Voriconazole, a novel wide-spectrum triazole: oral pharmacokinetics and safety

Abstract

Aims

Voriconazole is a potent new triazole with broad-spectrum antifungal activity against clinically significant and emerging pathogens. The present study evaluated the safety, toleration, and pharmacokinetics of oral voriconazole after single and multiple dosing.

Methods

Sixty-four healthy subjects were randomized to receive treatment and 56 completed the study. Groups of eight subjects each received voriconazole doses of 2 mg kg⁻¹ twice daily, 4 mg kg⁻¹ once daily, 2 mg kg⁻¹ three times daily, or 3 mg kg⁻¹ twice daily. Eleven subjects received 1.5 mg kg⁻¹ three times daily, and 21 subjects were administered placebo.

Results

Voriconazole exhibited nonlinear (dose- and time-dependent) pharmacokinetics. This deviation from linear pharmacokinetics was confirmed by linearity ratios of >1 and decreasing k_el values on multiple dosing, with a consequent increase in the terminal phase t_1/2. There was also notable intersubject variability in C_max and AUC_τ. The absorption of voriconazole was rapid (mean t_max = 0.9–1.7 h) after single and multiple dosing and the decline in plasma concentration–time curves after t_max was generally biphasic. By day 12, the C_max, AUC_τ, t_max, and t_1/2 values for the 3 mg kg⁻¹ twice-daily group were 2356 ng ml⁻¹, 11 170 ng·h ml⁻¹, 1.1 h, and 6.4 h, respectively. The observed accumulation of voriconazole after multiple dosing was greater than predicted from single-dose data. Accumulation ratios for C_max and AUC_τ, which were 1.97 and 3.55, respectively, for the group given voriconazole 3 mg kg⁻¹ twice daily, varied between treatment groups and appeared to be influenced by total daily dose and the frequency and duration of dosing. Visual inspection of C_min values together with statistical analyses of C_max and AUC_τ values suggest that steady-state levels were achieved by the fifth to sixth day of multiple dosing. Plasma concentrations of voriconazole were well above the minimum inhibitory concentrations (MICs) for Aspergillus spp., Candida spp., and for most emerging fungal pathogens (C_min > 0.8 µg ml⁻¹). Voriconazole was well tolerated: most treatment-related adverse events (abnormal vision, headache, dizziness) were mild and resolved within an hour of dosing.

Conclusions

The oral dosing regimen selected for subsequent Phase II/III clinical trials on the basis of these results was 200 mg twice daily, equivalent to 3 mg kg⁻¹ twice daily.

Introduction

Life-threatening opportunistic fungal infections are becoming an increasingly important clinical problem in patients who are severely immunocompromised due to cancer chemotherapy, organ or bone marrow transplantation, acquired immune deficiency syndrome (AIDS) or long-term antibiotic therapy [1–3]. Candida spp. (particularly C. albicans) and Aspergillus spp. are the most common organisms causing potentially fatal, secondary fungal infections in severely immunocompromised patients [4–6]. However, an increasingly divergent range of fungi, including Scedosporium and Fusarium spp., have emerged as clinically important pathogens in these patients [7–10]. Infections with these species are often refractory to conventional antifungal therapies, including amphotericin B and azole derivatives, such as ketoconazole, itraconazole, and fluconazole [11–13].

Amphotericin B has been the gold standard for the treatment of life-threatening opportunistic infections for many years. However, mortality rates in some patients with Aspergillus infection have been reported to be as high as 75–100%, despite amphotericin B therapy [14]. Furthermore, intravenous infusion of amphotericin B can result in side-effects such as fever, nausea, and renal toxicity [15, 16]. Although lipid formulations appear to be better tolerated than conventional amphotericin B, their use can be limited by cost considerations [17], and dosing recommendations have yet to be finalized [18].

Itraconazole has been used successfully to treat invasive aspergillosis in immunocompromised patients [19–23]. However, variable absorption following oral administration limits the utility of itraconazole in many patients, and low serum itraconazole concentrations have been correlated with treatment failure and poor outcome [19, 20]. Intravenous formulations of itraconazole, which result in improved bioavailability, are regarded as at least as effective as conventional amphotericin B [17], although direct clinical data comparing these agents are lacking [24].

The older azole antifungal agents, such as ketoconazole, fluconazole, and miconazole, are effective against many pathogenic fungi, but have only limited activity against Aspergillus spp. [25, 26]. Moreover, ketoconazole also has the potential to cause hepatotoxicity [27, 28].

Voriconazole is a new triazole antifungal agent, developed as oral and intravenous formulations, with potent activity against a wide spectrum of clinically significant pathogens, including Aspergillus and Candida spp. [29–31], and emerging fungal pathogens, such as Scedosporium and Fusarium spp. [32, 33].

The objectives of this study were to evaluate the safety, toleration, pharmacokinetics, and dose proportionality of voriconazole after single and multiple oral dose adminis-tration to healthy male volunteers. The doses of 2 mg kg⁻¹ twice daily, 4 mg kg⁻¹ once daily, 1.5 mg kg⁻¹ three times daily, 2 mg kg⁻¹ three times daily, and 3 mg kg⁻¹ twice daily were selected to identify the most appropriate dosing regimen with which to evaluate voriconazole in subsequent Phase II/III clinical trials.

Methods

Study subjects

Healthy male volunteers aged 18–45 years, weighing 60–94 kg, with a body mass index of between 18 and 25 according to Quetelet's index [weight(kg)/height²(m)] were eligible for inclusion in this study. Volunteers were excluded if they had laboratory or physical abnormalities, or a history of clinically significant allergies, especially to medical treatments.

Study design

This single-blind, multiple-dose, placebo-controlled, parallel-group, dose-finding study was conducted according to a study protocol approved by an independent review board at the study site (Besselaar Clinical Research Unit, Leeds, UK).

Five groups of 12 healthy men were randomized to receive either oral voriconazole at doses up to 6 mg kg⁻¹ day⁻¹ (i.e. 2 mg kg⁻¹ twice daily, 1.5 mg kg⁻¹ three times daily, 2 mg kg⁻¹three times daily, 3 mg kg⁻¹twice daily, 4 mg kg⁻¹ once daily) or placebo (active : placebo ratio 2 : 1) for 10 days. Subjects received a single dose at approximately 08.00 hours on day 1. On days 3–11 the twice-daily dose regimen was administered at approximately 08.00 and 20.00 hours and the three-times daily dose regimen was administered at approximately 08.00, 16.00 and 24.00 hours. A final dose was given at 08.00 hours on day 12. The dosage regimen for each treatment group is shown in Table 1.

Table 1.

Dosing regimens – subjects received either active drug in the regimens shown or matched placebo (active : placebo ratio 2 : 1).

Treatment group	Day 1	Days 3–11	Day 12
1	1.5 mg kg−1 once daily	1.5 mg kg−1 three-times daily	1.5 mg kg−1 once daily
2	2 mg kg−1 once daily	2 mg kg−1 three-times daily	2 mg kg−1 once daily
3	3 mg kg−1 once daily	3 mg kg−1 twice daily	3 mg kg−1 once daily
4	2 mg kg−1 once daily	2 mg kg−1 twice daily	2 mg kg−1 once daily
5	4 mg kg−1 once daily	4 mg kg−1 once daily	4 mg kg−1 once daily

Pharmacokinetic sampling

Venous blood samples (sufficient to provide 3 ml plasma) were collected by repeated venepuncture or via an indwelling cannula, and transferred into heparinized tubes. On day 1, these were collected immediately before dosing, at frequent intervals for up to 12 h post morning dose, and at 18, 24, 32, and 48 h. On day 12, plasma samples were taken at comparable times to day 1 with additional samples collected at 28 and 40 h following the morning dose in all groups. Frequent samples were collected up to 12 h following the morning dose on days 3 and 7 (Groups 1–3) and days 5 and 8 (Groups 4 and 5). Samples were also collected at 18 and 24 h from subjects in Group 5 (days 5 and 8). On days 4–11 (Groups 1–3) and days 3–11 (Groups 4 and 5) blood samples were additionally collected prior to the morning dose.

Blood samples were centrifuged at 1500 g for 10–15 min at 4 °C within 30 min of collection. Prior to analysis, the plasma samples were stored in screw-capped polypropylene tubes at −20 °C.

Voriconazole assay

Plasma samples were assayed using a previously validated high-performance liquid chromatography assay with UV detection [34]. The lower limit of quantification was 10 ng ml⁻¹and the calibration range was 10–3000 ng ml⁻¹. Where samples had a concentration of >3000 ng ml⁻¹, a 0.2-ml sample was diluted with 0.5 ml of blank human plasma. Nine calibration standards covering the range 10–3000 ng ml⁻¹ and six quality control samples were analysed daily with the samples. The samples were randomized in each run.

Safety assessments

All adverse events that occurred during treatment or up to 7 days after treatment were recorded. Where possible, information on the severity, time of onset and duration of adverse events was recorded, together with the investigator's assessment of their relationship to treatment. Investigators were also requested to report any serious adverse events occurring up to 30 days after the end of the study.

Routine clinical laboratory tests, haematology, clinical chemistry, and urinalysis were performed on samples taken at screening and at the following time points; 0 (predose), 24 and 48 h postdose on day 1; 0 (premorning dose) on day 7; 0 (predose), 24 and 48 h postdose on day 12.

Measurements of vital signs (supine and standing systolic and diastolic blood pressure and pulse rate) and a 12-lead electrocardiogram (ECG) were performed at screening, before administration, and at regular intervals throughout the study. In addition, a 24-h Holter recording was performed at screening, and starting 30 min before administration of the morning dose on days 1, 7, and 12.

Pharmacokinetic parameters

The maximum observed plasma concentration (C_max) and the time to the first occurrence of C_max (t_max) were obtained directly from the plasma concentration–time curves. The area under the plasma concentration–time curve to the last sample time above the limit of quantification (AUC_t) and from time zero (predose) until the end of the dosing interval (AUC_τ) were obtained by the linear trapezoidal rule. The area under the plasma concentration–time curve extrapolated to infinity (AUC_inf) was calculated from AUC_t + C_t/k_el, where C_t is the concentration at the last sample time above the limit of quantification and k_el is the terminal elimination phase rate constant. k_el was estimated by log-linear regression analysis on those data points visually assessed to be on the terminal log-linear phase. The terminal elimination phase half-life (t_1/2) was calculated as 0.693/k_el. Accumulation ratios were calculated from C_max and AUC_τ and the deviation from linearity was assessed from the ratio AUC_{τ(multiple dose)}/AUC_{(single dose)}. The predicted accumulation was calculated from the ratio AUC_(day1)/AUC_τ(day1). Dose proportionality was assessed by visual examination of the data only.

Statistical analysis

For each treatment group, natural log-transformed C_max and AUC_τ and untransformed t_max and k_el were subjected to an analysis of variance procedure, which allowed for variation due to subjects and days. For C_max and AUC_τ, treatment means were back transformed to provide geometric means on the original scale of measurement. Natural log-transformed C_max and AUC_τ accumulation ratios and the linearity ratio were subjected to analysis of variance procedure, which allowed for variation due to subjects and treatments. All analyses and tabulations were performed using SAS/STAT® (SAS Institute Inc., North Carolina, USA) software [35].

Results

Subject demographics

The demographic characteristics are summarized in Table 2. Three of the eight subjects originally randomized to receive voriconazole 1.5 mg kg⁻¹ three times daily (Group 1) were withdrawn early and replaced by three further subjects. Therefore, a total of 11 subjects received voriconazole 1.5 mg kg⁻¹ three times daily. A total of 21 subjects received placebo. All subjects who received voriconazole were included in the safety evaluation. Six subjects were excluded from the pharmacokinetic evaluation because they failed to complete the study; one of these subjects asked to be withdrawn from the study voluntarily.

Table 2.

Baseline demographic characteristics of all randomized subjects.

	Voriconazole
	2 mg kg−1twice daily (Group 4)	4 mg kg−1once daily (Group 5)	1.5 mg kg−1three-times daily (Group 1)	2 mg kg−1three-times daily (Group 2)	3 mg kg−1three-times daily (Group 3)	Placebo
Number of subjects	8	8	11	8	8	21
Mean age in years (range)	26 (20–36)	25 (20–37)	27 (20–45)	31 (21–44)	25 (18–30)	26 (18–43)
Mean weight in kg (range)	74 (66–89)	74 (66–94)	73 (60–90)	74 (64–87)	73 (61–87)	70 (61–86)
Mean height in cm (range)	180 (174–182)	178 (171–186)	178 (172–192)	177 (165–186)	179 (171–188)	178 (167–189)

Pharmacokinetics

Mean plasma concentration–time profiles of voriconazole after single-dose (day 1) and multiple-dose (day 12) administration are illustrated in Figures 1 and 2. Mean pharmacokinetic parameters in plasma are summarized in Table 3. Mean t_max values after the single dose were similar in all treatment groups, ranging from 0.9 h in the 1.5 mg kg⁻¹ three times daily group to 1.1 h in the 3 mg kg⁻¹ twice daily group. After multiple dosing, the values for t_max were similar to those seen after single dosing, ranging from 0.9 h in the 2 mg kg⁻¹ twice daily group to 1.7 h in the 3 mg kg⁻¹ twice daily group. Plasma concentration and t_max values indicated that voriconazole was absorbed rapidly after oral administration and there was a biphasic decline in plasma levels once t_max had been attained.

Figure 1.

Mean plasma concentration–time profiles at day 1 (single dose).

Figure 2.

Mean plasma concentration–time profiles at day 12 (multiple dose).

Table 3.

Summary of mean pharmacokinetic parameters for voriconazole in plasma.

Parameter	Day	2 mg kg−1twice daily	1.5 mg kg−1three-times daily	4 mg kg−1once daily	2 mg kg−1three-times daily	3 mg kg−1twice daily
Cmax (ng ml−1)*	1	485	364	1570	646	1194
	12	1007	1106	2066	2184	2356
AUCτ (ng·h ml−1)*	1	1179	882	5896	1435	3145
	12	4296	3789	13 185	9044	11 170
tmax (h)†	1	1.0	1.0	1.1	0.9	1.0
	12	1.1	0.9	1.7	1.1	1.1
kel (h−1)†	1	0.146	0.207	0.116	0.130	0.125
	12	0.107	0.108	0.105	0.095	0.109
t1/2 (h)‡	1	4.7	3.3	6.0	5.3	5.5
	12	6.5	6.4	6.6	7.3	6.4

^*Geometric mean.

^†Arithmetic mean.

^‡Harmonic mean.

Visual inspection of C_min plasma concentration–time profiles (Figure 3) and a statistical analysis of the contrast between individual days for C_max and AUC_τ indicated that steady state was attained by day 5 for the 2 mg kg⁻¹ twice-daily and 4 mg kg⁻¹ once-daily groups and day 7 for the 1.5 mg kg⁻¹ three-times daily, 2 mg kg⁻¹ three-times daily, and 3 mg kg⁻¹ twice-daily groups. For the 2 mg kg⁻¹ twice-daily and 4 mg kg⁻¹ once-daily groups, there was no significant difference in C_max or AUC_τ between days 5 and 8 or days 8 and 12. For the 1.5 mg kg⁻¹ three-times daily, 2 mg kg⁻¹ three-times daily, and 3 mg kg⁻¹ twice-daily groups, there was no significant difference in C_max or AUC_τ between days 7 and 12.

Figure 3.

Mean C_min values of multiple-dose oral regimens, days 1–10.

Comparison of single-dose and multiple-dose data across the treatment groups showed that the increase in adjusted geometric mean values of C_max and AUC_τ was not proportional to the increase in dose. Further-more, linearity ratios calculated from AUC_{τ(multiple dose)}/AUC_{(single dose)} on day 12 were >1 (range 2.12–4.37). This supports the evidence from single-dose data that voriconazole has nonlinear pharmacokinetics with respect to dose (Table 4).

Table 4.

Accumulation ratios after multiple dosing – relationship to frequency of administration.

	Accumulation ratio		Predicted	Linearity
Treatment group	AUCτ	Cmax	ratio	ratio
4 mg kg−1 once daily	2.24	1.32	1.06	2.12
2 mg kg−1 twice daily	3.64	2.07	1.19	3.03
3 mg kg−1 twice daily	3.55	1.97	1.19	2.98
1.5 mg kg−1 three times daily	4.30	3.04	1.26	3.43
2 mg kg−1 three times daily	6.30	3.38	1.44	4.37

Multiple dosing resulted in significant accumulation of voriconazole across all dosage groups. Observed mean accumulation ratios ranged from 1.32 to 3.48 for C_max and from 2.24 to 6.30 for AUC_τ, which were greater than predicted from single-dose data (range 1.06–1.35). Accumulation was generally associated with an apparent increase in mean terminal t_1/2 and was not directly dose related, although it did appear to increase with increasing frequency of administration (Table 4).

There was wide intersubject variability in pharmacokinetic parameters, as evidenced by the standard deviations for C_max, t_max, k_el, AUC_τ and t_1/2. Mean t_1/2 values were greater after multiple dosing than after the single dose, with the most marked difference evident in the 2 mg kg⁻¹ twice-daily group (Table 3).

Safety

Five of the subjects who received voriconazole withdrew from the study due to the following adverse events: visual disturbances (n = 3) reported during the 2 mg kg⁻¹ three-times daily treatment, a short run of ventricular tachycardia (three beats) (n = 1), and ST depression (n = 1) reported on days 7 and 9 of the 1.5 mg kg⁻¹ three times daily treatment, respectively. None of these events was thought to be related to treatment. Two subjects from the placebo group withdrew from the study, one as the result of a vasovagal attack following the provision of a blood sample, and another as a consequence of a possible epileptic seizure.

Treatment-emergent adverse events were recorded for 29/43 (67%) subjects who received voriconazole treatment compared with 17/21 (81%) subjects who received placebo. One subject in the placebo group experienced a serious adverse event, a possible epileptic seizure, but the majority of events were reported as mild in nature. The most common adverse events are summarized in Table 5.

Table 5.

Numbers of subjects reporting adverse events (n > 2 in any treatment group).

	Voriconazole
Adverse event	2 mg kg−1twice daily (n = 8)	4 mg kg−1once daily (n = 8)	1.5 mg kg−1three-times daily (n = 11)	2 mg kg−1three-times daily (n = 8)	3 mg kg−1twice daily (n = 8)	Placebo (n = 21)
Abnormal vision	0	5	0	4	6	5
Photophobia	0	1	0	0	3	1
Headache	0	3	4	6	7	12
Dizziness	0	2	1	1	3	6

Visual disturbances, including abnormal vision, conjunctivitis, eye pain, lacrimation disorder, and photophobia were reported by a total of 16 subjects on active treatment; six subjects with voriconazole 4 mg kg⁻¹ once daily and 3 mg kg⁻¹ twice daily, and four subjects with voriconazole 2 mg kg⁻¹ three times daily. Fourteen of the 16 subjects reported a change in brightness of vision. With the exceptions of a single moderate case of photophobia in the 3 mg kg⁻¹ group and a single report of moderate conjunctivitis in the 2 mg kg⁻¹ group, all visual adverse events were mild in nature. Visual adverse events were also reported by six subjects in the placebo group. All visual adverse events cleared without intervention or following discontinuation of study drug. Examination of the blood pressure, pulse rate, ECG and Holter data did not identify any trends associated with voriconazole administration.

Discussion

This study evaluated the pharmacokinetic and safety profile of single and multiple oral dosing regimens of the new antifungal agent voriconazole in healthy male volunteers.

The pharmacokinetic data from this study show that voriconazole exhibits nonlinear (dose- and time-dependent) pharmacokinetics after single and multiple dosing. In particular, increases in C_max and AUC_τ were not in proportion with increasing dose. The deviation from linear pharmacokinetics was confirmed in this multiple-dosing study by linearity ratios with values >1, as well as decreased k_el values, which led to an increase in the terminal phase t_1/2 compared with the single dose. There was also wide intersubject variability in pharmacokinetic parameters, particularly C_max and AUC_τ. Voriconazole was rapidly absorbed (mean t_max 0.9–1.7 h) after single and multiple dosing and the decline in plasma concentration following the attainment of C_max was generally biphasic. After multiple dosing, voriconazole accumulation was greater than was predicted from the single-dose data, and was generally associated with an increase in mean terminal t_1/2. Accumulation ratios for C_max and AUC_τ varied widely between dosage groups and appeared to be influenced by the total daily dose, as well as the frequency and duration of dosing. Visual inspection of C_min values with statistical analyses of C_max and AUC_τ values suggested that steady-state levels were achieved by the third or fifth day of multiple dosing. The nonlinear pharmacokinetics of voriconazole may possibly be explained by partial saturation of hepatic first-pass metabolism and of systemic clearance with increasing exposure to the drug.

Multiple-dose administration of oral voriconazole was very well tolerated, even at daily doses of up to 6 mg kg⁻¹. The most commonly reported adverse events were transient episodes of visual disturbance, headache, and dizziness. In addition, no clinically significant changes in laboratory safety tests or vital signs were reported in any of the subjects who received voriconazole. The visual adverse events were experienced by approximately 35% of voriconazole-treated subjects, and approximately 30% of placebo-treated subjects. All of these events were mild to moderate in nature, transient, and resolved spontaneously.

This study demonstrates that the concentrations of voriconazole achieved in plasma after oral administration are well above the minimum inhibitory concentrations (MICs) of voriconazole for Aspergillus spp. [geometric mean (GM) MIC 0.35–0.58 µg ml⁻¹], Candida spp. (GMMIC 0.001–0.39 µg ml⁻¹), and for many emerging fungal pathogens [36, 37]. The results justify further studies to establish the clinical efficacy of voriconazole in patients with opportunistic fungal infections. The 200 mg twice-daily (equivalent to 3 mg kg⁻¹ twice daily) oral dosage regimen was selected for Phase II/III trials on the basis of its toleration, C_min values that remained above the MIC of the key opportunistic pathogens on multiple dosing, and the practicality of a twice-daily dosing regimen.