Pharmacokinetics of Zanamivir following Intravenous Administration to Subjects with and without Renal Impairment

Abstract

Intravenous zanamivir is in clinical development for the treatment of influenza in hospitalized patients, many of whom have renal impairment. This open-label study evaluated zanamivir pharmacokinetics and clinical safety following a single 100-mg intravenous infusion dose in subjects with impaired renal function compared with normal renal function. Male and female subjects between 18 and 79 years of age were recruited, four subjects to each renal function group (normal function and mild, moderate, and severe impairment). Serial blood samples were collected up to 24 h after dose administration (48 h for the severe renal impairment group) to estimate zanamivir serum pharmacokinetic parameters. Urine was collected over the same 24-h (or 48-h) period for estimation of renal clearance (CL_R). Zanamivir pharmacokinetics were assessed by regression analysis of systemic clearance (CL) and CL_R as a function of creatinine clearance (CL_CR). Safety evaluations included adverse-event monitoring, vital signs, electrocardiogram, and clinical laboratory assessments. Zanamivir clearance (total and renal) significantly decreased with decreasing renal function, with corresponding increases in area under the concentration-time curve and elimination half-life. Renal impairment had no apparent effects on peak concentration or volume of distribution. Regression analysis indicated that zanamivir clearance was highly correlated (r² = 0.89) with creatinine clearance: CL ≅ 7.08 + 0.826 · CL_CR. There were no patterns or trends in adverse events, and no new safety concerns were identified following administration of intravenous zanamivir. Results from this study support the inclusion of subjects with renal impairment, with appropriate dose adjustment, in studies to evaluate intravenous zanamivir in the treatment of influenza.

INTRODUCTION

Zanamivir is a selective inhibitor of viral neuraminidase and a potent inhibitor of clinical isolates of influenza A and B viruses. Administered as a dry powder for oral inhalation, zanamivir has been used extensively for both the treatment and prophylaxis of acute uncomplicated illness due to influenza A and B virus in adults, adolescents, and children (licensed for children aged ≥5 years in most countries, ≥7 years in the United States for treatment, and ≥7 years in Canada for treatment and prophylaxis), with approvals in more than 120 countries for treatment and 60 countries for prophylaxis. An intravenous (i.v.) formulation of zanamivir is in clinical development for use in hospitalized patients for whom a parenteral formulation may be considered most appropriate or for use when the currently available oral or oral inhaled influenza medications are not suitable, for example, due to impaired absorption from the gut or inability to administer medication via the inhaled route. Additionally, widespread resistance to the adamantanes and reports of resistance to oseltamivir (most commonly due to the H275Y mutation, against which zanamivir retains full activity) further indicate a need for more treatment options (1, 2).

Findings from studies with healthy volunteers conducted early in the development program, using the intravenous formulation of zanamivir, indicated that zanamivir does not undergo metabolism (∼90% of the drug is excreted unchanged in urine within 24 h, with no evidence of biotransformation from chromatography) and that pharmacokinetics (PK) are dose proportional over the dose range studied (1 mg to 600 mg) (3). A study of low-dose (2 mg and 4 mg) intravenous zanamivir in subjects with impaired renal function was previously conducted to assess the need for dosage adjustment in patients administered inhaled zanamivir. The results indicated that renal impairment significantly affects zanamivir PK, with a decrease in clearance, an increase in elimination half-life (t_1/2), and a corresponding increase in systemic exposure, but that no dosage adjustment is needed for subjects with renal impairment receiving zanamivir by the inhaled route of administration because of the low systemic concentrations achieved (4). However, influenza is often associated with impaired renal function in the hospital setting, and dosage adjustment for subjects with impaired renal function is anticipated to be important in the medical management of hospitalized patients treated with i.v. zanamivir, which provides considerably higher systemic concentrations.

An intravenous regimen of 600 mg twice daily, the highest repeat-dose regimen administered to humans, was found to be well tolerated and to exert a significant prophylactic effect in an experimental human influenza A virus challenge study (3, 5). Accordingly, this regimen was chosen for evaluation in clinical studies of hospitalized patients with influenza. However, because of the low systemic concentrations achieved with the low doses used in the prior study supporting the oral inhaled formulation, it was considered warranted to further evaluate the effect of renal impairment on zanamivir PK using a higher intravenous dose. Given that subjects in the earlier study with severe renal impairment had an average zanamivir clearance approximately one-sixth of that for healthy volunteers (4), this study was designed to evaluate the effects of renal impairment on zanamivir PK at a 100-mg dose, anticipated to provide a systemic exposure similar to that for normal renal function from the highest dose (600 mg) previously studied in humans.

(This study was presented in part at the 48th Annual Meeting of the Infectious Diseases Society of America, 21 to 24 October 2010, Vancouver, British Columbia, Canada.)

MATERIALS AND METHODS

Study design.

This phase I, open-label, single-dose study (NAI108127) was conducted at three centers in the United States (DaVita Clinical Research Inc., Minneapolis, MN; New Orleans Center for Clinical Research, New Orleans, LA; and Orlando Clinical Research Center, Orlando, FL). Subjects were stratified according to Food and Drug Administration (FDA) definitions of renal function (available at http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm072127.pdf) using creatinine clearance (CL_CR) determined from 24-h urine collection at screening (normal function, ≥80 ml/min; mild impairment, 50 to 79 ml/min; moderate impairment, 30 to 49 ml/min; and severe impairment, <30 ml/min). Subjects from the mild, moderate, and severe impairment groups were enrolled in parallel. Following enrollment of subjects to the moderate impairment group, control subjects with normal renal function, matched for gender, age (±10 years), and body mass index (BMI; ±15%), were subsequently enrolled. All subjects received a single zanamivir dose of 100 mg administered by continuous intravenous infusion over 30 min.

All subjects underwent screening assessments within 30 days of dosing and were then admitted to the study center the day before study drug administration (day −1), remaining in the study center until the final study assessment was completed on day 2 (normal renal function and mild and moderate impairment groups) or day 3 (severe renal impairment group). A follow-up visit was conducted 7 to 10 days after the last treatment assessment (or withdrawal from the study).

Study population and procedures.

Male and female subjects between 18 and 79 years of age with a BMI of 18 to 35 kg/m² and body weight of at least 50 kg were eligible for recruitment. All subjects were required to be clinically stable and to have stable renal function, defined as a ≤15% difference between estimated creatinine clearance calculated on two occasions over >4 weeks from serum creatinine measurements, and at least one of the measurements must have been within 30 days of dosing. Subjects were required to abstain from alcohol and caffeine from 48 h prior to the start of dosing until after the final study assessment. The use of prescription or nonprescription medications was prohibited unless considered medically necessary, safe, and to not interfere with study procedures and the medication had been taken consistently on the same dosing schedule for at least 2 weeks prior to study drug administration. Subjects receiving renal replacement therapy were excluded from the study.

Blood samples for zanamivir PK assessments were collected predose, at 30 min (end of infusion), and at 45 min and 1, 1.25, 1.5, 2, 3, 4, 6, 8, 12, and 24 h after the start of the infusion; subjects in the severe renal impairment group had an additional sample collected at 48 h after the start of the infusion. Blood samples were obtained by individual needle puncture or via intravenous cannula. Following a predose void, urine was collected at 0 to 4 h, 4 to 8 h, 8 to 12 h, and 12 to 24 h after dosing; subjects in the severe renal impairment group had an additional collection from 24 to 48 h. Two aliquots were taken from each urine sample collection for assay, one for zanamivir concentration and one for creatinine concentration. Serum and urine zanamivir concentrations were determined by validated analytical methods. Zanamivir concentrations in serum samples were analyzed by protein precipitation and liquid chromatography with tandem mass spectroscopy (LC-MS-MS) in the positive ion turbo ion spray mode. The calibration curve range for zanamivir in serum was 10 to 10,000 ng/ml using a 50-μl sample aliquot of human serum. Concentrations in urine samples were analyzed by dilution and LC-MS-MS; the calibration curve range for zanamivir in urine was 10,000 to 640,000 ng/ml using a 10-μl sample aliquot of human urine.

Safety assessments were conducted throughout the study: adverse events (AEs; day −1, day 1, day 2, and follow-up, plus day 3 for the severe renal impairment group); vital signs (predose within 90 min prior to dosing; at 30 min [end of infusion]; 1, 2, and 4 h after the end of infusion; and follow-up); 12-lead electrocardiogram (ECG; day 1 predose, at end of infusion, and at follow-up); and clinical laboratory assessments, including hematology, clinical chemistry, and urinalysis (day −1, day 2, and follow-up, plus day 3 for the severe impairment group).

The study was approved by the institutional review boards for the centers, and written informed consent was obtained from each subject prior to commencement of any study-specific procedures.

Statistical and pharmacokinetic analyses.

The primary endpoints of the study were the serum zanamivir PK parameters peak concentration (C_max), area under the concentration-time curve to last quantifiable concentration (AUC_0-t), and AUC extrapolated to infinity (AUC_0-∞). Secondary PK parameters included time to C_max (t_max), t_1/2, systemic clearance (CL), and terminal-phase volume of distribution (V_z). Serum PK parameter estimates were based on actual sample collection times and determined by standard noncompartmental analysis using WinNonlin Professional Edition, version 4.1 (Pharsight Corporation, Mountain View, CA). Other secondary endpoints included the urine PK parameters amount excreted in urine (A_e) and renal clearance (CL_R), as well as the safety and tolerability parameters (AEs, vital signs, ECGs, and clinical laboratory assessments). A sample size of four subjects per renal function group (16 subjects in total) was considered sufficient to be able to detect PK differences for dosage adjustment considerations.

The effect of renal impairment on zanamivir pharmacokinetics was assessed by two approaches: (i) a comparison of PK parameter estimates for each renally impaired group relative to the normal renal function group using analysis of variance (ANOVA) and (ii) regression analyses of zanamivir CL and CL_R as a function of the 24-h CL_CR measured at screening.

For the ANOVA, the dependent variable was the log-transformed PK parameter of interest (C_max, AUC_0-∞, AUC_0-t, t_1/2, CL, and V_z) and the independent variable included a fixed effect for group (A, normal function; B, mild impairment; C, moderate impairment; and D, severe impairment). The estimated differences in least-squares means for B − A, C − A, and D − A and associated 90% confidence intervals (CIs) obtained on the log scale were exponentiated to provide estimates of the impaired-to-healthy ratios (B/A, C/A, and D/A) and their associated CIs on the original scale.

Safety data were descriptively assessed and summarized by renal function group. The Division of AIDS toxicity tables were used to standardize severity grading between subjects (6).

RESULTS

Study population.

The study was conducted between September 2006 and April 2007. Sixteen subjects were enrolled, four subjects in each of the four renal function groups. One subject with mild renal impairment withdrew from the study, after completion of PK sampling, due to a serious AE (myocardial infarction); all others completed the study. Baseline characteristics and demography are summarized in Table 1.

Table 1.

Demography and baseline characteristics of study subjects

Parameter	Value for subjects in renal function category
	Normal function (n = 4)	Mild impairment (n = 4)	Moderate impairment (n = 4)	Severe impairment (n = 4)
Mean age (SD), yrs	54.0 (11.86)	68.0 (11.60)	55.8 (14.43)	73.0 (3.37)
Female, n (%)	2 (50)	1 (25)	2 (50)	3 (75)
Mean wt (SD), kg	86 (15.0)	85 (5.3)	86 (17.1)	83 (3.8)
Mean BMI (SD), kg/m2	26.5 (0.87)	28.1 (5.16)	29.0 (2.40)	28.8 (2.63)
Race, n (%)
Black	0	0	1 (25)	2 (50)
White	4 (100)	4 (100)	3 (75)	2 (50)

Pharmacokinetics.

Median serum zanamivir concentration-time profiles for the four renal function groups are displayed in Fig. 1, and summary PK parameter estimates are presented in Table 2. Results showed increases in AUC and t_1/2, and decreases in CL and CL_R, with worsening renal function. Values for C_max, t_max, and V_z appeared similar across the renal function groups.

Fig 1.

Median zanamivir concentration-time profiles from administration of a 100-mg single intravenous dose to subjects with normal (group A), mildly impaired (group B), moderately impaired (group C), and severely impaired (group D) renal function.

Table 2.

Summary of zanamivir pharmacokinetic parameter estimates

Pharmacokinetic parameter	Geometric mean (CVb,a %) in renal function category
	Normal function (n = 4)	Mild impairment (n = 4)	Moderate impairment (n = 4)	Severe impairment (n = 4)
Cmax, μg/ml	7.29 (16)	6.93 (12)	8.50 (20)	6.96 (43)
tmax,b h	0.53 (0.5–0.8)	0.50 (0.5–0.5)	0.5 (0.5–0.5)	0.5 (0.5–1.0)
AUC0-t, μg · h/ml	16.8 (37)	26.1 (23)	39.8 (39)	77.6 (28)
AUC0-∞, μg · h/ml	17.0 (36)	26.5 (24)	42.9 (45)	89.4 (48)
t1/2, h	2.44 (22)	3.88 (22)	5.79 (45)	12.8 (80)
CL, ml/min	97.2 (35)	62.4 (24)	38.8 (45)	18.6 (48)
Vz, liters	20.5 (18)	20.9 (12)	19.4 (12)	20.6 (34)
Ae,c mg	89.7 (6)	75.4 (15)	74.0 (43)	61.3 (11)
CLR, ml/min	89.0 (39)	48.2 (37)	31.0 (58)	13.2 (39)

^aCVb, between-subject coefficient of variation.

^bPresented as median and range.

^cCumulative zanamivir recovery in urine over 24 h for normal function and mild and moderate impairment groups and 48 h for severe impairment group.

The results from group comparisons by the ANOVA approach show that subjects with renal impairment had reduced zanamivir clearances (both total and renal), higher serum zanamivir AUCs, and longer t_1/2s than did subjects with normal renal function (Table 3). Renal impairment had no apparent effects on zanamivir C_max or V_z.

Table 3.

Zanamivir pharmacokinetic comparisons of renally impaired groups with normal function group

Pharmacokinetic parameter	Geometric least squares mean ratio (90% CI)
	Mild impairment vs normal function	Moderate impairment vs normal function	Severe impairment vs normal function
Cmax	0.951 (0.694, 1.30)	1.17 (0.851, 1.60)	0.954 (0.697, 1.31)
AUC0-t	1.55 (1.04, 2.31)	2.37 (1.59, 3.53)	4.62 (3.10, 6.88)
AUC0-∞	1.56 (0.970, 2.51)	2.53 (1.57, 4.06)	5.27 (3.27, 8.47)
t1/2	1.59 (0.91, 2.76)	2.37 (1.36, 4.12)	5.22 (3.00, 9.08)
CL	0.641 (0.400, 1.03)	0.399 (0.249, 0.640)	0.192 (0.120, 0.307)
Vz	1.02 (0.79, 1.32)	0.95 (0.73, 1.23)	1.00 (0.77, 1.30)
Aea	0.840 (0.630, 1.12)	0.824 (0.618, 1.099)	0.683 (0.512, 0.910)
CLR	0.541 (0.319, 0.918)	0.348 (0.205, 0.590)	0.148 (0.087, 0.251)

^aCumulative zanamivir recovery in urine over 24 h for normal function and mild and moderate impairment groups and over 48 h for severe impairment group.

The results from the regression approach to characterize the relationship between zanamivir CL or CL_R and CL_CR (unit = ml/min for each) indicate that zanamivir CL and CL_R were each highly correlated with CL_CR: CL ≅ 7.08 + 0.826 · CL_CR, r² = 0.89, and CL_R ≅ −0.086 + 0.801 · CL_CR, r² = 0.87. For both regressions, the slopes were highly significant (P < 0.0001) and the intercepts were not significantly different from zero. The relationship between zanamivir CL and CL_CR is displayed in Fig. 2.

Fig 2.

Regression relationship between zanamivir CL and CL_CR, CL = 7.08 + 0.826 · CLcr, r² = 0.89. Dashed lines indicate 95% confidence interval for the regression line.

Safety.

A total of 22 AEs were reported by 11 subjects during the study. Only two AEs were reported for more than one subject (diarrhea and headache, both reported for three subjects) (Table 4). All other AEs occurred in one subject each.

Table 4.

Summary of all adverse events

Adverse event	No. (%) of subjects in renal function category with adverse event
	Normal function (n = 4)	Mild impairment (n = 4)	Moderate impairment (n = 4)	Severe impairment (n = 4)
Any adverse event	3 (75)	2 (50)	2 (50)	4 (100)
Diarrhea	0	0	1 (25)	2 (50)
Abdominal pain	1 (25)	0	0	0
Headache	1 (25)	2 (50)	0	0
Dizziness	0	0	0	1 (25)
Dizziness, postural	0	1 (25)	0	0
Syncope	0	1 (25)	0	0
Myocardial infarction	0	1 (25)	0	0
Palpitations	0	0	0	1 (25)
Asthenia	0	0	0	1 (25)
Chest pain	0	1 (25)	0	0
Upper respiratory tract infection	0	0	1 (25)	1 (25)
Blood creatinine increase	0	1 (25)	0	0
Lipase increase	0	0	0	1 (25)
Myalgia	0	1 (25)	0	0
Cough	1 (25)	0	0	0
Nasal congestion	1 (25)	0	0	0
Rash	0	0	0	1 (25)

Four subjects experienced AEs considered possibly drug related. One subject with normal renal function experienced mild abdominal pain, one subject with mild renal impairment experienced moderate headache, one subject with moderate renal impairment experienced moderate diarrhea, and one subject with severe renal impairment experienced mild weakness and lightheadedness, intermittent pounding sensation, and mild rash.

One subject with mild renal impairment was withdrawn from the study due to a serious AE (myocardial infarction) that was not considered related to the study medication. This 51-year-old male smoker had underlying coronary artery disease, hypertension, and hyperlipidemia and developed symptoms of acute myocardial infarction 1 day after administration of intravenous zanamivir at 100 mg. He required hospitalization and underwent coronary angioplasty, with placement of three stents.

No clinically significant changes in laboratory values, vital signs, or ECGs were observed during the study.

DISCUSSION

There has been widespread use of zanamivir dry powder for oral inhalation since the first regulatory approval in 1999, as an antiviral drug effective for the treatment and prophylaxis of illness caused by influenza A and B viruses. However, there is an unmet medical need for a parenteral formulation for administration to hospitalized patients.

Results from an early PK study with low-dose (2 mg and 4 mg) intravenous zanamivir, conducted to support the inhaled formulation, indicated that renal impairment altered zanamivir pharmacokinetics. This study was conducted to further investigate the relationship between zanamivir pharmacokinetics and renal impairment using a higher (100-mg) dose more relevant as support for the development of intravenous zanamivir.

Results from this study were consistent with historical observations (3, 4), showing that zanamivir pharmacokinetics are highly correlated with renal function. Zanamivir total clearance and renal clearance significantly decreased with decreasing renal function, with corresponding increases in zanamivir AUC and t_1/2. However, as expected given single-dose administration and relatively short infusion duration, zanamivir C_max appeared essentially unchanged with differences in renal function. Similarly, there was no apparent difference in V_z with differences in renal function. Statistical comparisons of PK parameters between subjects with renal impairment relative to those with normal renal function indicated that zanamivir AUC_0-∞s were approximately 56%, 153%, and 427% greater in subjects with mild, moderate, and severe renal impairment, respectively, than in subjects in the normal renal function group. Results nearly identical to those for AUC_0-∞ were observed for t_1/2 in the renally impaired groups relative to those with normal renal function. Based on results from regression analysis for the relationship between zanamivir CL and CL_CR (i.e., CL = 7.08 + 0.826 · CL_CR) and the fundamental pharmacokinetic definition of clearance (CL = dose/AUC), doses proposed for subjects with renal impairment to provide AUCs similar to those in subjects with normal renal function receiving a 600-mg intravenous dose were 400 mg for CL_CR of 50 to <80 ml/min, 250 mg for CL_CR of 30 to <50 ml/min, 150 mg for CL_CR of 15 to <30 ml/min, and 60 mg for CL_CR of <15 ml/min. Following a common 600-mg initial dose, this dosing has subsequently been implemented during twice-daily maintenance dosing for adults in ongoing phase II and phase III studies of hospitalized patients with influenza (NCT01014988 and NCT01231620).

In this study, there was no pattern or trend in the mild to moderate AEs reported in the population of subjects with underlying renal disease and no clinically significant changes in other safety assessments. No new safety concerns were identified following administration of intravenous zanamivir in this study. One serious AE, myocardial infarction, occurred 1 day following study drug administration but was not considered related to intravenous zanamivir based on a history of coronary artery disease and multiple cardiac risk factors.

In conclusion, results from this study provide a characterization of the strong relationship between zanamivir clearance and creatinine clearance following administration of intravenous zanamivir in subjects with renal impairment and, as a consequence, the need for dosage adjustment in these subjects. The results support the inclusion of subjects with renal impairment in studies to evaluate intravenous zanamivir in the treatment of influenza, with appropriate dose adjustment for the degree of renal impairment.