Exposure-clinical response analysis of paricalcitol in patients with chronic kidney disease (stage 5) on hemodialysis or peritoneal dialysis.

Paricalcitol injection and capsules are approved for the prevention and treatment of secondary hyperparathyroidism. Exposure-response analyses were performed to describe paricalcitol pharmacokinetics and the relationship to clinical responses (intact parathyroid hormone [iPTH], serum calcium, and phosphorus) following administration of paricalcitol capsules or injection to patients with chronic kidney disease (stage 5). Paricalcitol pharmacokinetics were similar following intravenous and oral administration with mean oral clearance of 1.75 L/h and bioavailability of 75.1%. Exposure-clinical response was best described by an indirect effects model where serum iPTH, calcium, and phosphorus production rates were directly affected by paricalcitol. Significant covariates in the response model included screening iPTH, calcium, and phosphorus on their corresponding synthesis rates; age on iPTH EC(50); and bone-specific alkaline phosphatase on calcium EC(50) (CRIT). This exposure-response model was used in extensive clinical trial simulations to assess alternative dose regimens for CKD stage 5 patients.

Safety and efficacy of ABT-089 in pediatric attention-deficit/hyperactivity disorder: results from two randomized placebo-controlled clinical trials.

OBJECTIVE: To assess the safety and efficacy of ABT-089, a novel α(4)ß(2) neuronal nicotinic receptor partial agonist, vs. placebo in children with attention-deficit/hyperactivity disorder (ADHD). METHOD: Two multicenter, randomized, double-blind, placebo-controlled, parallel-group studies of children 6 through 12 years of age were conducted. Study 1 (n = 274) assessed six treatment groups over 8 weeks: 4 once-daily (QD) ABT-089 doses (0.085-0.700 mg/kg), QD atomoxetine, and placebo. Study 2 (n = 119) assessed three treatment groups over 6 weeks: 2 QD ABT-089 doses (0.7 mg/kg, 1.4 mg/kg) and placebo. The primary efficacy variable was the investigator-administered Attention-Deficit/Hyperactivity Disorder Rating Scale-IV: Home Version (ADHD-RS-IV [HV]) Total Score. Safety was assessed by adverse event (AE) monitoring, laboratory tests, vital signs, physical examinations, and electrocardiogram measures. RESULTS: There was no statistically significant difference between ABT-089 and placebo in mean change from baseline to final evaluation of ADHD-RS-IV (HV) Total Score or other outcome measures at any dose in either study. In Study 1, atomoxetine showed statistically significant improvement for the primary and most secondary endpoints. ABT-089 was generally safe and well tolerated, with no statistically significant difference between any ABT-089 dose and placebo in the overall incidence of any specific AE, and no clinically significant changes in other safety measures. CONCLUSIONS: ABT-089 did not show efficacy on the primary efficacy variable, the ADHD-RS-IV (HV) Total Score, or other measures of ADHD symptomatology in children with ADHD, and had a safety profile similar to placebo. These results contrast with published reports of efficacy of nicotinic modulators in adults with ADHD.

Toxicokinetic study of recombinant human heparin-binding epidermal growth factor-like growth factor (rhHB-EGF) in female Sprague Dawley rats.

PURPOSE: To determine the toxicity and pharmacokinetics of recombinant heparin-binding epidermal growth factor-like growth factor in female Sprague Dawley rats following intra-bladder and intravenous administration. MATERIALS AND METHODS: rhHB-EGF was administered once daily for 6 or 27 days at doses of 3, 10, or 30 microg/kg. 125I-rhHB-EGF was administered on day 7 or 28 for pharmacokinetic analysis. Toxicity was assessed by general appearance and behavior, gross necropsy, blood chemistry and microscopic evaluation. RESULTS: Plasma AUCss of [125I] rhHB-EGF equivalents following IB administration for 7 days were 4.28+/-2.29, 7.75+/-2.70, and 7.11+/-1.42 ng ml(-1) h(-1) at doses of 3, 10, and 30 microg/kg, respectively. Following IV administration, the AUCss on day 7 increased from 27.0+/-2.66 to 124+/-5.09 and 385.11+/-7.57 ng ml(-1) h(-1) with increasing the dose from 3 to 10 and 30 microg/kg. Similar AUCss data was obtained after 28 day administration. No toxicity was evident upon gross examination. Histologic examination revealed subacute inflammation and lymphocytic infiltration of the urinary bladder in animals from all groups dosed by the IB route. CONCLUSIONS: Plasma and bladder concentrations of recombinant human [125I] rhHB-EGF equivalents were significantly lower following the IB route than following IV administration. Histologic tissue examination indicated no toxicity attributable to rhHB-EGF.

Phase I and pharmacokinetic study of flavopiridol followed by 1-beta-D-arabinofuranosylcytosine and mitoxantrone in relapsed and refractory adult acute leukemias.

PURPOSE: The serine/threonine kinase inhibitor flavopiridol targets multiple cyclin-dependent kinases, induces checkpoint arrest, and interrupts transcriptional elongation. We designed a phase I clinical trial using a timed sequential therapy approach where flavopiridol was given for the dual purpose of initial cytoreduction and enhancing cell cycle progression of the remaining leukemia cell cohort followed by cycle-dependent drugs 1-beta-D-arabinofuranosylcytosine (ara-C) and mitoxantrone. EXPERIMENTAL DESIGN: Flavopiridol was given by 1-hour infusion daily for 3 days beginning day 1 followed by 2 g/m2/72 h ara-C beginning day 6 and 40 mg/m2 mitoxantrone beginning day 9. In vivo correlates included pharmacokinetics, modulation of blast cycle regulators, and serum and marrow supernatant vascular endothelial growth factor levels. RESULTS: Of 34 adults receiving induction therapy, 16 (47%) evinced direct leukemia cytotoxicity with > or =50% drop in peripheral blast counts and tumor lysis in 9 (26%). Four (12%) died during therapy (two fungal infections and two sudden death). Dose-limiting toxicity occurred at 60 mg/m2/d with profound neutropenia >40 days duration, and maximal tolerated dose was 50 mg/m2/d. Overall response rate was 31% in 26 acute myelogenous leukemia and 12.5% in acute lymphoblastic leukemia. Pharmacokinetics showed that a linear two-compartment model with first-order elimination provided the best fit of the observed concentration versus time data. Flavopiridol down-regulated one or more target proteins in marrow blasts in vivo. Vascular endothelial growth factor was detected in sera and marrow supernatant pretreatment, and sera obtained on day 3 inhibited bovine aortic endothelial cell proliferation by a mean of 32% (range, 10-80%). CONCLUSIONS: Our data suggest that flavopiridol is cytotoxic to leukemic cells and, when followed by ara-C and mitoxantrone, exerts biological and clinical effects in patients with relapsed and refractory acute leukemias. These findings warrant continuing development of flavopiridol at 50 mg/m2/d x 3 days in combination with cytotoxic and biological agents for acute leukemias.

A phase I and pharmacologic study of idarubicin, cytarabine, etoposide, and the multidrug resistance protein (MDR1/Pgp) inhibitor PSC-833 in patients with refractory leukemia.

This study was conducted to define the maximum tolerated dose (MTD), dose limiting toxicity (DLT), and pharmacokinetics of idarubicin when administered with and without the P-glycoprotein inhibitor PSC-833 in combination with cytarabine, and etoposide. Fifteen patients with relapsed and refractory acute leukemia were enrolled and received cytarabine as a 7-day continuous infusion, with etoposide and idarubicin administered for any three consecutive days during the cytarabine infusion. Two hours prior to the second dose of idarubicin, PSC-833 administration was initiated. The pharmacokinetics of idarubicin alone and with PSC-833 was assessed at three idarubicin dose levels (6, 8 and 10 mg/m(2)). The MTD of idarubicin in this combination was 8 mg/(m(2) day) with a DLT of oral mucositis. The complete remission rate (on an intent-to-treat basis) for this regimen was 33%, with a median duration of 6 months. The clearance of idarubicin was 140 +/- 200 and 181 +/- 94.3 l/h for idarubicin alone and with PSC-833, respectively. The volume of distribution of the central compartment was 423 +/- 443 and 337 +/- 394 l for idarubicin alone and in combination with PSC-833, respectively. This combination including PSC-833 was well tolerated. Although a pharmacokinetic interaction might have been expected, PSC-833 did not significantly alter the disposition of idarubicin.

Liquid chromatography method for the quantitation of the breast cancer resistance protein ABCG2 inhibitor fumitremorgin C and its chemical analogues in mouse plasma and tissues.

Fumitremorgin C (FTC) was recently discovered to be a potent and selective inhibitor of the breast cancer resistance protein (BCRP/ABCG2). FTC was shown to reverse multidrug resistance mediated by BCRP and to increase the cytotoxicity of several anticancer agents in vitro. To support in vivo studies a reverse phase HPLC method with ultraviolet detection was developed to quantitate FTC in mouse plasma and tissues. Further, assay method validation was performed for the determination of FTC in mouse plasma. Plasma standard curves ranged from 0.03 to 30 microg/ml, while the various tissue assay ranges differed to some extent. The sample preparation consisted of acetonitrile precipitation with separation accomplished with a C18 Novapak column and a C18 pre-column utilizing an isocratic mobile phase of ammonium acetate and acetonitrile. UV detection was set at 225 nm for FTC and at 312 nm for roquefortine, the internal standard. The retention times were approximately 9.5 min for FTC and 13.0 min for roquefortine. The recoveries for FTC and roquefortine from plasma were 90.8+/-5.8% and 111.6+/-13.6, respectively. The reported assay can be used for future study of BCRP resistance in vivo in different biological matrices. Further, we found that a more potent analogue of FTC, Ko143, was able to be extracted and detected, with a maximal UV absorbance at 320 nm under the conditions reported.

Evaluation of P-glycoprotein-mediated renal drug interactions in an MDR1-MDCK model.

STUDY OBJECTIVE: To evaluate P-glycoprotein (P-gp)-mediated renal drug interactions in an in vitro model of tubular secretion. DESIGN: In vitro experiment. SETTING: University-affiliated pharmacokinetics laboratory. CELL LINES: Madin-Darby canine kidney (MDCK), multidrug-resistant-1 (MDR1)-MDCK, and human colon carcinoma (Caco-2) cells. INTERVENTION: Transepithelial transport (basolateral-to-apical and apical-to-basolateral) of cimetidine was assessed in the absence and presence of various concentrations of the P-gp inhibitors itraconazole and PSC-833 in a renal P-gp cell culture model (MDR1-MDCK). MEASUREMENTS AND MAIN RESULTS: Apparent permeability of cimetidine was characterized, and level of P-gp expression was determined by Western blot analysis, in MDCK (wild type), MDR1-MDCK, and Caco-2 cells (for relative comparison). In the presence of PSC-833, cimetidine's apparent permeability value for basolateral-to-apical transport decreased from 2.96 to 1.15 x 10(-6) cm/second, coupled with a decrease in efflux ratio from 2.36 to 1.80. The effect of itraconazole was concentration dependent, with cimetidine's apparent permeability value for basolateral-to-apical transport decreasing from 3.96 to 1.92 x 10(-6) cm/second (p < 0.05), resulting in a 50% decrease in efflux ratio. Expression of P-gp was negligible in MDCK (wild-type) cells, but high-level expression was confirmed in both MDR1-MDCK and Caco-2 cells. CONCLUSION: P-glycoprotein plays a significant role in the renal tubular secretion of organic cations such as cimetidine, and the high level of P-gp expression in MDR1-MDCK cells makes this a well-suited model for evaluating mechanisms of renal drug interactions.