Inhibitory Effect Of Ketoconazole Research Articles

Inhibitory effect of ketoconazole, quinidine and 1-aminobenzotriazole on pharmacokinetics of l-tetrahydropalmatine and its metabolite in rats

l-tetrahydropalmatine (l-THP) is mainly metabolised by CYP450 enzymes. This study was to investigate the possible effect of co-administered CYP inhibitors on the pharmacokinetics of l-THP and its metabolites in rats. An established LC-MS/MS method has been applied for the evaluation of drug-drug interaction between l-THP and CYP inhibitors. Following the administration of CYP inhibitors, a single dose of l-THP (9 mg/kg) was orally administrated. With regard to l-THP, the AUC0–48 were significantly increased by 4.3, 3.79, and 11.39 folds, and C max were increased by 4.74, 3.64, and 2.76 folds in the ketoconazole group (KET), quinidine group (QD), and 1-aminobenzotriazole group (ABT), respectively. KET and QD both significantly increased the AUC0–48 of 2-DM and 2-DM-Glu by 1.38 ∼ 2.43 times, while C max was significantly decreased by 41.3 and 78.0% in the ABT group, respectively. The C max of 3-DM was reduced by 51.38, 48.02, and 63.31% after pre-treatment with KET, QD, and ABT, respectively, and C max of 3-DM-Glu decreased correspondingly by 29.6, 22.1, and 58.0%. Results indicated that CYP inhibitors could markedly influence the systemic level of l-THP and its metabolites. To guarantee the safe use of l-THP, attention should be paid when l-THP was co-administered with CYP inhibitors, particularly with CYP3A4 and 2D6 inhibitors.

Comparison of the inhibitory effect of ketoconazole, voriconazole, fluconazole, and itraconazole on the pharmacokinetics of bosentan and its corresponding active metabolite hydroxy bosentan in rats

1. This study aimed to investigate the inhibitory effect of azole antifungal agents, including ketoconazole, voriconazole, fluconazole, and itraconazole, on the pharmacokinetics of bosentan (BOS) and its active metabolite hydroxy bosentan (OHBOS) in Sprague–Dawley (SD) rats.2. A total of 25 healthy male SD rats were divided into five groups and treated with various azole antifungal agents by gavage, followed by a single dose of BOS after 30 min.3. The study found that ketoconazole led to a significant increase (5.1-fold) in the AUC(0-t) of BOS, associated with a 5.8-fold elevation in the Cmax, which was greater than that for fluconazole (2.6- and 2.9-fold) and voriconazole (1.1- and 1.7-fold). Accordingly, the Vz/F and CLz/F of BOS reduced by 89.2% and 83.7%, respectively, on administering ketoconazole concomitantly. However, fluconazole caused a decrease in Vz/F and CLz/F by 77.4% and 72.2%, respectively, compared with voriconazole that exhibited a decrease in CLz/F by 51.7% with a negligible change in Vz/F. Also, obvious differences were observed in the pharmacokinetic parameters of OHBOS between the control and treated groups.4. Collectively, treatment with ketoconazole resulted in a prominent inhibitory effect on the metabolism of BOS, followed by treatment with fluconazole, voriconazole, and itraconazole. Therefore, these details of animal studies may help draw more attention to the safety of BOS while combining it with ketoconazole, voriconazole, fluconazole, or itraconazole clinically.

Evaluation of Ketoconazole and Its Alternative Clinical CYP3A4/5 Inhibitors as Inhibitors of Drug Transporters: The In Vitro Effects of Ketoconazole, Ritonavir, Clarithromycin, and Itraconazole on 13 Clinically-Relevant Drug Transporters.

Ketoconazole is a potent CYP3A4/5 inhibitor and, until recently, recommended by the Food and Drug Administration (FDA) and the European Medicines Agency as a strong CYP3A4/5 inhibitor in clinical drug-drug interaction (DDI) studies. Ketoconazole sporadically causes liver injury or adrenal insufficiency. Because of this, the FDA and European Medicines Agency recommended suspension of ketoconazole use in DDI studies in 2013. The FDA specifically recommended use of clarithromycin or itraconazole as alternative strong CYP3A4/5 inhibitors in clinical DDI studies, but many investigators have also used ritonavir as an alternative. Although the effects of these clinical CYP3A4/5 inhibitors on other CYPs are largely established, reports on the effects on the broad range of drug transporter activities are sparse. In this study, the inhibitory effects of ketoconazole, clarithromycin, ritonavir, and itraconazole (and its CYP3A4-inhibitory metabolites, hydroxy-, keto-, and N-desalkyl itraconazole) toward 13 drug transporters (OATP1B1, OATP1B3, OAT1, OAT3, OCT1, OCT2, MATE1, MATE2-K, P-gp, BCRP, MRP2, MRP3, and BSEP) were systematically assessed in transporter-expressing HEK-293 cell lines or membrane vesicles. In vitro findings were translated into clinical context with the basic static model approaches outlined by the FDA in its 2012 draft guidance on DDIs. The results indicate that, like ketoconazole, the alternative clinical CYP3A4/5 inhibitors ritonavir, clarithromycin, and itraconazole each have unique transporter inhibition profiles. None of the alternatives to ketoconazole provided a clean inhibition profile toward the 13 drug transporters evaluated. The results provide guidance for the selection of clinical CYP3A4/5 inhibitors when transporters are potentially involved in a victim drug's pharmacokinetics.

Inhibitory effect of ketoconazole and voriconazole on the pharmacokinetics of carvedilol in rats

The aim of this study was to investigate the effect of orally administered ketoconazole and voriconazole on the pharmacokinetics of carvedilol and its metabolites in rats. Fifteen healthy male Sprague–Dawley (SD) rats were randomly divided into three groups: A group (30 mg/kg ketoconazole), B group (30 mg/kg voriconazole) and C group (control group). A single dose of carvedilol was administered orally 30 min after administration of ketoconazole and voriconazole. Carvedilol and its metabolites plasma levels were measured by ultra-high performance liquid chromatography-mass spectrometry method (UPLC–MS/MS), and pharmacokinetic parameters were calculated by DAS 3.0 software. The co-administrated with ketoconazole could significantly increase the maximal plasma concentration (Cmax) and area under the curve (AUC) of carvedilol (p < 0.01). And the Cmax of its three metabolites 4′-hydroxyphenyl carvedilol (4′-HPC), 5′-hydroxyphenyl carvedilol (5′-HPC) and o-desmethyl carvedilol (o-DMC) decreased drastically by 39.4% (p < 0.01), 45.0% (p < 0.01) and 40.8% (p < 0.05), respectively. Following co-administered with voriconazole, Tmax of carvedilol and o-DMC increased, and the Cmax of 5′-HPC decreased by 27.7% (p < 0.05), while other drugs pharmacokinetic parameters performed no significant differences. Therefore, in clinical, when carvedilol was co-administrated with ketoconazole, dose adjustment of carvedilol should be taken into account.

Inhibitory Effect of Ketoconazole on the Pharmacokinetics of a Multireceptor Tyrosine Kinase Inhibitor BMS‐690514 in Healthy Participants: Assessing the Mechanism of the Interaction With Physiologically‐Based Pharmacokinetic Simulations

BMS-690514, a selective inhibitor of the ErbB and vascular endothelial growth factor receptors, has shown antitumor activity in early clinical development. The compound is metabolized by multiple enzymes, with CYP3A4 responsible for the largest fraction (34%) of metabolism. It is also a substrate of P-glycoprotein (P-gp) in vitro. To assess the effect of ketoconazole on BMS-690514 pharmacokinetics, 17 healthy volunteers received 200 mg BMS-690514 alone followed by 100 mg BMS-690514 with ketoconazole (400 mg once daily for 4 days). The AUC(∞) of 100 mg BMS-690514 concomitantly administered with ketoconazole was similar to that of 200 mg BMS-690514 alone. The dose-normalized C(max) and AUC(∞) of BMS-690514 from the 100-mg BMS-690514/400-mg ketoconazole treatment increased by 55% and 127%, respectively, relative to those from 200 mg BMS-690514 alone. Prediction of the drug-drug interaction (DDI) using a population-based simulator (Simcyp) indicated that, in addition to CYP3A4 inhibition, the inhibition of P-gp by ketoconazole in the intestine, liver, and kidneys must be invoked to fully account for the DDI observed. This finding suggests that the inhibition of P-gp by ketoconazole, along with its effect on CYP3A4, needs to be considered when designing a DDI study of ketoconazole with a victim drug that is a dual substrate.

Impact of nonlinear midazolam pharmacokinetics on the magnitude of the midazolam-ketoconazole interaction in rats

Numerous groups have described the rat as an in vivo model for the assessment and prediction of drug–drug interactions (DDIs) in humans involving the inhibition of cytochrome P450 3A forms. Even for a well-established substrate-inhibitor pair like midazolam-ketoconazole, however, the magnitude of the DDI in rats (e.g. 1.5- to 5-fold) does not relate to what is observed clinically (e.g. 5- to 16-fold).Because nonlinear substrate pharmacokinetics (PK) may result in a weaker interaction, it was hypothesized that the lower magnitude of interaction observed in rats was due to the saturation of metabolic pathway(s) of midazolam at the doses used (10–20 mg/kg). Therefore, the inhibitory effects of ketoconazole were reevaluated at lower oral (1 and 5 mg/kg) and intravenous (IV) (1 mg/kg) doses of midazolam.In support of the hypothesis, oral exposure at 5 mg/kg dose of midazolam was 18-fold higher compared to that at 1 mg/kg. Furthermore, when the interaction was investigated at the lower midazolam dose (1 mg/kg), ketoconazole increased the IV and oral exposure of midazolam by 7-fold and 11-fold, respectively. A weaker DDI (1.5- to 1.8-fold) was observed at the higher oral midazolam dose.Collectively, these results suggest that the lower reported interaction in rats is likely due to saturation of midazolam clearance at the doses used. Therefore, when the rat is used as a DDI model to screen and differentiate compounds, or predict CYP3A inhibition in humans, it is important to use low doses of midazolam and ensure linear PK.

Auto-inhibition of verapamil metabolism in rat hepatocytes of gel entrapment culture

Mechanism-based inactivation (MBI) of cytochrome P450 (CYP) 3A by verapamil and the resulting drug-drug interactions have been studied in vitro, but the inhibition of verapamil on its own metabolic clearance in clinic, namely auto-inhibition of verapamil metabolism, has never been reproduced in vitro. This paper aimed to evaluate the utility of gel entrapped rat hepatocytes in reflecting such metabolic auto-inhibition using hepatocyte monolayer as a control. Despite being a similar concentration- and time-dependent profile, auto-inhibition of verapamil metabolism showed apparent distinctions between the two culture models. Firstly, gel entrapped hepatocytes were more sensitive to such inhibition, which could be largely due to their higher CYP3A activity detected by the formation rates of 6β-hydroxy testosterone and 1’-hydroxy midazolam. Furthermore, the inhibitory effect of ketoconazole and verapamil on CYP 3A activity as well as the reduction of verapamil intrinsic clearance ( CL int ) by ketoconazole was only observed in gel-entrapped hepatocytes. In this respect, the involvement of CYP3A in auto-inhibition of verapamil metabolism could be illustrated in gel-entrapped hepatocytes but not in hepatocyte monolayer. All of these results indicated that hepatocytes of gel entrapment reflected more of verapamil metabolic auto-inhibition than hepatocyte monolayer and could serve as a suitable system for investigating drug metabolism.

Prednisone reduces ketoconazole-induced skeletal defects in rat fetuses

Ketoconazole (KT) is a broad-spectrum antifungal agent whose pharmacological activity is based on the capability to interfere with steroid biosynthesis through an interaction with fungal cytochrome P-450 enzymes and thereby avoiding the formation of fungal walls. As the inhibition of fungal cytochrome P-450 by KT is not specific, the mammalian cytochrome P-450 species, which play an important role in the biosynthesis of steroidogenesis, are also affected. The reproductive and developmental toxicity of KT have been assessed. This antimycotic agent has been reported as embryotoxic and teratogenic when administered in high doses (80 mg/kg) to pregnant rats. The mechanisms by which KT exert teratogenic effects remains to be elucidated. When considering the potential inhibitory effect of KT on mammalian steroid biosynthesis as a possible responsible for the skeletal anomalies induced by this drug, this study aimed at determining whether steroid maternal supplementation may prevent the skeletal anomalies induced by KT. To test this hypothesis, maternal supplementation with prednisone (PRED) (0.1, 0.2 or 0.4 mg/kg) and 80 mg/kg of KT were administered to pregnant Wistar rats (n = 10) during organogenesis period. On gestational day 21, the dams were euthanized and examined for standard parameters of reproductive outcome. In summary, the results showed that PRED supplementation therapy may cause reductions in the incidence of KT-induced cranial and appendicular skeletal anomalies as well as cleft palate in the rat, being these results more consistent with 0.4 mg/kg of this drug. These results suggest an important role for glucocorticoids in KT-induced teratogenesis.

Inhibitory Effects of Ketoconazole, Cimetidine and Erythromycin on Hepatic CYP3A Activities in Cats

Inhibitory effects of ketoconazole (KTZ), cimetidine (CIM), and erythromycin (ERY) were examined on CYP3A activities. Midazolam 1'- and 4-hydroxylation (MDZ1'H and MDZ4H) were used to determine CYP3A activities in hepatic microsomes obtained from cats (n=4). The results showed that, all the examined drugs inhibited the reactions in a noncompetitive manner. The inhibitory constants (Ki) of KTZ were 2.80 +/- 0.70 and 115 +/- 28 microM for MDZ1'H and MDZ4H, respectively. Those of CIM were 3.13 and 3.27 mM and of ERY were 3.14 and 6.41 mM for MDZ1'H and MDZ4H, respectively. Mechanism-based inhibition was also examined in this study. KTZ significantly reduced MDZ reactions in a time-dependent manner; while CIM and ERY did not. Also, the effects of KTZ and CIM on the pharmacokinetics of quinidine (QUN) were studied. KTZ or CIM (10 mg/kg/day, for one week) was given orally to cats (n=5). QUN (2 mg/kg, i. v.) was injected 2 hr after the last dose of KTZ or CIM. The analysis of the obtained pharmacokinetic parameters showed that, KTZ significantly reduced total body clearance of QUN by 35%, while CIM did not. These results suggest that, KTZ inhibits CYP3A activities (both in vitro and in vivo), but CIM does not. In clinical practice, therefore, KTZ may result in inhibition based drug-drug interaction with CYP3A substrates in cat patients, whereas CIM and ERY are unlikely to lead to interaction involving CYP3A substrates.

The metabolism of amiodarone by various CYP isoenzymes of human and rat, and the inhibitory influence of ketoconazole

To evaluate the metabolism of amiodarone (AM) to desethylamiodarone (DEA) by selected human and rat cytochrome P450, and the inhibitory effect of ketoconazole (KTZ). Some important CYP isoenzymes (rat CYP1A1, 1A2, 2C6, 2C11, 2D1, 2D2, and 3A1 and human CYP1A1, 1A2, 2D6 and 3A4) were spiked with various concentrations of AM to determine the relative kinetic parameters for formation of DEA in the presence and absence of various concentrations of KTZ. The formation of DEA was observed when AM was exposed to each of the CYP tested, although the rates were varied. Human CYP1A1 followed by 3A4 had the highest intrinsic clearance (CLint) for DEA formation whereas in rat, CYP2D1 followed by CYP2C11 had the highest CLint. Human and rat CYP1A2 seemed to have the lowest CLint. At high concentrations of AM and KTZ, near those expected in vivo, significant inhibition of all isoforms except for rat CYP1A2 was observed. At lower concentration ranges of both drugs, the inhibitory constant was determined. At these levels, KTZ was found to potently inhibit human CYP1A1 and 3A4 and rat 2D2 and 1A1. Human CYP1A1 and 3A4 and rat CYP2D1 and 2C11 were most efficient in converting AM to DEA. For DEA formation, the in vivo administration of KTZ could inhibit other CYP isoforms besides CYP3A in human and rat.

MDR- and CYP3A4-Mediated Drug–Drug Interactions

P-glycoprotein (P-gp), multiple drug resistance associated proteins (MRPs), and cytochrome P450 3A4 together constitute a highly efficient barrier for many orally absorbed drugs. Multidrug regimens and corresponding drug-drug interactions are known to cause many adverse drug reactions and treatment failures. Available literature, clinical reports, and in vitro studies from our laboratory indicate that many drugs are substrates for both P-gp and CYP3A4. Our primary hypothesis is that transport and metabolism of protease inhibitors (PIs) and NNRTIs will be altered when administered in combination with azole antifungals, macrolide, fluroquinolone antibiotics, statins, cardiovascular agents, immune modulators, and recreational drugs [benzodiazepines, cocaine, lysergic acid dithylamide (LSD), marijuana, amphetamine (Meth), 3,4-methylenedioxymethamphetamine (MDMA), and opiates] due to efflux, and/or metabolism at cellular targets. Therefore, such drug combinations could be a reason for the unexpected and unexplainable therapeutic outcomes. A number of clinical reports on drug interaction between PIs and other classes (macrolide antibiotics, azole antifungals, cholesterol lowering statins, cardiovascular medicines, and immunomodulators) are discussed in this article. MDCKII-MDR1 was employed as an in vitro model to evaluate the effects of antiretrovirals, azole antifungals, macrolide, and fluroquinolone antibiotics on efflux transporters. Ketoconazole (50 muM) enhanced the intracellular concentration of (3)H ritonavir. The inhibitory effects of ketoconazole and MK 571 on the efflux of (3)H ritonavir were comparable. An additive effect was observed with simultaneous incorporation of ketoconazole and MK 571. Results of (3)H ritonavir uptake studies were confirmed with transcellular transport studies. Several fluroquinolones were also evaluated on P-gp-mediated efflux of (3)H cyclosporin and 14C erythromycin. These in vitro studies indicate that grepafloxacin, levofloxacin, and sparfloxacin are potent inhibitors of P-gp-mediated efflux of 14C erythromycin and (3)H cyclosporin. Simultaneous administration of fluoroquinolones and macrolides could minimize the efflux and metabolism of both of the drugs. Effects of erythromycin and ketoconazole on carbamazepine metabolism were examined. Formation of 10,11-epoxy carbamazepine, a major CBZ metabolite, was significantly inhibited by these agents. Therefore, drug efflux proteins (P-gp, MRPs) and metabolizing enzyme (CYP450) are major factors in drug interactions. Overlapping substrate specificities of these proteins result in complex and sometimes perplexing pharmacokinetic profiles of multidrug regimens. Drug-drug interactions with PIs and other coadministered agents for human immunodeficiency virus (HIV) positive population have been discussed in light of efflux transporters and metabolizing enzymes. This article provides an insight into low and variable oral bioavailability and related complications leading to loss of therapeutic activity of MDR and CYP 450 substrates.

Studies on the Interactions between Drugs and Estrogen: Analytical Method for Prediction System of Gynecomastia Induced by Drugs on the Inhibitory Metabolism of Estradiol Using Escherichia coli Coexpressing Human CYP3A4 with Human NADPH-Cytochrome P450 Reductase

To establish a prediction system for drug-induced gynecomastia in clinical fields, a model reaction system was developed to explain numerically this side effect. The principle is based on the assumption that 50% inhibition concentration (IC50) of drugs on the in vitro metabolism of estradiol (E2) to its major product 2-hydroxyestradiol (2-OH-E2) can be regarded as the index for achieving this purpose. By using human cytochrome P450s coexpressed with human NADPH-cytochrome P450 reductase in Escherichia coli as the enzyme, the reaction was examined. Among the nine enzymes (CYP1A1, 1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4) tested, CYP3A4 having a Vmax/Km (ml/min/nmol P450) value of 0.32 for production of 2-OH-E2 was shown to be the most suitable enzyme as the reagent. The inhibitory effects of ketoconazole, cyclosporin A, and cimetidine toward the 2-hydroxylation of E2 catalyzed by CYP3A4 were obtained, and their IC50 values were 7 nM, 64 nM, and 290 μM, respectively. The present results suggest that IC50 values thus obtained can be substituted as the prediction index for gynecomastia induced by drugs, considering the patients' individual information.

Zolpidem metabolism in vitro: responsible cytochromes, chemical inhibitors, and in vivo correlations.

To determine the human cytochromes mediating biotransformation of the imidazopyridine hypnotic, zolpidem, and the clinical correlates of the findings. Kinetic properties of zolpidem biotransformation to its three hydroxylated metabolites were studied in vitro using human liver microsomes and heterologously expressed individual human cytochromes. The metabolic product termed M-3 accounted for more than 80% of net intrinsic clearance by liver microsomes in vitro. Microsomes containing human cytochromes CYP1A2, 2C9, 2C19, 2D6, and 3 A4 expressed by cDNA-transfected human lymphoblastoid cells mediated zolpidem metabolism in vitro. The kinetic profile for zolpidem metabolite formation by each individual cytochrome was combined with estimated relative abundances based on immunological quantification, yielding projected contributions to net intrinsic clearance of: 61% for 3 A4, 22% for 2C9, 14% for 1A2, and less than 3% for 2D6 and 2C19. These values were consistent with inhibitory effects of ketoconazole and sulfaphenazole on zolpidem biotransformation by liver microsomes. Ketoconazole had a 50% inhibitory concentration (IC50 ) of 0.61 microm vs formation of the M-3 metabolite of zolpidem in vitro; in a clinical study, ketoconazole coadministration reduced zolpidem oral clearance by approximately 40%, somewhat less than anticipated based on the IC50 value and total plasma ketoconazole levels, but much more than predicted based on unbound plasma ketoconazole levels. The incomplete dependence of zolpidem clearance on CYP3A activity has clinical implications for susceptibility to metabolic inhibition.

Effects of ketoconazole on the iodide uptake by FRTL-5 cells.

Ketoconazole is an imidazole derivative used as an antimycotic agent with reported effects on the endocrine system, but very little is known about its possible actions on thyroid function. Our purpose was to study the influence of this substance on the basal and TSH-stimulated iodide uptake in the rat thyroid cell strain FRTL-5. Ketoconazole (1-50 mumol/l) was shown to slightly increase the basal iodide uptake but, at higher concentrations (75-100 mumol/l), it sharply decreased iodide uptake below the basal levels. When the cells were cultured under bTSH stimulation (30 UI/l), the inhibitory effect of ketoconazole was exerted at concentrations as low as 25 mumol/l. This inhibition was observed even if it was added to the culture medium immediately before the Na125I addition. Forskolin, a stimulator of adenylate cyclase activity, was unable to prevent the iodide uptake inhibition. Low doses of ketoconazole increased cAMP concentrations. In the presence of TSH this effect was more evident in an inverse dose-dependent way. Because of its dual action, it can be assumed that ketoconazole could influence the iodide uptake in the FRTL-5 cells through more than one mechanism.

Effect of ketoconazole on steroidogenic human granulosa-luteal cells in culture

Ketoconazole (KCZ), a widely used antifungal drug, has been reported in humans to inhibit adrenal and testicular steroidogenesis by interfering with the cytochrome p-450-dependent enzymes. The purpose of this study was to investigate the drug effect on steroidogenic human granulosa-luteal cells, obtained by follicular aspiration from mature follicles of gonadotropin-treated women. Cells were cultured in long-term monolayers, and the steroid production was assayed by radioimmunoassay. A profound inhibition of ovarian cell secretion of progesterone (P), testosterone (T) and estradiol was found. At a low concentration (5 μg/ml), KCZ failed to inhibit the conversion of pregnenolone to P, mediated by the non-cytochrome 3β-hydroxysteroid dehydrogenase-isomerase enzyme (3β-HSDH). At a similar concentration, P secretion by human chorionic gonadotropin (hCG; 100 mIU/ml) -treated cells was decreased by 68% ( P < 0.001) and therefore, an inhibitory effect of KCZ on the cholesterol side-chain cleavage enzyme ( P-450 scc) was assumed. A similar marked inhibitory effect (81%) ( P < 0.001) on T secretion was observed for hCG-stimulated cells given pregnenolone as substrate. The P-450 aromatase was profoundly inhibited (86%) ( P < 0.001) in a reversible manner, by a similar concentration (5 μg/ml) of KCZ. These findings suggest that KCZ has the capability to suppress human ovarian steroidogenesis similarly as in testis and adrenal.

ブタ精巣ミクロソームに存在する△16-C19-ステロイド合成活性及び17α-ヒドロキシラーゼ/リアーゼ活性に及ぼすKetoconazole及び各種ステロイドの阻害効果

ブタ精巣ミクロソームに存在する△<SUP>16</SUP>-C<SUB>19</SUB>-ステロイド合成活性及び17α-ヒドロキシラーゼ/リアーゼ活性に及ぼすKetoconazole及び各種ステロイドの阻害効果

Interaction of azole antifungal agents with cytochrome P-450 14DM purified from Saccharomyces cerevisiae microsomes

Mechanism of action of azole antifungal agents was studied by analyzing interaction of ketoconazole, itraconazole, triadimefon and triadimenol with a purified yeast cytochrome P-450 which catalyzes lanosterol 14α-demethylation (P-450 14DM). These antifungal agents formed low-spin complexes with P-450 14DM, indicating the interaction of their azole nitrogens with the heme iron. Affinity of these antifungal agents for the cytochrome was extremely high compared with usual nitrogenous ligands. Upon reduction with sodium dithionite, the azole complexes of ferric P-450 14DM were converted to the corresponding ferrous derivatives. Spectral analysis of these complexes suggested that geometric orientation of the azole moiety of an antifungal agent to the ferrous heme iron was regulated by the interaction between the N-1 substituent and the heme environment. CO could not readily replace ketoconazole or itraconazole co-ordinating to the heme iron of ferrous P-450 14DM while triadimefon and triadimenol complexes of the cytochrome were promptly converted to the CO complexes. The inhibitory effects of ketoconazole and itraconazole on the P-450 14DM-dependent lanosterol 14α-demethylation were higher than that of triadimenfon. The substituents at N-1 of the azole moieties of ketoconazole and itraconazole are extremely large while those of triadimefon and triadimenol are relatively small. Accordingly, observations described above suggest that the N-1 substituent of an azole antifungal agent regulates the mobility of the molecule in the heme crevice of ferrous P-450 14DM and determines the inhibitory effect of the compound.

Inhibition of hyphal development in Trichophyton mentagrophytes arthroconidia by ketoconazole and miconazole.

In the presence of 0.5 mg/l ketoconazole and miconazole, arthroconidia from three isolates of Trichophyton mentagrophytes produced germ tubes, which continued to grow for 12 h before further elongation ceased. Lower concentrations reduced the rate of elongation, but did not halt the process. Higher concentrations had no greater effect than 0.5 mg/l. The inhibitory effect of ketoconazole was independent of time of addition of drug during the first six hours of germination. Ketoconazole inhibition was reversible after 12 h contact, whereas miconazole inhibition was not. Morphological effects of drug treatment were investigated by scanning electron microscopy. In the absence of imidazoles, hyphae were straight and regular; ketoconazole treated hyphae were short, irregular and branching; miconazole treatment produced extensive debris and spores forming within the hyphae were visible.