of various co-administered drugs including quinine.

OBJECTIVE

To assess the effect of ketoconazole on plasma concentrations of mefloquine in healthy Thai male volunteers.

METHODS

In an open, randomized two-phase crossover study separated by a 1-month period, eight healthy Thai male volunteers received a single oral dose of 500 mg mefloquine alone or co-administration with 400 mg/day ketoconazole orally for 10 days. Serial blood samples were collected at specific time points for a 56-day period. Plasma mefloquine and mefloquine carboxylic metabolite concentrations during 56 days were measured by a modified and validated high-performance liquid chromatographic method with UV detection.

RESULTS

Co-administration with ketoconazole markedly increased the mean values of mefloquine AUC0-t, t(1/2), and Cmax when compared with mefloquine alone by 79% (P < 0.001), 39% (P < 0.05) and 64% (P < 0.001) respectively. The AUC0-t , and Cmax of mefloquine carboxylic acid metabolite were decreased by 28% (P < 0.05) and 31% (P < 0.05), respectively when compared with mefloquine alone.

CONCLUSIONS

Co-administration with ketoconazole increased plasma mefloquine concentrations in healthy human volunteers. One of possible mechanisms of the increase in plasma mefloquine concentrations may be the result of the inhibition of CYP3A4 by ketoconazole. In case of mefloquine is co-administered with ketoconazole, drug-drug interactions should be recognized and the dose of mefloquine should be adjusted to maximize the therapeutic efficacy and to reduce the cost of therapy.

Blood concentrations of everolimus are markedly increased by ketoconazole

The authors sought to quantify the influence of the CYP3A and P-glycoprotein inhibitor ketoconazole on the pharmacokinetics of everolimus in healthy subjects. This was a 2-period, single-sequence, crossover study in 12 healthy subjects. In period 1, subjects received the reference treatment of a single 2-mg dose of everolimus. In period 2, they received the test treatment of ketoconazole 200 mg twice daily for a total of 8 days and a single dose of everolimus coadministered on the fourth day of ketoconazole therapy. The test/reference ratio and 90% confidence interval were derived for everolimus maximum concentration and area under the curve. During ketoconazole coadministration, everolimus maximum concentration increased 3.9-fold (90% confidence interval, 3.4-4.6) from 15 +/- 4 ng/mL to 59 +/- 13 ng/mL. Everolimus area under the curve increased 15.0-fold (90% confidence interval, 13.6-16.6) from 90 +/- 23 ng*h/mL to 1324 +/- 232 ng*h/mL. Everolimus half-life was prolonged by 1.9-fold from 30 +/- 4 hours to 56 +/- 5 hours. Everolimus did not appear to alter ketoconazole predose concentrations. Given the magnitude of this drug interaction, use of ketoconazole should be avoided if possible in everolimus-treated patients.

IN VITRO METABOLISM OF THE CALMODULIN ANTAGONIST DY-9760e (3-[2-[4-(3-CHLORO-2-METHYLPHENYL)-1-PIPERAZINYL]ETHYL]-5,6-DIMETHOXY-1-(4-IMIDAZOLYLMETHYL)-1H-INDAZOLE DIHYDROCHLORIDE 3.5 HYDRATE) BY HUMAN LIVER MICROSOMES: INVOLVEMENT OF CYTOCHROMES P450 IN ATYPICAL KINETICS AND POTENTIAL DRUG INTERACTIONS

Human cytochrome P450 (P450) isozyme(s) responsible for metabolism of the calmodulin antagonist 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e) and kinetic profiles for formation of its six primary metabolites [M3, M5, M6, M7, M8, and DY-9836 (3-[2-[4-(3-chloro-2-methylphenyl)piperazinyl]ethyl]-5,6-dimethoxyindazole)] were identified using human liver microsomes and recombinant P450 enzymes. In vitro experiments, including an immunoinhibition study, correlation analysis, and reactions with recombinant P450 enzymes, revealed that CYP3A4 is the primary P450 isozyme responsible for the formation of the DY-9760e metabolites, except for M5, which is metabolized by CYP2C9. Additionally, at clinically relevant concentrations, CYP2C8 and 2C19 make some contribution to the formation of M3 and M5, respectively. The formation rates of DY-9760e metabolites except for M8 by human liver microsomes are not consistent with a Michaelis-Menten kinetics model, but are better described by a substrate inhibition model. In contrast, the enzyme kinetics for all metabolites formed by recombinant CYP3A4 can be described by an autoactivation model or a mixed model of autoactivation and biphasic kinetics. Inhibition of human P450 enzymes by DY-9760e in human liver microsomes was also investigated. DY-9760e is a very potent competitive inhibitor of CYP2C8, 2C9 and 2D6 (Ki 0.25-1.7 microM), a mixed competitive and noncompetitive inhibitor of CYP2C19 (Ki 2.4 microM) and a moderate inhibitor of CYP1A2 and 3A4 (Ki 11.4-20.1 microM), suggesting a high possibility for human drug-drug interaction.

Blockade of HERG cardiac K+ current by antifungal drug miconazole

1. Miconazole, an imidazole antifungal agent, is associated with acquired long QT syndrome and ventricular arrhythmias. Miconazole increases the plasma concentration of QT-prolonging drugs by inhibiting the hepatic cytochrome P450 metabolic pathway, but whether it has direct effects on cardiac ion channels has not been elucidated. 2. To determine the mechanism underlying these clinical findings, we investigated the effect of miconazole on human ether-a-go-go-related gene (HERG) K+ channels. 3. HERG channels were heterologously expressed in human embryonic kidney 293 (HEK293) cells and whole-cell currents were recorded using a patch-clamp technique (23 degrees C). 4. Miconazole inhibited HERG peak tail current in a concentration-dependent manner (0.4-40 microM) with an IC50 of 2.1 microM (n=3-5 cells at each concentration, Hill coefficient 1.2). HERG block was not frequency-dependent. It required channel activation, occurred rapidly, and had very slow dissociation properties. 5. The activation curve was shifted in a negative direction (V(1/2): -9.5+/-2.3 mV in controls and -15.3+/-2.4 mV after 4 microM miconazole, P<0.05, n=6). Miconazole did not change other channel kinetics (activation, deactivation, onset of inactivation, recovery from inactivation, steady-state inactivation). 6. The S6 domain mutation, F656C, abolished the inhibitory action of miconazole on HERG current indicating that miconazole preferentially binds to an aromatic amino-acid residue within the pore-S6 region. 7. Our findings indicate that miconazole causes HERG channel block by binding to a common drug receptor, and this involves preferential binding to activated channels. Thus, miconazole prolongs the QT interval by direct inhibition of HERG channels.

Classification of a large microarray data set: algorithm comparison and analysis of drug signatures

A large gene expression database has been produced that characterizes the gene expression and physiological effects of hundreds of approved and withdrawn drugs, toxicants, and biochemical standards in various organs of live rats. In order to derive useful biological knowledge from this large database, a variety of supervised classification algorithms were compared using a 597-microarray subset of the data. Our studies show that several types of linear classifiers based on Support Vector Machines (SVMs) and Logistic Regression can be used to derive readily interpretable drug signatures with high classification performance. Both methods can be tuned to produce classifiers of drug treatments in the form of short, weighted gene lists which upon analysis reveal that some of the signature genes have a positive contribution (act as "rewards" for the class-of-interest) while others have a negative contribution (act as "penalties") to the classification decision. The combination of reward and penalty genes enhances performance by keeping the number of false positive treatments low. The results of these algorithms are combined with feature selection techniques that further reduce the length of the drug signatures, an important step towards the development of useful diagnostic biomarkers and low-cost assays. Multiple signatures with no genes in common can be generated for the same classification end-point. Comparison of these gene lists identifies biological processes characteristic of a given class.

Pharmacotherapy of onychomycosis

Fungal infections of the nails are frequent in some segments of the population. Dermatophytes, yeasts and moulds are potential pathogens. A series of antifungal treatments are available to the clinician, differing by both their mechanistic nature and mode of administration. The pharmacodynamic and pharmacokinetic properties of each antifungal agent are distinct. This review focuses on the characteristics of amorolfine, bifonazole, ciclopirox, fluconazole, griseofulvin, itraconazole, ketoconazole, ravuconazole, R126638 and terbinafine. Single drug treatments and combined therapies are presented. None of the current drug regimens have demonstrated reliable efficacy against all cases of onychomycosis. Treatment failures, relapses and reinfections remain stubborn problems in the management of onychomycosis.

The influence of age and sex on the clearance of cytochrome P450 3A substrates

Cytochrome P450s (CYPs) are an important family of enzymes in the metabolism of many therapeutic agents and endogenous metabolic reactions. The CYP3A subfamily is especially prominent in these metabolic activities. This review article focuses on how the factors of age and sex may influence the in vivo activity of human CYP3A. The functional activity of CYP3A varies based on issues such as interaction with one or more substrates and between individuals and/or localisation. For CYP3A substrates, intrinsic clearance is the component of total clearance that is contributed by the enzymes. Depending on the route of administration and the contribution of hepatic blood flow to overall clearance, sensitivities to changes in CYP3A activities may differ. Additionally, age may influence the hepatic blood flow and, in turn, affect CYP3A activity. A review of the literature regarding age influences on the clearance of CYP3A substrates does suggest that age can affect the clearance of certain CYP3A substrates.CYP3A is responsible for a large number of endogenous metabolic reactions involving steroid hormones, and enzyme activity has been reported to be induced and/or inhibited in the presence of some sex steroids. Based on published studies for most CYP3A substrates, sex does not appear to influence clearance; however, with certain substrates significant sex-related differences are found. In such cases, women primarily have higher clearance than men.

Interactions between xenoestrogens and ketoconazole on hepatic CYP1A and CYP3A, in juvenile Atlantic cod (Gadus morhua)

BACKGROUND: Xenoestrogens and antifungal azoles probably share a common route of metabolism, through hepatic cytochrome P450 (CYP) enzymes. Chemical interactions with metabolic pathways may affect clearance of both xenobiotics and endobiotics. This study was carried out to identify possible chemical interactions by those substances on CYP1A and CYP3A, in Atlantic cod liver. We investigated effects of two xenoestrogens (nonylphenol and ethynylestradiol) and of the model imidazole ketoconazole, alone and in combination. RESULTS: Treatment with ketoconazole resulted in 60% increase in CYP1A-mediated ethoxyresorufin-O-deethylase (EROD) activity. Treatment with nonylphenol resulted in 40% reduction of CYP1A activity. Combined exposure to ketoconazole and nonylphenol resulted in 70% induction of CYP1A activities and 93% increase in CYP1A protein levels. Ketoconazole and nonylphenol alone or in combination had no effect on CYP3A expression, as analyzed by western blots. However, 2-dimensional (2D) gel electrophoresis revealed the presence of two CYP3A-immunoreactive proteins, with a more basic isoform induced by ketoconazole. Treatment with ketoconazole and nonylphenol alone resulted in 54% and 35% reduction of the CYP3A-mediated benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD) activity. Combined exposure of ketoconazole and nonylphenol resulted in 98% decrease in CYP3A activity. This decrease was greater than the additive effect of each compound alone. In vitro studies revealed that ketoconazole was a potent non-competitive inhibitor of both CYP1A and CYP3A activities and that nonylphenol selectively non-competitively inhibited CYP1A activity. Treatment with ethynylestradiol resulted in 46% decrease in CYP3A activity and 22% decrease in protein expression in vivo. In vitro inhibition studies in liver microsomes showed that ethynylestradiol acted as a non-competitive inhibitor of CYP1A activity and as an uncompetitive inhibitor of CYP3A activity. CONCLUSIONS: Ketoconazole, nonylphenol and ethynylestradiol all interacted with CYP1A and CYP3A activities and protein expression in Atlantic cod. However, mechanisms of interactions on CYP1A and CYP3A differ between theses substances and combined exposure had different effects than exposure to single compounds. Thus, CYP1A and CYP3A mediated clearance may be impaired in situations of mixed exposure to those types of compounds.

Effect of ketoconazole on the pharmacokinetics of rosiglitazone in healthy subjects

AIMS

Fungal infection is a significant comorbidity in patients with diabetes mellitus, and ketoconazole, an antifungal agent, causes a number of drug interactions with coadministered drugs. Rosiglitazone is a novel thiazolidinedione antidiabetic drug, mainly metabolized by CYP2C8 and to a lesser extent CYP2C9. We investigated the possible effect of ketoconazole on the pharmacokinetics of rosiglitazone in humans.

METHODS

Ten healthy Korean male volunteers were treated twice daily for 5 days with 200 mg ketoconazole or with placebo, using a randomized, open-label, two-way crossover study. On day 5, a single dose of 8 mg rosiglitazone was administered orally, and plasma rosiglitazone concentrations were measured.

RESULTS

Ketoconazole increased the mean area under the plasma concentration-time curve for rosiglitazone by 47%[P = 0.0003; 95% confidence interval (CI) 23, 70] and the mean elimination half-life from 3.55 to 5.50 h (P = 0.0003; 95% CI in difference 1.1, 2.4). The peak plasma concentration of rosiglitazone was increased by ketoconazole treatment by 17% (P = 0.03; 95% CI 5, 29). The apparent oral clearance of rosiglitazone decreased by 28% after ketoconazole treatment (P = 0.0005; 95% CI 18, 38).

CONCLUSIONS

This study revealed that ketoconazole affected the disposition of rosiglitazone in humans, probably by the inhibition of CYP2C8 and CYP2C9, leading to increasing rosiglitazone concentrations that could increase the efficacy of rosiglitazone or its adverse events.

Multiple P450 substrates in a single run: rapid and comprehensive in vitro interaction assay

The dramatically increased number of new chemical entities (NCE) used in drug discovery has raised a demand for efficient and rapid drug metabolism screening techniques. The aim of this study was to develop a global in vitro metabolic interaction screening test utilising the N-in-1 approach. A cocktail consisting of 10 CYP-selective probes with known kinetic, metabolic and interaction properties in vivo was incubated in a pool of human liver microsomes, and metabolites of melatonin (CYP1A2), coumarin (CYP2A6), bupropion (CYP2B6), amodiaquine (CYP2C8), tolbutamide (CYP2C9), omeprazole (CYP2C19 and CYP3A4), dextromethorphan (CYP2D6), chlorzoxazone (CYP2E1), midazolam (CYP3A4) and testosterone (CYP3A4) were analysed simultaneously using LC/TOF-MS. Performance of the method was assessed with cDNA expressed P450s and diagnostic CYP-specific inhibitors. The results were in good accordance with literature and our previous studies. The cocktail developed is suitable for fast and reliable in vitro screening of the interaction potential and characteristics of NCEs.

High-throughput screening of inhibitory potential of nine cytochrome P450 enzymes in vitro using liquid chromatography/tandem mass spectrometry

The early detection of potential drug-drug interactions is an important issue of drug discovery that has led to the development of high-throughput screening (HTS) methods for potential drug interactions. We developed a HTS method for potential interactions of inhibitory drugs for nine human P450 enzymes using cocktail incubation and tandem mass spectrometry in vitro. This new method involves incubation of two cocktail doses and single cassette analysis. The two cocktail doses in vitro were developed to minimize solvent effects and mutual drug interactions among substrates: cocktail A was composed of phenacetin for CYP1A2, coumarin for CYP2A6, paclitaxel for CYP2C8, S-mephenytoin for CYP2C19, dextromethorphan for CYP2D6, and midazolam for CYP3A4; and cocktail B was composed of three substrates including bupropion for CYP2B6, tolbutamide for CYP2C9, and chlorzoxazone for CYP2E1. In the incubation study of these cocktails, the reaction mixtures were pooled and simultaneously analyzed using liquid chromatography/tandem mass spectrometry employing a fast gradient. The method was validated by comparing the inhibition data obtained from the incubation of each individual probe substrate alone with data from the new method. The IC50 value of each inhibitor in the cocktail agreed well with that of the individual probe drug as well as with values previously reported in the literature. As a HTS method for potential interactions of the inhibition of these nine P450 enzymes, this new method will be useful in the drug discovery process and for the mechanistic understanding of drug interactions.

The novel antifungal agent PLD-118 is neither metabolized by liver microsomes nor inhibits cytochrome P450in vitro

PLD-118 is a novel, oral antifungal drug, under development for the treatment of Candida infections. Possible metabolism of PLD-118 by rat, dog and human S9 liver homogenates and inhibition of human cytochrome P450 (CYP) enzymes were investigated. PLD-118 (10 and 100 microM) incubated for 0-60 min with S9 fractions and NADPH was determined by HPLC, using the Waters AccQ.Tag method after derivatization of amino acids to stable, fluorescent derivatives. CYP assays were performed using pooled human liver microsomes with substrates, selective towards human CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A, incubated at concentrations around the Km. Incubation mixtures were preincubated with PLD-118 (0.1-100 microM) or control inhibitor for 5 min. No metabolism of PLD-118 was detected with rat and dog S9 fractions. A small (8%) decrease in PLD-118 at 100 microM (not detected at 10 microM) with human microsomes was considered to be biologically irrelevant. PLD-118 did not inhibit any of the tested CYPs. PLD-118, at concentrations up to 100 microM, is not metabolized by rat, dog or human liver S9 homogenates and does not inhibit human CYPs in vitro, suggesting little likelihood for interaction of PLD-118 with drugs metabolized by these enzymes.

Effect of Antifungal Drugs on Cytochrome P450 (CYP) 2C9, CYP2C19, and CYP3A4 Activities in Human Liver Microsomes

The effects of five antifungal drugs, fluconazole, itraconazole, micafungin, miconazole, and voriconazole, on cytochrome P450 (CYP) 2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, and CYP3A4-mediated nifedipine oxidation activities in human liver microsomes were compared. In addition, the effects of preincubation were estimated to investigate the mechanism-based inhibition. The IC50 value against tolbutamide hydroxylation was the lowest for miconazole (2.0 microM), followed by voriconazole (8.4 microM) and fluconazole (30.3 microM). Similarly, the IC50 value against S-mephenytoin 4'-hydroxylation was the lowest for miconazole (0.33 microM), followed by voriconazole (8.7 microM) and fluconazole (12.3 microM). On the other hand, micafungin at a concentration of 10 or 25 microM neither inhibited nor stimulated tolbutamide hydroxylation and S-mephenytoin 4'-hydroxylation, and the IC50 values for itraconazole against these were greater than 10 microM. These results suggest that miconazole is the strongest inhibitor of CYP2C9 and CYP2C19, followed by voriconazole and fluconazole, whereas micafungin would not cause clinically significant interactions with other drugs that are metabolized by CYP2C9 or CYP2C19 via the inhibition of metabolism. The IC50 value of voriconazole against nifedipine oxidation was comparable with that of fluconazole and micafungin and higher than that of itraconazole and miconazole. The stimulation of the inhibition of CYP2C9-, CYP2C19-, or CYP3A4-mediated reactions by 15-min preincubation was not observed for any of the antifungal drugs, suggesting that these drugs are not mechanism-based inhibitors.

Pharmacokinetic Drug Interactions of Gefitinib with Rifampicin, Itraconazole and Metoprolol

BACKGROUND AND OBJECTIVES

Gefitinib (IRESSA, ZD1839), an epidermal growth factor receptor tyrosine kinase inhibitor, has been approved in several countries for the treatment of advanced non-small-cell lung cancer. Preclinical studies were conducted to determine the cytochrome P450 (CYP) isoenzymes involved in the metabolism of gefitinib and to evaluate the potential of gefitinib to cause drug interactions through inhibition of CYP isoenzymes. Based on these findings, three clinical studies were carried out to investigate pharmacokinetic drug interactions in vivo with gefitinib.

METHODS

In preclinical studies radiolabelled gefitinib was incubated with: (i) hepatic microsomal protein in the presence of selective CYP inhibitors; and (ii) expressed CYP enzymes. Human hepatic microsomal protein was incubated with selective CYP substrates in the presence of gefitinib. Clinical studies were all phase I, open-label, single-centre studies; two had a randomised, two-way crossover design and the third was nonrandomised. The first and second studies investigated the pharmacokinetics of gefitinib in the presence of a potent CYP3A4 inducer (rifampicin [rifampin]) or inhibitor (itraconazole) in healthy male volunteers. The third study investigated the effects that gefitinib had on the pharmacokinetics of metoprolol, a CYP2D6 substrate, in patients with solid tumours.

RESULTS

The results of preclinical studies demonstrated that CYP3A4 is involved in the metabolism of gefitinib and that gefitinib is a weak inhibitor of CYP2D6 activity. In clinical studies when gefitinib was administered in the presence of rifampicin, geometric mean (gmean) maximum concentration and area under the plasma concentration-time curve (AUC) were reduced by 65% and 83%, respectively; these changes were statistically significant. When gefitinib was administered in the presence of itraconazole, gmean AUC increased by 78% and 61% at gefitinib doses of 250 and 500 mg, respectively; these changes also being statistically significant. Coadministration of metoprolol with gefitinib resulted in a 35% increase in the metoprolol area under plasma concentration-time curve from time zero to the time of the last quantifiable concentration; this change was not statistically significant. There was no apparent change in the safety profile of gefitinib as a result of coadministration with other agents.

CONCLUSIONS

Although CYP3A4 inducers may reduce exposure to gefitinib, further work is required to define any resultant effect on the efficacy of gefitinib. Exposure to gefitinib is increased by coadministration with CYP3A4 inhibitors, but since gefitinib is known to have a good tolerability profile, a dosage reduction is not recommended. Gefitinib is unlikely to exert a clinically relevant effect on the pharmacokinetics of drugs that are dependent on CYP2D6-mediated metabolism for their clearance, but the potential to increase plasma concentrations should be considered if gefitinib is coadministered with CYP2D6 substrates that have a narrow therapeutic index or are individually dose titrated.

Characterization of human cytochrome P450 enzymes involved in thein vitro metabolism of perospirone

In vitro studies were carried out to identify the major contribution of CYP2C8, CYP2D6 and CYP3A4 to the metabolism of perospirone (cis-N-[4-[4-(1,2-benzisothiazol-3-yl)-1-piperazinyl]butyl]cyclohexane-1,2-dicarboximide monohydrochloride dehydrate), a novel antipsychotic agent, using human liver microsomes and expressed P450 isoforms. Quinidine (a specific inhibitor of CYP2D6) did not markedly affect the metabolism of perospirone, whereas quercetin (an inhibitor of CYP2C8) and ketoconazole (an inhibitor of CYP3A4) caused a decrease in the metabolism with human liver microsomes in a concentration dependent fashion. With 10 microM quercetin, the metabolism of perospirone was inhibited by 60.0% and with 1 microM ketoconazole almost complete inhibition was apparent. Anti-CYP2C8 and anti-CYP2D6 antisera did not exert marked effects, whereas anti-CYP3A4 antiserum caused almost complete inhibition. With expressed P450s, K(m) and V(max) values were 1.09 microM and 1.93 pmol/min/pmol P450 for CYP2C8, 1.38 microM and 5.73 pmol/min/pmol P450 for CYP2D6, and 0.245 microM and 61.3 pmol/min/pmol P450 for CYP3A4, respectively. These results indicated that the metabolism of perospirone in human liver was mainly catalysed by CYP3A4, and to a lesser extent CYP2C8 and CYP2D6 were responsible because kinetic data (K(m) and V(max)) of CYP2C8 and CYP2D6 suggested catalytic potential.

Effect of Antifungal Drugs on Cytochrome P450 (CYP) 1A2, CYP2D6, and CYP2E1 Activities in Human Liver Microsomes

The effects of five antifungal drugs, fluconazole, itraconazole, micafungin, miconazole, and voriconazole, on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresorufin O-deethylation, CYP2D6-mediated debrisoquine 4-hydroxylation, and CYP2E1-mediated chlorzoxazone 6-hydroxylation activities in human liver microsomes were compared. In addition, the effect of preincubation was estimated in order to investigate the mechanism-based inhibition. IC50 values of miconazole against CYP1A2 and CYP2D6 activities were 2.90 and 6.46 microM, respectively, and miconazole at 10 microM concentration slightly inhibited CYP2E1 activity. On the other hand, other antifungal drugs neither inhibited nor stimulated all of the metabolic activities. The stimulation of the inhibition of the metabolic activities mediated by CYP1A2, CYP2D6, or CYP2E1 by 15-min preincubation was not observed for any of the antifungal drugs, suggesting that these antifungal drugs are not mechanism-based inhibitors. These results suggest that miconazole is the strongest inhibitor against CYP1A2, CYP2D6, and CYP2E1 among the antifungal drugs investigated.

Antimycotic Drug Discovery in the Age of Genomics

Genomic-based methodologies are increasingly used at all stages of drug development. The most extensive applications have occurred in early drug discovery stages due to advances in technologies that allow for automated synthesis and characterization of organic compounds, and for high-throughput screening of these molecules against known drug targets. The adaptation of genomic-based methodologies in later stages of drug development presents a more difficult task. In this review we describe how genomics can be used to identify previously uncharacterized pharmacologic actions that provide a basis for the development of new classes of antimycotic agents or for adverse event aversion. Clinically, novel antimycotics are gravely needed. This review provides a perspective on new technologies that will bridge the gap between drug discovery and development that may enable more rapid access to new antimycotic agents.

Fatal Hypoglycemia Associated with Levofloxacin

Fluoroquinolones are generally regarded as safe antimicrobial agents with relatively few adverse effects or drug interactions. Thus, they enjoy widespread use for treatment of community- and hospital-acquired infections. Although uncommon, hypoglycemia has been reported with all the fluoroquinolones and appears to occur most frequently in elderly patients with type 2 diabetes mellitus who are receiving therapy with oral hypoglycemics. The exact mechanism of this effect is unknown but is postulated to be a result of blockage of adenosine 5'-triphosphate-sensitive potassium channels in pancreatic beta-cell membranes. We report a case of fatal hypoglycemia related to levofloxacin administration in an elderly patient with diabetes. As with other fluoroquinolones, levofloxacin can cause profound and prolonged hypoglycemia. Clinicians should be cognizant of this potential adverse effect in patients with diabetes who are receiving levofloxacin therapy.

The novel azole R126638 is a selective inhibitor of ergosterol synthesis in Candida albicans, Trichophyton spp., and Microsporum canis

R126638 is a novel triazole with in vitro activity similar to that of itraconazole against dermatophytes, Candida spp., and Malassezia spp. In animal models of dermatophyte infections, R126638 showed superior antifungal activity. R126638 inhibits ergosterol synthesis in Candida albicans, Trichophyton mentagrophytes, Trichophyton rubrum, and Microsporum canis at nanomolar concentrations, with 50% inhibitory concentrations (IC(50)s) similar to those of itraconazole. The decreased synthesis of ergosterol and the concomitant accumulation of 14 alpha-methylsterols provide indirect evidence that R126638 inhibits the activity of CYP51 that catalyzes the oxidative removal of the 14 alpha-methyl group of lanosterol or eburicol. The IC(50)s for cholesterol synthesis from acetate in human hepatoma cells were 1.4 microM for itraconazole and 3.1 microM for R126638. Compared to itraconazole (IC(50) = 3.5 microM), R126638 is a poor inhibitor of the 1 alpha-hydroxylation of 25-hydroxyvitamin D(3) (IC(50) > 10 microM). Micromolar concentrations of R126638 and itraconazole inhibited the 24-hydroxylation of 25-hydroxyvitamin D(3) and the conversion of 1,25-dihydroxyvitamin D(3) into polar metabolites. At concentrations up to 10 microM, R126638 had almost no effect on cholesterol side chain cleavage (CYP11A1), 11 beta-hydroxylase (CYP11B1), 17-hydroxylase and 17,20-lyase (CYP17), aromatase (CYP19), or 4-hydroxylation of all-trans retinoic acid (CYP26). At 10 microM, R126638 did not show clear inhibition of CYP1A2, CYP2A6, CYP2D6, CYP2C8, CYP2C9, CYP2C10, CYP2C19, or CYP2E1. Compared to itraconazole, R126638 had a lower interaction potential with testosterone 6 beta hydroxylation and cyclosporine hydroxylation, both of which are catalyzed by CYP3A4, whereas both antifungals inhibited the CYP3A4-catalyzed hydroxylation of midazolam similarly. The results suggest that R126638 has promising properties and merits further in vivo investigations for the treatment of dermatophyte and yeast infections.

Disposition of posaconazole following single-dose oral administration in healthy subjects

Posaconazole is a potent, broad-spectrum triazole antifungal agent currently in clinical development for the treatment of refractory invasive fungal infections. Eight healthy male subjects received a single 399-mg (81.7 microCi) oral dose of [(14)C]posaconazole after consuming a high-fat breakfast. Urine, feces, and blood samples were collected for up to 336 h postdose and assayed for total radioactivity; plasma and urine samples were also assayed for parent drug. Posaconazole was orally bioavailable, with a median maximum posaconazole concentration in plasma achieved by 10 h postdose. Thereafter, posaconazole was slowly eliminated, with a mean half-life of 20 h. The greatest peak in the radioactivity profile of pooled plasma extracts was due to posaconazole, with smaller peaks due to a monoglucuronide, a diglucuronide, and a smaller fragment of the molecule. The mean total amount of radioactivity recovered was 91.1%; the cumulative excretion of radioactivity in feces and in urine was 76.9 and 14.0% of the dose, respectively. Most of the fecal radioactivity was associated with posaconazole, which accounted for 66.3% of the administered dose; however, urine contained only trace amounts of unchanged posaconazole. The radioactivity profile of pooled urine extracts included two monoglucuronide conjugates and a diglucuronide conjugate of posaconazole. These observations suggest that oxidative (phase 1) metabolism by cytochrome P450 isoforms represents only a minor route of elimination for posaconazole, and therefore cytochrome P450-mediated drug interactions should have a limited potential to impact posaconazole pharmacokinetics.

Unusual hypersensitivity to warfarin in a critically ill patient

A patient was admitted to the intensive care unit because of respiratory failure, and warfarin therapy was started at 2 mg/day for the treatment of pulmonary embolism, together with other medications. Despite the low dosage of warfarin, international normalized ratio (INR) was markedly elevated from 1.15 to 11.28 for only 4 days, and bleeding symptoms concurrently developed. Vitamin K2 was infused along with discontinuation of warfarin. One day later, the INR was found to have decreased, and bleeding was also improved. An objective causality assessment indicated a probable relationship between clotting abnormality and warfarin administration, although the degree of elevation of the INR was unusual in the light of the daily warfarin dose and duration of its exposure. Based on the clinical status of the patient, it was suspected that several conditions contributed to the abnormal hypersensitivity to warfarin. Contributory factors probably included pharmacokinetic interactions with co-administrated drugs, vitamin K deficiency caused by decreased dietary intake, reduced gut bacterial production, impaired intestinal absorption and hepatic synthetic capacity, and increased consumption of clotting factors. In view of our experience in the present case, it should be stressed that close monitoring of coagulation capacity is necessary in critically ill patients in order to avoid fatal haemorrhage after initiating warfarin therapy regardless of the dosage.

Drug interactions in the hematopoietic stem cell transplant (HSCT) recipient: what every transplanter needs to know

Pharmacokinetic drug interactions among hematopoietic stem cell transplant recipients can result in either increases in serum concentrations of medications, which may lead to enhanced toxicity; or reduced serum concentrations, which can lead to treatment failure and the emergence of post transplant complications. The use of drugs that have a narrow therapeutic index, such as cyclosporine/tacrolimus (calcineurin inhibitors), increases the significance of these interactions when they occur. This report will review the clinical data evaluating the drug interactions of relevance to HSCT clinical practice, focusing on the pharmacokinetic interactions, and provides recommendations for managing these interactions to avoid both toxicity and treatment failure.

In vitro evaluation of cytochrome P450-mediated drug interactions between cytarabine, idarubicin, itraconazole and caspofungin

PURPOSE

Antifungal prophylaxis is an important component of induction therapy for patients with acute myeloid leukemia (AML). Azole antifungal agents are increasingly used in this context. In vitro assays were performed to assess whether cytochrome P450 (CYP450) enzymes were affected by combinations of cytarabine or idarubicin with itraconazole or caspofungin.

METHODS

The high throughput microtiter assay was used to determine whether cytarabine, idarubicin and itraconazole or caspofungin were CYP450 isoenzyme substrates, inhibitors of CYP450 isoenzymes, and to determine potential CYP450 metabolism interactions between these agents.

RESULTS

Idarubicin is a substrate for CYP450 2D6 and 2C9. Cytarabine is a substrate of CYP450 3A4. Idarubicin inhibits CYP450 2D6, and cytarabine, itraconazole, and caspofungin inhibit CYP450 3A4. Cytarabine metabolism was significantly decreased when combined with caspofungin or itraconazole.

CONCLUSIONS

The inhibition of cytarabine metabolism may have important clinical implications. These in vitro findings warrant investigation with in vivo pharmacokinetic studies.

INTERACTION OF TRIAZOLAM AND KETOCONAZOLE IN P-GLYCOPROTEIN-DEFICIENT MICE

The role of P-glycoprotein (P-gp) on the distribution of the benzodiazepine triazolam (TRZ) and the azole antifungal agent ketoconazole (KET), and on the TRZ-KET interaction, was studied using mdr1a(-) or mdr1a/b(-/-) mice (P-gp-deficient mice) and matched controls. TRZ and KET also were studied in Caco-2 cells in Transwell culture. After single i.p. injections of TRZ or KET in separate groups of control mice, brain concentrations of TRZ exceeded those in serum [brain/serum area under the concentration curve (AUC) ratio, 5.0], whereas brain/serum AUC ratios for KET were approximately 0.5. On the basis of single time points, brain concentrations of TRZ, or brain/serum ratios, were similar in P-gp-deficient animals compared with controls, whereas P-gp-deficient animals had significantly higher KET brain concentrations and brain/serum ratios. Coadministration of KET with TRZ increased TRZ concentrations in serum, liver, and brain, both in controls and in P-gp-deficient animals, probably attributable to impairment by KET of CYP3A-mediated clearance of TRZ. However, KET did not increase brain/serum ratios of TRZ in either group. In Caco-2 cells, basal-to-apical flux of TRZ was higher than apical-to-basal flux. However, verapamil (100 microM) did not alter flux in either direction. KET inhibited basal-to-apical transport of rho-damine-123, with a 50% inhibitory concentration of 2.7 microM. Thus, TRZ does not appear to undergo measurable blood-brain barrier efflux transport by P-gp in this animal model. KET impairs clearance of TRZ but does not increase tissue uptake. However, KET itself may be a substrate for efflux transport at the blood-brain barrier.

Inhibition of cytochrome P450 enzymes participating in p-nitrophenol hydroxylation by drugs known as CYP2E1 inhibitors

p-Nitrophenol hydroxylation is widely used as a probe for microsomal CYP2E1. Several drugs are known as CYP2E1 inhibitors because of their capability to inhibit p-nitrophenol hydroxylation. Our results suggest further participation of CYP2A6 and CYP2C19 enzymes in p-nitrophenol hydroxylation. Moreover, CYP2A6 and CYP2C19 may be considered as the primary catalysts, whereas CYP2E1 can also contribute to the hydroxylation of p-nitrophenol. Further aim of our study was to evaluate the selectivity of p-nitrophenol hydroxylase inhibitors towards cytochrome P450 enzymes. The effects of antifungals: bifonazole, econazole, clotrimazole, ketoconazole, miconazole; CNS-active drugs: chlorpromazine, desipramine, fluphenazine, thioridazine; and the non-steroidal anti-inflammatory drug: diclofenac were investigated on the enzyme activities selective for CYP2A6, CYP2C9, CYP2C19, CYP2E1 and CYP3A4. None of the drugs could be considered as a potent inhibitor of CYP2E1. Strong inhibition was observed for CYP3A4 by antifungals with IC(50) values in submicromolar range. However, ketoconazole was the only imidazole derivative that could be considered as a selective inhibitor of CYP3A4. The CNS-active drugs investigated were found to be weak inhibitors of CYP2A6, CYP2C9, CYP2C19, CYP2E1 and CYP3A4. Diclofenac efficiently inhibited CYP2C9 and to a less extent CYP3A4 enzyme.

Inhibition of the metabolism of etizolam by itraconazole in humans: evidence for the involvement of CYP3A4 in etizolam metabolism

OBJECTIVE

To clarify the involvement of cytochrome P450 (CYP) 3A4 in the metabolism of etizolam.

METHODS

The effects of itraconazole, a potent and specific inhibitor of CYP3A4, on the single oral dose pharmacokinetics and pharmacodynamics of etizolam were examined. Twelve healthy male volunteers received itraconazole (200 mg/day) or placebo for 7 days in a double-blind randomized crossover manner, and on the 6th day they received a single oral 1-mg dose of etizolam. Blood samplings and evaluation of psychomotor function using the Digit Symbol Substitution Test and Stanford Sleepiness Scale were conducted up to 24 h after etizolam dosing. Plasma concentration of etizolam was measured by means of high-performance liquid chromatography.

RESULTS

Itraconazole treatment significantly increased the total area under the plasma concentration-time curve (AUC; 213+/-106 ng rectangle h/ml versus 326+/-166 ng rectangle h/ml, P<0.001) and the elimination half-life (12.0+/-5.4 h versus 17.3+/-7.4 h, P<0.01) of etizolam. The 90% confidence interval of the itraconazole/placebo ratio of the total AUC was 1.38-1.68, indicating a significant effect of itraconazole. No significant change was induced by itraconazole in the two pharmacodynamic parameters.

CONCLUSION

The present study suggests that itraconazole inhibits the metabolism of etizolam, providing evidence that CYP3A4 is at least partly involved in etizolam metabolism.

Posaconazole: a potent, extended-spectrum triazole anti-fungal for the treatment of serious fungal infections

Posaconazole is a potent, extended-spectrum, investigational triazole anti-fungal that is highly active in pre-clinical in vitro and in vivo models against a wide array of yeasts and moulds, including Aspergillus, Fusarium and Zygomycetes, which are often refractory to polyenes and older azoles. In humans, orally administered posaconazole is absorbed under fed or fasted conditions; however, absorption is significantly improved when it is coadministered with food or liquid nutritional supplements and when the daily dose is divided (into two or four daily doses). Unlike newer azoles, posaconazole is not extensively metabolised by cytochrome P450 (CYP) enzymes and is primarily excreted as parent compound in the faeces. Posaconazole is a CYP3A4 inhibitor, but it does not inhibit the activity of other CYP enzymes. Therefore, in comparison with other azole anti-fungal drugs, posaconazole may have the potential for fewer drug interactions. The pharmacokinetics of posaconazole are not influenced by age, gender or race. Dose adjustments for renal or hepatic impairment do not appear to be indicated based on results from single-dose studies. Preliminary efficacy data from clinical trials are promising. As salvage therapy, posaconazole elicited complete or partial responses in 44 to 75% of patients (N = 97) with invasive fungal infections who were intolerant of, or who had disease refractory to, amphotericin B or itraconazole. In an analysis of patients with aspergillosis, a 42% success rate was observed in the posaconazole arm (n = 107) compared with a 26% success rate in the control arm (n = 86). Importantly, Kaplan-Meier analysis demonstrated a survival benefit in posaconazole-treated patients. Moreover, posaconazole yielded complete or partial responses in 71% of patients with zygomycosis (N = 24). Posaconazole appears to be well tolerated over long-term administration (>1 year) and may represent an important addition to the anti-fungal armamentarium.

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.

Voriconazole potentiates warfarin-induced prothrombin time prolongation

AIMS

Voriconazole is a novel triazole with broad-spectrum antifungal activity. It is likely that some patients receiving voriconazole may also require treatment with the anticoagulant warfarin. Cytochrome P450 isoenzymes are important in the metabolism of both these drugs. This study investigated the effect of voriconazole on the pharmacodynamics of warfarin by measuring prothrombin time, and also evaluated the safety and tolerability of the coadministered drugs.

METHODS

This was a double-blind, placebo-controlled, two-way crossover study in which healthy male subjects received either 300 mg voriconazole or placebo twice daily on days 1-12, plus a single oral dose of 30 mg warfarin on day 7 of each study period. Volunteers were randomized to one of the following treatment sequences: voriconazole + warfarin followed by placebo + warfarin or placebo + warfarin followed by voriconazole + warfarin. There was a washout of at least of 7 days between treatment periods.

RESULTS

The mean Cmax, AUCtau and tmax for voriconazole were 3736 ng ml-1, 25 733 ng.h ml-1, and 1.66 h, respectively. Both the mean maximum change from baseline prothrombin time and the mean area under the effect curve (AUEC) for prothrombin time during coadministration with voriconazole (17 s and 3211 s.h, respectively) were statistically significantly greater than the mean values observed during the placebo period (8 s and 2282 s.h ). Prothrombin times were still increased by a mean value of 5.4 s 144 h post warfarin dose following coadministration with voriconazole compared with a mean value of 0.6 s in the placebo treatment period.

CONCLUSIONS

Coadministration of voriconazole and warfarin potentiates warfarin-induced prothrombin time prolongation. Regular monitoring of prothrombin time is recommended if these drugs are coadministered, with appropriate adjustment of the dose of warfarin.

Voriconazole does not affect the steady-state pharmacokinetics of digoxin

AIMS

Voriconazole is a triazole antifungal agent with potent fungicidal activity against Aspergillus species. Digoxin is a commonly prescribed cardiac glycoside with a narrow therapeutic index. This aim of this study was to investigate the effect of multiple-dose voriconazole on the steady-state pharmacokinetics of digoxin in healthy male volunteers.

METHODS

This was a double-blind, randomized, placebo-controlled, parallel-group study. All subjects received daily administration of oral digoxin for a total of 22 days (0.5 mg twice daily on day 1, 0.25 mg twice daily on day 2 and 0.25 mg once daily on days 3-22). In addition, on days 11-22 the subjects were randomized to receive either voriconazole (200 mg twice daily) or matching placebo.

RESULTS

Concomitant administration with voriconazole did not significantly alter the Cmax, AUCtau, tmax or CLR of digoxin at steady state. The ratios between groups for Cmax and AUCtau at day 22, corrected for baseline (day 10) were 109.8%[90% confidence interval (CI) 97.1, 124.1] and 100.5% (90% CI 91.4, 110.5), respectively. In addition, group mean Cmin values were similar in both treatment groups throughout the study. There were no significant differences between treatments with respect to the incidence of adverse events, all of which were classified as mild and transient in nature.

CONCLUSIONS

The steady-state pharmacokinetics of digoxin are not affected in a clinically relevant manner by the concomitant administration of voriconazole.

DEVELOPMENT OF AN IN VIVO PRECLINICAL SCREEN MODEL TO ESTIMATE ABSORPTION AND FIRST-PASS HEPATIC EXTRACTION OF XENOBIOTICS. II. USE OF KETOCONAZOLE TO IDENTIFY P-GLYCOPROTEIN/CYP3A-LIMITED BIOAVAILABILITY IN THE MONKEY

The effect of P-glycoprotein (Pgp) and/or CYP3A on the disposition of xenobiotics has been extensively investigated and is often of interest during drug discovery lead optimization. We have previously described a monkey pharmacokinetic screen to rapidly estimate absorption and first-pass extraction. In the present work, this monkey screen has been expanded to include an assessment of Pgp/CYP3A effects on absorption and first-pass extraction, using ketoconazole as a prototypic dual Pgp/CYP3A inhibitor. To generate a ketoconazole dosing regimen, the pharmacokinetics of ketoconazole were first determined in the monkey and were found to be consistent with that previously described in the rat, dog, and human. Dose-ranging experiments demonstrated that a single 10-mg/kg intraduodenal ketoconazole dose would provide an appropriate exposure; this dose was used throughout subsequent interaction experiments. Next, erythromycin and propranolol were explored as positive and negative control substrates for Pgp/CYP3A interactions, respectively. As anticipated, ketoconazole produced no change in the absorption or first-pass extraction of propranolol but resulted in a substantial increase in absorption and decrease in first-pass extraction of erythromycin. Finally, this ketoconazole-based monkey screen was deployed in a drug discovery setting, and examples of such use are presented. These experiments have allowed a more complete characterization of ketoconazole as a prototypic dual Pgp/CYP3A inhibitor and its use as a tool in a preclinical setting and further demonstrate the use of the monkey to investigate the role of Pgp/CYP3A in limiting the oral bioavailability of new drug candidates.

Antifungal activity of fluconazole in combination with lovastatin and their effects on gene expression in the ergosterol and prenylation pathways in Candida albicans

The sterol pathway in Candida albicans is the target for several classes of antifungal drugs. Intermediates in the sterol pathway are involved in ergosterol synthesis, prenylation and dolichol synthesis. This study examines gene expression of the sterol pathway in response to lovastatin, an inhibitor of HMG-CoA reductase (Hmg1p), and fluconazole, an inhibitor of 14 alpha-lanosterol demethylase (Erg11p). Minimum inhibitory concentration (MIC) studies indicated that lovastatin acts synergistically with fluconazole in vitro. Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) results indicated that genes in the early part of the sterol pathway, such as HMG1 and ERG20, did not alter expression in the presence of both lovastatin and fluconazole, whereas genes in the later part of the sterol pathway, such as ERG9 and ERG11, had increased expression in response to these drugs in mid-logarithmic growth. Genes involved in prenylation, such as RAM1 and RAM2, also respond to these drugs in mid-logarithmic growth, although another prenylation gene, CDC43, was not affected. After 24 h of growth, the relative expression of ERG20, ERG9, and ERG11 remained unchanged or increased in the presence of both drugs, while all other genes decreased in expression under all drug treatments.

Factors affecting the clinical development of cytochrome p450 3A substrates

The objective of this review is to evaluate the risks associated with the discovery and development of cytochrome p450 (CYP) 3A substrates. CYP3A is the most abundant p450 enzyme in human liver and is highly expressed in the intestinal tract. The enzyme contributes substantially to metabolism of approximately 50% of currently marketed drugs that undergo oxidative metabolism. As a result, drug-drug interactions involving inhibitors of CYP3A-mediated metabolism can be of great clinical consequence. It is the position of the authors that, because of the factors responsible for the broad substrate specificity of CYP3A, discovery and development of compounds across a large and broad portfolio that are completely devoid of CYP3A metabolism is not feasible. Thus, it is important that scientifically valid approaches to the discovery and development of compounds metabolised by CYP3A be realised. The clinical relevance of CYP3A metabolism is dependent on a multitude of factors that include the degree of intestinal and hepatic CYP3A-mediated first-pass extraction, the therapeutic index of the compound and the adverse event associated with inhibition of CYP3A metabolism. Thus, a better understanding of the disposition of a CYP3A-metabolised compound relative to the projected or observed therapeutic index (or safety margin) can provide ample evidence to support the continued development of a CYP3A substrate. This document will highlight current practices as well as the benefits and risks associated with those practices.

Bicalutamide

Bicalutamide is a nonsteroidal pure antiandrogen given at a dosage of 150 mg once daily as monotherapy for the treatment of early (localised or locally advanced) nonmetastatic prostate cancer. It is used at a dosage of 50 mg once daily in combination with a luteinising hormone-releasing hormone analogue or surgical castration for the treatment of advanced prostate cancer. Bicalutamide is a racemate and its antiandrogenic activity resides almost exclusively in the (R)-enantiomer, with little, if any, activity in the (S)-enantiomer. (R)-Bicalutamide is slowly and saturably absorbed, but absorption is unaffected by food. It has a long plasma elimination half-life (1 week) and accumulates about 10-fold in plasma during daily administration. (S)-Bicalutamide is much more rapidly absorbed and cleared from plasma; steady-state concentrations (Css) of (R)-bicalutamide are 100-fold higher than those of (S)-bicalutamide. Css increases linearly with doses up to 50 mg, but nonlinearly at higher doses, reaching a plateau above 300 mg. Css is higher in Japanese than in Caucasians, but no relationship with degree of renal impairment, bodyweight or age exists. Although mild-to-moderate hepatic impairment does not affect pharmacokinetics, there is evidence for slower elimination of (R)-bicalutamide in subjects with severe hepatic impairment. Bicalutamide metabolites are excreted almost equally in urine and faeces with little or no unchanged drug excreted in urine; conversely, unchanged drug predominates in plasma. Bicalutamide in faeces is thought to arise from hydrolysis of bicalutamide glucuronide and from unabsorbed drug. Bicalutamide appears to be cleared almost exclusively by metabolism; this is largely mediated by cytochrome P450 (CYP) for (R)-bicalutamide, but glucuronidation is the predominant metabolic route for (S)-bicalutamide. (S)-Bicalutamide is metabolised in vitro by CYP3A4, and it is probable that this isoenzyme is also responsible for the metabolism of (R)-bicalutamide. In vitro data suggest that (R)-bicalutamide has the potential to inhibit CYP3A4 and, to a lesser extent, CYP2C9, 2C19 and 2D6. However, using midazolam as a specific CYP3A4 marker, no clinically relevant inhibition is observed in vivo with bicalutamide 150mg. Although bicalutamide is a CYP inducer in laboratory animals, dosages < or = 150 mg/day have shown no evidence of enzyme induction in humans. Daily administration of bicalutamide increases circulating levels of gonadotrophins and sex hormones; although testosterone increases by up to 80%, concentrations in most patients remain within the normal range. Bicalutamide produces a dose-related decrease in prostate-specific antigen (PSA) at dosages < or = 150 mg/day. However, little relationship is observed between median PSA reduction and (R)-bicalutamide Css.

Selecting antibacterials for outpatient parenteral antimicrobial therapy : pharmacokinetic-pharmacodynamic considerations

Some infectious diseases require management with parenteral therapy, although the patient may not need hospitalisation. Consequently, the administration of intravenous antimicrobials in a home or infusion clinic setting has now become commonplace. Outpatient parenteral antimicrobial therapy (OPAT) is considered safe, therapeutically effective and economical. A broad range of infections can be successfully managed with OPAT, although this form of treatment is unnecessary when oral therapy can be used. Many antimicrobials can be employed for OPAT and the choice of agent(s) and regimen should be based upon sound clinical and microbiological evidence. Assessments of cost and convenience should be made subsequent to these primary treatment outcome determinants. When designing an OPAT treatment regimen, the pharmacokinetic and pharmacodynamic characteristics of the individual agents should also be considered. Pharmacokinetics (PK) is the study of the time course of absorption, distribution, metabolism and elimination of drugs (what the body does to the drug). Clinical pharmacokinetic monitoring has been used to overcome the pharmacokinetic variability of antimicrobials and enable individualised dosing regimens that attain desirable antimicrobial serum concentrations. Pharmacodynamics (PD) is the study of the relationship between the serum concentration of a drug and the clinical response observed in a patient (what the drug does to the body). By combining pharmacokinetic properties (peak [C(max)] or trough [C(min)] serum concentrations, half-life, area under the curve) and pharmacodynamic properties (susceptibility results, minimum inhibitory concentrations [MIC] or minimum bactericidal concentrations [MBC], bactericidal or bacteriostatic killing, post-antibiotic effects), unique PK/PD parameters or indices (t > MIC, C(max)/MIC, AUC(24)/MIC) can be defined. Depending on the killing characteristics of a given class of antimicrobials (concentration-dependent or time-dependent), specific PK/PD parameters may predict in vitro bacterial eradication rates and correlate with in vivo microbiologic and clinical cures. An understanding of these principles will enable the clinician to vary dosing schemes and design individualised dosing regimens to achieve optimal PK/PD parameters and potentially improve patient outcomes. This paper will review basic principles of useful PK/PD parameters for various classes of antimicrobials as they may relate to OPAT. In summary, OPAT has become an important treatment option for the management of infectious diseases in the community setting. To optimise treatment course outcomes, pharmacokinetic and pharmacodynamic properties of the individual agents should be carefully considered when designing OPAT treatment regimens.