Pharmacokinetic and Pharmacodynamic Characteristics of Tripegfilgrastim, a Pegylated G-CSF, in Pediatric Patients with Solid Tumors

A long-acting granulocyte colony-stimulating factor, tripegfilgrastim, was approved in Korea for the prevention of chemotherapy-induced neutropenia in adult patients. In this study, we evaluated the pharmacokinetics, pharmacodynamics, and safety of tripegfilgrastim in pediatric patients. A phase I, open-label, single ascending-dose study was performed in pediatric patients with solid tumors or lymphoma (ClinicalTrials.gov, NCT02963389). The patients were stratified according to age groups (aged 6 to 12 or 12 to 19 years) and received a single subcutaneous dose of tripegfilgrastim 60 μg/kg or 100 μg/kg. Tripegfilgrastim was administered 24 hours after the end of the chemotherapy, and serial blood sampling and safety monitoring were conducted. Twenty-seven patients with solid tumors were enrolled in this study. Tripegfilgrastim was detectable in plasma for an extended period (terminal half-life > 40 hours), and plasma concentrations increased slightly less than dose proportionally. The mean duration of grade 4 neutropenia was reduced as the average tripegfilgrastim concentration during the initial neutrophil recovery process increased. No substantial differences in the pharmacokinetic and pharmacodynamic responses were observed between the two age groups. When stratified by body weight, weighing more than 45 kg has a higher risk of a prolonged neutropenia period when receiving the lower dose (60 μg/kg) of tripegfilgrastim. Tripegfilgrastim was generally safe and well-tolerated in the pediatric patients. These results justify further clinical investigations of tripegfilgrastim at 100 μg/kg dose in pediatric patients.

Effects of age and sex on the hematology and blood chemistry of Tibetan macaques (Macaca thibetana)

Tibetan macaques (Macaca thibetana), also known as Chinese stump-tailed macaques, are a threatened primate species. Although Tibetan macaques are Old World monkeys in the genus of Macaca, limited age- and sex-related physiologic data are available for this particular species. We used 69 apparently healthy Tibetan male and female macaques to explore the effect of age and sex on physiologic parameters. Somatometric measurements, biochemistry, and hematologic parameters were analyzed. Significant age-related differences were found for weight, BMI, RBC count, Hgb, Hct, neutrophils, eosinophil count, ALT, AST, ALP, GGT, creatine kinase (muscle and brain subtypes), LDH, α-amylase, creatinine, apolipoprotein A1, total protein, albumin, cholesterol, HDL, and potassium. Significant differences by sex were noted for weight, BMI, ALT, total bilirubin, and indirect bilirubin. An interaction between age and sex accounted for statistically significant differences in the values for weight, BMI, and lymphocyte and eosinophil counts. These physiologic data will provide veterinarians and researchers with important age- and sex-specific reference ranges for evaluating experimental results from Tibetan macaques.

Cardiovascular safety of anagrelide in healthy subjects: effects of caffeine and food intake on pharmacokinetics and adverse reactions

Background

Essential thrombocythaemia (ET) is a rare clonal myeloproliferative disorder characterized by a sustained elevation in platelet count and megakaryocyte hyperplasia. Anagrelide is used in the treatment of ET, where it has been shown to reduce platelet count. Anagrelide is metabolized by cytochrome P450 (CYP) 1A2, and previous studies of the effect of food on the bioavailability and pharmacokinetics of anagrelide were conducted prior to the identification of the active metabolite, 3-hydroxyanagrelide.

Objectives

The objectives of this study were to determine the effect of food and caffeine on the pharmacokinetics of anagrelide and its active metabolite, 3-hydroxyanagrelide, to monitor electrocardiogram (ECG) parameters following drug administration, and to document the relationship between palpitations, ECG changes and caffeine intake

Methods

Thirty-five healthy subjects who received 1 mg of anagrelide following either a 10-h fast or within 30 min of a standardized breakfast, including two cups of coffee, were studied.

Results

Time to maximum (peak) plasma concentration (C_max) of anagrelide was 4.0 h in the fed and 1.5 h in the fasted group (p < 0.05); similar results were observed for 3-hydroxyanagrelide. The mean C_max of anagrelide was 4.45 ± 2.32 ng/mL and 5.08 ± 2.99 ng/mL in the fed/caffeine and fasted groups, respectively; peak concentrations were higher for 3-hydroxyanagrelide in both the fed/caffeine and fasted groups. The most frequent adverse events (AEs) were headache (60 %) and palpitations (40 %). There were no serious AEs and all ECGs were normal, although significant reductions in PR interval, QRS length and QT interval were observed in both groups. Heart rate increased after anagrelide administration in both fed/caffeine and fasted states (p < 0.01); however, increased heart rate was significantly more frequent in the fed/caffeine state than in the fasted state (p < 0.001 for heart rate increase in the first hour after drug administration). There was a trend towards a greater heart rate increase in subjects reporting palpitations than in those without (mean heart rate ± SD at 1 h: 10.1 ± 6.4 vs. 8.0 ± 8.4 beats/min [p = 0.35]; at 4 h: 12.7 ± 7.5 vs. 9.1 ± 8.8 beats/min [p = 0.10], respectively).

Conclusion

We conclude that food/caffeine delayed absorption of anagrelide. Anagrelide was generally well tolerated and had small effects on ECG parameters and heart rate. Caffeine may be implicated in a higher increase in heart rate and increased frequency of palpitations observed following administration of anagrelide with food/caffeine versus fasting.

Interconversion and tissue distribution of pentoxifylline and lisofylline in mice

The aim of this study was to assess the interconversion pharmacokinetics and tissue distribution of pentoxifylline and the active (R)-enantiomer of its metabolite M1, lisofylline in male CD-1 mice. Both compounds were administered intravenously at a dose of 50 mg/kg on two separate occasions. Serum and tissues were collected at different time points following drug administration. In addition, the (S)-enantiomer of M1 was administered to a group of mice and serum samples were obtained. Analyte concentrations were measured by chiral HPLC. All serum concentration versus time data were fitted simultaneously to a pharmacokinetic model incorporating interconversion processes of parent drug and metabolites. The estimated conversion clearance of (-)-(R)-M1 to pentoxifylline (CL21) was six times greater than that for the reverse process (CL12). The interconversion of pentoxifylline and (+)-(S)-M1 was faster as reflected by the values of conversion clearances CL13 and CL31 which were approximately 16 and 7 times greater in comparison with the corresponding clearances for the interconversion of pentoxifylline and (-)-(R)-M1. When fitting pharmacokinetic data of both parent compounds to a one-compartment model, the values of elimination clearances assessed were close to those obtained on the basis of the interconversion model. After administration of pentoxifylline, tissue-to-serum AUC ratios ranged from 0.1 for liver and lungs to 0.32 for brain tissue. Serum levels of its metabolite, (-)-(R)-M1 were very low, whereas its tissue levels exceeded serum concentrations. The highest value of metabolite-to-parent AUC ratio (4.98) was observed in lungs. When (-)-(R)-M1 was given as a parent drug, tissue-to-serum AUC ratios in liver, kidney, and lungs were very close and ranged from 0.64 to 0.72. At the same time, levels of its metabolite, pentoxifylline were relatively low both in serum and all tissues studied. In consequence, metabolite-to-parent AUC ratios did not exceed the value of 0.27. In conclusion, reversible metabolism plays a modest role in the disposition of pentoxifylline and (-)-(R)-M1. It seems that pentoxifylline has less favourable pharmacokinetic properties than (-)-(R)-M1 due to lower concentrations attained in target organs. High levels of (-)-(R)-M1 observed after pentoxifylline administration in certain tissues such as liver or lungs suggest that pentoxifylline may constitute an effective prodrug for (-)-(R)-M1 in these organs.

Effects of different dialysis membranes on serum concentrations of epoetin alfa, darbepoetin alfa, enoxaparin, and iron sucrose during dialysis

BACKGROUND

Numerous substances are administered during dialysis for anticoagulation and the treatment of anemia and iron deficiency. The availability of current dialysis membranes is diverse, but assessment of the effects of different membranes on these routinely administered substances is lacking. This prospective study appraises specific effects of 7 dialysis membranes (4 low-flux membranes, 3 high-flux membranes) on the handling of 4 commonly administered agents (epoetin alfa, darbepoetin alfa, enoxaparin, and iron sucrose) during dialysis.

METHODS

Using a different membrane sequentially, 6 stable hemodialysis patients were treated with epoetin alfa, enoxaparin, and iron sucrose, and 6 patients with darbepoetin alfa. Serum concentrations (predialyzer and postdialyzer) of each substance were assessed after administration and after 4 hours of dialysis (predialyzer).

RESULTS

Overall, use of low-flux membranes resulted in similar serum concentrations for all compounds. However, use of high-flux membranes showed reduced antifactor Xa levels immediately (predialyzer, P = 0.028; postdialyzer, P = 0.027) and 4 hours after (P = 0.001) administration of enoxaparin compared with low-flux membranes. Variable changes in darbepoetin concentrations also were found between the high-flux membranes during dialysis (P = 0.009). Although peak serum concentrations of all compounds were inversely proportional to body weight, the percentage of change during dialysis was not related to dosage or body weight.

CONCLUSION

High-flux membranes may require greater doses of enoxaparin to ensure adequate anticoagulation during dialysis and may be associated with variable changes in darbepoetin concentrations. For other compounds, no noteworthy difference among membranes was defined.

Dosing regimen and hematologic effects of pentoxifylline and its active metabolites in normal dogs

The disposition of pentoxifylline and two of its active metabolites (metabolite 1 [M1] and metabolite 5 [M5]) were studied following i.v. (8 mg/kg) and p.o. (30 mg/kg) administration to eight normal dogs using a randomized crossover design. Blood samples were collected at fixed time intervals after drug administration for determination of drug concentrations, platelet aggregation, and plasma fibrinogen. Complete blood counts, serum chemistry profiles, fibrinogen, and urinalysis were monitored at the beginning and end of each phase of the study (p.o. versus i.v. administration). Pentoxifylline was readily metabolized and bioavailable (50% +/- 26%). Both M1 and M5 were present throughout the study, with M5 predominating. Human drug therapeutic concentrations (1,000 ng/ml) were present for 170 +/- 24 minutes following i.v. administration and 510 +/- 85 minutes after p.o. dosing. These findings suggest that a 12-hour dosing regimen is appropriate. None of the dogs experienced any adverse effects after pentoxifylline administration. The lack of hematologic effects suggests that the immunologic effects of pentoxifylline may be of more importance in dogs.

Comparative bioavailability study of two controlled-release pentoxifylline tablet preparations

The bioavailability of a generic preparation of pentoxifylline sustained-release (SR) tablet was evaluated in comparison with a proprietary product (Trental 400). For the study, 12 healthy male volunteers participated; the study was conducted according to a randomized, two-way crossover design. The bioavailability was compared using the parameters total area under the plasma level-time curve AUC0-infinity, peak plasma concentration Cmax, and time to reach peak plasma concentration Tmax. No statistically significant difference was observed between the values of the two products in all three parameters. The 90% confidence interval for the ratio of the logarithmic transformed AUC0-infinity values of the generic pentoxifylline over those of Trental 400 was found to lie between 0.83 and 1.00, while that of the parameter Cmax was between 0.91 and 1.29. In addition, elimination half-life t1/2 and apparent volume of distribution Vd were calculated. There was no statistically significant difference between the t1/2 Vd values obtained from the data of the two preparations.

Pharmacokinetics of pentoxifylline in dogs after oral and intravenous administration

OBJECTIVE

To evaluate the pharmacokinetics of pentoxifylline (PTX) and its 5-hydroxyhexyl-metabolite, metabolite 1 (M1), in dogs after IV administration of a single dose and oral administration of multiple doses.

ANIMALS

7 sexually intact, female, mixed-breed dogs.

PROCEDURE

A crossover study design was used so that each of the dogs received all treatments in random order. A drug-free period of 5 days was allowed between treatments. Treatments included IV administration of a single dose of PTX (15 mg/kg of body weight), oral administration of PTX with food at a dosage of 15 mg/kg (q 8 h) for 5 days, and oral administration of PTX without food at a dosage of 15 mg/kg (q 8 h) for 5 days. Blood samples were taken at 0.25, 0.5, 1, 1.5, 2, 2.5, and 3 hours after the first and last dose of PTX was administered PO, and at 5, 10, 20, 40, 80, and 160 minutes after PTX was administered IV.

RESULTS

PTX was rapidly absorbed and eliminated after oral administration. Mean bioavailability after oral administration ranged from 15 to 32% among treatment groups and was not affected by the presence of food. Higher plasma PTX concentrations and apparent bioavailability were observed after oral administration of the first dose, compared with the last dose during the 5-day treatment regimens.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, oral administration of 15 mg of PTX/kg results in plasma concentrations similar to those produced by therapeutic doses in humans, and a three-times-a-day dosing regimen is the most appropriate.