Tolrestat pharmacokinetic and pharmacodynamic effects on red blood cell sorbitol levels in normal volunteers and in patients with insulin-dependent diabetes.

OBJECTIVES: To examine the effect of diabetes mellitus on the pharmacokinetics of tolrestat and to investigate its effect on red blood cell sorbitol levels according to a new pharmacodynamic model for this class of drugs. METHODS: Single and multiple doses of tolrestat (200 mg/twice a day) were administered to 12 patients with insulin-dependent (type I) diabetes and 12 healthy volunteers in an open parallel trial. RESULTS: Tolrestat disposition was characterized by first-order absorption and biexponential disposition: In normal subjects the terminal disposition half-life (t1/2) was 13 +/- 3 hours (mean +/- SD) and the apparent oral clearance (CL/F) was 48 +/- 9 ml/hr/kg, similar to the values in patients with type I diabetes mellitus (t1/2 = 14 +/- 4 hours; CL/F = 55 +/- 10 ml/hr/kg). Red blood cell sorbitol concentrations, which declined because of tolrestat's inhibition of aldose reductase, were characterized by an indirect-response model including a 50% inhibition constant (IC50) for production of sorbitol by aldose reductase. The removal of sorbitol (kout) was slower in patients with diabetes. The plasma IC50 averaged 2.0 +/- 1.3 micrograms/ml in normal subjects and 2.5 +/- 1.9 micrograms/ml in patients with diabetes. IC50 values expressed in free (unbound) concentrations (fu = 0.64%), which ranged from 12 to 16 ng/ml, were similar to the in vitro IC50 for inhibition of sorbitol accumulation in human red blood cells. CONCLUSIONS: Tolrestat pharmacokinetics were similar in normal subjects and in patients with diabetes; however, the patients with diabetes had higher baseline sorbitol levels (11 versus 5 nmol/ml for normal subjects) and slower sorbitol efflux rates. The proposed biochemically realistic, dynamic model characterized well the red blood cell sorbitol response patterns after administration of single and multiple doses of tolrestat.

Effects of increased liver blood flow on the kinetics and dynamics of recombinant tissue-type plasminogen activator.

OBJECTIVE: To investigate the influence of increased liver blood flow on the pharmacokinetics and pharmacodynamics of recombinant tissue-type plasminogen activator (rt-PA) and to study the changes in endogenous urokinase-type plasminogen activator (u-PA). METHODS: This open, randomized, crossover trial was carried out in a clinical research unit. Eight healthy, nonsmoking volunteers received linear infusions of 24 mg rt-PA and 92 mg indocyanine green over 160 minutes. Sixty minutes after the infusions were started, the subjects consumed a standardized meal to increase liver blood flow on one occasion and abstained from taking food on the other occasion. Plasma concentrations of indocyanine green, tissue-type plasminogen activator (t-PA) antigen, t-PA activity, total u-PA antigen, plasmin-activatable single-chain u-PA (scu-PA), active two-chain u-PA (tcu-PA), fibrinogen, total fibrin, and fibrinogen/fibrin degradation products (TDP), and alpha 2-antiplasmin were measured. RESULTS: After the consumption of the meal, the area under the curve (AUC) was 35% (95% confidence interval [CI]: 25%, 43%) lower for indocyanine green, 15% (CI: 6%, 24%) lower for t-PA antigen, and 11% (CI: 2%, 19%) lower for t-PA activity compared to the AUC after subjects abstained from food. No changes were observed in fibrinogen, TDP, or alpha 2-antiplasmin concentrations that were attributable to the intake of food. The infusion of rt-PA caused a fivefold increase in the concentration of active tcu-PA and a concomitant decrease in scu-PA concentrations by more than 50%. CONCLUSIONS: Increased liver blood flow results in an increase in t-PA clearance. The conversion of the inactive zymogen scu-PA to the active tcu-PA is increased by an infusion of rt-PA, but total u-PA antigen concentrations remain unchanged.

Effects of liver blood flow on the pharmacokinetics of tissue-type plasminogen activator (alteplase) during thrombolysis in patients with acute myocardial infarction.

BACKGROUND: The removal of recombinant tissue-type plasminogen activator (rt-PA; alteplase) by the liver is so rapid that liver blood flow becomes rate determining for its clearance. In patients with myocardial infarction changes in liver blood flow may result from impaired cardiac performance or drug treatment. OBJECTIVE: To estimate the effect of variations in liver blood flow on t-PA plasma concentrations during thrombolytic therapy. METHODS: Fifteen patients with acute myocardial infarction were investigated in an open single-center study at the coronary care unit of University Hospital Leiden. Patients received thrombolytic treatment with 100 mg rt-PA over 3 hours. Liver blood flow was estimated by indocyanine green clearance and by Doppler echocardiography. Concentrations of t-PA antigen, t-PA activity, indocyanine green, alpha 2-antiplasmin, fibrinogen, and fibrin and fibrinogen degradation products were measured. RESULTS: Indocyanine green clearance and clearance of both t-PA antigen (r = 0.78; p < 0:01) and t-PA activity (r = 0.54; p < 0.05) were significantly related. Significant associations between t-PA antigen and fibrin and fibrinogen degradation products and between t-PA antigen and alpha 2-antiplasmin were also found. CONCLUSIONS: The liver blood flow of patients with myocardial infarction is inversely correlated with plasma concentrations of t-PA. In patients with severely impaired liver blood flow and heart failure, high t-PA plasma concentrations may occur if standard doses are given. This finding could contribute to optimization of the dosage of t-PA in certain patient groups.

Effects of changing liver blood flow by exercise and food on kinetics and dynamics of saruplase.

OBJECTIVE: To investigate the influence of changes in liver blood flow on the pharmacokinetics and pharmacodynamics of single-chain unglycosylated urokinase-type plasminogen activator. METHODS: This open, randomized, crossover trial was carried out in the clinical research unit. Infusions of 37.5 mg saruplase and 90 mg indocyanine green were administered over 150 minutes to 10 healthy male volunteers. After 60 minutes the subjects consumed a standardized meal to increase liver blood flow or performed an exercise test (20 minutes) to decrease liver blood flow. Indocyanine green concentrations, total urokinase-type plasminogen activator (u-PA) antigen, two-chain u-PA activity, fibrinogen, total degradation products, alpha 2-antiplasmin, and factor XII-dependent fibrinolytic activity were measured. Blood flow was measured after food intake in a portal vein branch with Doppler echography. RESULTS: The weighted average indocyanine green concentration after exercise was increased by 29% compared with baseline (steady-state concentration) values (95% confidence intervals [CI]: +6%, +56%). After food, the concentration was 27% lower compared with baseline values (95% CI: -35%, -19%), and portal vein flow was increased by a maximum of 103% (95% CI: +71%, +136%). Average maximal concentrations of u-PA antigen after exercise were increased by 130 ng/ml compared with baseline concentrations (95% CI: +65, +195 ng/ml) and, unexpectedly, 156 ng/ml higher after food (95% CI: +59, +253 ng/ml). Although not significant, an increase in average u-PA antigen concentration compared with baseline values was detected after both exercise (7%) and food (13%). This tendency toward a larger effect after food compared with the effect after exercise was reflected by minor changes in the pharmacodynamics. CONCLUSIONS: u-PA plasma concentrations were increased by reduced liver blood flow induced by exercise. Food intake produced an unexpected increase in u-PA concentrations despite increases in liver blood flow.

On the role of C1-inhibitor as inhibitor of tissue-type plasminogen activator in human plasma.

An enzyme immuno assay was developed to measure complexes of tissue-type plasminogen activator (t-PA) with C1-inhibitor in order to study the role of C1-inhibitor as an inhibitor of t-PA in plasma. In vitro experiments with melanoma and recombinant t-PA learned that purified C1-inhibitor reacts with both single chain t-PA and two chain t-PA. The rate constants ranged from 3.0 to 5.2 M-1s-1. In plasma, melanoma and recombinant two chain t-PA were hardly inhibited by C1-inhibitor, in contrast to melanoma and recombinant single chain t-PA which were inhibited to the same extent by endogenous C1-inhibitor as they were by purified C1-inhibitor. In vivo, t-PA/C1-inhibitor complex could be measured in plasma in a few cases in healthy volunteers (0.62 +/- 0.43 ng/ml t-PA equivalents), after exercise (0.84 +/- 0.25 ng/ml t-PA equivalents) and after a desmopression infusion (0.26 +/- 0.04 ng/ml t-PA equivalents). However, t-PA/C1-inhibitor complex was found in plasma in all cases after venous occlusion (1.7 +/- 0.5 ng/ml t-PA equivalents), in peritoneal fluid from patients suffering from peritoneal inflammatory disease (2.2 +/- 1.3 ng/ml t-PA equivalents) and in plasma from healthy volunteers during a t-PA infusion (27.7 +/- 18.5 ng/ml t-PA equivalents at peak level). In the last case, about 8% of the infused dose of recombinant t-PA (alteplase) was inhibited by C1-inhibitor at peak level.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of isotretinoin on endogenous tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor 1 (PAI-1) in humans.

The effect of isotretinoin on fibrinolysis was investigated in 10 healthy, male volunteers in a randomized, double-blind, crossover-designed study. Isotretinoin (40 mg) was administered in the morning and in the evening for 5 days. t-PA, u-PA and PAI-1 antigen and activity in plasma were measured every morning at 9 a.m. on days 1 to 4 and every 3 hours over 24 hours on day 5. Isotretinoin treatment had no significant stimulatory effect on endogenous t-PA antigen and activity in morning plasma samples nor on their circadian variation. Also, u-PA antigen levels did not change after isotretinoin treatment. Mean PAI-1 antigen and PAI activity in 9 a.m. plasma samples were non-significantly higher during isotretinoin than during placebo treatment. After treatment with isotretinoin a significant rise of fasting triglyceride plasma levels was observed as compared to placebo. The study shows that isotretinoin has no clinically significant effect on endogenous fibrinolysis.

Effect of changes in liver blood flow on the pharmacokinetics of saruplase in patients with acute myocardial infarction.

BACKGROUND: The recombinant unglycosylated single chain urokinase-type plasminogen activator saruplase is cleared for a large part by the liver. A large interindividual variation in saruplase concentration is found in acute myocardial infarction (AMI) patients. The variable cardiac performance after an infarct may induce differences in liver blood flow that could explain the concentration diversity. This study was performed to investigate the relation between hepatic blood flow and the pharmacokinetic and pharmacodynamic properties of saruplase. METHODS AND RESULTS: Thirteen AMI patients were enrolled in this open label study. Patients received a bolus injection of 20 mg saruplase followed by a one-hour infusion of 60 mg saruplase. Concurrently 36 mg intravenous indocyanine green (ICG) was given over 1 h to measure hepatic blood flow. Blood samples were taken at regular time intervals to measure plasma levels of urokinase-type plasminogen activator (u-PA) antigen and activity, the two-chain form (tcu-PA) activity, indocyanine green, fibrinogen, fibrin and fibrin degradation products, alpha2-antiplasmin and thrombin antithrombin III complex. A correlation was seen between the clearance of ICG and both those of u-PA antigen (r = 0.62; p <0.05) and u-PA activity (r = 0.57; p <0.05). A negative correlation was seen between the area under the curve of tcu-PA activity and the areas under the effect curves of both fibrinogen and alpha2-antiplasmin (r = -0.84; p <0.01 and r = -0.65; p <0.05). CONCLUSIONS: Liver blood flow is an important determinant of the clearance of u-PA antigen and activity and reduction of flow in patients with heart failure will lead to an increase in plasma concentrations. High plasma concentrations of tcu-PA activity lead to increased systemic fibrinogenolysis. These results may be used to optimize saruplase treatment in patients with impaired cardiac function or after co-medication with drugs that affect liver blood flow.

Drug interactions with thrombolytic agents. Current perspectives.

Thrombolytic agents are widely used for the treatment of acute thromboembolic diseases, especially acute myocardial infarction (AMI). These compounds include streptokinase, anistreplase, alteplase, urokinase and, although not commercially available yet, saruplase (prourokinase). The therapeutic window of these compounds is relatively small and subtherapeutic or toxic plasma concentrations may have serious clinical implications (insufficient thrombolysis, reocclusion and bleeding). Among the factors that affect the pharmacokinetics and pharmacodynamics of thrombolytic agents, comedication is especially relevant since these drug interactions are partly predictable and sometimes preventable. Based on knowledge of the pharmacology of thrombolytic agents and general mechanisms by which pharmacokinetic drug interactions occur, interactions with alteplase and saruplase are expected. The clearance of alteplase is dependent on hepatic blood flow (HBF), and scientific evidence is emerging that saruplase is also a high-clearance compound. Each pharmacological agent that alters HBF and is given concurrently with one of these agents can change the plasma concentrations of those thrombolytics. Although there are no published data confirming drug-induced changes in the metabolism of alteplase or saruplase by this mechanism in humans, indirect supportive evidence (clinical observations and animal experiments) is available. An overview is presented of the anticipated effects of compounds that are frequently coadministered with thrombolytic agents on the pharmacokinetics of the thrombolytics with high-clearance properties. Since the clearance of these thrombolytics may be strongly affected by hypoperfusion of the liver as a result of cardiogenic haemodynamic failure, the role of circulatory changes in potential drug-drug interactions is also discussed. Pharmacodynamic drug interactions are highly relevant in the treatment of acute thrombotic lesions and are still being evaluated to further optimise treatment strategies. As most of these treatments exist as combinations of thrombolytic, antithrombin and antiplatelet compounds, beneficial effects are partly offset by bleeding complications. Changes in the pharmacokinetics and/or pharmacodynamics of thrombolytic agents may have serious consequences. It becomes imperative for the practising physician to be aware of benefits and risks of interactions with thrombolytic agents and especially of the fact that the principal way by which the pharmacokinetics of alteplase and, presumably, saruplase can be affected is by drug- and/or haemodynamic failure-induced changes of HBF.

The effect of m-CPP on tics and obsessive-compulsive phenomena in Gilles de la Tourette syndrome.

RATIONALE: Family genetic and phenomenological studies support an interrelationship between Gilles de la Tourette syndrome (GTS) and obsessive-compulsive disorder (OCD). Some authors consider GTS as part of a serotonergically mediated cluster of OCD spectrum disorders. OBJECTIVE: To study serotonergic mechanisms in GTS, the effect of the relatively selective 5-HT2c agonist meta-chlorophenylpiperazine (m-CPP) was assessed. METHODS: We studied the behavioural effects of m-CPP on tics, obsessions, compulsions and impulsions of GTS. Twelve medication-free GTS patients (ten men, two women) were included in a single dose 0.5 mg/kg oral m-CPP challenge study with a double-blinded placebo-controlled cross-over design. Global symptom scores, target symptom scores as well as biochemical measures were followed up to 24 h after baseline. RESULTS: While m-CPP caused a significant rise in plasma cortisol and prolactin levels, no significant effects were found on the tics, obsessions and compulsions. Impulsions showed a trend to ameliorate. CONCLUSIONS: This study does not support a predominant role for 5-HT on the tics in GTS. The trend of impulsions to ameliorate after m-CPP can be interpreted as circumstantial support for impulsivity-related 5-HT hypofunctionality in GTS. However, the large variability of m-CPP plasma concentrations found in this study casts doubts upon the reliability of m-CPP as a probe for challenge studies.

A cross-over comparison of the anti-clotting effects of three low molecular weight heparins and glycosaminoglycuronan.

1. The anti-clotting effects after intravenous administration of three low molecular weight (LMW) heparins, Fragmin (KABI 2165), Fraxiparine (CY 216), Clexane (PK 10169) and the LMW mixture of glycosaminoglycuronans Orgaran (Org 10172) were compared in a randomized cross-over study in 12 healthy male volunteers. 2. The time courses of the anti-Xa activity of Fragmin, Fraxiparine and Clexane (five subjects) were best fitted by a monoexponential function and had comparable half-lives of 1.9 h, 2.3 h and 2.8 h, respectively. The time courses of the anti-Xa activity of Orgaran and Clexane (four subjects) were described by a biexponential function with terminal half-lives of 56.8h and 27.7 h, respectively. They were longer than those of Fraxiparine and Fragmin. Orgaran injection was associated with a significantly smaller 'clearance' (0.8 +/- 0.2 l h-1) of the plasma anti-Xa activity compared with Fragmin (2.0 +/- 0.5), Fraxiparine (1.7 +/- 0.5) and Clexane (1.6 +/- 0.5). 3. In comparison with the three LMW heparins, the terminal half-life of plasma anti-IIa activity after Orgaran was longer and the 'clearance' of Orgaran was lower than that after Clexane. The area under the curve of the plasma anti-IIa activity after administration of Orgaran was negligible compared with that obtained after injection of the LMW heparins. 4. Orgaran caused the smallest and Fragmin the greatest prolongation of the activated partial thromboplastin time (Orgaran 5.8 +/- 1.2 s vs Fragmin 18.5 +/- 5.2 s) and the thrombin clotting time (Orgaran 2.9 +/- 1.7 s vs Fragmin 47.8 +/- 0.9 s).(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetic and pharmacodynamic interactions of ramipril with propranolol.

We have studied the pharmacodynamic effects of ramipril, propranolol, and their combination, as well as the effect of propranolol on the pharmacokinetics of ramipril in 12 healthy men (age 24 (SD 6) y, weight 72 (7) kg). Propranolol and placebo, ramipril and placebo, or propranolol and ramipril were given orally for four days in a crossover, double-blind fashion. The pharmacokinetics of ramipril and ramiprilat were investigated on day 4. Effects on plasma renin activity, ACE activity, and heart rate and blood pressure both before and after a standardized exercise test were measured on days 1 and 4. On day 4 the combination reduced the mean arterial pressure by 2.8 mmHg compared with propranolol alone and by 3.7 mmHg compared with ramipril alone. Ramipril had no effect on the bradycardia induced by propranolol. Propranolol reduced exercise mean arterial pressure by 9 mmHg (day 4) and heart rate by 7 beats.min-1 (day 4) compared with ramipril; this was not affected by co-administration of ramipril. On day 4 the average plasma renin activity was not significantly higher than after the combination. ACE activity was not affected by propranolol. The pharmacokinetics of ramipril and ramiprilat were not influenced by propranolol. The combination of ramipril and propranolol has additive pharmacodynamic effects that may be useful in the treatment of hypertension.

Pharmacokinetics, pharmacodynamics and bioavailability of the ACE inhibitor ramipril.

The pharmacokinetics and pharmacodynamics of the prodrug ramipril and its active ACE-inhibiting metabolite ramiprilat were investigated in an open, randomised, three-way cross-over study in 12 healthy male volunteers. Subjects received 2.5 mg ramipril orally, 2.5 mg ramipril intravenously and 2.5 mg ramiprilat intravenously. The absolute bioavailability as judged by ramipril plasma AUC was 15%, by ramiprilat plasma AUC, 44%. Ramiprilat formation from intravenous ramipril was 53% and from oral ramipril 28%. Urinary recovery of oral ramipril was 23%, i.v. ramipril 49%, and i.v. ramiprilat 68% of the given dose. Maximum ACE inhibition was highest (100%) after i.v. ramiprilat; it was 99% after i.v. ramipril and 84% following oral ramipril. ACE inhibition over 24 h was highest after i.v. ramipril, 2% less with i.v. ramiprilat and 34% less with oral ramipril. Ramiprilat renal clearance was concentration dependent. The biological availability of ramipril can best be judged by ramiprilat AUC, urinary recovery of ramipril and metabolites, or ACE inhibition over 24 h. It is concluded that the bioavailability of oral ramipril seems to be in the range of 44-66%.

The oral bioavailability of pentosan polysulphate sodium in healthy volunteers.

OBJECTIVE: Pentosan polysulphate sodium (PPS), a heparin-like drug, is supposed to be orally applicable. The objective of the present study was to assess the oral bioavailability of PPS. However, since specific assays for PPS do not exist, this was done by using primary and secondary effect parameters. METHODS: The study was carried out using a three-way randomized crossover design with 18 healthy young male volunteers. The subjects received three treatments: PPS i.v. (50 mg), PPS orally (1500 mg) and placebo (orally). Blood sampling was done for activated partial thromboplastin time (APTT), anti-Xa activity, hepatic triglyceride lipase, lipoprotein lipase, tissue plasminogen activator (t-PA) activity, fibrin plate lysis, total triglyceride, total cholesterol, HDL and LDL. RESULTS: Intravenously administered PPS significantly increased APTT, anti-Xa activity, hepatic triglyceride lipase and lipoprotein lipase compared with placebo in a magnitude comparable to other i.v. heparin-like compounds. Orally administered PPS did not significantly influence any of the parameters when compared with placebo. Point estimates for the oral bioavailability of PPS were in the range of 0% with small confidence intervals (CIs). CONCLUSION: The oral bioavailability of PPS is negligible in young healthy males.

Loss of anticoagulant effect of heparin during circulation of human blood in vitro.

Device-induced thrombogenesis was studied in an in vitro model using human blood circulated through an artificial ventricle. A new constant pressure filtration technique was used to detect circulating microemboli, the activated partial thromboplastin time (APTT) test was used to monitor the blood for the presence of anticoagulant activity of heparin, and hemolysis was quantified by measuring the plasma free hemoglobin level. Circulation of blood through a 20-ml stroke volume pneumatically driven ventricle for 6-9 h resulted in a significant reduction of APTT, indicating the loss of the anticoagulant effect of heparin. Microemboli concentration was minimal until the APTT decreased below 125 s, at which time the microemboli concentration increased rapidly. This was presumed to be due to the formation of thrombi following a decrease in heparin activity. A significant increase in hemolysis was also noted when blood was pumped. None of these changes was noted in the nonpumped control blood. Spontaneous loss of heparin activity in blood circulated by a pneumatically driven pump may have clinical implications and may help understanding of the problems associated with device-induced thrombogenesis.

The effect of warfarin on the pharmacokinetics and pharmacodynamics of napsagatran in healthy male volunteers.

OBJECTIVE: The effect of oral warfarin on the pharmacokinetics and pharmacodynamics of the synthetic direct thrombin inhibitor napsagatran was investigated. METHODS: In an open, randomised, two-way crossover study, 12 healthy male volunteers were infused napsagatran (80 micrograms/min) for 48 h. Each subject was administered 25 mg warfarin (Coumadin) at the start of the infusion in either the first or second treatment period. Sampling was performed regularly over the treatment period and 24 h thereafter for measurement of plasma levels of napsagatran, activated partial thromboplastin time (APTT) and prothrombin time (PT). RESULTS: The pharmacokinetic parameters of napsagatran were not significantly influenced by co-administration of warfarin. Napsagatran administration was followed by increases in APTT and PT. Co-administration of warfarin increased the AUEC (area under the effect curve) calculated for the period 0-48 h (corrected for baseline) for APTT by 45% (95% CI: 28-65%) and for PT by 438% (95% CI: 272-678%) compared to the treatment with napsagatran alone. CONCLUSION: Warfarin has no effect on the pharmacokinetics of napsagatran, but has a marked influence on the pharmacodynamic parameters (APTT, PT) of napsagatran. In clinical practice, this interaction between the two compounds should be taken into account. The PT cannot be used to monitor the effect of oral anticoagulants during the switch from this group of direct thrombin inhibitors to full oral anticoagulant therapy.