Pharmacokinetics of the triazole antifungal agent genaconazole in healthy men after oral and intravenous administration.

The pharmacokinetics of genaconazole, a potent new difluorophenyl-triazole antifungal agent, was studied in 12 healthy male volunteers following a single oral or intravenous administration of the drug. In a randomized two-way crossover design, each volunteer received either two 50-mg genaconazole tablets orally or a parenteral preparation containing 100 mg of genaconazole given as a 30-min intravenous infusion. Both dosage regimens were well tolerated. Blood and urine samples were collected up to 10 days after drug administration. Concentrations of genaconazole in plasma and urine were determined by a specific high-performance liquid chromatography assay with a limit of quantitation of 0.1 microgram/ml. Pharmacokinetic evaluation following oral and intravenous doses indicated that mean values for the area under the concentration-time curve from 0 h to infinity (137 and 136 micrograms.h/ml), half-life (50 and 49 h), volume of distribution (52 and 52 liters), and clearance (12 and 12 ml/min) were independent of the route of drug administration. The oral and intravenous administrations of genaconazole yielded virtually superimposable plasma concentration-time curves, resulting in an absolute bioavailability of 100%. Amounts of unchanged genaconazole found in urine samples from 0 to 240 h after oral and intravenous doses were comparable, and urinary excretion accounted for 76 and 78% of the administered dose, respectively. Renal clearances for the two routes of administration were also similar, and renal clearance accounted for over 80% of the total body clearance. The 100% absolute bioavailability of genaconazole regardless of the route of administration provides greater dosing flexibility in various clinical settings than currently exists.

Following excretion accounted for about 73 to 87% of the dose, primarily as the unchanged drug (9,16). There were no detectable metabolites in either serum or urine samples, indicating negligible biotransformation of genaconazole in men (9,14,16).
The objective of this two-way crossover study was to determine the absolute bioavailability (F) and pharmacokinetic profile of genaconazole following a 100-mg oral dose or intravenous infusion of genaconazole to healthy volunteers.
(This work was presented in part at the 30th Interscience Conference on Antimicrobial Agents and Chemotherapy, Atlanta, Ga., 1990.)

MATERIALS AND METHODS
Dose form. Tablets of genaconazole (50 mg) were manufactured at Schering-Plough Corporation (Kenilworth, N.J.). The intravenous-dose form was prepared in a two-vial system. The first glass vial contained 54 mg of genaconazole in 90 ml of hydrochloric acid (0.6 mg/ml, 0.015 N), and the second plastic vial contained 23 ml of 1 N sodium hydroxide. The contents of the vials were mixed together prior to dosing to provide 105 ml of deliverable volume containing 50 mg of the drug. The two-vial mixing system was necessary to provide up to 4 h of stability for the final injectable solution when stored between 15 and 30°C.
Study design. Twelve healthy male volunteers ranging in age from 19 to 37 years (mean, 28 years) and weighing 54 to 76 kg (mean, 70 kg) participated in this randomized, two-way crossover study. Each subject in the study was enrolled on the basis of his medical history, a physical examination, an electrocardiogram, and clinical laboratory tests (hematology, blood chemistries, and urinalysis). All subjects signed a written informedconsent form prior to study participation. The volunteers were confined to the clinical site 24 h prior to the start of each study phase. A light snack was served on the night before the drug administration, after which an overnight fast was maintained. In the morning, each volunteer received one of the two drug treatments as determined by a computergenerated random code: treatment A, two 50-mg genaconazole tablets administered with 120 ml of tap water, or treatment B, 210 ml of a solution containing 100 mg of genaconazole administered by intravenous infusion over a 30-min interval. A 3-week washout period separated the two phases of the crossover study. Seven milliliters of blood was drawn into heparinized Vacutainer tubes immediately prior to drug administration (0 h) and at 0.5, 1, 2, 4, 6,8,12,16,24,36,48,72,96,120,144,168,192,216, and 240 h after oral and intravenous administration so that concentrations of unchanged genaconazole in plasma could be determined. Blood samples were immediately centrifuged for 15 min, and the plasma was frozen at -20°C pending analysis. All subjects remained supine and refrained from eating until the 4-h blood sample was collected, after which a light lunch was served. Regular meals were resumed 8 h after dosing. All subjects were confined to the clinical site until the 240-h blood sample was collected.
Urine samples were collected immediately prior to drug administration (0 h) and then in blocks at 0 to 8, 8 to 16, and 16 to 24 h after dosing and every 24 h thereafter until 240 h after dosing. All volunteers were instructed to void at the end of the collection interval; urine samples collected during the collection period were refrigerated and subsequently pooled in each block sample. A 0.5-ml aliquot of each well-mixed block sample was stored frozen at -20°C pending analysis.
Analytical methods. Concentrations of genaconazole as the racemate in plasma were determined by a specific, sensitive, and reproducible high-performance liquid chromatography (HPLC) method with UV detection at 205 nm. The limit of quantitation (LOQ) was 0.1 ,ug/ml. A mixture of 0.5 ml of plasma and 0.08 ml of internal standard (800 ng of dextrophan per ml) was alkalinized by the addition of 0.1 ml of 4.5 M ammonium hydroxide, mixed well, and extracted with 4.0 ml of 30% methylene chloride in n-hexane. Following extraction for 10 min by shaking and 5 min of centrifugation (at 3,000 rpm), the organic layer was transferred into a clean tube and evaporated to dryness at 45 to 50°C. The residue was dissolved in 200 ,ul of mobile phase (15% acetonitrile and 1.6% tetrahydrofuran in 0.02 M monobasic potassium phosphate buffer); a 25to 50-,ul aliquot of this was injected onto the HPLC column (50 by 4.6 mm, C18), with the mobile-phase flow rate at 2.2 ml/min. Quantitation was performed with a calibration curve determined by the regression line defining the linear relationship between the peak-height ratio of the drug to the internal standard and the plasma standard concentrations (0.1 to 3.5 ,ug/ml). The interassay coefficients of variation (CV) at the LOQ (0.1 ,ig/ml) and the highest standard concentration (3.5 jig/ml) were 14.5 and 0.4%, respectively. Interassay variability for the four quality control samples (0.10 ,ug/ml, CV = 11.0%; 0.40 pug/ml, CV = 6.6%; 1.5 ,ug/ml, CV = 3.9%; and 3.26 ,ug/ml, CV = 2.0%) was within the acceptable range.
Drug concentrations in the urine samples were also determined by the HPLC method discussed above, and this entailed the direct injection of a suitable dilution (usually 1:5 in distilled water) of the sample onto the column. The CV at drug concentrations of 0.1 and 3.5 ,ug/ml were 9.1 and 1.7%, respectively, while the average interassay CV was 4.5%. Recently, a report on a slightly modified HPLC procedure for the determination of genaconazole concentrations in human serum (LOQ = 0.2 ,ug/ml) and urine (LOQ = 0.5 ,ug/ml) was published by our laboratories (7). Pharmacokinetic analysis. Concentrations of genaconazole (racemate) in plasma above the LOQ (0.1 jig/ml) were used for pharmacokinetic analysis using model-independent methods (6). For all subjects, the maximum concentration in plasma ache was common, occurring in all eight volunteers reporting adverse experiences. Other adverse experiences included nausea and heartburn. Thus, genaconazole (100 mg) administered orally and intravenously was safe and generally well tolerated.
The mean plasma concentration-time curves obtained following a 100-mg dose of genaconazole administered either orally or intravenously to 12 healthy volunteers are presented in Fig. 2. There was no apparent difference between the two treatments at any time point except during the first 2-h interval, during which concentrations of genaconazole in plasma were lower following oral administration than after intravenous infusion.
The mean values for the pharmacokinetic parameters of genaconazole (AUCtf, AUCG O, t112, V, and CL) following oral and intravenous administration were similar ( Table 1). The mean AUCO, following oral dosing was almost identical to that following intravenous infusion (137 and 136 ,ugh/ml, respectively), demonstrating an F of 100% (1.0) for genaconazole ( Table 2).
The mean values for the urinary excretion of genaconazole after oral and intravenous administrations for each collection interval over the 10-day study period are also listed in Table 2. An average of 76 or 78% of the dose was excreted in the urine as unchanged drug following either an oral or intravenous dose, respectively ( Table 2). Mean CLR values were also similar following both dosage regimens (-10 ml/min), with intersubject variabilities of 16 and 18% for the intravenous and oral routes, respectively.

DISCUSSION
The values for the pharmacokinetic parameters of genaconazole, a potent difluorophenyl-triazole antifungal agent, were shown to be similar for the oral and intravenous routes of administration. Mean plasma concentration-time profiles after oral and intravenous doses were superimposable. Mean values for the pharmacokinetic parameters (Table 1) were therefore shown to be independent of the route of administration.
Absorption of genaconazole after oral dosing was essentially complete, with an F value of 1.00 ± 0.08 (mean ± standard deviation) ( Table 2). This represents a clinically relevant improvement in F after oral dosing over ketoconazole (75%) and miconazole (<50%) (1,5). Other investigators have reported that gastric alkalinization can significantly decrease the absorption of triazole antifungal agents administered via the oral route; the F of ketoconazole decreased almost 50% at a gastric pH of 6.0 compared with a pH of .3, and therapeutic failures resulted (10,12).
In a separate clinical study with nine healthy male volunteers (8), concomitant administration of antacid (60 ml of Mylanta) or cimetidine (300 mg four times daily for 3 days followed by a single 300-mg dose on the fourth day) did not alter the F of genaconazole. This is clinically significant because of the increased gastric pH often observed in immunocompromised (AIDS) subjects, patients with relative achlorhydria, and those who may be receiving antacid and/or H2-antagonist treatment. The apparent V of genaconazole was approximately 0.75 liter/kg (Table 1), which indicated that the drug was moderately distributed throughout the body. This V value is comparable to the reported value for fluconazole of 0.7 + 0.6 liter/kg (mean + standard deviation) but in contrast to those for ketoconazole (0.1 to 0.3 liter/kg) and miconazole (2 to 3 liters/kg) (1,5).
Peak concentrations of genaconazole in plasma were achieved within 4 h of oral dosing; this was followed by a very slow terminal phase (t112 = 50 h), and as a result, concentrations of the drug in plasma could be detected 10 days after the administration of a single 100-mg dose. These values are consistent with the time to maximum concentration (3.3 h) and t1/2 (57 h) values obtained in our previous studies involving a single 100-mg oral dose of genaconazole in healthy male volunteers (9,16). The prolonged t1/2 of genaconazole gives it an advantage for once-daily or alternate-day dosing over ketoconazole and fluconazole, which have relatively short and intermediate terminal-phase tl/2 values of 8 h (1) and 22 to 36 h (5), respectively.
Urinary excretion of unchanged genaconazole accounted for 76 and 78% of the administered doses after oral and intravenous administrations, respectively, which was consistent with our previous finding in men (9,16). In addition, CLR following oral and intravenous dosing (10 ml/min [ Table 2]) accounted for more than 80% of the total body CL (12 ml/min [ Table 1]). Therefore, urinary excretion of the unchanged drug and not systemic biotransformation was responsible for most of the elimination of genaconazole in humans. Since renal excretion of the unchanged drug is the main elimination pathway for this compound, dosage adjustment may be needed in patients with renal insufficiency. This was also the case for fluconazole (5) but not for ketoconazole or miconazole (1) because of their shorter elimination tl/2.
In comparison with other antifungal agents such as ketoconazole and miconazole which undergo 95 and 50% biotransformation (1), respectively, genaconazole undergoes negligible biotransformation in men (11,13,16). Therefore, drug-drug interactions of concurrently prescribed medications are expected to be minimal.
Genaconazole is a potent new N-substituted difluorophenyltriazole, broad-spectrum antifungal agent which exhibits complete absorption after oral administration, a prolonged terminal-phase elimination t12, and negligible biotransformation in humans. The compound represents a therapeutic advantage over other available antifungal agents for the treatment of fungal infections because of its superior clinical efficacy and pharmacokinetic profile. Oral and intravenous administrations of the drug result in nearly identical concentration profiles of the drug in plasma, providing greater dosing flexibility in various clinical situations.