Stereospecific metabolism of itraconazole by CYP3A4: dioxolane ring scission of azole antifungals.

Itraconazole (ITZ) is a mixture of four cis-stereoisomers that inhibit CYP3A4 potently and coordinate CYP3A4 heme via the triazole nitrogen. However, (2R,4S,2'R)-ITZ and (2R,4S,2'S)-ITZ also undergo stereoselective sequential metabolism by CYP3A4 at a site distant from the triazole ring to 3'-OH-ITZ, keto-ITZ, and N-desalkyl-ITZ. This stereoselective metabolism demonstrates specific interactions of ITZ within the CYP3A4 active site. To further investigate this process, the binding and metabolism of the four trans-ITZ stereoisomers by CYP3A4 were characterized. All four trans-ITZ stereoisomers were tight binding inhibitors of CYP3A4-mediated midazolam hydroxylation (IC(50) 16-26 nM), and each gave a type II spectrum upon binding to CYP3A4. However, instead of formation of 3'-OH-ITZ, they were oxidized at the dioxolane ring, leading to ring scission and formation of two new metabolites of ITZ. These two metabolites were also formed from the four cis-ITZ stereoisomers, although not as efficiently. The catalytic rates of dioxolane ring scission were similar to the dissociation rates of ITZ stereoisomers from CYP3A4, suggesting that the heme iron is reduced while the triazole moiety coordinates to it and no dissociation of ITZ is necessary before catalysis. The triazole containing metabolite [1-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl)ethanone] also inhibited CYP3A4 (IC(50) >15 µM) and showed type II binding with CYP3A4. The dioxolane ring scission appears to be clinically relevant because this metabolite was detected in urine samples from subjects that had been administered the mixture of cis-ITZ isomers. These data suggest that the dioxolane ring scission is a metabolic pathway for drugs that contain this moiety.

Pharmacokinetic interaction of ketoconazole and itraconazole with ciprofloxacin.

The effect of the concomitant administration of the antifungal drugs ketoconazole (KTC) and itraconazole (ITC) on the pharmacokinetics of ciprofloxacin (CIP) following short- and long-term administration in mice was investigated. Animals received either a dose of CIP (20 mg/kg, i.p.), CIP (20 mg/kg, i.p.) together with KTC (50 mg/kg, p.o.) or CIP (20 mg/kg, i.p.) and ITC (30 mg/kg, p.o.). The same treatments were repeated for 7 days. Blood samples were collected up to 4 h following drug administration and two urine samples were collected at 2 h and 4 h after drug administration. CIP plasma concentrations were significantly higher in KTC- and ITC-treated groups compared with the corresponding control groups. The concomitant administration of KTC or ITC with CIP also significantly (p<0.05) increased C(max), t(1/2), MRT and AUC(0-infinity) with no change in T(max). CIP clearance was significantly reduced by both agents. KTC and ITC reduced CIP urinary excretion. This study suggests that an important pharmacokinetic interaction between CIP and KTC or ITC is likely to occur when either of the two antifungal drugs is administered concomitantly with CIP. The results may suggest possible reductions in total clearance of CIP, owing to inhibition of its renal tubular excretion by KTC and ITC.

Effect of food on the pharmacokinetics of a new hydroxypropyl-beta-cyclodextrin formulation of itraconazole.

STUDY OBJECTIVE: To compare the pharmacokinetics of a single 100-mg oral dose of itraconazole administered as 10 ml of a 10-mg/ml itraconazole solution in hydroxypropyl-beta-cyclodextrin under fasting versus postprandial conditions. DESIGN: Open-label, two-way, randomized, crossover study. SETTING: Janssen Research Foundation, Belgium. PATIENTS: Twelve healthy volunteers. INTERVENTIONS: Blood samples were obtained for pharmacokinetic analyses immediately before dosing and at regular intervals up to 96 hours after each dose. Blood and urine samples were obtained for hematologic, biochemical, and urinary safety analyses at baseline and at the end of the study. MEASUREMENTS AND MAIN RESULTS: The mean peak plasma concentrations of both itraconazole and its active metabolite hydroxy-itraconazole were significantly higher under fasting conditions than under postprandial conditions. The mean times to peak concentration for both the parent compound and its metabolite were significantly shorter under fasting than under nonfasting conditions. The mean areas under the curve (AUC0-infinity and AUC0-24 hrs) were also significantly higher under fasting than under postprandial conditions. CONCLUSIONS: Our findings suggest that the higher bioavailability of this new formulation of itraconazole may be of benefit in seriously ill patients who are not able to ingest adequate quantities of food. The fact that the solution was also well tolerated and was not associated with clinically significant changes in any laboratory value further underscores the potential utility of this dosing form.