Drug-Drug Interaction of Antifungal Drugs

Exploring the impact of CYP2D6 and UGT2B7 gene-drug interactions, and CYP-mediated DDI on oxycodone and oxymorphone pharmacokinetics using physiologically-based pharmacokinetic modeling and simulation

Oxycodone is one of the most commonly used opioids to treat moderate to severe pain. It is metabolized mainly by CYP3A4 and CYP2D6, while only a small fraction of the dose is excreted unchanged into the urine. Oxymorphone, the metabolite primarily formed by CYP2D6, has a 40- to 60-fold higher mu-opioid receptor affinity than the parent compound. While CYP2D6-mediated gene-drug-interactions (GDIs) and drug-drug interactions (DDIs) are well-studied, they only account for a portion of the variability in oxycodone and oxymorphone exposure. The combined impact of CYP2D6-mediated GDIs and DDIs, CYP3A4-mediated DDIs, and UGT2B7 GDIs is not fully understood yet and hard to study in head-to-head clinical trials given the relatively large number of scenarios. Instead, we propose the use of a physiologically-based pharmacokinetic model that integrates available information on oxycodone's metabolism to characterize and predict the impact of DDIs and GDIs on the exposure of oxycodone and its major, pharmacologically-active metabolite oxymorphone. To this end, we first developed and verified a PBPK model for oxycodone and its metabolites using published clinical data. The verified model was then applied to determine the dose-exposure relationship of oxycodone and oxymorphone stratified by CYP2D6 and UGT2B7 phenotypes respectively, and administered perpetrators of CYP-based drug interactions. Our simulations demonstrate that the combination of CYP2D6 UM and a UGT2B7Y (268) mutation may lead to a 2.3-fold increase in oxymorphone exposure compared to individuals who are phenotyped as CYP2D6 NM / UGT2B7 NM. The extent of oxymorphone exposure increases up to 3.2-fold in individuals concurrently taking CYP3A4 inhibitors, such as ketoconazole. Inhibition of the CYP3A4 pathway results in a relative increase in the partial metabolic clearance of oxycodone to oxymorphone. Oxymorphone is impacted to a higher extent by GDIs and DDIs than oxycodone. We predict oxymorphone exposure to be highest in CYP2D6 UMs/UGT2B7 PMs in the presence of ketoconazole (strong CYP3A4 index inhibitor) and lowest in CYP2D6 PMs/UGT2B7 NMs in the presence of rifampicin (strong CYP3A4 index inducer) covering a 55-fold exposure range.

A novel UHPLC‒MS/MS method for quantitative analysis of zanubrutinib in rat plasma: application to an in vivo interaction study between zanubrutinib and triazole antifungal

BACKGROUND

This study establishes a UHPLC‒MS/MS method for the detection of zanubrutinib and explores its interaction with fluconazole and isavuconazole in rats.

METHODS

A protein precipitation method using acetonitrile was used to prepare plasma samples using ibrutinib as an internal standard. Chromatographic separation and mass spectrometric detection of the analytes and internal standards were performed on a Shimadzu 8040 UHPLC‒MS/MS equipped with a Shim-pack velox C18 column (2.1 × 50 mm, 2.7 µm). Methanol and 0.1% formic acid-water were used as mobile phases. Intraday and interday precision and accuracy, extraction recoveries, and matrix effects of this method were determined. The linearity and sample stability of the method were assessed. Eighteen male Sprague‒Dawley (SD) rats were randomly divided into three groups with zanubrutinib (30 mg/kg) alone, zanubrutinib in combination with fluconazole (20 mg/kg) or zanubrutinib in combination with isavuconazole (20 mg/kg). Blood samples (200 µL) were collected at designated time points (ten evenly distributed time points within 12 h). The concentration of zanubrutinib was determined using the UHPLC‒MS/MS method developed in this study.

RESULTS

The typical fragment ions were m/z 472.15 → 290.00 for zanubrutinib and m/z 441.20 → 138.10 for ibrutinib (IS). The range of the standard curve was 1-1000 ng/mL with a regressive coefficient (R2) of 0.999. The recoveries and matrix effects were 91.9-98.2% and 97.5-106.3%, respectively, at different concentration levels. The values for intra- and interday RSD% were lower than 9.8% and 5.8%, respectively. The RSD% value was less than 10.3%, and the RE% value was less than ± 4.0% under different storage conditions. Analysis of pharmacokinetic results suggested that coadministration with isavuconazole or fluconazole significantly increased the area under the curve (1081.67 ± 43.81 vs. 1267.55 ± 79.35 vs. 1721.61 ± 219.36), peak plasma concentration (332.00 ± 52.79 vs. 396.05 ± 37.19 vs. 494.51 ± 130.68), and time to peak (1.83 ± 0.41 vs. 2.00 ± 0.00 vs. 2.17 ± 0.41) compared to zanubrutinib alone.

CONCLUSION

This study provides information to understand the metabolism of zanubrutinib with concurrent use with isavuconazole or fluconazole, and further clinical trials are needed to validate the results in animals.

Integrated Use of In Vitro and In Vivo Information for Comprehensive Prediction of Drug Interactions Due to Inhibition of Multiple CYP Isoenzymes

BACKGROUND

Mechanistic static pharmacokinetic (MSPK) models are simple, have fewer data requirements, and have broader applicability; however, they cannot use in vitro information and cannot distinguish the contributions of multiple cytochrome P450 (CYP) isoenzymes and the hepatic and intestinal first-pass effects appropriately. We aimed to establish a new MSPK analysis framework for the comprehensive prediction of drug interactions (DIs) to overcome these disadvantages.

METHODS

Drug interactions that occurred by inhibiting CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A in the liver and CYP3A in the intestine were simultaneously analyzed for 59 substrates and 35 inhibitors. As in vivo information, the observed changes in the area under the concentration-time curve (AUC) and elimination half-life (t1/2), hepatic availability, and urinary excretion ratio were used. As in vitro information, the fraction metabolized (fm) and the inhibition constant (Ki) were used. The contribution ratio (CR) and inhibition ratio (IR) for multiple clearance pathways and hypothetical volume (VHyp) were inferred using the Markov Chain Monte Carlo (MCMC) method.

RESULT

Using in vivo information from 239 combinations and in vitro 172 fm and 344 Ki values, changes in AUC, and t1/2 were estimated for all 2065 combinations, wherein the AUC was estimated to be more than doubled for 602 combinations. Intake-dependent selective intestinal CYP3A inhibition by grapefruit juice has been suggested. By separating the intestinal contributions, DIs after intravenous dosing were also appropriately inferred.

CONCLUSION

This framework would be a powerful tool for the reasonable management of various DIs based on all available in vitro and in vivo information.

Risk prediction of drug-drug interaction potential of phenytoin and miconazole topical formulations

The drug-drug interaction (DDI) risk of phenytoin with several topical formulations of miconazole is still unclear. The present investigation conducted in vitro-in vivo extrapolation to predict the potential risks. Our data indicated that miconazole potently inhibited phenytoin hydroxylation in both pooled human liver microsomes (HLMs) and recombinant cytochrome P450 2C9 (CYP2C9) with the K_i values of 125 ± 7 nM and 30 ± 2 nM, respectively. Quantitative prediction of DDI risk suggests that, beside intravenous administration or swallowed tablet, combination of phenytoin and miconazole high dose oral gel or buccal tablet may also result in a clinically significant increase of phenytoin AUC (>53%) by the inhibition of miconazole against phenytoin hydroxylation, consequently a higher frequency of adverse events, while the coadministration of miconazole vaginal formulation and phenytoin will be safe.

Plausible drug interaction between cyclophosphamide and voriconazole via inhibition of CYP2B6

The inhibitory activities of eight cytochrome P450 (CYP) isoenzymes for representative or suspected inhibitors of CYPs, including pesticides, were evaluated simultaneously using an in vitro cocktail incubation method to demonstrate the importance of systematic evaluation of CYP inhibitory risks in drug interaction (DI). Potent inhibition of CYP2B6 was noticeable for some azoles, including voriconazole. When voriconazole and cyclophosphamide were co-administered in mice, cyclophosphamide-induced alopecia and leukopenia were significantly suppressed by approximately 50% with increased blood concentrations of cyclophosphamide. The formation of an active metabolite of cyclophosphamide was suppressed effectively by voriconazole in the mouse liver microsomes. Surveys of adverse event reporting databases in Japan (JADER) and the U.S. (FAERS) showed that the proportional reporting ratios of neutropenia, hemorrhagic cystitis, and alopecia for cyclophosphamide, which is principally activated by CYP2B6 in humans, were mostly reduced, or tended to be reduced when azoles, including voriconazole, were prescribed in combination. It is highly likely that DIs between cyclophosphamide and azoles occur in the clinical setting. This study also suggests that more proper consideration of CYP2B6-mediated DIs is warranted. The combination of the in vitro cocktail method and a survey of adverse event reporting databases was a useful method to comprehensively detect pharmacokinetic DIs.

Effects of Miconazole Oral Gel on Blood Concentrations of Tacrolimus and Cyclosporine: A Retrospective Observational Study

BACKGROUND

Although azole antifungal agents have been shown to affect the pharmacokinetics of calcineurin inhibitors such as tacrolimus (TAC) and cyclosporine (CyA) by inhibiting drug metabolism, there are few clinical reports on drug interactions between miconazole (MCZ) oral gel and calcineurin inhibitors. In this study, the effects of MCZ oral gel on the blood concentrations of TAC and CyA were investigated.

METHODS

In this retrospective study, 18 patients concomitantly administered MCZ oral gel and TAC (9 for dermatomyositis, 3 for myasthenia gravis, 2 for systemic lupus erythematosus, 2 for rheumatoid arthritis, 1 for polymyositis, 1 for prevention of graft-versus-host disease after bone marrow transplantation), and 15 patients concomitantly administered MCZ oral gel and CyA (11 for interstitial pneumonia, 2 for pemphigus, 1 for eosinophilic granulomatosis with polyangiitis, 1 for systemic lupus erythematosus) were evaluated. The dose-adjusted blood concentrations of TAC or CyA were compared before and after the initiation of MCZ oral gel.

RESULTS

The trough blood concentration/dose (C/D) ratios of TAC and CyA increased significantly with the administration of MCZ oral gel. The median C/D ratios of TAC and CyA increased by 108% (range: -44% to 216%) and 44% (range: -34% to 195%), respectively.

CONCLUSIONS

These results suggest that MCZ oral gel affects the pharmacokinetics of TAC and CyA. Detailed monitoring of the blood concentrations of these drugs, followed by dose adjustments, is needed for each patient because of the difficulties associated with accurately predicting the degree of the effects of MCZ oral gel.

Effects of CYP3A5 polymorphism on the pharmacokinetics of a once-daily modified-release tacrolimus formulation and acute kidney injury in hematopoietic stem cell transplantation

Background

Tacrolimus is metabolized by cytochrome P450 (CYP) 3A4 and 3A5. We investigated the influence of CYP3A5 polymorphism and concurrent use of azole antifungal agents (AZ) on the pharmacokinetics of a once-daily modified-release tacrolimus formulation (Tac-QD) in patients after hematopoietic stem cell transplantation (HSCT).

Design and methods

Twenty-four patients receiving allogeneic HSCT were enrolled. Genotyping for CYP3A5*3 was done by a PCR-restriction fragment length polymorphism method. Trough blood concentrations (C₀) of tacrolimus were measured by chemiluminescence magnetic microparticle immunoassay. Continuous infusion of tacrolimus was administered from the day before transplantation and was switched to Tac-QD after adequate oral intake.

Results

Thirteen patients had a CYP3A5*3/*3 genotype, and 11 patients had a CYP3A5*1/*1 or *1/*3 genotype. No significant difference was observed in daily dosages and the C₀ of tacrolimus between the two genotype groups without AZ. However, in patients who were co-administered AZ, the C₀ values of tacrolimus were higher in patients with the CYP3A5*3/*3 allele than with the CYP3A5*1 allele (P = 0.034), although daily doses of Tac-QD in patients with CYP3A5*3/*3 were significantly lower than those with the CYP3A5*1 allele (P = 0.041). The cumulative incidence of acute kidney injury was higher in patients with the CYP3A5*3/*3 than with the CYP3A5*1 allele when AZ was co-administered. The decrement for daily dosage of Tac-QD was significantly greater in patients expressing the CYP3A5*3/*3 than the CYP3A5*1 allele.

Conclusions

CYP3A5 genotyping may be useful for safe and effective immunosuppressive therapy with Tac-QD in HSCT patients in whom the use of AZ is anticipated.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-016-3060-4) contains supplementary material, which is available to authorized users.

Efficacy and safety of micafungin for febrile neutropenia in pediatric patients with hematological malignancies: a multicenter prospective study

BACKGROUND

Invasive fungal infections are a major cause of infectious mortality in neutropenic patients receiving chemotherapy or hematopoietic stem cell transplantation. However, little is known about the efficacy and safety of micafungin (MCFG), an echinocandin antifungal agent, in pediatric patients with febrile neutropenia (FN).

PROCEDURE

This study was conducted as a prospective multicenter trial to evaluate the efficacy and safety of MCFG for FN in pediatric patients with hematological diseases. Efficacy was assessed based on the response to the 5 composite endpoints established by Walsh and colleagues in addition to body temperature and C-reactive protein values.

RESULTS

Thirty episodes of FN were enrolled in the study. The median dose and duration of MCFG treatment were 3.0 mg/kg/d and 13.5 days, respectively. Using the criteria of Walsh and colleagues, MCFG was effective in 56.7% of the patients. No breakthrough invasive fungal infection occurred during MCFG treatment. Body temperatures on the last day of neutropenia during administration of MCFG and on the last day of MCFG therapy and C-reactive protein values after administration of MCFG were significantly lower than on the day MCFG therapy was started. Adverse effects in the form of mild liver dysfunction were seen in only 2 patients.

CONCLUSIONS

MCFG is a very effective and safe antifungal drug for FN in children. Physicians should administer MCFG early in febrile episode in patients in whom first-line antibiotics are not effective in treating FN.

Efficacy of micafungin in empirical therapy of deep mycosis in surgically ill patients

Micafungin (MCFG), an echinocandin antifungal agent, exhibits antifungal activity against Candida albicans and non-albicans Candida. The fungicidal activity of MCFG against clinical isolates of Candida species was investigated, and the clinical efficacy of MCFG in therapy of deep mycosis in surgery was studied using the AKOTT algorithm. The minimum inhibitory concentration and minimum fungicidal concentration values of fluconazole were ≤0.06-4 and >64 μg/ml, respectively, for each strain, whereas these values of MCFG were 0.008-0.5 and 0.016-1 μg/ml, suggesting that MCFG provided superior fungicidal ability against Candida albicans and non-albicans Candida. The subjects were separated into two groups: group A consisted of 20 subjects with both persisting fever refractory to broad-spectrum antibiotics and positive reaction to β-D-glucan test, and group B consisted of 20 subjects with either of those conditions. The overall response was evaluated as "effective" in 17 patients (85%) and 20 patients (100%) in groups A and B, respectively. In total, response was evaluated as "effective" in 37 patients (92.5%) and "ineffective" in 3 patients (7.5%). These findings suggest that MCFG administration should be used as empirical therapy for deep mycosis in surgically ill patients as it was shown to be an effective antifungal drug lacking serious adverse effects.

Effect of clarithromycin and fluconazole on the pharmacokinetics of montelukast in human volunteers

OBJECTIVE

Montelukast, a leukotriene receptor antagonist, is used in the treatment of asthma. The objective of the study reported here was to determine whether multiple doses of clarithromycin or fluconazole affect the pharmacokinetics of montelukast.

METHODS

This was a four-phase cross-over study with a washout period of 2 weeks between phases. In phase 1, 12 volunteers received a single oral dose of 10 mg montelukast. In phase 2, the volunteers received a single, oral dose of 1,000 mg clarithromycin once daily for 2 days, followed by, on day 3, a single oral dose of 10 mg montelukast co-administered with clarithromycin. In phase 3, a single oral dose of 50 mg fluconazole was given once daily for 6 days, followed by, on day 7, a single oral dose of 10 mg montelukast co-administered with 50 mg fluconazole. In the last phase (phase 4), a single oral dose of 150 mg fluconazole was given once daily for 6 days, followed by, on day 7, a single oral dose of 10 mg montelukast co-administered with 150 mg fluconazole. The plasma concentration of montelukast was measured by high performance liquid chromatography for 24 h.

RESULTS

Following clarithromycin co-administration, the area under the concentration-time curve from zero to infinity ( AUC(0-∞)) of montelukast increased by 144% [90% confidence interval (CI) 2.03-2.86]. The co-administration of a single oral dose of 150 and 50 mg fluconazole decreased the montelukast AUC(0-∞) by 30.7 (90% CI 0.53-0.81) and 38.8% (90% CI 0.57-0.69), respectively.

CONCLUSIONS

Clarithromycin increased the plasma concentrations of montelukast whereas fluconazole reduced the plasma concentrations of montelukast. The mechanism of the interaction is probably due to interference of the interacting drugs with transporters mediating the uptake of montelukast.

Theoretical considerations on quantitative prediction of drug-drug interactions

The prediction of drug-drug interactions (DDIs) associated with change in clearance for metabolism is reviewed, particularly focusing on pharmacokinetic theories for prediction based on in vitro and in vivo observation. First, there is discussion about how quantitative determination of the contribution of major clearance pathways is fundamental for the accurate prediction of DDIs. Secondly, the concentrations of causative drugs at sites of interactions are discussed. Although DDIs have been predicted from in vitro pharmacokinetic parameters based on predicted hepatic unbound concentrations of inhibitors and inducers, there are noticeable discrepancies between predicted and observed magnitudes of these DDIs. To solve these issues, a method for the prediction of unbound hepatic concentration is proposed based on theoretical considerations. Finally, a pharmacokinetic model to describe the intestinal first pass metabolism is considered, particularly focusing on the importance of the Q(gut) model. Although this Q(gut) model was proposed as an empirical model, theoretical considerations suggest that the model is regarded as a physiologically-based pharmacokinetic model that can predict significance of intestinal DDIs. Theoretical considerations proposed in the present article may be helpful for future analysis of DDIs.

Prediction of pharmacokinetic drug-drug interaction caused by changes in cytochrome P450 activity using in vivo information

The aim of the present paper was to present an overview of the current status of the methods used to predict the magnitude of pharmacokinetic drug-drug interactions (DDIs) which are caused by apparent changes in cytochrome P450 (CYP) activity with an emphasis on a method using in vivo information. In addition, more than a hundred representative CYP substrates, inhibitor and inducer drugs involved in significant pharmacokinetic DDIs were selected from the literature and are listed. Although the magnitude of DDIs has been conventionally predicted based on in vitro experiments, their predictability is restricted occasionally due to several difficulties, including a precise determination of the unbound inhibitor concentrations at the enzyme site and a reliable in vitro measurement of the inhibition constant (K(i)). Alternatively, a simple method has been recently proposed for the prediction of the magnitude of DDIs based on information fully available from in vivo clinical studies. The new in vivo-based method would be applicable to the adjustment of dose regimens in actual pharmacotherapy situations although it requires a prior clinical study for the prediction. In this review, theoretical and quantitative relationships between the in vivo- and the in vitro-based prediction methods are considered. One of the interesting outcomes of the consideration is that the K(i)-normalized dose (dose/in vitro K(i)) of larger than approximately 20L (2-200L, when variability is considered) may be a pragmatic index which predicts significant in vivo DDIs. In the last part of the article, the relevance of the inclusion of the in vivo-based method into the process of new drug development is discussed for good prediction of in vivo DDIs.

Comprehensive in vitro analysis of voriconazole inhibition of eight cytochrome P450 (CYP) enzymes: major effect on CYPs 2B6, 2C9, 2C19, and 3A

Voriconazole is an effective antifungal drug, but adverse drug-drug interactions associated with its use are of major clinical concern. To identify the mechanisms of these interactions, we tested the inhibitory potency of voriconazole with eight human cytochrome P450 (CYP) enzymes. Isoform-specific probes were incubated with human liver microsomes (HLMs) (or expressed CYPs) and cofactors in the absence and the presence of voriconazole. Preincubation experiments were performed to test mechanism-based inactivation. In pilot experiments, voriconazole showed inhibition of CYP2B6, CYP2C9, CYP2C19, and CYP3A (half-maximal [50%] inhibitory concentrations, <6 microM); its effect on CYP1A2, CYP2A6, CYP2C8, and CYP2D6 was marginal (<25% inhibition at 100 microM voriconazole). Further detailed experiments with HLMs showed that voriconazole is a potent competitive inhibitor of CYP2B6 (K(i) < 0.5), CYP2C9 (K(i) = 2.79 microM), and CYP2C19 (K(i) = 5.1 microM). The inhibition of CYP3A by voriconazole was explained by noncompetitive (K(i) = 2.97 microM) and competitive (K(i) = 0.66 microM) modes of inhibition. Prediction of the in vivo interaction of voriconazole from these in vitro data suggests that voriconazole would substantially increase the exposure of drugs metabolized by CYP2B6, CYP2C9, CYP2C19, and CYP3A. Clinicians should be aware of these interactions and monitor patients for adverse effects or failure of therapy.

Effects of ketoconazole and quinidine on pharmacokinetics of pactimibe and its plasma metabolite, R-125528, in humans

Pactimibe sulfate is a novel acyl coenzyme A:cholesterol acyltransferase inhibitor developed for the treatment of hypercholesterolemia and atherosclerotic diseases. Pactimibe has two equally dominant clearance pathways forming R-125528 by CYP3A4 and M-1 by CYP2D6 in vitro. R-125528 is a plasma metabolite and is cleared solely by CYP2D6 despite its acidity. To evaluate contributions of the cytochrome P450 enzymes on the pharmacokinetics of pactimibe and R-125528 in humans, drug-drug interaction studies using ketoconazole and quinidine were conducted. Eighteen healthy male subjects were given a single dose of pactimibe sulfate without and with 400 mg of ketoconazole (q.d.). With the concomitant treatment, the area under the plasma concentration-time curve (AUC(0-inf)) of pactimibe modestly increased 1.7-fold and AUC(0-tz) of R-125528 decreased by 55%. In addition, 17 healthy male subjects were given a single dose of pactimibe sulfate without and with 600 mg of quinidine (b.i.d.). With the concomitant treatment, the AUC(0-inf) for pactimibe modestly increased 1.7-fold. On the other hand, the AUC(0-tz) of R-125528 was markedly elevated 5.0-fold, although the AUC(0-inf) could not be adequately defined because the terminal elimination phase of R-125528 was not obtained in the study period up to 72 h. As the f(m CYP3A4) and f(m CYP2D6) values of pactimibe estimated from in vitro studies were 0.40 and 0.33, respectively, AUC increase ratios of pactimibe were estimated to be 1.7 with ketoconazole and 1.5 with quinidine. These values were well in accordance with the values observed in this study. Moreover, the f(m CYP2D6) of R-125528 estimated to be almost 1 would well explain the accumulation of R-125528 observed with the quinidine treatment.

Ocular distribution of intravenously administered micafungin in rabbits

The ocular distribution of micafungin (MCFG), which has antifungal activity against Candida and Aspergillus species, was followed after the systemic administration of MCFG in rabbits. After MCFG (10 mg/kg) plus fluconazole (FLCZ; 10 mg/kg) was administered intravenously, the rabbits were killed, and MCFG and FLCZ concentrations in retina-choroid, vitreous humor, and plasma were determined by high performance liquid chromatography or liquid chromatography/mass spectrometry. The mean concentrations of MCFG in the retina-choroid at 0.25, 0.75, 4, 8, and 24 h after administration were 20.18, 15.97, 13.19, 6.27, and 0.75 microg/g, respectively, and were comparable with the MCFG plasma concentrations. The MCFG concentrations in retina-choroid and plasma exceeded the minimal antifungal inhibitory concentrations for endophthalmitis, although MCFG was not detected in the vitreous humor. These results suggest that the intravenous administration of MCFG is an effective treatment for endogenous fungal endophthalmitis when the causative fungus is localized in the retina and choroid.

Farmacología de los azoles

Azole antifungals have different pharmacokinetic characteristics: complete oral absorption for Voriconazole, and to a lesser extent for fluconazole. The absorption of posaconazole and itraconazole increases with food intake. All of them have high tissue distribution with low plasma concentrations, especially low in the case of posaconazole and itraconazole. Posaconazole and itraconazole have high plasmatic protein binding and consequently both have a very low free fraction. Elimination of azole antifungals is through a metabolic pathway with CYP450 isoenzymes, and has a non linear pharmacokinetics with a high risk of interation with other drugs since azoles have the ability of CYP450 isoenzymes inhibition. Possibly the parameter that defines more precisely their efficacy is AUIC with an optimum value near 20, although cut-off values must be defined since some azoles may have difficulty to reach this value.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.

Change of the Blood Concentration of Tacrolimus after the Switch from Fluconazole to Voriconazole in Patients Receiving Allogeneic Hematopoietic Stem Cell Transplantation

The purpose of this study was to assess the impact by switching co-administered triazole antifungal agent from fluconazole (FCZ) to voriconazole (VCZ) on the blood concentration of tacrolimus (FK506) in patients receiving allogeneic hematopoietic stem cell transplantation. We performed a retrospective study presented as case reports. The blood concentration of FK506 was increased after the switch from FCZ to VCZ, resulting in increase of the concentration/dose (C/D) ratio of FK506. Thus, the mean C/D ratios of FK506 with oral administration was surprisingly increased over 4.5-fold after the switch. Therefore, it was necessary to reduce the FK506 dose when co-administered FCZ is switched to VCZ. We should be careful when interpreting the results of these case reports; however, in some patients, it is recommended that the dose of FK506 be reduced to one-fifth after the switch.