The influence of reduced liver blood flow on the pharmacokinetics and pharmacodynamics of recombinant tissue factor pathway inhibitor

Exercise Is Medicine, But Does It Interfere With Medicine?

Exercise frequently is prescribed therapeutically, either on its own or combined with drugs. A drug's absorption, distribution, metabolism, and excretion can be affected by the user's anatomy and physiology, which are both changed by the myriad of complex adaptations to acute and chronic exercise. This article reviews the research that suggests exercise may influence a drug's plasma concentration, and thus its efficacy and safety.

Discovery and SAR of a Series of Agonists at Orphan G Protein-Coupled Receptor 139

GPR139 is an orphan G-protein coupled receptor (GPCR) which is primarily expressed in the central nervous system (CNS). In order to explore the biological function of this receptor, selective tool compounds are required. A screening campaign identified compound 1a as a high potency GPR139 agonist with an EC50 = 39 nM in a calcium mobilization assay in CHO-K1 cells stably expressing the GPR139 receptor. In the absence of a known endogenous ligand, the maximum effect was set as 100% for 1a. Screening against 90 diverse targets revealed no cross-reactivity issues. Assessment of the pharmacokinetic properties showed limited utility as in vivo tool compound in rat with a poor whole brain exposure of 61 ng/g and a brain/plasma (b/p) ratio of 0.03. Attempts to identify a more suitable analogue identified the des-nitrogen analogue 1s with a reduced polar surface area of 76.7 Å(2) and an improved b/p ratio of 2.8. The whole brain exposure remained low at 95 ng/g due to a low plasma exposure.

Pilot study on the influence of liver blood flow and cardiac output on the clearance of propofol in critically ill patients

OBJECTIVE

To investigate the effect of cardiac output and liver blood flow on propofol concentrations in critically ill patients in the intensive care unit.

METHODS

Five medical/surgical critically ill patients were enrolled in this preliminary study. Liver blood flow was measured using sorbitol. The cardiac output was measured by bolus thermodilution. NONMEM ver. V was applied for propofol pharmacokinetic analysis.

RESULTS

The clearance of propofol was positively influenced by the liver blood flow (P < 0.005), whereas no significant correlation between cardiac output and propofol clearance was found. A correlation between liver blood flow and cardiac output or cardiac index could not be assumed in this patient group.

CONCLUSIONS

Liver blood flow is a more predictive indicator than cardiac output for propofol clearance in critically ill patients when the techniques of hepatic sorbitol clearance and bolus thermodilution, respectively, are used. Further study is needed to determine the role played by liver blood flow and cardiac output on the pharmacokinetics of highly extracted drugs in order to reduce the observed high interindividual variabilities in response in critically ill patients.

Effect of food on pharmacokinetics of an inhaled drug: a case study with a VLA-4 antagonist, HMR1031

HMR1031 is a potent and specific antagonist of the integrin VLA-4 (alpha4beta1) binding to vascular cell adhesion molecule-1 (VCAM-1) and fibronectin. HMR1031 is an inhaled drug being developed for the treatment of asthma using an Ultrahaler dry-powder inhalation device. A pharmacoscintigraphic study of HMR1031 suggests a lung deposition of approximately 25% and gastrointestinal tract deposition of approximately 75%. Since oral absorption may be contributing to systemic plasma concentrations, the effect of food on HMR1031 was assessed. This was a single-dose (3 mg), open-label, randomized, two-way crossover (fasted vs. fed) study in 8 healthy male subjects. Blood samples were collected at predose and up to 24 hours postdose. Plasma concentrations were determined by the LC/MS/MS method. HMR1031 was rapidly absorbed, with median tmax values of 1.0 and 0.75 hours under fasted and fed conditions, respectively. Under fasted conditions, mean AUCinfinity and Cmax values were 16.4 ng x h/mL and 4.56 ng/mL, respectively. Under fed conditions, mean AUCinfinity and Cmax values decreased to 11.7 ng x h/mL and 2.81 ng/mL, respectively. The mean terminal elimination half-life (t1/2) for both treatment groups was similar (2.7 h). HMR1031 population estimates of the apparent clearance, apparent volume of distribution, and absorption rate were 225 L/h (4.1% coefficient of variation [CV]), 44.5 L (26% CV), and 0.340 h-1 (7.0% CV), respectively. Food is a significant covariate on clearance. These data suggest that food unexpectedly decreases the systemic exposure of inhaled HMR1031 by approximately 30%, probably due to increased liver blood flow and increased biliary excretion. This decrease in systemic exposure is unlikely to affect the topical effect of the drug but may result in increased variability in plasma pharmacokinetics. The disposition and food effect of HMR1031 can be described using mixed-effect modeling.

Quantification of heparin-induced TFPI release: a maximum release at low heparin dose

AIMS

Heparin releases tissue factor pathway inhibitor (TFPI) from the endothelium and this release may decrease after repeated high dose heparin administration. The primary aim was to investigate and quantify this phenomenon during a short low dose heparin infusion. Also, the effects of heparin on tissue plasminogen activator (t-PA) were studied.

METHODS

Nine healthy, nonsmoking, male volunteers (range 19-23 years) received a continuous heparin infusion (2000 IU) over 40 min. The endothelial TFPI release rate was estimated from the total TFPI concentration profile using a pharmacokinetic model.

RESULTS

Mean +/- s.d. total and free TFPI increased from 62.9 +/- 9.4/8.3 +/- 2.1 ng ml-1 at baseline to 237.2 +/- 40.9/111.0 +/- 19.9 ng ml-1 after 40 min infusion. The relationship between heparin concentration (anti-IIa activity) and TFPI concentration followed a maximum effect model and a clockwise loop (proteresis) was observed. The TFPI release rate rapidly increased to maximum of 200 +/- 45 micro g min-1 after 17.5 min heparin infusion but did not increase further although heparin concentrations further doubled. In contrast to TFPI, t-PA antigen decreased from 5.6 +/- 1.0 at baseline to 4.5 +/- 1.0 ng ml-1 at the end of infusion (t = 40 min) (difference of 1.1 ng ml-1 (95% confidence interval; 0.9, 1.3).

CONCLUSIONS

Our application of concentration-effect models and pharmacokinetic principles to these haemostatic variables showed that endothelial TFPI release has a maximum that is already reached at low heparin dose, corresponding with an anti-IIa activity of 0.08 IU ml-1. The relationship between anti-IIa activity and TFPI release rate showed signs of acute tolerance (clockwise loop) indicating exhaustion of endothelial TFPI pools. These findings may be of importance for the heparin dose used in conditions such as unstable angina, in which the favourable effects of heparin have been ascribed to its ability to release TFPI.

Role of tissue factor pathway inhibitor in the regulation of tissue factor-dependent blood coagulation

Tissue factor pathway inhibitor (TFPI) is a multivalent, Kunitz-type plasma proteinase inhibitor that modulates tissue factor-dependent coagulation in vivo. TFPI possesses a peculiar two-step mechanism of action; it directly inhibits activated factor X and subsequently produces feedback inhibition of the factor VIIa/tissue factor catalytic complex in a factor Xa-dependent fashion. TFPI biochemistry and physiology have been extensively studied during the last decade. Its pathophysiologic role in thrombotic disorders has, however, only recently started to be unraveled. In particular, circulating plasma TFPI levels have been found to modulate the activity of the tissue factor-dependent coagulation cascade. In animal models, neutralization of circulating TFPI activity results in restoration of intravascular thrombus formation previously abolished by aspirin. In patients with acute myocardial infarction, TFPI plasma levels measured in blood samples obtained from the coronary sinus were significantly lower than those measured in blood obtained from the ascending aorta, indicating acute consumption of TFPI within the coronary circulation of patients with intracoronary thrombosis. Finally, recent data indicate that transfection of the arterial wall with the gene coding for TFPI is an effective therapeutic intervention to prevent intravascular thrombus formation. Taken together, these observations underline the pathophysiologic importance of TFPI in regulating the procoagulant activity of tissue factor and open new potential therapeutic approaches for the treatment of thrombotic disorders.

No Influence of acute hypertriglyceridemia on plasma t-PA in healthy male volunteers

Dietary effects on liver blood flow may have biased the previously observed effects of hypertriglyceridemia on systemic tissue-type plasminogen activator (t-PA) concentrations. Therefore, in this study the effects of hypertriglyceridemia on plasma t-PA were determined by inducing hypertriglyceridemia with an intravenous fat emulsion (Intralipid) infusion. In a randomised crossover fashion, eight healthy male volunteers received Intralipid 10% (1.5 ml/min) or 0.9% saline for 2 h and 45 min. After 2 h of infusion, t-PA antigen, t-PA activity, t-PA/plasminogen activator inhibitor (PAI-1) complex, and PAI-1 activity were determined. Concomitantly, the effects of Intralipid t-PA clearance were determined from steady-state t-PA antigen concentrations of a 45-min recombinant tissue-type plasminogen activator (rt-PA) infusion (31.25 microg/min). Liver blood flow was assessed from steady-state concentrations of a continuous sorbitol infusion. Differences between treatments were calculated using the prevalue as the covariate. No significant differences were observed in mean+/-S.D. endogenous concentrations of t-PA antigen, 4.5+/-0.9/4.1+/-0.9 ng/ml (Intralipid vs. saline infusion; difference of 0.3 ng/ml, 95% confidence interval, CI: -0.2, 0.8); t-PA activity, 0.69+/-0.21/0.68+/-0.21 U/ml (difference of 0.04 U/ml, CI: -0.17, 0.25); t-PA/PAI-1 complex, 2.0+/-1.3/1.6+/-1.0 ng/ml (difference of 0.1 ng/ml, CI: -0.8, 0.6); and PAI-1 activity, 7.3+/-5.1/7.1+/-5.1 U/ml (difference of 0.26 U/ml, CI: -3.7, 4.3). Mean t-PA clearance and liver blood flow were unaffected by the Intralipid infusion. These results indicate that acute hypertriglyceridemia does not alter plasma fibrinolytic parameters in healthy male volunteers.

Tissue factor inhibition and clinical trial results of tissue factor pathway inhibitor in sepsis

Tissue factor mediated pathways leading to microvascular thromboses and endothelial activation appear to play an important role in the development of multiple organ failure associated with severe sepsis. Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of tissue factor associated coagulation cascades. In experimental models of severe sepsis, treatment with TFPI results in significant reduction in mortality. Similarly, a recently completed Phase II 210-patient study comparing placebo and infusions of TFPI showed trends toward a relative reduction in day 28 all-cause mortality in TFPI treated patients. These data suggest that coagulation cascades involving tissue factor contribute to organ dysfunction in critically ill septic patients. TFPI may be a useful therapy in improving outcome of severe sepsis.