Average Terminal Elimination Half-life Research Articles

Pharmacokinetics, Mass Balance, Tissue Distribution and Metabolism of [14C]101BHG-D01, a Novel Muscarinic Receptor Antagonist, in Rats.

101BHG-D01, a novel long-acting and selective muscarinic receptor antagonist for the treatment of chronic obstructive pulmonary disease (COPD), is undergoing Phase Ib clinical trial in patients and has shown its potential efficacy. Its preparation method and medical use thereof have been patented in the United States (Patent No.US9751875B2). In this study, the pharmacokinetics, mass balance, tissue distribution and metabolism of radioactive 101BHG-D01 were investigated in rats after an intravenous dose of 1 mg/kg [14C]101BHG-D01 (100 μCi/kg). Radioactivity in rat plasma, urine, feces, and tissues was measured by liquid scintillation counting (LSC), and metabolite profiling and identification were conducted by UHPLC-β-RAM and UHPLC-Q-Exactive Plus MS. The total radioactivity of the study drug in rat plasma rapidly declined with an average terminal elimination half-life of 0.35 h. The radioactivity in most tissues reached the maximum concentration at 0.25 h post-- dosing. The radioactivity mainly concentrated in the kidney and pancreas. The drug-related substances tended to be distributed into the blood cells in the circulation. At 168 h post dosing, the mean recovery of the total radioactivity in urine and feces was 78.82%. Fecal excretion was the major excretion route, accounting for approximately 61% of the radioactive dose. The study drug was metabolized extensively, and a total of 17 metabolites were identified in rat plasma, urine, and feces. The major metabolic pathways involved oxidation, oxidation and dehydrogenation, and O-dephenylation. In conclusion, the study results are useful for better understanding the pharmacokinetic profiles of 101BHG-D01 and provide a robust foundation for subsequent clinical studies.

A Phase I Open-Label, Multi-Dose Escalation Study of the Dual Syk/Jak Inhibitor PRT062070 (Cerdulatinib) in Patients with Relapsed/Refractory B Cell Malignancies

Introduction: Preclinical studies of the Syk-mediated B-cell receptor pathway and Jak-mediated cytokine pathways have demonstrated a potential therapeutic advantage for the dual inhibition of both Syk and Jak kinases in the treatment of B-cell malignancies. Cerdulatinib (PRT062070) was identified from a chemistry screen as a potent and selective inhibitor of Syk, Jak1, Jak3, and Tyk2, with minimal activity against Jak2. Cerdulatinib is efficacious in rodent models of B-cell lymphoma and autoimmune disease (Coffey et al., ASH 2012) and has demonstrated anti-tumor activity in genetically diverse B-cell lymphoma cell lines that is greater than that of Syk- or Jak- selective inhibitors alone (Ma et al., ASH 2013).Methods: This Phase 1 3+3 dose escalation study is evaluating cerdulatinib, given continuously on either a once daily (QD) or twice daily (BID) schedule, for relapsed/refractory chronic lymphocytic leukemia (CLL) or B-cell non-Hodgkin lymphoma (NHL). The primary objective is to determine the maximum tolerated dose (MTD) of cerdulatinib in patients with CLL or NHL. Secondary objectives are to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of cerdulatinib and to make a preliminary assessment of antitumor activity. Toxicity is graded according to the National Cancer Institute - Common Terminology Criteria for Adverse Events (NCI-CTCAE) v4. Clinical response is evaluated according to published criteria (Hallek et al., Blood 2008:111:5446-5456; Cheson et al., J. Clin. Oncol. 2012: 25:579-586). The level of inhibition of Syk and Jak is determined using a variety of whole blood assays measuring signaling via receptors for the B-cell antigen, IL2, IL4, IL6, and GM-CSF. Serum markers of tumor burden, including CCL3, CCL4, and other markers of inflammation, are also being measured.Results: As of 4 August 2014, twelve patients have been enrolled in once daily dose cohorts of 15 mg QD, 30 mg QD, and 45 mg QD. No dose-limiting toxicities have been reported. Grade ≥3 adverse events (AEs), regardless of causality, were: Grade 3 anemia (n=1), Grade 3 neutropenia (n=1), Grade 3 fatigue (n=1), Grade 3 hypotension (n=1), Grade 3 AST increased (n=1), Grade 3 hematochezia (n=1), and Grade 5 Pneumocystis pneumonia (PCP; n=1). The patient who experienced PCP pneumonia was a 76 year old male with CLL who had received prior therapy with bendamustine and rituximab.Cerdulatinib is well-absorbed with an average terminal elimination half-life at steady state of 14 hours. Selective inhibition of Syk and Jak in whole blood assays was observed post-treatment, with IC25-IC50 (Cmin to Cmax at steady-state) against these targets achieved at the 15 mg dose level, and IC50-IC80 (Cmin to Cmax at steady-state) achieved at the 30 mg and 45 mg doses. Reductions of >50% in serum markers of inflammation, as well as in CCL3 and CCL4, were noted at all dose levels post-treatment. Two patients treated at the 15 mg dose (1 CLL, 1 follicular lymphoma [FL]) remained on study for >230 and >200 days, respectively, with stable disease (SD) prior to disease progression. One patient treated at the 30 mg dose (diffuse large B-cell lymphoma [DLBCL], who did not respond to prior R-CHOP therapy), remained on study with SD for 140 days. One patient treated at the 30 mg dose (CLL) experienced a >60% decrease in peripheral lymphocyte count prior to coming off study for PCP pneumonia. Another patient treated at the 30 mg dose (CLL) experienced early lymphocytosis and a 33% reduction in lymph node size at the end of Cycle 2 and remains on study in Cycle 3. One patient treated at the 45 mg dose (FL) experienced a 40% decrease in lymph node size at the end of Cycle 4 and remains on study in Cycle 5.Conclusions: Cerdulatinib has been well tolerated in the initial cohorts of this Phase 1 study, with no dose-limiting toxicities and preliminary evidence of anti-tumor activity. Dose escalation continues and Phase 2 expansion cohorts are planned in CLL, DLBCL and FL. DisclosuresHamlin:Gilead, Spectrum, Seattle Genetics, Genentech: Consultancy; Spectrum, GSK, Jansen and Jansen/Pharmacyclics, Portola, Seattle Genetics: Research Funding. Strickland:SCRI Development Innovations: Employment. Pandey:Portola Pharmaceuticals, Inc.: Employment; Portola Pharmaceuticals, Inc.: Equity Ownership. Coffey:Portola Pharmaceuticals: Employment, Equity Ownership. Leeds:Portola Pharmaceuticals, Inc.: Employment. Levy:Portola Pharmaceuticals: Employment; University of Michigan: Patents & Royalties. Curnutte:Portola Pharmaceuticals, Inc.: Employment, Equity Ownership; Sea Lane Biotechnologies: Consultancy; 3-V Biosciences: Equity Ownership. Wagner-Johnston:Gilead: Consultancy; Gilead: Speakers Bureau; Celgene: Research Funding. Flinn:Portola Pharmaceuticals, Inc.: Research Funding.

Pharmacokinetics and Bioequivalence Evaluation of Cyclobenzaprine Tablets

The purpose of this study was to investigate cyclobenzaprine pharmacokinetics and to evaluate bioequivalence between two different tablet formulations containing the drug. An open, randomized, crossover, single-dose, two-period, and two-sequence design was employed. Tablets were administered to 23 healthy subjects after an overnight fasting and blood samples were collected up to 240 hours after drug administration. Plasma cyclobenzaprine was quantified by means of an LC-MS/MS method. Pharmacokinetic parameters related to absorption, distribution, and elimination were calculated. Cyclobenzaprine plasma profiles for the reference and test products were similar, as well as absorption pharmacokinetic parameters AUC (reference: 199.4 ng∗h/mL; test: 201.6 ng∗h/mL), Cmax (reference: 7.0 ng/mL; test: 7.2 ng/mL), and T max (reference: 4.5 h; test: 4.6 h). Bioequivalence was evaluated by means of 90% confidence intervals for the ratio of AUC (93%–111%) and C max (93%–112%) values for test and reference products, which were within the 80%–125% interval proposed by FDA. Cyclobenzaprine pharmacokinetics can be described by a multicompartment open model with an average rapid elimination half-life (t (1/2)β) of 3.1 hours and an average terminal elimination half-life (t (1/2)γ) of 31.9 hours.

Pharmacokinetics of GST-TatdMt, a recombinant fusion protein possessing potent anti-obesity activity, in Mice

This study examined the absorption and pharmacokinetic disposition of 125I-GST-TatdMt, a recombinant Tat protein possessing potent anti-obesity activity, in mice after vascular and extravascular administration. GST-TatdMt was over-expressed in E. coli, purified, and radioiodinated using the IODO-GEN method. 125I-GST-TatdMt was administered to mice by i.v., i.p. and oral administration at doses of 652.7 nCi (102.3 microg). Upon i.v. injection, the average terminal elimination half-life (t1/2,lambdaz), AUC and AUMC were 6.4 h, 318.2 nCixh/mL and 2518 nCixh2/ mL, respectively. The highest radioactivity was observed in lung followed by liver, spleen, heart and kidney. The t1/2lambdaz values obtained from i.v., i.p., and oral administration were comparable from each other (range 5.8-6.4 h). The absolute bioavailability of 125I-GST-TatdMt was 42.8% and 60.5% after p.o. and i.p. administration, respectively. Given the cell-penetrating nature, 125I-GST-TatdMt may be absorbed into the systemic circulation to a relatively high extent after extravascular administration.

Ranolazine for the Treatment of Chronic Angina and Potential Use in Other Cardiovascular Conditions

Chronic angina, a condition that impairs quality of life and is associated with decreased life expectancy, affects &6.4 million Americans.1 Current therapies that reduce angina frequency and nitrate consumption and increase the threshold at which demand-induced myocardial ischemic symptoms become evident include drugs (nitrates, β-blockers, calcium antagonists), exercise conditioning, enhanced external counterpulsation, and coronary revascularization.1–3 Several new investigational drugs are being tested for the treatment of chronic angina.4–9 This review will focus on sustained-release ranolazine, a drug that reduces angina symptoms, with a mechanism of action different from that of currently available pharmacological therapies.8–29 Ranolazine was approved on January 27, 2006, in the United States for use in patients with chronic angina who continue to be symptomatic on β-blockers, calcium antagonists, or nitrates. Ranolazine ([(+) N -(2,6-dimethylphenyl)-4(2-hydroxy-3-(2-methoxyphenoxy)-propyl)-1-piperazine acetamide dihydrochloride]) is an active piperazine derivative that was patented in 1986 and is available in an oral and intravenous form (Figure 1). The immediate-release ranolazine (not in current use) had an average terminal elimination half-life ranging from 1.4 to 1.9 hours and a 10-fold peak/trough difference with dosing of 240 to 400 mg 3 times per day.19 Early studies with immediate-release ranolazine provided evidence of antiischemic/antianginal properties in patients with chronic angina without clinically significant changes in heart rate or blood pressure and are reviewed elsewhere.20–24 Unless otherwise stated, the remainder of this review refers to sustained-release ranolazine. Figure 1. Chemical structure and metabolism of ranolazine. Reprinted with permission from J Clin Pharmacol . 2005;45:422–433.17 Ranolazine (Ranexa; CV Therapeutics Inc, Palo Alto, Calif) is manufactured in a sustained-release form that has a prolonged absorption phase with maximal plasma concentrations (Cmax) typically seen 4 to 6 hours after administration. The average terminal elimination half-life is &7 hours after multiple dosing to steady state, and the …

Pharmacokinetics of gemcitabine and its primary metabolite in dogs after intravenous bolus dosing and its in vitro pharmacodynamics

Gemcitabine is a chemotherapeutic agent used to treat a variety of cancers in humans and dogs. In this study, the plasma pharmacokinetics of gemcitabine and its inactive metabolite, 2',2'-difluorodeoxyuridine (dFdU), were investigated in dogs after intravenous bolus gemcitabine doses of 3, 10, and 30 mg/kg. Furthermore, the intracellular accumulation of the active metabolite gemcitabine triphosphate, as a surrogate pharmacodynamic endpoint, was also determined in vitro in canine melanoma cells. Gemcitabine was characterized by linear kinetics, while dFdU dose proportionality remains unknown. The average gemcitabine clearance was 0.560 L/h.kg and volume of distribution at steady-state of 1.27 L/kg. The average terminal elimination half-life, depending on dose, ranged from 1.75 to 3.23 h. Plasma concentrations of dFdU peaked at approximately 2 h post-dosing. In vitro intracellular gemcitabine triphosphate accumulation was saturated with increasing extracellular gemcitabine concentrations. These data can be used to rationally design gemcitabine dosage regimes for canine oncology patients and as a basis for future investigations on the in vivo intracellular accumulation of gemcitabine triphosphate in dogs.

Dose-linear pharmacokinetics, tissue distribution, and excretion of a recombinant fusion protein 125I-GST-TatdMt possessing potent anti-obesity activity

This study first examined the pharmacokinetic disposition of GST-TatdMt, a recombinant Tat protein possessing potent anti-obesity activity, in rats after i.v. injection. GST-TatdMt was over-expressed in E. coli, purified, and radioiodinated using the IODO-GEN method. The radioiodinated 125I-GST-TatdMt was administered to rats at doses of 9 μg (1640 nCi), 18 μg (3388 nCi), and 35 μg (6420 nCi). Upon administration, the total radioactivity in serum declined bi-exponentially, with the average terminal elimination half-life ranging from 13.7 to 15.7 h. There was a linear relationship between dose and AUC INF ( r 2=1.000) and between dose and Co ( r 2=0.999). The fraction of administered radioactivity excreted in feces was low (mean range 1.5–2.8%), while the majority of the radioactivity was excreted in urine (mean range 54.9–61.4%). The radioactivity found in the liver, lungs, spleen, and kidneys were higher than in serum, but the tissue-to-serum ratios were relatively low (<1.64). The radioactivity in testes, adipose tissue, heart, and brain was lower than in serum (tissue-to-serum ratios 0.046–0.27). The findings of this study indicate dose-linear pharmacokinetics of 125I-GST-TatdMt in rats over the i.v. dose range studied.

A phase I and pharmacokinetic clinical trial of the orally administered retinoic acid receptor-α Agonist, AGN 195183

2022 Background: AGN 195183 is a novel retinoid that trans-activates retinoic acid receptor-α (RAR-α). In preclinical models, AGN 195183 caused less skin toxicity compared to RAR interactive agents lacking RAR-α specificity and demonstrated anti-tumor activity in breast cancer and leukemia models. We initiated a clinical trial of AGN 195183 in advanced solid tumor patients (pts) in order to establish toxicity and pharmacokinetic profiles and to establish the maximum tolerated dose (MTD). Methods: Fifteen pts with advanced solid tumors meeting standard phase I entry criteria were enrolled on study; mean age was 60 years (range 45–79). Pts took AGN 195183 (5 and 50 mg soft gelatin capsules) by mouth with or without food on a continuous daily dosing schedule. Pharmacokinetic (PK) blood samples were collected on the days 1 and 14 prior to dosing and at 0.5, 1, 1.5, 2, 3, 5, 8, and 24 hours post-dose and prior to and 1 hour post-dose on days 7, 21, and 28. Results: Five pts were treated at the starting dose level of 60 mg/m2/d; 2 pts had a dose limiting toxicity (DLT) including grade 3 elevation of alk phos (pt also had progressing liver metastases) and gr 3 mucositis. Drug was de-escalated to 30 mg/m2/d; 2 of 4 pts treated had gr 3 elevation of alkaline phosphatase. Further de-escalation to 15 mg/m2/d has been well tolerated by 6 pts for 17 treatment cycles, with no grade 3 or higher toxicity noted. Preliminary PK studies for 60 mg/m2/d dose level show the drug is absorbed rapidly and reached peak concentration at about one hour post-dose. The average terminal elimination half-life was 4.17 hours. Cmax ranged from 684 to 7660 ng/mL and AUC from 4140 to 31246 95183 ng-hr/mL in 3 pts. Conclusion: AGN 195183 is a novel retinoid that trans-activates retinoic acid receptor-α (RAR-α); it has been well tolerated on an oral daily dosing schedule of 15 mg/m2/d, which is the MTD and recommended Phase II dose. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Allergan Allergan Allergan

Oral bioavailability and pharmacokinetics of elimination of 9-hydroxybenzo[a]pyrene and its glucoside and sulfate conjugates after administration to male and female American lobsters, Homarus americanus.

The pharmacokinetics of [(3)H]-9-hydroxybenzo[a]pyrene (9-OH-BaP), a highly lipophilic primary metabolite of benzo(a)pyrene, were examined after intrapericardial (iv) or oral doses of 50 or 200 microg/kg to intermolt American lobsters, Homarus americanus. Combining data for all lobsters, the average terminal elimination half-life of parent 9-OH-BaP was 97.3 h after iv and 56.5 h after oral administration, considerably less than found previously for benzo(a)pyrene (720 h). The oral bioavailability of parent 9-OH-BaP, calculated from the area under the hemolymph concentration curve, was 15.9%. The low bioavailability and variable elimination rates were attributed to extensive first-pass conjugation and sequestration in the hepatopancreas. BaP-9-sulfate was the major metabolite. Hemolymph concentrations of BaP-9-sulfate increased up to one day after the dose, and then decreased, with a terminal elimination half-life of 45 h. BaP 9-beta-D-glucoside was a minor metabolite in most hemolymph and tissue samples; an exception was hemolymph from the iv high-dose group. Concentrations of 9-OH-BaP and metabolites in the edible muscle tissue were similar to those in hemolymph, and 9-OH-BaP residues at 10 to 16 days after the dose were 3 to 12 ng/g muscle. Sulfotransferase and UDP-glucosyltransferase (UGT) activities with 9-OH-BaP were found in the antennal gland, intestinal mucosa, and hepatopancreas (UGT only). Sulfatase activity with BaP-9-sulfate, found in both the hepatopancreas and the antennal gland, was thought to contribute to metabolite cycling. These studies showed that 9-OH-BaP was readily conjugated to sulfate and glucose in the lobster, and that despite their high lipophilicity, 9-OH-BaP and conjugates were excreted from the lobster hemolymph and tissues much more rapidly than benzo[a]pyrene.

Absorption, first-pass metabolism, and disposition of itraconazole in rats.

This study examined the pharmacokinetic disposition, oral absorption and hepatic extraction of itraconazole and its active metabolite, hydroxyitraconazole, in rats. After i.v. injection, serum itraconazole concentrations decreased biexponentially, with an average terminal elimination half-life, volume of distribution and systemic clearance of 4.9 h, 6.0 l/kg and 14.2 ml/min/kg, respectively. When given orally, its absorption was low, with a mean absolute bioavailability of 16.6%. The metabolite to parent drug area under the curve (AUC) ratio was higher after oral administration compared with i.v. injection (mean ratio, 2.7 vs. 0.9). The hepatic drug extraction ratio determined after femoral and portal vein administration averaged 18.5%. When hydroxyitraconazole was injected i.v., the elimination half-life, volume of distribution and systemic clearance of itraconazole averaged 10.0 h, 2.4 l/kg and 3.4 ml/min/kg, respectively. The fraction of the systemically available itraconazole that was metabolized to hydroxyitraconazole was 21.0% and 76.0% after i.v. and oral administration, respectively. In summary, this study is the first reporting the hepatic extraction of itraconazole and the i.v. disposition characteristics of hydroxyitraconazole in rats. Itraconazole is a drug with a low hepatic extraction ratio and its systemic clearance appears to be largely accounted for by hepatic metabolism.

The Population Pharmacokinetics of Amphotericin B Colloidal Dispersion in Patients Receiving Bone Marrow Transplants

The purpose of this study was to identify the pharmacokinetics of Amphotericin B Colloidal Dispersion in patients undergoing bone marrow transplantations with systemic fungal infections and to assess the influence of ABCD on renal function. Seventy-five patients (42 females, 33 males) with a median age of 34.5 years and median weight of 70.0 kg were enrolled in the study. The plasma concentration data was available in 51/75 patients and was best described by a two-compartment model; both plasma clearance and volume of distribution increased with escalating doses; the overall average terminal elimination half-life was 29 h. Serum creatinine values over the duration of therapy were available in 59/75 patients. Overall, there was no net change in renal function over the duration of therapy.

Population pharmacokinetics and renal function-sparing effects of amphotericin B colloidal dispersion in patients receiving bone marrow transplants

The purpose of this study was to evaluate the pharmacokinetics of amphotericin B colloidal dispersion and its effect on creatinine clearance in bone marrow transplant patients with systemic fungal infections. Seventy-five patients (42 females and 33 males) with a median age of 34.5 years and a median weight of 70.0 kg were enrolled in the study. Patients received 1 of 15 dose levels (range, 0.5 to 8.0 mg/kg of body weight) daily for a mean duration of 28 days and a mean cumulative dose amount of 8 g. Plasma samples for amphotericin B determination (median number, 4; range, 2 to 30) and daily serum creatinine values were obtained for each patient. Iterative two-stage analysis, one of several approaches to population pharmacokinetic and pharmacodynamic modelling, was employed for the pharmacokinetic analysis. The plasma data were available for 51 of 75 patients and were best described by a two-compartment model. Both plasma clearance and volume of distribution increased with escalating doses; the overall average terminal elimination half-life was 29 h. Of the covariates studied, only body weight and dose size were significant. Serum creatinine values over the duration of therapy were available for 59 of 75 patients. Overall, there was no net change in renal function over the duration of therapy; 12 patients had > 30% increases in creatinine clearance, whereas 13 had > 30% decreases. No measure of amphotericin B colloidal dispersion exposure, demographic values, or concomitant treatment with other medications was related to changes in the creatinine clearance.

A dose finding study of prochlorperazine as an antiemetic for cancer chemotherapy

This phase I study determined the maximum tolerated dose of prochlorperazine when used as an antiemetic prior to cytotoxic chemotherapy. Initially, cohorts of three patients were given prochlorperazine at escalating doses of 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2 mg/kg as an intravenous infusion over 20 min. The maximum tolerated dose was 1.2 mg/kg. The dose-limiting toxicity was hypotension which was reversed by a fluid load. The other major toxicities were extrapyramidal reactions which were dose related. All patients at the 1.2 mg/kg dose reported restlessness while five of six were restless and two of six at 1.0 mg/kg had muscle spasms. Two of seven patients reported restlessness at the 0.8 mg/kg level. Sedation and dry mouth were reported at all dose levels but were more common at higher doses. Prochlorperazine in plasma was assayed by high performance liquid chromatography with electrochemical detection and pharmacokinetics were determined for three patients at the 1.0 mg/kg dose level. The average terminal elimination half life was 7.6 ± 0.4 h, plasma clearance 27 ± 5 ml/min/kg and volume of distribution 17.7 ± 4.5 l/kg. The dose of prochlorperazine recommended for further studies of antiemetic efficacy is 0.8 mg/kg intravenously.

Pharmacokinetic and pharmacodynamic modelling of atenolol in rabbits maintained on continuous peritoneal dialysis.

The pharmacokinetic and pharmacodynamic profiles of atenolol were studied in adult male rabbits on continuous peritoneal dialysis given 3 mg/kg i.v. before and during renal failure. The average terminal elimination half-life for the drug was 2.5 h calculated from blood, dialysate or urinary data. This value increased about nine times in anuric conditions. Although atenolol was eliminated in the peritoneal fluid, the amount excreted was relatively low both in normal conditions and renal failure, respectively 0.6 and 7% of the administered dose. The pharmacokinetic model was extended by an "effect compartment", which has no influence on the predetermined mass of drug in the body, to analyse the relationship between heart rate fall and changes in atenolol blood concentrations. After drug administration, heart rate fell rapidly about 90 beats in both states. The mean equilibration half-time of atenolol effect and blood concentrations was 0.7 and 1.5 h in normal and pathological states, respectively. The mean blood concentration required to produce 50% of heart rate fall was similar in both conditions, 0.23 mg/l. The nine-fold decrease of atenolol elimination in anuria was in good agreement with the increase in duration of the drug's effect, and was suitably described by the "effect model".

Bioavailability and pharmacokinetics of ketanserin in elderly subjects.

The bioavailability of ketanserin has been examined in a cross-over experiment in 21 elderly subjects (aged 59-72 years) by administration of tablets (40 mg), solution (40 mg) and injectable solution (10 mg). After two weeks of treatment with 40 mg ketanserin tablets further 18 blood samples for analysis were collected under steady-state conditions. Plasma levels were measured by HPLC. The absolute bioavailability of ketanserin tablets was 52.7%; their relative bioavailability compared to a solution containing an equal quantity of active compound was 85.5%. Therefore, the low absolute bioavailability of ketanserin cannot be attributed to the formulation. The active compound was rapidly liberated from the tablet, reaching a peak of 103.8 ng/ml after 0.97 h. Individual plasma level-time curves fitted to an open three compartment model and a half-life of 17.7 +/- 7.26 h was calculated for the terminal elimination phase. An average terminal elimination half-life of 15.4 +/- 4.2 ng/ml was found after administration of the ketanserin solution. Multiple dosing with 40 mg tablets b.d.s. resulted in an AUC over one dosing interval at steady-state of 666 +/- 201 ng X h/ml. The AUC extrapolated to infinity was 1200 +/- 405 ng X h/ml for the last tablet. This is 1.8-times the AUC in one dosing interval, and 2.3-times the AUC of a single dose. Under steady-state conditions, the mean peak plasma level was 155.1 ng/ml (1.08 h after dosing) and the terminal half-life was 19.1 +/- 5.1 h. For the metabolite ketanserinol terminal half-lives of 21.4 h after a single tablet and 31.0 h after discontinuation of multiple dosing were calculated. (ABSTRACT TRUNCATED AT 250 WORDS)