Intratracheal Administration of Recombinant Human Factor IX (BeneFix™) Achieves Therapeutic Levels in Hemophilia B Dogs

The purpose of this paper was to establish proof of concept for administration of human recombinant F.IX (rF.IX) by inhalation for therapy of hemophilia B. The pharmacokinetics of intratracheal (IT) administration of rF.IX was studied in nine hemophilia B dogs randomized into 3 groups that received 200 IU/kg IT, 1000 IU/kg IT, or 200 IU/kg intravenously (IV). IT rF.IX produced therapeutic levels of F.IX antigen and activity and the pharmacokinetic parameters were consistent with a slow release from a depot site within the lungs. Bio-availability compared to IV administration was 11% for 200 IU/kg IT and 4.9% for 1000 IU/kg. The whole blood clotting time began to shorten at 2 h but F.IX bioactivity was not detected until 8 h post infusion in both IT groups. In all groups, F.IX activity was detected through 72 h post administration. These data demonstrate that biologically active rF.IX can reach the systemic circulation when given IT. Aerosolization of rF.IX may provide a needle-free therapeutic option for delivery of rF.IX to hemophilia B patients.

Intratracheal administration of recombinant human factor IX (BeneFix) achieves therapeutic levels in hemophilia B dogs

The purpose of this paper was to establish proof of concept for administration of human recombinant F.IX (rF.IX) by inhalation for therapy of hemophilia B. The pharmacokinetics of intratracheal (IT) administration of rF.IX was studied in nine hemophilia B dogs randomized into 3 groups that received 200 IU/kg IT, 1,000 IU/kg IT, or 200 IU/kg intravenously (IV). IT rF.IX produced therapeutic levels of F.IX antigen and activity and the pharmacokinetic parameters were consistent with a slow release from a depot site within the lungs. Bioavailability compared to IV administration was 11% for 200 IU/kg IT and 4.9% for 1,000 IU/kg. The whole blood clotting time began to shorten at 2 h but F.IX bioactivity was not detected until 8 h post infusion in both IT groups. In all groups, F.IX activity was detected through 72 h post administration. These data demonstrate that biologically active rF.IX can reach the systemic circulation when given IT. Aerosolization of rF.IX may provide a needle-free therapeutic option for delivery of rF.IX to hemophilia B patients.

Pharmacokinetics, pharmacodynamics, allometry, and dose selection of rPSGL-Ig for phase I trial

rPSGL-Ig is a recombinant, soluble, and chimeric form of P-selectin glycoprotein ligand-1, which is developed as an antagonist to P-selectin. Allometric and pharmacokinetic/pharmacodynamic modeling was used to select doses for human clinical trials. Pharmacokinetic parameters of rPSGL-Ig such as clearance (CL), volume of distribution (Vc), and t(1/2) across animal species are well described by power functions with body weight as an independent variable. The power functions for CL, Vc, and t(1/2) were CL = 0.37. W(0.93) ml/h (r(2) = 0.94), Vc = 45.0.W(1.064) ml (r(2) = 0.988), and t(1/2) = 190.W(0.159) h (r(2) = 0.75), respectively. These functions provide a means to predict pharmacokinetics of rPSGL-Ig in humans. For a 70-kg human, the values of CL, Vc, and t(1/2) are predicted to be 19.9 ml/h, 4138 ml, and 15.5 days, respectively. The predicted pharmacokinetics in humans is used in conjunction with pharmacological data to estimate appropriate doses for clinical trials. The doses that may provide potential effects in humans range from 0.13 to 4.7 mg/kg. The predicted doses produce concentrations above those that are associated with efficacy in animal disease models and, maintain concentrations above the EC(50) of in vitro binding between rPSGL-Ig and stimulated human platelets. Hence, rPSGL-Ig in clinical trials may provide therapeutic activities for P-selectin-mediated diseases.

Phase I and pharmacologic study of oral fluorouracil on a chronic daily schedule in combination with the dihydropyrimidine dehydrogenase inactivator eniluracil

PURPOSE

To determine the maximum-tolerated dose (MTD), toxicities, and pharmacokinetics of oral fluorouracil (5-FU) administered twice daily in combination with oral eniluracil, an inactivator of dihydropyrimidine dehydrogenase, administered for 28 days every 35 days.

PATIENTS AND METHODS

Oral 5-FU 1.35 mg/m(2) twice daily was administered with oral eniluracil 10 mg daily for 14 to 28 days, followed by a 1-week rest period. Eniluracil was started 1 day before 5-FU. Patients then received escalated doses of oral 5-FU 1. 35 to 1.8 mg/m(2) twice daily with an increased dose of eniluracil 10 mg twice daily for 28 days. A reduced dose of 5-FU 1.0 mg/m(2) with eniluracil 20 mg twice daily was evaluated.

RESULTS

Thirty-six patients with solid malignancies were enrolled onto the study. Diarrhea was the principal dose-limiting toxicity of oral 5-FU and eniluracil given on this chronic schedule. The recommended phase II dose is 5-FU 1.0 mg/m(2) twice daily with eniluracil 20 mg twice daily. Mean (SD) values for terminal half-life, apparent volume of distribution, and systemic clearance of 4.5 hours (0.83 hours), 19 L/m(2) (3.0 L/m(2)), and 51 mL/min/m(2) (13 mL/min/m(2)), respectively. An average of 77% of 5-FU was excreted unchanged in urine after 28 days of treatment. The mean (range) 5-FU C(SS,min) values achieved at the 1.0 mg/m(2) dose level were 22 ng/mL (8 to 38 ng/mL).

CONCLUSION

Chronic oral administration of 5-FU with oral eniluracil is tolerable and produces 5-FU steady-state concentrations similar to those achieved with protracted intravenous administration of 5-FU on clinically relevant dose schedules. Eniluracil provides an attractive means of administering 5-FU on protracted schedules.

Phase I clinical and pharmacologic study of eniluracil plus fluorouracil in patients with advanced cancer

PURPOSE

To determine the highest dose of fluorouracil (5-FU) that could be safely administered with Eniluracil (776C85; Glaxo Wellcome Inc, Research Triangle Park, NC), an inactivator of dihydropyrimidine dehydrogenase (DPD), on a daily schedule for 5 days, and to define the toxicities of the combination and the pharmacokinetics of 5-FU when administered with 776C85.

PATIENTS AND METHODS

Patients with advanced solid tumors refractory to standard therapy were enrolled at two institutions. The study consisted of three periods designed to evaluate the safety, pharmacokinetics, and pharmacodynamics of 776C85 alone (period 1); the effects of 776C85 on the pharmacokinetics of 5-FU (period 2); and the maximum-tolerated dose (MTD) of 5-FU, with or without leucovorin, that could be safely administered with 776C85 (period 3). Cohorts of at least three patients each received oral 776C85 alone at doses of 3.7 mg/m2/d, 18.5 mg/m2/d and 0.74 mg/m2/d. After a 14-day washout period, each patient then received 776C85 daily for 3 days, with a single intravenous (i.v.) bolus dose of 5-FU 10 mg/m2 on day 2. After a second washout period, patients were treated with 776C85 daily for 7 days and 5-FU i.v. bolus on days 2 through 6. The starting dose of 5-FU 10 mg/m2/d was escalated until the MTD was determined. After determination of the MTD of 5-FU given with 776C85, oral leucovorin 50 mg/d on days 2 through 6 was added to determine the MTD of 5-FU with leucovorin in the presence of 776C85. Near the completion of the study, additional cohorts of patients were treated with 776C85 at 50 mg/d and oral 5-FU with or without leucovorin.

RESULTS

Sixty-five patients were enrolled onto the study and 60 were assessable for toxicity and response. Bone marrow suppression was the primary and dose-limiting toxicity of this regimen. Other toxicities included diarrhea, mucositis, anemia, anorexia, nausea, vomiting, and fatigue. 776C85 suppressed DPD activity in peripheral-blood mononuclear cells (PBMCs) by at least 90% for at least 24 hours at all dose levels tested. In the presence of 776C85, 5-FU half-life was prolonged, clearance was reduced, and the drug displayed linear pharmacokinetics. Recommended doses for further testing on a daily for 5-day schedule are 776C85 10 mg/d with i.v. 5-FU 25 mg/m2/d; 776C85 10 mg/d with i.v. 5-FU 20 mg/m2/d plus leucovorin 50 mg/d; 776C85 50 mg/d with 5-FU given orally at 15 mg/m2/d with leucovorin at 50 mg/d.

CONCLUSION

5-FU can be safely administered with 776C85; however, the MTDs are considerably lower than those conventionally used, caused, at least in part, by marked alterations in 5-FU plasma pharmacokinetics.

Pharmacokinetics of RheothRx injection in healthy male volunteers

The objectives of this study were to evaluate the safety and tolerability of RheothRx (poloxamer 188) injection administered as an intravenous (i.v.) infusion to healthy male volunteers and to determine the pharmacokinetic profile of poloxamer 188. Thirty-six healthy male volunteers were enrolled in a randomized, double-blind, placebo-controlled, dose-escalation trial for RheothRx injection. The volunteers were randomized to three treatment groups (12 per treatment group, with eight receiving active therapy and four receiving placebo). In each treatment group, volunteers received RheothRx injection or placebo as an i.v. infusion on two occasions at least 3 weeks apart to make a total of six doses being studied (10, 30, and 45 mg/kg/h for 72 h, 60 mg/kg/h for 43.3 to 72 h, 60 and 90 mg/kg/h for 24 h). Serial plasma samples were collected during and up to 36 h after the end of the infusions; urine was collected over intervals from the start of the infusion until 36 h after the infusions were terminated. Plasma and urine samples were assayed for poloxamer 188 by gel-permeation chromatography. Pharmacokinetic parameter values were calculated by noncompartmental and compartmental methods. Poloxamer 188 was eliminated primarily by renal excretion. Estimates of clearance, elimination rate constant, and apparent volume of distribution at steady state values were independent of infusion rate. Poloxamer 188 displayed no apparent infusion rate dependence in its pharmacokinetics.

Dihydropyrimidine dehydrogenase inactivation and 5-fluorouracil pharmacokinetics: allometric scaling of animal data, pharmacokinetics and toxicodynamics of 5-fluorouracil in humans

The pharmacokinetics of 5-fluorouracil (5-FU) in different animal species treated with the dihydropyrimidine dehydrogenase (DPD) inactivator, 5-ethynyluracil (776C85) were related through allometric scaling. Estimates of 5-FU dose in combination with 776C85 were determined from pharmacokinetic and toxicodynamic analysis.

METHOD

The pharmacokinetics of 5-FU in the DPD-deficient state were obtained from mice, rats and dogs treated with 776C85 followed by 5-FU. The pharmacokinetics of 5-FU in humans were then estimated using interspecies allometric scaling. Data related to the clinical toxicity for 5-FU were obtained from the literature. The predicted pharmacokinetics of 5-FU and the clinical toxicity data were then used to estimate the appropriate dose of 5-FU in combination with 776C85 in clinical trials.

RESULTS

The allometric equation relating total body clearance (CL) of 5-FU to the body weight (B) (CL = 0.47B0.74) indicates that clearance increased disproportionately with body weight. In contrast, the apparent volume of distribution (Vc) increased proportionately with body weight (Vc = 0.58 B0.99). Based on allometric analysis, the estimated clearance of 5-FU (10.9 l/h) in humans with DPD deficiency was comparable to the observed values in humans lacking DPD activity due to genetic predisposition (10.1 l/h), or treatment with 776C85 (7.0 l/h) or (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdUrd, 6.6 l/h). The maximum tolerated dose (MTD) of 5-FU in combination with 776C85 was predicted from literature data relating toxicity and plasma 5-FU area under the concentration-time curve (AUC). Based on allometric analysis, the estimated values for the MTD in humans treated with 776C85 and receiving 5-FU as a single i.v. bolus dose, and 5-day and 12-day continuous infusions were about 110, 50 and 30 mg/m2 of 5-FU, respectively.

DISCUSSION

The pharmacokinetics of 5-FU in the DPD-deficient state in humans can be predicted from animal data. A much smaller dose of 5-FU is needed in patients treated with 776C85.

Pharmacokinetic, oral bioavailability, and safety study of fluorouracil in patients treated with 776C85, an inactivator of dihydropyrimidine dehydrogenase

PURPOSE

To study the absolute bioavailability and pharmacokinetics of an oral solution of fluorouracil (5-FU) in patients treated with 776C85, an oral inactivator of dihydropyrimidine dehydrogenase (DPD), and to evaluate the feasibility of administering oral 5-FU and 776C85 on a multiple-daily dosing schedule.

PATIENTS AND METHODS

Twelve patients with refractory solid tumors were enrolled onto this three-period study. In periods 1 and 2, patients were randomly assigned to treatment with 5-FU 10 mg/m2 on day 2 given by either the oral or intravenous (IV) route with oral 776C85 3.7 mg/m2/d on days 1 and 2. In period 3, patients received escalating doses of 5-FU (10 to 25 mg/ m2/d) orally for 5 days (days 2 to 6) with 776C85 3.7 mg/m2/d orally (days 1 to 7) every 4 weeks. Pharmaco-kinetic studies were performed in periods 1 and 2, and after the fifth oral dose of 5-FU in period 3.

RESULTS

Twelve patients completed the bioavailability and pharmacokinetic studies. Following oral 5-FU 10 mg/m2, the bioavailability was 122% +/- 40% (mean +/- SD), the terminal half-life (t1/2 beta) was 4.5 +/- 1.6 hours, the apparent volume of distribution (V beta) was 21.4 +/- 5.9 L/ m2, and the systemic clearance (Clsys) was 57.6 +/- 16.4 mL/min/m2. A correlation was observed between oral 5-FU systemic clearance and calculated creatinine clearance (r = .74; P = .009). Multiple-daily dosing did not appear to affect the pharmacokinetics of oral 5-FU. Neutropenia was the principal toxicity of oral 5-FU and 776C85, precluding escalation of oral 5-FU to doses greater than 25 mg/m2/d for 5 days every 4 weeks with 776C85.

CONCLUSION

The oral DPD inactivator 776C85 enables oral administration of 5-FU and may alter conventional 5-FU administration practices.

Area-based estimation of the initial volume of distribution and elimination rate constant following intravenous bolus injection

We evaluate here an area term, the area under the rate of change of concentration-time curve (AURC), which allows the determination of the initial or central volume of distribution (V1). It has previously been shown that AURC is equal to the sum of the coefficients of a multiexponential equation and, therefore, V1 = dose/AURC. It is also shown that the normalized moment, AURC/AUC, is equal to the elimination rate constant, K10, where AUC is the area under the concentration-time curve. This area-based method to estimate V1 and K10 has been evaluated with simulation of three model equations and compared with nonlinear regression analysis of the same data. Random errors of 10 and 15% were introduced into the concentration values. The AURC method provides values of both parameters that are similar to those obtained from nonlinear regression analysis and which are reasonably accurate estimates of the theoretically correct values. The potential limitations of this area method are discussed. Good correlations were also observed for values of V1 and K10 obtained by AURC and regression methods for data obtained from the literature for 13 different drugs.

Potential error in the measurement of tissue to blood distribution coefficients in physiological pharmacokinetic modeling. Residual tissue blood. II. Distribution of phencyclidine in the rat

A model for predicting the magnitude of error (% Err) in measuring tissue concentrations of a compound that have not been corrected for residual blood in the tissue was previously developed. The model was tested using data for phencyclidine tissue distribution in the rat. It is shown that % Err may be expressed as a function of volume fraction of blood in tissue (VF)B and tissue-to-blood distribution coefficient. Correction for residual blood is important when the volume fraction of the blood in the tissue is large and when the compound is not taken up substantially by the tissue. On the other hand, a correction may not be necessary when (VF)B is small and uptake of the compound into the tissue is substantial.

Potential error in the measurement of tissue to blood distribution coefficients in physiological pharmacokinetic modeling. Residual tissue blood. I. Theoretical considerations

Physiological pharmacokinetic models require the determination of tissue to blood distribution coefficients. A theoretical model has been developed and the resulting equations indicate that under certain conditions it is necessary to correct for the presence of drug in the residual blood remaining in the tissue. The potential error in ignoring this residual blood is expressed mathematically in terms of several important factors that include the anatomical features of the tissue (volume fractions of the blood, interstitial fluid, and cellular space) as well as the physicochemical properties of the drug (extent of binding in the blood and tissues). These theoretical considerations and resulting simulations have been applied to experimental literature data for several compounds (methotrexate, digoxin, and biperiden). We conclude that correction for the residual blood is necessary when the values of tissue to blood distribution coefficients are very small or large (relative to one) and when the volume fraction of the blood in tissue is substantial.