Population pharmacokinetics of cabazitaxel in patients with advanced solid tumors.

PURPOSE: To develop a population pharmacokinetic (PK) model for cabazitaxel in patients with advanced solid tumors and examine the influence of demographic and baseline parameters. METHODS: One hundred and seventy patients who received cabazitaxel (10-30 mg/m(2), 1-h IV infusion) every 7 or 21 days in five Phase I-III studies were analyzed by non-linear mixed-effect modeling (NONMEM VI). Model evaluation comprised non-parametric bootstrap and visual predictive checks. RESULTS: Cabazitaxel PK was best described by a linear three-compartment model with: first-order elimination; interindividual variability on clearance (CL), central volume of distribution (V1), and all intercompartmental rate constants except K21; interoccasion variability in CL and V1; proportional residual error of 27.8%. Cabazitaxel CL was related to body surface area (BSA) and tumor type (breast cancer; finding confounded by study). Typical CL for a non-breast cancer patient with a BSA of 1.84 m(2) was 48.5 L/h, with V1 26.0 L, steady-state volume of distribution 4,870 L and alpha, beta, and gamma half-lives of 4.4 min, 1.6, and 95 h, respectively. Sex, height, weight, age, Caucasian race, renal/hepatic function, and cytochrome P450 inducer use did not significantly further explain the PK of cabazitaxel. Bootstrap and posterior predictive checks confirmed the adequacy of the model. CONCLUSIONS: Cabazitaxel PK appears unaffected by most baseline patient factors, and the influence of BSA on CL is addressed in practice by BSA-dependent doses. This analysis suggests consistent cabazitaxel PK and exposure across most solid tumor types, although the potential influence of breast cancer on CL requires further confirmation.

Pharmacokinetics and safety of tanaproget, a nonsteroidal progesterone receptor agonist, in healthy women.

OBJECTIVE: This study aimed to evaluate the pharmacokinetics, pharmacodynamics and safety of the nonsteroidal progesterone receptor agonist, tanaproget. METHODS: A randomized, double-blind, placebo-controlled, sequential-group study of ascending single doses of tanaproget was conducted in healthy, 25- to 45-year-old women on cycle days 8 to 12. Eight subjects (six active, two placebo) per cohort received a dose of 0.1, 0.3, 1, 3, 7 (+/-high-fat meal) or 15 mg. RESULTS: The maximum concentration (C(max)) of tanaproget occurred approximately 2 to 3 h after administration. The elimination half-life (t(1/2)) ranged from 12 to 30 h, and the oral clearance was approximately 70 L/h. The pharmacokinetics of tanaproget was not noticeably altered with a high-fat meal. All doses of tanaproget decreased cervical mucus scores (using a modified Insler method), indicating poor production and poor quality of cervical mucus. The most frequent treatment-emergent adverse events were vaginal bleeding/spotting, abdominal cramping and vomiting; their incidence was not dose related and most events were mild. CONCLUSIONS: Tanaproget was safe and well tolerated, decreased cervical mucus scores and had a pharmacokinetic profile acceptable for use as a once-daily oral contraceptive.

Excretion of pantoprazole in human breast.

OBJECTIVE: To measure the amount of pantoprazole in human milk following its oral administration to a breast-feeding mother and to estimate human exposure. STUDY DESIGN: One woman was studied over a 24-hour interval after oral administration of 40-mg pantoprazole. Serial plasma and milk samples were collected over 24 hours, and pantoprazole concentrations were measured by high-performance liquid chromatography. A milk/plasma ratio of 0.022 was observed at tmax, 2 hours after dose administration. Infant exposure was measured as maximum concentration in milk multiplied by an estimated maximum consumption of 200 mL at this time. RESULTS: The relative infant dose was estimated to be 7.3 microg of pantoprazole, which is equivalent to 0.14% of the weight-normalized dose received by the mother. Because pantoprazole is unstable in acidic pH, the systemic dose received by the infant is expected to be lower if the ingested pantoprazole is exposed to acid in the infant's stomach. The mother detected no adverse events in the infant. CONCLUSION: These limited data show that pantoprazole is minimally excreted into breast milk. While it is not known if pantoprazole affects breast milk production, women who are breast-feeding do not have to stop breastfeeding when taking pantoprazole chronically.

Oral bioavailability of pantoprazole suspended in sodium bicarbonate solution.

The bioavailability of pantoprazole when administered as a suspension in sodium bicarbonate solution and as the oral tablet was studied. In an open-label, randomized, two-period crossover study, healthy fasting subjects received either one enteric-coated 40-mg pantoprazole tablet by mouth with 240 mL of water or 20 mL of a suspension prepared from one crushed pantoprazole tablet and 840 mg of sodium bicarbonate solution and administered via a nasogastric tube. Treatments were separated by a 48-hour washout period. Blood samples were collected at intervals up to 24 hours after drug administration for measurement of pantoprazole concentration by high-performance liquid chromatography (HPLC) and estimation of pharmacokinetic values. A separate study was conducted to determine pantoprazole's stability in the suspension for up to three months at 25, 5, and -20 degrees C; concentrations were measured by HPLC. Twelve subjects completed the study. The suspension yielded pantoprazole Cmax values similar to those of the tablet formulation, but the drug was 25% less bioavailable. There was no lag time for the suspension. The suspension was stable for up to two weeks at 5 degrees C and up to three months at -20 degrees C. A suspension of pantoprazole in sodium bicarbonate solution yielded a Cmax similar to that of the tablet formulation, and the drug was quickly absorbed. However, bio-availability was slightly lower with the suspension than with the tablet.

Lack of pharmacokinetic interaction between retigabine and phenobarbitone at steady-state in healthy subjects.

AIMS: To evaluate potential pharmacokinetic interactions between phenobarbitone and retigabine, a new antiepileptic drug. METHODS: Fifteen healthy men received 200 mg of retigabine on day 1. On days 4-32, phenobarbitone 90 mg was administered at 22.00 h. On days 26-32, increasing doses of retigabine were given to achieve a final dose of 200 mg every 8 h on day 32. The pharmacokinetics of retigabine were determined on days 1 and 32, and those for phenobarbitone on days 25 and 31. RESULTS: After administration of a single 200 mg dose, retigabine was rapidly absorbed and eliminated with a mean terminal half-life of 6.7 h, a mean AUC of 3936 ng x ml(-1) x h and a mean apparent clearance of 0.76 l x h(-1) x kg(-1). Similar exposure to the partially active acetylated metabolite (AWD21-360) of retigabine was observed. After administration of phenobarbitone dosed to steady-state, the pharmacokinetics of retigabine at steady-state were similar (AUC of 4433 ng x ml(-1) x h and t1/2 of 8.5 h) to those of retigabine alone. The AUC of phenobarbitone was 298 mg x l(-1) x h when administered alone and 311 mg x ml(-1) x h after retigabine administration. The geometric mean ratios and 90% confidence intervals of the AUC were 1.11 (0.97, 1.28) for retigabine, 1.01 (0.88, 1.06) for AWD21-360 and 1.04 (0.96, 1.11) for phenobarbitone. Individual and combined treatments were generally well tolerated. One subject was withdrawn from the study on day 10 due to severe abdominal pain. Headache was the most commonly reported adverse event. No clinically relevant changes were observed in the electrocardiograms, vital signs or laboratory measurements. CONCLUSIONS: There was no pharmacokinetic interaction between retigabine and phenobarbitone in healthy subjects. No dosage adjustment is likely to be necessary when retigabine and phenobarbitone are coadministered to patients.

Effects of age and sex on the disposition of retigabine.

BACKGROUND: The novel antiepileptic drug retigabine is the first selective M-current potassium channel opener for KCNQ2/3 and KCNQ3/5 channels. Retigabine undergoes phase II metabolism (N-glucuronidation, acetylation) exclusively and renal excretion. OBJECTIVE: Our objective was to evaluate the effects of age and sex on the pharmacokinetics of retigabine. METHODS: Healthy young (age range, 18-40 years) and elderly (age range, 66-81 years) white subjects (12 men and 12 women in each group) received a single 200-mg oral dose of retigabine. After dosing, blood was collected over a 72-hour period to determine plasma concentrations of retigabine and its acetylated metabolite, AWD21-360. Pharmacokinetics was compared for age group and sex by ANOVA. RESULTS: In young men, retigabine was rapidly absorbed, with the maximum concentration occurring within 2 hours, and was eliminated with an apparent clearance of 0.67 L x h(-1) x kg(-1) and a mean terminal half-life of 8.5 hours. Subjects were similarly exposed to AWD21-360. Compared with young men, young women had higher retigabine maximum concentration (56%) and exposure (20%) but similar clearance (0.68 L x h(-1) x kg(-1)); these differences were related to differences in body weight. Although maximum concentration was similar in elderly subjects, retigabine elimination was slower (30% lower apparent clearance normalized for weight), resulting in higher exposure (42%) and a longer half-life (30%). Because phase II metabolism is scarcely affected by age, these differences may be related to the known decline of renal function with age. CONCLUSIONS: Although there are no substantial sex-related differences in the disposition of retigabine, a relevant decrease in clearance resulting in higher exposure occurs in elderly patients. The results suggest that decline of renal function with age may account for some of the observed changes.

Proton pump activation in stimulated parietal cells is regulated by gastric acid secretory capacity: a human study.

Under normal physiological conditions, gastric acid production is controlled by a negative feedback mechanism. Proton pump inhibitors, such as pantoprazole, inhibit gastric acid secretion by irreversibly binding and inactivating luminally active hydrogen potassium ATPase. Recovery of acid production after treatment with a proton pump inhibitor is driven by new pump synthesis, activation of existing cytoplasmic pumps, or reversal of proton pump inhibition. The authors measured the time course of the inhibition and recovery of acid secretion in healthy volunteers following intravenous administration of pantoprazole to determine the rate of proton pump activation under maximally stimulated conditions. Gastric acid production was measured in 27 Helicobacter pylori negative healthy volunteers (mean age = 31 +/- 7 years; 17 men, 10 women) who received single doses of intravenous pantoprazole (20, 40, 80, or 120 mg) in the presence of a continuous intravenous infusion of 1 ug/kg/h of pentagastrin. From the time profile of acid secretion, the authors described the rate of change of acid output using an irreversible pharmacodynamic response model represented by the equation dR/dt = -k x R x Cpanto + Ln2/PPR x (Ro-R) and correlated the parameter values with demographic factors and gastric acid measurements. Mean stimulated acid output secretion was 21.6 +/- 18.4 mEq/h (range: 1.6-90.5) prior to the administration of pantoprazole and remained steady for 25 hours after placebo administration. Intravenous pantoprazole inhibited acid output in a dose-response fashion, with maximal inhibition (99.9%) occurring after an 80 mg dose. Mean proton pump recovery time was 37.1 +/- 21.0 hours (range: 6.7-75), and recovery was independent of the dose of pantoprazole. There was no association noted between proton pump recovery time and gender, age, race, body weight, or pantoprazole dose. However, there was an inverse correlation between acid output during baseline stimulation and recovery of acid secretion. Mean proton pump recovery time in stimulated normal human volunteers was 37.1 +/- 21.0 hours, with a range of 6.7 to 75 hours. The authors hypothesize that there may be a normal homeostatic mechanism that maintains acid secretory capability within a normal range by altering the rate of proton pump activation dependent on the individual's parietal cell mass. Abnormalities of this process may be responsible for the development of acid peptic disease in susceptible individuals.

Multiple-dose, linear, dose-proportional pharmacokinetics of retigabine in healthy volunteers.

Retigabine, a first-in-class selective M-current potassium channel opener, is a novel antiepileptic compound currently in clinical development. The purpose of this randomized placebo-controlled study was to assess retigabine oral safety and pharmacokinetics in healthy male volunteers (N = 45). Subjects received one dose on day 1 and doses every 12 hours for the next 14 days. Fixed doses were given to the first four groups (200, 400, 500, and 600 mg per day). Titrated doses were given to group 5 in 100 mg increases every 4 days, achieving 700 mg per day on day 15. Serial blood samples were collected on days 1 and 15. Pharmacokinetic parameters were compared between days and among dose groups. After administration of a single dose, retigabine was rapidly absorbed, with maximum concentrations of 387 ng/ml (normalized to a 100 mg dose) occurring within 1.5 hours. Retigabine was eliminated with a mean terminal half-life of 8.0 hours and an apparent oral clearance of 0.70 L/h/kg in white subjects. In black subjects, retigabine clearance and volume of distribution were 25% and 30% lower, respectively, after normalizing by body weight, leading to higher exposure in this population. Retigabine's pharmocokinetics was linearly dose proportional. Steady-state pharmacokinetics was in agreement with single-dose pharmacokinetics, and the accumulation ratio was about 1.5. Retigabine and AWD21-360 trough evening concentrations were significantly lower (about 30% to 35%) than morning values. The titration regimen allowed for higher doses to be tolerated compared to the fixed-dose regimen. In conclusion, the pharmacokinetics of retigabine is linearly dose proportional for daily doses of 100 to 700 mg and is not modified on multiple administrations.