Fibrin formation and proteolysis during ancrod treatment. Evidence for des-A-profibrin formation and thrombin independent factor XIII activity.

Ancrod is a purified fraction of venom from the Malayan pit viper Calloselasma rhodostoma, containing a serine protease that cleaves fibrinopeptides A from fibrinogen. We report on a study that involved intravenous and subcutaneous application of ancrod in healthy subjects in which it was shown that ancrod induces the formation of desAA-fibrin complexes that are partially crosslinked by factor XIII proenzyme, and act as cofactor in tPA induced plasminogen activation. The plasmin generated degrades fibrin, as well as fibrinogen, leading to the appearance of large amounts of fibrinogen and fibrin degradation products in the circulation, including fragment D-dimer. At low concentrations of ancrod, formation of desAA-fibrin is preceded by production of desA-profibrin, lacking only one fibrinopeptide A.

Plasminogen activation without changes in tPA and PAI-1 in response to subcutaneous administration of ancrod.

Ancrod is a purified fraction of venom from the Malayan pit viper, Calloselasma rhodostoma, currently under investigation for treatment of ischemic stroke. The therapeutic effect is ascribed to a lowering of plasma fibrinogen. Thirty-two healthy volunteers received subcutaneous ancrod at doses of 1.0, 1.5 and 2.0 IU/kg body weight or placebo. Blood samples were drawn before the injection and at various time points until 96 h after the injection. Ancrod leads to the formation of desAA-fibrin, which serves as cofactor in tissue plasminogen activator activity (tPA)-induced plasminogen activation. Unchanged concentrations of prothrombin fragment F1.2 and thrombin-antithrombin complex (TAT) indicate that fibrin formation occurs independent of thrombin. Plasmin generation is independent of an increase in tPA activity or changes in plasminogen activator inhibitor-1 (PAI-1) concentration in plasma. Subcutaneous injection of ancrod leads to a generalized fibrino(geno)lytic response caused solely by providing tPA with soluble fibrin as its cofactor in plasminogen activation. Maximal plasmin activity is present 12 h after subcutaneous injection.

Analysis of fibrin formation and proteolysis during intravenous administration of ancrod.

Ancrod is a purified fraction of venom from the Malayan pit viper, Calloselasma rhodostoma, currently under investigation for treatment of acute ischemic stroke. Treatment with ancrod leads to fibrinogen depletion. The present study investigated the mechanisms leading to the reduction of plasma fibrinogen concentration. Twelve healthy volunteers received an intravenous infusion of 0.17 U/kg body weight of ancrod for 6 hours. Blood samples were drawn and analyzed before and at various time points until 72 hours after start of infusion. Ancrod releases fibrinopeptide A from fibrinogen, leading to the formation of desAA-fibrin monomer. In addition, a considerable proportion of desA-profibrin is formed. Production of desA-profibrin is highest at low concentrations of ancrod, whereas desA-profibrin is rapidly converted to desAA-fibrin at higher concentrations of ancrod. Both desA-profibrin and desAA-fibrin monomers form fibrin complexes. A certain proportion of complexes carries exposed fibrin polymerization sites E(A), indicating that the terminal component of the protofibril is a desAA-fibrin monomer unit. Soluble fibrin complexes potentiate tissue-type plasminogen activator-induced plasminogen activation. Significant amounts of plasmin are formed when soluble fibrin in plasma reaches a threshold concentration, leading to the proteolytic degradation of fibrinogen and fibrin. In the present setting, high concentrations of soluble fibrin are detected after 1 hour of ancrod infusion, whereas a rise in fibrinogen and fibrin degradation products, and plasmin-alpha(2)-plasmin inhibitor complex levels is first detected after 2 hours of ancrod infusion. Ancrod treatment also results in the appearance of cross-inked fibrin degradation product D-dimer in plasma. (Blood. 2000;96:2793-2802)

Pharmacodynamic and safety results of PEG-Hirudin in healthy volunteers.

PEG-Hirudin, a chemically defined conjugate of recombinant hirudin and two molecules of polyethylene glycol (PEG)-5000 is a highly selective direct thrombin inhibitor with a significantly longer duration of action than non-conjugated recombinant hirudin permitting once daily subcutaneous administration. A series of placebo-controlled, randomized, Phase I clinical trials were conducted in 75 healthy volunteers to investigate the anticoagulant effects, safety and pharmacodynamics of PEG-Hirudin when administered intravenously as a bolus injection, infusion, and subcutaneously. After single i.v. injections of various doses of PEG-Hirudin (0.03-0.3 mg/kg) dose-dependent increases in anti-IIa activity and APTT were observed. Four hours after injection of 0.3 mg/kg, mean plasma concentration expressed in terms of anti-IIa activity was still 0.89 micrograms/ml, corresponding to a 1.8-fold prolongation of APTT. Continuous intravenous infusions of 0.01 and 0.02 mg/kg/h PEG-Hirudin resulted in maximum anti-IIa activities of 0.42 micrograms/ml and 0.77 micrograms/ml, respectively, at the end of a six-hour infusion period without having reached steady state at this time. After termination of the infusion, anticoagulant activity displayed an immediate exponential decrease. The anticoagulant activities of single subcutaneous doses of 0.05 to 0.6 mg/kg were studied in a further series of investigations and slow increases and prolonged durations of anti-IIa activity and APTT prolongation were found. Repeated, once daily subcutaneous administrations of 0.2 to 0.4 mg/kg for five days resulted in dose-dependent prolongations of APTT and increases in anti-IIa activity without completely reaching steady state conditions. In a further study, 0.3 mg/kg of PEG-Hirudin was given as an i.v. bolus injection followed by three repeated single daily s.c. injections. In this trial, the APTT was shorter than expected from previous studies; therefore, a direct comparison of various APTT reagents was made in the intravenous infusion trial. Of the APTT reagents tested, BioMérieux Silimat and IL-ellagic acid proved to be the most sensitive to PEG-Hirudin. The hirudin derivative PEG-Hirudin was tolerated very well without immuno-allergic side effects. In view of the significantly prolonged anticoagulant efficacy in comparison to non-conjugated r-hirudin, PEG-Hirudin is a promising compound especially for repeated once daily subcutaneous administration.

MAO-A inhibition in brain after dosing with esuprone, moclobemide and placebo in healthy volunteers: in vivo studies with positron emission tomography.

OBJECTIVE: The aim of the study was to investigate whether or not esuprone binds substantially to MAO-A in the human brain. METHODS: In a randomised double-blind placebo-controlled study 16 male healthy volunteers were examined with positron emission tomography (PET) with [11C]harmine. Eight of the volunteers were given daily doses of 800 mg esuprone, four were given bi-daily doses of 300 mg moclobemide, and four volunteers were given placebo tablets. PET was performed before initiation of a 7-day treatment period. On day 7, one investigation was made immediately before administration of the drug, representing 23 h after the previous day's treatment for esuprone and 11 h after the last tablets of moclobemide. Further investigations were made 4 h and 8 h after the morning dose on day 7. RESULTS: PET showed a high degree of binding of [11C]harmine, a high-affinity ligand for MAO-A, before the start of treatment, and a marked and similar reduction after treatment with esuprone and moclobemide. A slight tendency for normalisation of enzyme binding was observed at the last time point. In the placebo group no change was observed. Plasma kinetics of esuprone showed a rapid elimination with a half-life of about 4 h. CONCLUSION: The study demonstrates that esuprone was comparable to moclobemide in its effect on MAO-A inhibition in the brain at the doses given. This is an illustration of the potential of PET to monitor drug effects directly on target biochemical systems in the brain in human volunteers, and the possibility of using these data, rather than pharmacokinetic data, for the determination of dosing intervals.

Investigation of the pharmacokinetic behavior of barucainide in man during an early phase I study.

The pharmacokinetic behavior of the class Ib antiarrhythmic drug barucainide was investigated in a phase I study in a group of 6 healthy male volunteers after oral administration of an initial single dose of 20 mg and incremental doses between 30 and 70 mg barucainide hydrochloride. After a lag time of about 1 h, median plasma concentration peaked at ca. 48 ng/ml barucainide hydrochloride 2.5 h after administration of 20 mg. The drug was finally distributed in a total volume of VB/f of about 630 l. With a terminal half-life of ca. 12.5 h (8-26 h) it was eliminated rather slowly. Elimination was predominantly due to metabolic processes; however, a median of 21% of the dose (7-28%) was recovered unchanged in the urine. Barucainide, in the dose range studied, was not subject to any appreciable first-pass effect; its metabolism apparently depended on the hydroxylation capacity of the volunteers. The doses administered were well tolerated. There were no changes in the cardiovascular parameters investigated, no adverse effects and no impairment of general well-being.

Metabolism of the calcium antagonist gallopamil in man.

The metabolism of gallopamil (5-[(3,4-dimethoxyphenyl)methylamino]-2-(3,4,5-trimethoxyphenyl) -2- isopropylvaleronitrile hydrochloride, Procorum, G) was studied after single administration (2 mg i.v., 50 mg p.o.) of unlabelled and labelled G (14G, 2H). TLC, HPLC, GLC, MS and RIA were used for assessment of G and its metabolites in plasma, urine and faeces. G clearance is almost completely metabolic, with only minimal excretion of unchanged drug. Metabolites represent most of the plasma radioactivity after p.o. administration. They are formed by N-dealkylation and O-demethylation with subsequent N-formylation, or glucuronidation, respectively. Compound A, derived by loss of the 3,4-dimethoxyphenethyl moiety of G is the main metabolite in plasma and urine (about 20% of the dose). This metabolite is accompanied by its N-formyl derivative (C), by the N-demethylated compound (H) and the acid (F), formed by oxidative deamination of A. Only 3 unconjugated monphenoles from several O-demthylated products showed distinct plasma levels which were nevertheless lower than metabolite A. These metabolites had no relevance to the pharmacodynamic action. Conjugated monophenolic and diphenolic products represented the major part in plasma and were excreted predominantly via the bile: they represented almost the whole faecal metabolite fraction. Less than 1% of the dose was recovered unchanged in the urine. About 50% of the dose is excreted by urine and 40% by faeces.

Comparative pharmacokinetics and clinical pharmacology of propafenone enantiomers after oral administration to man.

The pharmacodynamic and pharmacokinetic behavior of (R)- and (S)-propafenone was investigated in a group of seven healthy volunteers, one of whom belonged to the phenotype of poor debrisoquine hydroxylators. Each volunteer received 250 mg of either enantiomer as a solution in randomized order with a washout period of one week in between. The pharmacodynamic evaluation comprised cardiovascular parameters (HR, PQ, QRS, QT, BP) and tolerability (self-assessment questionnaire, hematology, clinical chemistry). For pharmacokinetic purposes plasma levels of the parent compounds (R, S) and their 5-hydroxylated metabolites (5-R, 5-S) were measured. As expected, there was a small but distinct increase of PQ interval with a maximum 2 h after drug intake. No difference was observed between both enantiomers tested. In the poor hydroxylator prolongation of PQ interval was less compared to extensive metabolizers, though plasma concentrations of the unchanged drug were considerably higher. Inspection of the individual concentration time profiles in the other subjects provided additional evidence that the 5-OH-metabolite also contributes to this effect. Other ECG parameters, heart rate and blood pressure remained unaffected. Both enantiomers were well tolerated: no drug-related side effects concerning general well-being and laboratory parameters were observed. In contrast to pharmacodynamic effects (on ECG) a distinct enantioselectivity of metabolic and/or distributive processes can be observed in the group of efficient hydroxylators manifesting itself in a lower clearance for R (ratio 0.50 +/- 0.19, probability of error less than 1%), in spite of a higher terminal elimination rate constant (ratio 1.64 +/- 0.63, probability of error less than 10%). This difference cannot be accounted for by the different degrees of protein binding of the enantiomers (fu(R) = 0.076; fu(S) = 0.049). The experience obtained with one poor hydroxylator seems to indicate that enantioselectivity in terms of oral clearance Cl/F might be lost in this phenotype. The distinctly lower clearance values for the poor hydroxylator when compared to the corresponding data for efficient hydroxylators, seem to be the reflection of the lower metabolic capacity of this phenotype.

Pharmacokinetic-dynamic study on different oral biperiden formulations in volunteers.

The pharmacodynamic and kinetic profiles of two oral biperiden formulations (tablet with instant-release and sugar-coated tablet with slow-release) were studied in a total of 12 healthy subjects after the administration of a 4 mg dose and compared in part to placebo. Biperiden as slow-release formulation showed much slower absorption than the instant-release tablet; whereas plasma levels peaked as early as 1-2 h after administration of the tablet, with the slow-release formulation a first peak was seen approximately 4.5 h after intake in the majority of the subjects. In some subjects this was followed by a trough, in others by formation of a shoulder at around 0.5 ng/ml. In all subjects a peak of about 1.0 ng/ml was reached after 10-12 h. The instant-release tablet and the slow-release formulation showed comparable bioavailability. Plasma concentrations for the slow-release formulation at 24 h were around 0.5 ng/ml, about twice as high as those for the instant-release formulation. The ratio of peak to 24 h values showed the marked reduction which is characteristic for a slow-release formulation compared with the instant-release tablet. The subjective well-being of the volunteers was not influenced by the slow-release formulation, whereas after the instant-release tablet slight CNS effects (dizziness, drowsiness and fatigue) were reported up to 6 h after ingestion. Furthermore, objectively quantifiable pharmacodynamic ocular parameters (near-point accomodation, pupil size) and the secretion of saliva proved to be less affected by the slow-release formulation than by the instant-release tablet, or not affected at all.

Biperiden effects and plasma levels in volunteers.

The pharmacokinetics of biperiden was studied and compared with pharmacodynamics (pupil size, accommodation, self-rating mood scale) in 6 healthy volunteers. A single-blind cross-over design was employed with placebo and biperiden (4 mg as commercially available tablets). After a lag time of 0.5 h, biperiden was rapidly absorbed with a half-life of 0.3 h, plasma peak levels of 5 ng/ml being reached after 1.5 h. Biperiden showed good tissue penetration (distribution half-life 0.6 h; ratio of total to central distribution volume 9.6), the terminal half-life time of plasma concentration was 18 h, and the oral clearance was 146 l/h. The pharmacodynamic maximum lagged behind the plasma peak concentration by 1 (self-rating) to 4 h (accommodation).

Beta-blocking and electrophysiological effects of propafenone in volunteers.

The chemical structure of propafenone (P) and certain experimental findings suggest that this antiarrhythmic compound could possess beta-blocking properties. To evaluate the clinical relevance of the latter cardiovascular effects of P during exercise were studied. After oral administration of P 150 and 300 mg in solution, six healthy volunteers were subjected to graded exercise. These doses of P, which are usually effective against arrhythmias, decreased exercise-induced tachycardia, whereas the systolic blood pressure was lowered but only at rest, and the diastolic pressure was slightly raised. However, taking into account dose ratio, and the intensity and duration of the reduction in exercise tachycardia, this effect of P was only about 5% at its maximum compared to propranolol and similar active beta-blocking compounds. The reduction in heart rate produced by P was not correlated with the plasma level nor did it show dose dependency, in contrast to beta-blocking agents, and also in contrast to its electrophysiological effects on the PQ interval.