The impact of P-gp functionality on non-steady state relationships between CSF and brain extracellular fluid.

In the development of central nervous system (CNS)-targeted drugs, the prediction of human CNS target exposure is a big challenge. Cerebrospinal fluid (CSF) concentrations have often been suggested as a 'good enough' surrogate for brain extracellular fluid (brainECF, brain target site) concentrations in humans. However, brain anatomy and physiology indicates prudence. We have applied a multiple microdialysis probe approach in rats, for continuous measurement and direct comparison of quinidine kinetics in brainECF, CSF, and plasma. The data obtained indicated important differences between brainECF and CSF kinetics, with brainECF kinetics being most sensitive to P-gp inhibition. To describe the data we developed a systems-based pharmacokinetic model. Our findings indicated that: (1) brainECF- and CSF-to-unbound plasma AUC0-360 ratios were all over 100 %; (2) P-gp also restricts brain intracellular exposure; (3) a direct transport route of quinidine from plasma to brain cells exists; (4) P-gp-mediated efflux of quinidine at the blood-brain barrier seems to result of combined efflux enhancement and influx hindrance; (5) P-gp at the blood-CSF barrier either functions as an efflux transporter or is not functioning at all. It is concluded that in parallel obtained data on unbound brainECF, CSF and plasma concentrations, under dynamic conditions, is a complex but most valid approach to reveal the mechanisms underlying the relationship between brainECF and CSF concentrations. This relationship is significantly influenced by activity of P-gp. Therefore, information on functionality of P-gp is required for the prediction of human brain target site concentrations of P-gp substrates on the basis of human CSF concentrations.

Sugammadex is not associated with QT/QTc prolongation: methodology aspects of an intravenous moxifloxacin-controlled thorough QT study.

OBJECTIVE: Sugammadex is a novel γ-cyclodextrin and the first selective relaxant binding agent to be developed for the reversal of rocuronium and vecuroniuminduced neuromuscular blockade. According to International Conference on Harmonization (ICH) E14, a thorough QT/QTc study is required for most new compounds to assess the potential to cause QT prolongation, because a delay in cardiac repolarization may create an electrophysiological environment that favors the development of cardiac arrhythmias, most notably Torsade de Pointes. Therefore a thorough QTc study was conducted to evaluate the effect of sugammadex on the individually corrected QTc interval (QTcI). METHODS: Following two baseline electrocardiogram (ECG) days (Day -2 and Day -1), in this randomized, double-blind, cross-over study, healthy volunteers received a sequence of four treatments comprising single intravenous doses of placebo, moxifloxacin 400 mg (positive control, open label), sugammadex 4 mg/kg and sugammadex 32 mg/kg. ECGs were recorded in triplicate at 12 time points up to ~ 24 h after study drug administration, and the QT intervals were evaluated manually under blinded conditions. The pre-specified primary endpoint was the largest time-matched mean QTcI difference compared with placebo across all time points. RESULTS: A total of 62 subjects received treatment, of which 58 completed the study. After intravenous moxifloxacin, QTcI prolongations compared with placebo exceeded the ICH E14 safety margin of 10 msec and the one-sided 95% lower confidence limit exceeded 5 msec, confirming assay sensitivity. For both sugammadex doses, the one-sided 95% upper confidence limits for the largest time-matched mean QTcI differences compared with placebo were ≤ 5.3 msec at each timepoint and thus considerably below the 10 msec safety margin. Unexpectedly, the two full-day baseline ECGs indicated systematically prolonged QTc values when comparing the first baseline with the second baseline day, reaching a maximum mean difference of 3.8 msec. CONCLUSION: Single therapeutic (4 mg/kg) and supra-therapeutic (32 mg/kg) intravenous doses of sugammadex are not associated with clinically important QTc prolongation.

Sugammadex is cleared rapidly and primarily unchanged via renal excretion.

Sugammadex is a modified γ-cyclodextrin which rapidly reverses rocuronium-and vecuronium-induced neuromuscular blockade. Previous studies suggest that sugammadex is mostly excreted unchanged via the kidneys. This single-center, open-label, non-randomized study used (14)C-labeled sugammadex to further investigate the excretion, metabolic and pharmacokinetic (PK) profiles of sugammadex in six healthy male volunteers. (14)C-labeled sugammadex 4 mg/kg (0.025 MBq/kg of (14)C-radioactivity) was administered as a single intravenous bolus. Blood, urine, feces and exhaled air samples were collected at pre-defined intervals for assessment of sugammadex by liquid chromatography-mass spectrometry (LC-MS) and for radioactivity measurements. Adverse events were also assessed. Excretion of sugammadex was rapid with ∼70% of the dose excreted within 6 h and ∼90% within 24 h. Less than 0.02% of radioactivity was excreted in feces or exhaled air. Ninety-five percent of the radioactivity detected in urine could be attributed to sugammadex, as determined by LC-MS, suggesting very limited metabolism of sugammadex. LC-MS analysis of plasma samples found that sugammadex accounted for 100% of total (14)C-radioactivity in the plasma. In general, PK parameters determined from radioactivity and sugammadex plasma concentrations were very similar. Any adverse events were of mild-to-moderate intensity, and judged unrelated to sugammadex. These findings demonstrate that sugammadex is cleared rapidly, almost exclusively via the kidney, with minimal or no metabolism.

Assessment of the potential for displacement interactions with sugammadex: a pharmacokinetic-pharmacodynamic modelling approach.

BACKGROUND: Sugammadex is a γ-cyclodextrin that binds with high affinity to the neuromuscular blocking agents (NMBAs) rocuronium (bromide) and vecuronium (bromide) by encapsulation. Cyclodextrins are known to form inclusion complexes with other compounds. OBJECTIVES: We utilized a previously developed pharmacokinetic-pharmacodynamic model to identify potential clinically relevant displacement interactions with sugammadex. The potential for sugammadex to capture other drug molecules, thereby reducing their efficacy, is not discussed here. METHODS: Isothermal titration calorimetry (ITC) was used to determine the binding affinity (estimated by association rate constant [k(ass)]) between sugammadex and 300 commonly prescribed drugs. The screening included drugs commonly used in or shortly after anaesthesia, commonly prescribed drugs such as antidepressants and cardiovascular drugs, drugs (both steroidal and nonsteroidal) acting on steroidal receptors (such as the corticosteroids hydrocortisone, prednisolone and dexamethasone), and the selective estrogen receptor modulator toremifene. The model took into account the population pharmacokinetic-pharmacodynamic relationships of sugammadex, rocuronium and vecuronium, the binding affinities of the NMBAs and other compounds as determined by ITC, and the relationship between the free concentration of NMBA with sugammadex in the presence of a third complexed compound. Using the model, the critical concentrations of a concomitantly administered compound required to result in a train-of-four (TOF) ratio of <0.9, indicating reoccurrence of neuromuscular blockade, for each plasma concentration of sugammadex and NMBA were calculated. For compounds with a k(ass) value of ≥ 2.5 × 104 mol/L likely to be administered during sugammadex reversal, the combinations of k(ass) and maximum plasma drug concentration (C(max)) were entered into a graph, consisting of a critical line established using a conservative approach, and those compounds above this critical line potentially resulting in a TOF ratio <0.9 were subsequently identified. Clinical validation was performed in a post hoc analysis of data from ten sugammadex studies, in which the impact of various drugs administered perioperatively on neuromuscular recovery was assessed for up to 1 hour after sugammadex administration. RESULTS: ITC analysis demonstrated that the binding affinity of rocuronium and vecuronium for sugammadex was very high, with k(ass) values of 1.79 × 107 mol/L and 5.72 × 106 mol/L, respectively. Only three compounds (flucloxacillin, fusidic acid and toremifene) were found to have critical combinations of k(ass) and C(max), and thus the potential for displacement. Sugammadex was administered to 600 patients for reversal of rocuronium- or vecuronium-induced blockade in the ten analysed studies, in which 21 co-administered drugs were selected for analysis. No reoccurrence of blockade occurred in any patient. CONCLUSION: Of 300 drugs screened, only three (flucloxacillin, fusidic acid and toremifene) were found to have potential for a displacement interaction with sugammadex, which might potentially be noticed as a delay in recovery of the TOF ratio to 0.9. A clinical study found no evidence of a clinically relevant displacement interaction of flucloxacillin with sugammadex; these findings confirm the highly conservative nature of the modelling and simulation assumptions in the present study.

Safety, tolerability and pharmacokinetics of sugammadex using single high doses (up to 96 mg/kg) in healthy adult subjects: a randomized, double-blind, crossover, placebo-controlled, single-centre study.

BACKGROUND AND OBJECTIVE: Sugammadex facilitates rapid reversal of rocuronium- and vecuronium-induced neuromuscular blockade. This study aimed to evaluate the safety, tolerability and pharmacokinetics of high doses of sugammadex (up to 96 mg/kg) in healthy subjects. METHODS: In this randomized, double-blind, crossover, placebo-controlled, single-centre study, 13 healthy adults were scheduled to receive three single intravenous doses of sugammadex in ascending order (32, 64 and 96 mg/kg) and placebo (interspersed between sugammadex doses), each separated by a 1-week washout period. Subjects were randomized to one of four treatment sequences, receiving doses as constant rate infusions over 5 minutes. Safety was assessed by adverse events, 12-lead ECGs, vital signs, and blood and urine laboratory parameters; pharmacokinetics were evaluated from blood and urine sugammadex concentrations. RESULTS: Sugammadex was well tolerated in 12 of the 13 subjects, with adverse events being generally mild, of limited duration and more frequent at higher doses. The most common adverse event was dysgeusia; there were no serious adverse events. One subject was withdrawn from the study after experiencing several adverse events following first exposure to sugammadex, related to a probable hypersensitivity reaction to sugammadex. Pharmacokinetics were dose linear over the dose range studied (32-96 mg/kg), and 90-93% of the sugammadex dose was excreted unchanged in urine within 48 hours. CONCLUSION: High doses of sugammadex (up to 96 mg/kg) were well tolerated in 12 of the 13 subjects. One male subject experienced several adverse events associated with a probable hypersensitivity reaction to sugammadex. Pharmacokinetics were dose linear over the range 32-96 mg/kg, with elimination predominantly via the renal route.

Pharmacokinetic-pharmacodynamic model for the reversal of neuromuscular blockade by sugammadex.

BACKGROUND: Sugammadex selectively binds steroidal neuromuscular blocking drugs, leading to reversal of neuromuscular blockade. The authors developed a pharmacokinetic-pharmacodynamic model for reversal of neuromuscular blockade by sugammadex, assuming that reversal results from a decrease of free drug in plasma and/or neuromuscular junction. The model was applied for predicting the interaction between sugammadex and rocuronium or vecuronium. METHODS: Noninstantaneous equilibrium of rocuronium-sugammadex complex formation was assumed in the pharmacokinetic-pharmacodynamic interaction model. The pharmacokinetic parameters for the complex and sugammadex alone were assumed to be identical. After development of a pharmacokinetic-pharmacodynamic model for rocuronium alone, the interaction model was optimized using rocuronium and sugammadex concentration data after administration of 0.1-8 mg/kg sugammadex 3 min after administration of 0.6 mg/kg rocuronium. Subsequently, the predicted reversal of neuromuscular blockade by sugammadex was compared with data after administration of up to 8 mg/kg sugammadex at reappearance of second twitch of the train-of-four; or 3, 5, or 15 min after administration of 0.6 mg/kg rocuronium. Finally, the model was applied to predict reversal of vecuronium-induced neuromuscular blockade. RESULTS: Using the in vitro dissociation constants for the binding of rocuronium and vecuronium to sugammadex, the pharmacokinetic-pharmacodynamic interaction model adequately predicted the increase in total rocuronium and vecuronium plasma concentrations and the time-course of reversal of neuromuscular blockade. CONCLUSIONS: Model-based evaluation supports the hypothesis that reversal of rocuronium- and vecuronium-induced neuromuscular blockade by sugammadex results from a decrease in the free rocuronium and vecuronium concentration in plasma and neuromuscular junction. The model is useful for prediction of reversal of rocuronium and vecuronium-induced neuromuscular blockade with sugammadex.

Pharmacokinetics of a granisetron transdermal system for the treatment of chemotherapy-induced nausea and vomiting.

OBJECTIVE: To determine the pharmacokinetic (PK) profile of granisetron transdermal formulation and examine its possible relationship with age, gender, and renal function. METHODS: This article describes a Phase I PK study and a post hoc pooled population PK analysis. The Phase I study was a randomized, cross-over study that assessed PK parameters of three granisetron patch sizes and oral granisetron. The pooled population PK analysis included data from three trials in healthy subjects (n = 48) and from Phase II and III studies in patients with cancer (n = 793). The population PK model was used to investigate granisetron exposure and its possible relationship with age, gender, and renal function. RESULTS: Following oral dosing, plasma granisetron concentration was quantifiable at 1 h, and maximal mean concentration (4.7 ng/mL) was reached 2 h after administration. With transdermal application, maximal concentration was reached 48 h post-application; t(1/2) was 36 h. With oral dosing, overall exposure after 5 days was 306 ng/mL.h, and C(avg) 2.6 ng/mL. This corresponded to an AUC(0-infinity) for the 52 cm(2) patch of 420 ng/mL.h and C(avg) 2.2 ng/mL over 6 days. Clearance was not affected by age, gender, weight, or renal function. CONCLUSION: The 52 cm( 2) granisetron patch achieves a similar exposure to that of a 2 mg oral dose and provides continuous delivery of granisetron over 6 days. The patch may have utility in treating chemotherapy-induced nausea and vomiting where prolonged drug delivery is advantageous. No dose adjustments would be needed based on age or renal function.

Pharmacokinetic evaluation of three different intramuscular doses of nandrolone decanoate: analysis of serum and urine samples in healthy men.

The pharmacokinetics of nandrolone in serum and urine were investigated in healthy young men after a single im injection of 50 mg (n = 20), 100 mg (n = 17), or 150 mg (n = 17) nandrolone decanoate. Blood samples were collected before treatment and for up to 32 d after dosing. In addition, in the 50- and 150-mg groups, 24-h urine samples were collected before treatment and on d 1, 7, and 33 after treatment; in the 150-mg group, additional samples were collected after 3 and 6 months. Serum concentrations and the area under the curve of nandrolone increased proportionally with the dose administered. The peak serum concentration ranged from 2.14 ng/ml in the 50-mg group to 4.26 ng/ml in the 100-mg group and 5.16 ng/ml in the 150-mg group. The peak serum concentration was reached after 30 h (50 and 100 mg) and 72 h (150 mg), whereas the terminal half-life was 7-12 d. In urine, pretreatment concentrations of 19-norandrosterone (19-NA) and/or 19-noretiocholanolone (19-NE) were detected in five of 37 subjects (14%). In the 50-mg group, 19-NA and/or 19-NE could be detected at least until 33 d after injection in 16 of 17 subjects (94%). In the 150-mg group, who were presumed to have not previously used nandrolone, nandrolone metabolites could be detected for up to 6 months in eight of 12 subjects (67%) for 19-NE and in 10 of 12 subjects (83%) for 19-NA.

Cytochrome P4501A induction and testosterone hydroxylation in cultured hepatocytes of four fish species.

Primary hepatocytes of the rainbow trout (Oncorhynchus mykiss), flounder (Platychthis flesus), dab (Limanda limanda) and lemon sole (Microstomus kitt) were exposed to 3,3'4,4'5 pentachlorobiphenyl (PCB 126) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for two days. This resulted in a dose-dependent induction of cytochrome P4501A (CYP1A) activity, measured as ethoxyresorufin O-deethylase (EROD), or methoxyresorufin O-deethylase (MROD) activity. In all species, a linear relationship was observed between EROD and MROD activities, suggesting that the same CYP1A enzyme metabolizes the two alkoxy-resorufin substrates. Exposures of hepatocytes of flounder or dab to TCDD, resulted in a 59-fold and 8.2-fold induction of EROD activity, respectively. This did not concur with a change in the in vitro testosterone hydroxylation profiles of both species. These and other in vitro data indicate that TCDD exposure does not influence monooxygenase activities involved in testosterone hydroxylation. Furthermore, CYP1A is of minor importance for testosterone hydroxylation in these fish species.

Physiologically based pharmacokinetic modeling to investigate regional brain distribution kinetics in rats.

One of the major challenges in the development of central nervous system (CNS)-targeted drugs is predicting CNS exposure in human from preclinical data. In this study, we present a methodology to investigate brain disposition in rats using a physiologically based modeling approach aiming at improving the prediction of human brain exposure. We specifically focused on quantifying regional diffusion and fluid flow processes within the brain. Acetaminophen was used as a test compound as it is not subjected to active transport processes. Microdialysis probes were implanted in striatum, for sampling brain extracellular fluid (ECF) concentrations, and in lateral ventricle (LV) and cisterna magna (CM), for sampling cerebrospinal fluid (CSF) concentrations. Serial blood samples were taken in parallel. These data, in addition to physiological parameters from literature, were used to develop a physiologically based model to describe the regional brain pharmacokinetics of acetaminophen. The concentration-time profiles of brain ECF, CSF(LV), and CSF(CM) indicate a rapid equilibrium with plasma. However, brain ECF concentrations are on average fourfold higher than CSF concentrations, with average brain-to-plasma AUC(0-240) ratios of 121%, 28%, and 35% for brain ECF, CSF(LV), and CSF(CM), respectively. It is concluded that for acetaminophen, a model compound for passive transport into, within, and out of the brain, differences exist between the brain ECF and the CSF pharmacokinetics. The physiologically based pharmacokinetic modeling approach is important, as it allowed the prediction of human brain ECF exposure on the basis of human CSF concentrations.