Andrej Skerjanec

Pharmacokinetics and Pharmacodynamics of Zoledronic Acid in Cancer Patients with Bone Metastases

The pharmacokinetics, pharmacodynamics, and safety of zoledronic acid (Zometa®), a new‐generation bisphosphonate, were evaluated in 36 patients with cancer and bone metastases. Zoledronic acid (by specific radioimmunoassay) and markers of bone turnover were determined in plasma and urine after three consecutive infusions (qx28 days) of 4 mg/5 min (n = 5), 4 mg/15 min (n = 7), 8 mg/15 min (n = 12), or 16 mg/15 min (n = 12). Zoledronic plasma disposition was multiphasic, with half‐lives of 0.2 and 1.4 hours representing an early, rapid decline of concentrations from the end‐of‐infusion Cmax to < 1% of Cmax at 24 hours postdose and half‐lives of 39 and 4526 hours describing subsequent phases of very low concentrations between days 2 and 28 postdose. AUC0‐24h and Cmax were dose proportional and showed little accumulation (AUC0_24h ratio between the third and first dose was 1.28). Prolonging the infusion from 5 to 15 minutes lowered Cmax by 34%, with no effect on AUC0‐24h. Urinary excretion of zoledronic acid was independent of infusion duration, dose, or number of doses, showing average Ae0‐24h of 38% ± 13%, 41% ± 14%, and 37% ± 17%, respectively, after 4, 8, and 16 mg. Only trace amounts of drug were detectable in post 24‐hour urines. Renal clearance (Ae0‐24h)/(AUC0‐24h) was on average 69 ± 28, 81 ± 40, and 54 ± 34 ml/min after 4, 8, and 16 mg, respectively, and showed a moderate correlation (r = 0.5; p < 0.001) with creatinine clearance, which was 84 ± 23, 82 ± 25, and 80 ± 40 ml/min for the dose groups at baseline. Adverse events and changes from baseline in vital signs and clinical laboratory variables showed no relationship in terms of type, frequency, or severity with zoledronic acid dose or pharmacokinetic parameters. Zoledronic acid produced significant declines from baseline in serum and/or creatinine‐corrected urine C‐telopeptide (by 74%), N‐telopeptide (69%), pyridinium cross‐links (19–33%), and calcium (62%), with an increasing trend (by 12%) in bone alkaline phosphatase. There was no relationship of the magnitude and duration of these changes with zoledronic acid dose, Ae0‐24j, AUC0‐24h, or Cmax. The antiresorptive effects were evident within 1 day postdose and were maintained over 28 days across all dose levels, supporting monthly dosing with 4 mg zoledronic acid.

The Pharmacokinetics and Pharmacodynamics of Zoledronic Acid in Cancer Patients with Varying Degrees of Renal Function

An open‐label pharmacokinetic and pharmacodynamic study of zoledronic acid (Zometaθ) was performed in 19 cancer patients with bone metastases and known, varying levels of renal function. Patients were stratified according to creatinine clearance (CLcr) into different groups of normal (CLcr > 80 mL/min), mildly (CLcr = 50–80 mL/min), or moderately/severely impaired (CLcr = 10–50 mL/min) renal function. Three intravenous infusions of 4 mg zoledronic acid were administered at 1‐month intervals between doses. Plasma concentrations and amounts excreted in urine were determined in all subjects, and 4 patients were administered 14C‐labeled zoledronic acid to assess excretion and distribution of drug in whole blood. In general, the drug was well tolerated by the patients. Mean area under the plasma concentration versus time curve and mean concentration immediately after cessation of drug infusion were lower, and mean amounts excreted in urine over 24 hours from start of infusion were higher in normal subjects than in those with impaired renal function (36% vs. 28% of excreted dose), although the differences were not significant. Furthermore, with repeated doses, there was no evidence of drug accumulation in plasma or changes in drug exposure in any of the groups, nor was there any evidence of changes in renal function status. Serum levels of markers of bone resorption (serum C‐telopeptide and N‐telopeptide) were noticeably reduced after each dose of zoledronic acid across all three renal groups. It was concluded that in patients with mildly to moderately reduced renal function, dosage adjustment of zoledronic acid is likely not necessary.

Pharmacodynamics, pharmacokinetics, and safety of multiple doses of FTY720 in stable renal transplant patients: a multicenter, randomized, placebo-controlled, phase I study.

Background. FTY720, a novel immunomodulator, displays potent immunosuppressive activity in a variety of preclinical transplant models. This study examined the safety, pharmacodynamics, and pharmacokinetics of multiple doses of FTY720 in stable renal transplant patients. Methods. This randomized, multicenter, double-blind, placebo-controlled, phase I study included adults who had been maintained on a regimen of cyclosporine A (CsA) microemulsion and prednisone (or its equivalent) for at least 1 year after renal transplantation. Patients received once-daily doses of 0.125, 0.25, 0.5, 1.0, 2.5, or 5.0 mg FTY720, or placebo for 28 days. After completion of study drug administration, the patients were monitored until day 56 by serial laboratory tests, clinical examinations, and recording of adverse events. The study includes 76 treatment courses (61 FTY720 and 15 placebo), with 65 patients enrolled once and 11 reenrolled. Results. FTY720 doses greater than or equal to 1.0 mg/day produced a significant reduction in peripheral blood lymphocyte count by up to 85%, which reversed within 3 days after discontinuation of study medication. Compared with placebo-treated patients, FTY720 subjects did not show a major increase in adverse events or a change in renal function. Pharmacokinetic measurements revealed that FTY720 displayed linear relations of doses and concentrations over a wide range, but had no effect on CsA exposure. Conclusions. At doses up to 5.0 mg/day for 28 days, stable renal transplant patients treated with FTY720 in combination with CsA and prednisone displayed a dose-dependent, reversible decline in peripheral blood lymphocytes without an enhanced incidence of collateral toxicities, except possibly bradycardia.

In Vitro and in Vivo Induction of Cytochrome P450: A Survey of the Current Practices and Recommendations: A Pharmaceutical Research and Manufacturers of America Perspective

Cytochrome P450 (P450) induction is one of the factors that can affect the pharmacokinetics of a drug molecule upon multiple dosing, and it can result in pharmacokinetic drug-drug interactions with coadministered drugs causing potential therapeutic failures. In recent years, various in vitro assays have been developed and used routinely to assess the potential for drug-drug interactions due to P450 induction. There is a desire from the pharmaceutical industry and regulatory agencies to harmonize assay methodologies, data interpretation, and the design of clinical drug-drug interaction studies. In this article, a team of 10 scientists from nine Pharmaceutical Research and Manufacturers of America (PhRMA) member companies conducted an anonymous survey among PhRMA companies to query current practices with regards to the conduct of in vitro induction assays, data interpretation, and clinical induction study practices. The results of the survey are presented in this article, along with reviews of current methodologies of in vitro assays and in vivo studies, including modeling efforts in this area. A consensus recommendation regarding common practices for the conduct of P450 induction studies is included.

Pharmacodynamics of single doses of the novel immunosuppressant FTY720 in stable renal transplant patients.

FTY720, a new and potent immunosuppressant, causes in animal models a rapid, reversible reduction of all subsets of peripheral blood lymphocytes, inducing their migration to secondary lymphoid organs. In this human phase I trial, the pharmacodynamics of single oral doses of FTY720 were evaluated. A randomized, double‐blind, placebo‐controlled, time‐lagged study of six different single ascending oral doses of FTY720 ranging from 0.25 to 3.5 mg was conducted in stable renal transplant patients receiving a cyclosporine‐based regimen. Absolute and subset lymphocyte counts, as well as absolute differential leukocyte counts, were determined by differential blood counts and flow cytometry at screening and multiple intervals thereafter. A pharmacodynamic model was established. Twenty‐four single doses of FTY720 that were administered caused a transient, reversible pan‐lymphopenia within 4 h. Lymphocyte subgroup analysis revealed that almost all subsets declined, with CD4‐ and CD45RA‐positive cells being affected the most. Natural killer cells, granulocytes and monocytes were not influenced by FTY720. The lymphocyte count returned to baseline within 72 h in all dosing cohorts except the highest. Pharmacokinetik/pharmacodynamic modelling revealed a nonlinear dose effect and resulted in a good fit with observed values. These data show that FTY720 is highly effective in humans, with single oral doses of FTY720 ranging from 0.25 to 3.5 mg causing a reversible selective panlymphopenia.

Biodistribution and Plasma Protein Binding of Zoledronic Acid

The bisphosphonate zoledronic acid is a potent inhibitor of osteoclast-mediated bone resorption. To investigate drug biodistribution and elimination, 14C-zoledronic acid was administered intravenously to rats and dogs in single or multiple doses and assessed for its in vitro blood distribution and plasma protein binding in rat, dog, and human. Drug exposure in plasma, bones, and noncalcified tissues was investigated up to 240 days in rats and 96 h in dogs using radiometry after dissection. Drug biodistribution in the rat and within selected bones from dog was assessed by autoradiography. Concentrations of radioactivity showed a rapid decline in plasma and noncalcified tissue but only a slow decline in bone, to ∼50% of peak at 240 days post dose, whereas the terminal half-lives (50–200 days) were similar in bone and noncalcified tissues, suggesting redistribution of drug from the former rather than prolonged retention in the latter. Uptake was highest in cancellous bone and axial skeleton. At 96 h after dose, the fraction of dose excreted was 36% in rat and 60% in dog; 94 to 96% of the excreted radioactivity was found in urine. Blood/plasma concentration ratios were 0.52 to 0.59, and plasma protein binding of zoledronic acid was moderate to low in all species. The results suggest that a fraction of zoledronic acid is reversibly taken up by the skeleton, the elimination of drug is mainly by renal excretion, and the disposition in blood and noncalcified tissue is governed by extensive uptake into and slow release from bone.

Pharmacokinetics, pharmacodynamics and safety of QGE031 (ligelizumab), a novel high-affinity anti-IgE antibody, in atopic subjects

Using a monoclonal antibody with greater affinity for IgE than omalizumab, we examined whether more complete suppression of IgE provided greater pharmacodynamic effects, including suppression of skin prick responses to allergen.

QT and QTc Interval With Standard and Supratherapeutic Doses of Darifenacin, a Muscarinic M3 Selective Receptor Antagonist for the Treatment of Overactive Bladder

Prolongation of QT interval on an electrocardiogram is a valuable predictor of a drugs ability to cause potentially fatal ventricular tachyarrhythmia (torsades de pointes). Darifenacin is a muscarinic M3 selective receptor antagonist developed for the treatment of overactive bladder, a debilitating condition that is particularly prevalent in the older population. This 7‐day, randomized, parallel‐group study (n = 188) measured QT/QTc interval in healthy volunteers receiving once‐daily darifenacin at steady‐state therapeutic (15 mg) and supratherapeutic (75 mg) doses, alongside controls receiving placebo or moxifloxacin (positive control, 400 mg) once daily. There was no significant increase in QTcF interval with darifenacin treatment compared with placebo. Mean changes from baseline at pharmacokinetic Tmax versus placebo were −0.4 and −2.2 milliseconds in the darifenacin 15 mg and 75 mg groups, respectively, compared with +11.6 milliseconds in the moxifloxacin group (P <.01). This study demonstrates that darifenacin does not prolong QT/QTc interval.

The Clinical Pharmacokinetics of Darifenacin

Darifenacin hydrobromide is a selective muscarinic M3 receptor antagonist that is indicated for use in treatment of overactive bladder disorder. Darifenacin was found to have a short terminal elimination half-life after intravenous and immediate-release oral dosage forms (3–4 hours) but this increased with a prolonged-release (PR) formulation (14–16 hours). The absolute bioavailability of darifenacin from 7.5 and 15mg PR tablets was estimated to be 15.4% and 18.6%, respectively. With repeated once-daily oral administration of the PR formulation, peak plasma concentrations of darifenacin are achieved approximately 7 hours post-dose. After oral administration, darifenacin is well absorbed from the gastrointestinal tract and very little unchanged drug (<2%) is recovered in the faeces. Steady state is achieved after 6 days of once-daily administration of the PR formulation. As expected, values of peak plasma concentration (Cmax) and area under the plasma concentration-time curve are dose dependent, although the increase in plasma concentrations is proportionally greater than the increase in dose owing to saturation of presystemic metabolism. From intravenous administration, it has been established that darifenacin possesses a moderate-to-high hepatic extraction ratio, with high plasma clearance (36–52 L/h) and a volume of distribution (165–276L) that exceeds total body water. It is highly protein bound (98%), primarily to α1-acid glycoprotein. Darifenacin is subject to extensive hepatic metabolism, with 3% of unchanged drug excreted in urine and faeces. Metabolism is mediated by hepatic cytochrome P450 2D6 and 3A4, the main metabolic routes being monohydroxylation in the dihydrobenzfuran ring, dihydrobenzfuran ring opening, and N-dealkylation of the pyrrolidine nitrogen. Several possibly important drug-drug interactions have been identified with darifenacin, including ketoconazole, erythromycin and fluconazole, each of which increases darifenacin mean Cmax by 9.52-, 2.28- and 1.88-fold, respectively. When given with imipramine, darifenacin causes 1.6-fold higher plasma concentrations of the antidepressant and its major metabolite. Moderate hepatic impairment, but not renal insufficiency, has been shown to increase plasma concentrations of the drug. The pharmacokinetic profile of darifenacin is not affected by food.

FTY720, a novel immunomodulator in de novo kidney transplant patients : Pharmacokinetics and exposure-response relationship

The pharmacokinetics, safety, and preliminary efficacy of FTY720, a novel immunomodulator, were examined in de novo renal transplant patients. Both noncompartmental and population methods were used to estimate pharmacokinetic estimates in the patients. The steady‐state plasma concentrations of FTY720 increased in accordance with maintenance dose level, indicating linearity in clearance and volume of distribution over the 0.25‐ to 2.5‐mg dose range. The pharmacokinetics of FTY720 in de novo renal transplant patients were characterized by the long terminal phase half‐life of approximately 200 hours across doses, high volume of distribution (>3000 L), and low clearance (10.8 L/h). The intersubject variation of clearance was 55%, and the intrasubject variation of FTY720 concentrations was 28%. The population analysis revealed significant positive relationships between baseline alkaline phosphatase and clearance, as well as between baseline body weight on apparent volume of distribution. There was no relationship between FTY720 concentrations within a given FTY720 dose cohort and the rate of allograft rejection.