Single-dose pharmacokinetics and tolerability of pegylated interferon-α2b in young and elderly healthy subjects

Abstract

Aims

To assess the single-dose pharmacokinetics and tolerability of pegylated interferon-α2b (PEG-Intron) in young and elderly healthy subjects.

Methods

In this parallel-design study, a single 1 µg kg⁻¹ PEG-Intron dose was given subcutaneously to 24 subjects in the age groups 20–45, 65–69, 70–74 and 75–80 years (n = 6/group). Blood sampling and tolerability assessments were performed up to 168 h postdose.

Results

The pharmacokinetic parameters were similar in all age groups. The elderly to young subject ratios for C_max were 91.1, 79.5, and 107% for the 65–69 years, 70–74 years and 75–80 years groups, respectively. The corresponding values for AUC(0–∞) and CL/F were 111, 102 and 108%, and 82.5, 95.8 and 86.4%, respectively. Mean differences from the 20 to 45 years group and the 65–69 years, 70–74 years and 75–80 years groups for PEG-Intron Vd/F were 108, 128 and 104%, respectively. None of these differences was statistically significant based on ANOVA. Results from a Dunnett's test (as post hoc assessment) confirmed that the pharmacokinetic parameters of Group II, Group III or Group IV were not different from those of Group I. Almost all (23/24; 96%) subjects reported typical interferon-α side-effects (flu-like symptoms, headache). One elderly patient had a myocardial infarction 12 h postdose, but recovered fully.

Conclusions

There are no pharmacokinetic reasons for initial dose adjustment of PEG-Intron based on age.

Introduction

The kidney appears to be the principal site of interferon (IFN) clearance [1], whereas hepatic metabolism and subsequent biliary excretion is a minor pathway of elimination for IFN-α[2]. Although the mechanisms of the elimination of IFN have not been studied in man, preclinical studies indicate a primary role of renal filtration and catabolism [1]. Pegylated interferon-α2b (PEG-Intron) is a derivative of recombinant IFN-α2b containing a single straight chain molecule of polyethylene glycol with an average molecular weight of 12 000 Da, attached by a covalent linkage primarily to histadine-34 on IFN-α2b [3, 4]. PEG-Intron was developed to slow the elimination of IFN-α2b. Attachment of a single polyethylene glycol (PEG; MW 12 kDa) moiety to IFN-α2b does not alter its volume of distribution compared with nonpegylated IFN- α2b. However, this moiety reduces the renal clearance of PEG-Intron, resulting in an approximately 10-fold increase in elimination half-life [3, 4]. PEG-Intron is now approved in the USA and EU for the treatment of chronic hepatitis C.

The demographics of chronic hepatitis C show that a sizeable minority of patients are of advanced age [5]. Physiological changes associated with ageing may potentially alter drug disposition [6]. The objective of this study was to determine the effect of increasing age on the pharmacokinetics of PEG-Intron. In addition, as IFNs are eliminated renally [1], the relationship between pharmacokinetic parameters and renal function was also assessed.

Methods

This open-label study assessed the single-dose pharmacokinetics of PEG-Intron in 24 male and female volunteers, stratified into four age groups (sequential subject numbering) based on their age, each of six subjects: Groups I (20–45 years), II (65–69 years), III (70–74 years), and IV (75–80 years). Age range selection was mainly for stratification rather than any physiological reason. Prior to study initiation, the clinical study protocol and the written informed consent form were reviewed and approved by Peninsular Testing Corporation Protocol Review Committee, Miami, Florida, an Institutional Review Board. The Investigator agreed to comply with 21 CFR 50 of the US Code of Federal Regulations and with the World Medical Association Declaration of Helsinki concerning written informed consent and the rights of human subjects. Subjects were determined to be eligible to participate in the study based on medical history, physical examination, laboratory safety tests, vital signs, and an electrocardiogram. Subjects with significant medical disorders, histories of alcohol or drug abuse, smoking more than 10 cigarettes per day, abnormal laboratory results unrelated to age, or who had taken investigational drugs within 3 months prior to the study or any other medication within the prior 14 days, were not permitted to participate.

Subjects were confined to the study centre for at least 48 h prior to dosing until 168 h post dosing. Upon admission, a 24-h urine collection was obtained for the determination of creatinine clearance (CLcr [7]). On the morning of day 1, following a 10-h fast, each subject received a single subcutaneous dose of PEG-Intron 1.0 µg kg⁻¹. Blood samples were collected for pharmacokinetic assessment immediately prior to drug administration (0 h) and at 2, 4, 6, 8, 10, 12, 16, 24, 36, 48, 72, 96, 120, 144 and 168 h after dosing. Whole blood samples were collected into a plain tube and allowed to clot at room temperature for 15 min, and then centrifuged at 4 °C and 1500 g for 15 min. Serum was stored frozen until analysed. The assessment of tolerability included measurement of vital signs and ECGs, laboratory biochemistry, and recording of adverse events.

Serum PEG-Intron concentrations were determined as described previously using a validated electrochemiluminescence assay. The limit of quantification was 50 pg mL⁻¹, and the interassay/intra-assay coefficient of variability at this concentration was 12% at 50 pg mL⁻¹[8]. Pharmacokinetic parameters were estimated using noncompartmental methods (WinNonlin; Pharsight Corp., Mountain View, CA, USA). The maximum concentration (C_max), time to maximum concentration (T_max) and final quantifiable sampling time (t) were the observed values. Area under the serum concentration–time curve from 0 to t[AUC(0–t)] was determined by the linear trapezoidal rule.

AUC(0–∞) was calculated as AUC(0–t) + (Ct/k), where k is first-order rate constant of terminal portion of the curve and Ct is the estimated concentration corresponding to the time t. Apparent clearance (CL/F) was calculated from the expression dose/AUC(0–∞) and the apparent volume of distribution (Vd/F) was calculated from (CL/F)/k. Body weight normalized Vd/F (Vd/F kg⁻¹) was also estimated. The pharmacokinetic parameters were subjected to statistical analysis using an analysis of variance (ANOVA) test. The primary statistical comparisons were Groups II, III, and IV relative to Group I. The pharmacokinetic parameters were log-transformed and the 95% confidence intervals (CI) on the mean difference between the groups were expressed as a percent of each treatment mean. Dunnett's t-test, multiple comparison method, was performed to compare pharmacokinetic parameters from Groups II–IV against Group I as post hoc assessment. A P-value of less than 0.05 was considered significant. The study power was set at 80% to detect 40% change in AUC (α = 0.05).

Results

Twenty-four subjects (18 males, six females) enrolled in the study. Respectively, the mean (95% CI) ages for Groups I–IV were 36.2 (28, 44), 67.0 (65, 69), 71.7 (70, 73), and 76.8 (75, 79) years. The corresponding mean (95% CI) weights were 78.1 (70, 87), 71.7 (64, 80), 76.3 (69, 84), 72.8 (57, 89) kg and heights 176 (170, 182), 164 (154, 175), 161 (153, 170), and 169 (160, 178) cm, respectively.

Mean concentration–time profiles for PEG-Intron are shown in Figure 1 and mean pharmacokinetic parameters are displayed in Table 1a.Mean C_max occurred between 13.7 and 23.3 h. Subsequently, serum concentrations declined slowly, with most subjects having quantifiable concentrations 168 h postdose. Mean concentration–time profiles for Groups I–III, and mean C_max and AUC values for Groups I–III were similar (Figure 1, Table 1a, 1b), whereas mean values for Group IV appeared to be 59% higher than Group I, but 9% lower when an outlier, Subject 21, was excluded. There were no characteristics that distinguished Subject 21 from the others in Group IV, and the reason for their high exposure to the drug is unclear. Mean differences in the pharmacokinetic parameters of Group I were not statistically significant between those of Groups II–IV (Table 1b), probably because the power to detect a difference was low. The results of the post hoc confirmed that the pharmacokinetic parameters of Group II, Group III or Group IV did not differ from those of Group I. The mean T_max of the 20–45 years group was lower than those of three geriatric age groups (16–23 h), but this difference was not statistically significant (Table 1b). As expected, a positive correlation was noted between CLcr and age (r² = 0.664, P < 0.001, Pearson's correlation test). However, there were no discernible trends between PEG-Intron C_max, AUC, CL/F or Vd/F kg⁻¹ values and either age or CLcr.

Figure 1.

Mean serum pegylated interferon-α2b concentration–time profiles (inset log-linear plot) following a single subcutaneous dose of 1 µg kg⁻¹ to young and elderly volunteers. Symbols, mean values; vertical bars, SD. Group I (18–45 yr) (▪); group II (65–69 yr) (□); group III (70–74 yr) (▿); and group IV (75–80 yr) (▵).

Table 1a.

Mean (% CV) pharmacokinetic parameters for PEG-Intron following a single subcutaneous dose of 1 µg kg⁻¹ to young and elderly volunteers (n = 6/group).

Parameter	Group I (20–45 years)	Group II (65–69 years)	Group III (70–74 years)	Group IV (75–80 years)
Cmax (pg mL−1)	1044 (34)	959 (37)	846 (39)	1492 (65)†
Tmax (h)*	11.0 (10.0–24.0)	20.0 (12.0–48.0)	20.0 (12.0–36.0)	16.0 (12.0–48.0)†
AUC(0–t) (pg mL−1 h)	65830 (48)	70339 (31)	63160 (32)	104879 (106)†
AUC(0–∞) (pg mL−1 h)	71052 (48)	76520 (31)	70010 (29)	135964 (104)
t1/2 (h)	35.8 (15)	42.5 (21)	46.9 (19)	44.4 (25)††
20.4 (26)	16.8 (28)	19.7 (34)	14.4 (43)††
Vd/F kg−1 (L kg−1)	0.801 (27)	0.856 (31)	1.06 (40)	0.705 (46)††
CLcr (mL min−1)	149 (12)	94.3 (9)	95.7 (22)	97.8 (20)

^*Median (range).

^†Excluding Subject 21: C_max = 1134 (42); T_max = 16.0 (12.0–24.0); AUC(tf) = 60 266 (34); t = 168 (24–168); AUC(0–∞) = 72 780 (21); t_1/2 = 40.5 (20); CL/F = 17.0 (13); Vd/F kg⁻¹ = 0.823 (28).

^‡Could not be determined for Subject 24.

Table 1b.

Mean difference and 95% confidence intervals (CI) for the log-transformed pharmacokinetic parameters of PEG-Intron following a single subcutaneous dose of 1 µg kg⁻¹ to young and elderly volunteers.

	Group II (65–69 years)/ Group I (20–45 years)		Group III (70–74 years)/ Group I (20–45 yeasr)		Group IV (75–80 years)/ Group I (20–45 years)*†
Parameter	Mean difference‡	95% CI	Mean difference‡	95% CI	Mean Difference‡	95% CI
Cmax (pg mL−1)	91.1§	59–140	79.5§	52–122	107§	68–167
AUC(0–t) (pg mL−1 h)	110§	72–170	98.5§	64–152	92.8§	59–146
AUC(0-∞) (pg mL−1 h)	111§	76–164	102§	69–150	108§	70–167
CL/F (mL min−1)	82.5§	57–119	95.8§	67–138	86.4§	58–130
Vd/F (l kg−1)	106d	64–176	128§	77–212	104§	66–164

^*Excluding Subject 21.

^†Including Subject 21 the mean difference (95% CI) are as follows: C_max = 129 (78, 212); AUC(0–t) = 124 (68, 227); AUC(0–∞) = 152 (84, 274); CL/F = 64.1 (37, 110); Vd/F kg⁻¹ = 80.4 (47, 137).

^‡Expressed as percent (%).

^§Difference was not significant based on Dunnett's t-test.

Adverse events were reported by almost all subjects (23/24; 96%). The profile of adverse events was similar to those of other interferons, namely flu-like symptoms and headache. Cutaneous reactions to injection of PEG-Intron were also reported by 9/24 (38%) subjects. Overall there were no age-related trends in reporting of adverse events. One serious adverse event occurred. Subject 24 (76 years, female) experienced an acute myocardial infarction approximately 12 h following administration of PEG-Intron, and was withdrawn from the study. This subject recovered fully. Consistent with the effects of interferon-α, platelet and neutrophil counts were modestly lowered by PEG-Intron, with a reversal of these changes by the end of the study.

Discussion

The principal findings were that advancing age had no influence on the pharmacokinetics of PEG-Intron and that there was no correlation between PEG-Intron CL/F and CLcr.

Although the mechanisms by which interferon is cleared have not been studied in man, preclinical studies indicate a primary role for renal filtration and renal catabolism [1]. Clearance of nonpegylated interferon-α is significantly decreased by 64–79% in patients with severe renal dysfunction compared with controls [9, 10]. Thus, a correlation between CLcr and PEG-Intron CL/F might be expected, but none was found in the present study. Furthermore, in a recent population pharmacokinetic analysis of PEG-Intron, CLcr was not a significant covariate for PEG-Intron CL/F [11]. One explanation for this lack of correlation is that renal mechanisms account for a minor part of PEG-Intron clearance [12]. Pegylation may make the drug less susceptible to renal filtration, possibly as a result of increased molecular weight, or altered charge. The absence of age-related pharmacokinetic differences in the present study suggest that increasing age has little effect on nonrenal clearance mechanisms for interferons, which is supported by a recent analysis [11]. It is possible that the data seen in one elderly outlier subject reflect the highly variable pharmacokinetics of both pegylated and nonpegylated interferons [8, 11].

The tolerability of PEG-Intron was similar among age groups. Adverse effects and their time course were typical of those associated with interferon therapy [8]. The neutrophil and platelet decreases at 24–48 h post dose were of similar magnitude across all groups. A serious but unexpected finding was the myocardial infarction experienced by Subject 24, 12 h postdose. This subject was withdrawn from the study and after investigation and supportive medical care, recovered fully. Although rare, cardiac arrhythmias, myocarditis, cardiomyopathy and even myocardial infarction/ischaemia have been reported after interferon administration [13]. The mechanism of interferon-induced cardiotoxicity is unclear, but may be related to the febrile reaction induced by first exposure to interferon therapy, with the subsequent increase in oxygen demand precipitating a myocardial infarction or arrhythmia in a compromised myocardium [13]. Therefore, pre-existing heart disease may be considered a risk factor for interferon-induced arrhythmias or ischaemic manifestations [13].

In summary, this study suggests there are no pharmacokinetic reasons for initial dose adjustment of PEG-Intron based on age. Further controlled studies involving single or multiple dosing are required to confirm these preliminary findings.