Comparative pharmacology of low molecular weight heparins: implications of manufacturing processes on biological effects

With the recent development of numerous low molecular weight heparins (LMWHs), a certain amount of concern has become evident as to the equivalency of each agent. In a comprehensive study, we have taken the seven available LMWHs to directly compare their in vitro and in vivo (subcutaneous) antithrombotic properties in one laboratory setting. Where possible, various batches of one LMWH were evaluated. Our findings were that variations of in vivo activity were observed between the LMWHs studied. Some activities were significantly different from placebo, whereas others were not. Depending on the assay chosen significant differences could also be observed for the in vitro activity.

Could thrombus age be a modulator of heparin or L.M.W.H. activities?

The main thrombotic diseases are caused by old constituted thrombi. However, experiments to demonstrate the effects of heparin or heparin fragments on tPA release have been on fresh thrombi. This study on thrombi induced 6, 24, 48 or 72 hours before sampling shows variations in the main biological activities of both heparin and heparin fragment (CY222) as the thrombus ages. This effect is particularly observed on tPA release which is statistically reduced (p less than 0.001). Thrombus age seems to be a modulator of heparin and heparin fragment biological activities.

Inhibition of human liver microsomal epoxide hydrolase by valproate and valpromide: in vitro/in vivo correlation

On the basis of drug interactions with carbamazepine epoxide, it has been hypothesized that valproic acid and valpromide are inhibitors of epoxide hydrolase, but the role of epoxide hydrolase in these interactions has not been clearly established. In this study, therapeutic concentrations of valproic acid (less than 1 mmol/L) and valpromide (less than 10 mumol/L) inhibited hydrolysis of carbamazepine epoxide and styrene oxide in human liver microsomes and in preparations of purified human liver microsomal epoxide hydrolase. Valpromide (KI = 5 mumol/L) was 100 times more potent than valproic acid (KI = 550 mumol/L) as an inhibitor of carbamazepine epoxide hydrolysis in microsomes. After administration of carbamazepine epoxide to volunteers, the transdihydrodiol formation clearance was decreased 20% by valproic acid (blood concentration approximately 113 mumol/L) and 67% by valpromide (blood concentration less than 10 mumol/L). For both valproic acid and valpromide, a striking similarity exists between in vitro and in vivo inhibitory potencies. Valproic acid and valpromide are the first drugs known to inhibit microsomal epoxide hydrolase, an important detoxification enzyme, at therapeutic concentrations.

Antithrombotic activity of recombinant hirudin in the rat: a comparative study with heparin

Hirudin, a potent inhibitor of blood coagulation, differs in its antithrombotic activity according to the source of isolation. It was therefore of interest to study recombinant hirudin. Hirudin was obtained by a genetic process from E. coli. Its antithrombotic action was investigated in an experimental (rat) model of venous thrombosis and was compared to heparin whose results are known. Heparin (400 micrograms/kg) and hirudin (12.5, 25 and 50 micrograms/kg) present an antithrombotic effect and limit the extension of an existing thrombus (p less than 0.05). Higher heparin dosages increase the bleeding time mean value (p less than 0.05) whereas hirudin does not. So, recombinant hirudin presents the same antithrombotic action as heparin but with very inferior dosage. This activity seems not dose-dependent and is associated to weak hemorrhagic effects.

Thallium-201 imaging in the follow-up of differentiated thyroid carcinoma

Since thallium-201 imaging has been reported as a potential means of follow-up of patients with differentiated thyroid carcinoma (DTC) during ongoing thyroid suppression therapy, the authors evaluated the diagnostic sensitivity of this procedure in 31 patients known to have metastases or local recurrence. Among 51 tumor sites 201TI imaging had a detection rate of 45% whereas 84% was noted for imaging with 131I administered in therapeutic doses. Thus, even though the effectiveness of the two radionuclides is not strictly comparable due to the difference in the administered doses, Thallium imaging cannot be recommended as the only modality for the follow-up of patients with DTC. Six of the eight tumor sites negative with 131I were positive with 201TI (especially metastatic cervico-mediastinal lymph nodes). So 201TI imaging may particularly be helpful in localizing metastases or recurrences in patients with a negative 131I scan and abnormal levels of serum thyroglobulin.

Detection of anomalous systemic venous return and intraatrial baffle leakage by radionuclide angiocardiography

The case presented here is a 27-year-old patient who was born with common atrium and left superior vena cava (LSVC). Construction of interatrial septum and intraatrial baffle with pericardium was performed 16 years ago. Radionuclide angiocardiography (RAC) showed that a substantial amount of blood flow from the LSVC was directed to the inferior vena cava through the hemiazygos vein (HAV). It also detected a baffle leak and a left to right shunt at the atrial level. Subsequent RAC after reoperation initially showed insignificant flow through the atrial baffle, major flow through the HAV, and no shunt. Repeat RAC one year after surgery showed increased flow through the baffle and diminished flow through the HAV, without a satisfying explanation. This case illustrates the value of RAC in detecting various types of cardiovascular abnormality and subtle hemodynamic changes.

Grossularine-1 and grossularine-2, alpha carbolines from Dendrodoa grossularia, as possible intercalative agents

Dendrodoine A, grossularines-1 and -2, metabolites isolated from the tunicate Dendrodoa grossularia, have exhibited a cytotoxic activity on L1210 leukemia cells in culture. The inhibition of DNA synthesis induced by grossularines and the plane structure of the alpha-carboline common moiety were in favor of an intercalative process for their mechanism of action. In fact, the results of viscometry, fluorescence quenching and DNA melting experiments clearly indicated the intercalative properties of grossularine-2 explained by its quasi-planar structure and the non-intercalative DNA binding of grossularine-1 explained by the presence of a bulky indole chain at the 2-position of the alpha-carboline ring.

Effects of josamycin on carbamazepine kinetics

The steady state pharmacokinetics of oral carbamazepine in epileptic patients (n = 8) was compared before and after one week of treatment with josamycin (2 g/day). There was a small but statistically significant decrease in oral clearance of total (17%) and unbound (21.5%) drug. In spite of an unchanged AUC of 10,11-epoxide carbamazepine the ratio of metabolite to parent drug AUC was significantly decreased (20.2%). The plasma protein binding of carbamazepine and its 10,11-epoxide metabolite did not vary. The results demonstrate impairment by josamycin of the apparent clearance of carbamazepine. Care should be taken in patient receiving both carbamazepine and josamycin.

Immunosuppressive properties of new side chain sterol hydroperoxides and of the corresponding alcohols

New side chain sterol hydroperoxides derived from stigmastane and their corresponding alcohols could suppress the murine or human cell lymphoproliferation induced by T and B cell mitogens. The suppressive effect is dose and time dependent. Comparison of the activities of the different compounds suggests that the position of the hydrophilic group at C-29 is of greater importance than the hydroxyl or hydroperoxide function itself. Hence a new compound stigmasta-5,24 (28) diene-3,29 diol, appears to be highly effective.

Double-blind, placebo-controlled study of vigabatrin (gamma-vinyl GABA) in drug-resistant epilepsy

Vigabatrin (GVG) (3 g/day) and placebo were compared as an add-on to standard therapy in therapy-resistant epileptic patients using a double-blind crossover design with randomized treatment allocation. Twenty-three patients entered the trial, with four dropping out due to either increased seizure frequency following the cross-over from GVG to placebo (n = 1), intolerance to GVG therapy (n = 2), or poor seizure record (n = 1). Of the 19 patients who completed the study, 17 had partial seizures, eight of whom had secondary generalization and two who had primary generalized seizures. Compared with placebo, GVG was associated with a significant reduction in seizure frequency (p less than 0.01), with 11 of 19 patients experiencing greater than 50% reduction in weekly seizure occurrence, two showing a 25-50% reduction, four unchanged, and two showing an increase in seizures. Global efficacy ratings were greater in the GVG period for 15 patients (p less than 0.05) compared with one in whom there was no period difference and two in whom ratings were higher in the placebo period. Fourteen of the 19 patients indicated a preference for the GVG period. Adverse effects observed during GVG treatment were generally mild and consisted of drowsiness, confusion, nausea, irritability, and constipation. No clinically significant alterations in laboratory test results were observed. No treatment-related changes in plasma concentrations of concomitant antiepileptic drugs were noted. These results confirm the antiepileptic efficacy of oral GVG in refractory epileptics.

Eating seizures

An 18-year old man had a cluster of three seizures in a few hours and then remained seizure-free without medication; his mother has experienced seizures induced by movement. A 29-year-old man has had recurrent seizures for six years. In both cases, seizures were partial motor seizures induced by chewing. They are considered to be a particular variety of movement-induced seizures triggered by proprioceptive afferents of muscular origin. This explanation does not account for the great majority of the 63 published cases of seizures precipitated by eating. Eating seizures represent a heterogeneous group of seizures with discrete electroclinical signs and mechanisms. The term "eating seizures" should be preferred to the term "eating epilepsy."

Stiripentol kinetics in epilepsy: nonlinearity and interactions

Stiripentol kinetics during oral therapy were assessed in six patients with epilepsy who were receiving other antiepileptic drugs. Steady-state levels at 600, 1200, and 2400 mg/day increased in a nonlinear fashion, indicating Michaelis-Menten kinetics. Oral clearance of stiripentol at 600 mg/day was 41.5 +/- 23.4 l/day/kg (mean +/- SD), greater than that at 1200 mg/day (20.3 +/- 8.8 l/day/kg; P less than 0.05) or 2400 mg/day (8.5 +/- 3.8 l/day/kg; P less than 0.01). The apparent in vivo Michaelis-Menten parameters were determined from three mean steady-state concentrations. The average velocity of conversion of stiripentol to its metabolites (Vm), Michaelis constant (Km), and the ratio Vm/Km were 49.3 +/- 13.1 mg/day/kg, 1.35 +/- 1.08 mg/l, and 50.2 +/- 27.5 l/day/kg. Stiripentol reduced the elimination clearances of concomitant antiepileptic drugs. Phenytoin clearance was reduced in all five subjects who received this drug, from a mean control of 29.5 +/- 13.4 l/day to 18.5 +/- 4.6 l/day at a stiripentol dose of 1200 mg/day (P = 0.05) and to 6.48 +/- 2.59 l/day at 2400 mg/day (P less than 0.01). Stiripentol reduced the clearance of carbamazepine in one subject from a control value of 209 l/day to 128 l/day (1200 mg/day) and 61 l/day (2400 mg/day). Stiripentol reduced phenobarbital clearance in two subjects from 3.8 and 5.1 l/day to 2.3 and 3.4 l/day (2400 mg/day). The Michaelis-Menten kinetics of stiripentol, as well as its interactions with other antiepileptic drugs, have important implications in the designing of controlled clinical trials.

Michaelis-Menten kinetics of stiripentol in normal humans

Michaelis-Menten kinetic parameters for stiripentol, and anticonvulsant, were assessed in six normal volunteers. Stiripentol was administered orally three times a day in dosage increments of 600, 1,200, and 1,800 mg/day for consecutive periods of 3, 4, and 7 days, respectively. Stiripentol steady-state levels at the three dosing rates increased more than proportionally with dose. The mean +/- SD oral clearance of stiripentol at 600 mg/day (1,090 +/- 624 L/day) was significantly greater (p less than 0.01) than at 1,200 (506 +/- 219 L/day) or 1,800 (405 +/- 151 L/day) mg/day. Average steady-state concentrations predicted from individually determined Vm and Km parameters were in good agreement with experimentally observed levels, indicating that the kinetics of stiripentol are of the Michaelis-Menten type. The mean Vm, Km, and Vm/Km ratio were 2,299 +/- 490 mg/day, 2.20 +/- 1.28 mg/L, and 1,241 +/- 837 L/day, respectively. Neuropsychological tests carried out before and after 14 days of stiripentol treatment showed a significant decline in verbal learning ability (p = 0.038) and a significant improvement in a test of memory and attention (p less than 0.01).

Carbamazepine/valproic acid interaction in man and rhesus monkey

Sodium valproate (VPA) was administered for 1 week (1 g b.i.d.) to seven epileptic patients receiving chronic carbamazepine (CBZ) therapy. Steady-state CBZ levels determined before and after VPA therapy were reduced by 3-59% in six patients and were unchanged in one patient. The plasma concentration ratio of carbamazepine-10,11-epoxide ( CBZE ) to CBZ increased in all patients by 11-500%. The plasma binding of CBZ was determined in six healthy volunteers given a single 400 mg CBZ dose with and without the coadministration of 1 g VPA in a cross-over design. The mean CBZ free-fraction was increased in three of the subjects (p = 0.008-0.031), decreased in one subject (p less than 0.002), and remained unchanged in two subjects when VPA was administered. Four male rhesus monkeys were infused intravenously with CBZ (15 mg h-1) for 5 days and then three consecutive 24-h infusions were given: I, CBZ alone; II, CBZ with 75 mg h-1 VPA; III, CBZ with 150 mg h-1 VPA. The mean free-fraction of CBZ and CBZE increased during infusions II and III from 31.5 +/- 2.7% to 33.6 +/- 2.6% (p less than 0.05) and 37.7 +/- 1.3% (p less than 0.01) for CBZ and from 46.9 +/- 9.2% to 53.6 +/- 5.7% (p greater than 0.05) and 60.1 +/- 4.0% (p less than 0.01) for CBZE . The clearance of free CBZ declined from 7.96 +/- 1.75 to 4.84 +/- 1.26 (p less than 0.01) and 4.12 +/- 1.75 (p less than 0.01) 1 kg-1h-1 during infusions II and III, respectively. The mean free CBZE /CBZ ratio increased from 0.12 +/- 0.03 to 0.24 +/- 0.03 and 0.36 +/- 0.04 during infusions II and III, respectively (p less than 0.001). These findings indicate a decrease in the elimination clearance of CBZE possibly coupled with a decrease in its formation clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pharmacokinetics of apalcillin. Study of linearity]

Apalcillin is a new semi-synthetic penicillin active on the positive Gram bacteria, and on the enterobacteria, with a particular activity on Pseudomonas and Acinetobacter. The linearity study of the pharmacokinetic was carried out on 26 subjects who were given increasing doses (500, 1 000, 2 000, 3 000 mg) of apalcillin by the venous route. The dosages carried out by the HPLC and bacteriological methods, show a good correlation between the two methods. The serum concentrations, 5 mn. after injection, were respectively 72 micrograms/ml (500 mg); 145 micrograms/ml (1 g) ; 221 micrograms/ml (2 g) ; 290 micrograms/ml (3 g). Urinary excretion is around 20 %, and this, regardless of the dose. The dose increase seems to have no effect on the pharmacokinetic parameters, calculated on the basis of a bi- compartmental model. The areas under the time serum concentrations, increase proportionally, to the dose : 61 (500 mg) ; 146 (1 g) ; 285 (2 g) ; 367 (3 g) - micrograms/ml X h. the linear regression between the AUC (y) and the applied doses (X) is : y = 0,12 X + 14,27 ; r = 0,9046 ; n = 69. The correlation between the AUC and the doses is significant (p less than 0,001). The results obtained show that increasing the dosage has no effect on apalcillin pharmacokinetics, which appear linear.

Calmodulin during development and metamorphosis in urodelan amphibians

Calmodulin isolated and purified to homogeneity from young larvae is very similar to that obtained from adult Pleurodeles waltlii and these proteins are almost identical to previously described vertebrate calmodulins. During P. waltlii development, an increase in total individual calmodulin content is observed after the heart beating stage. In dorsal axial muscle, calmodulin level which is very high at the beginning of larval life (premetamorphosis) decreases strikingly in the first part of prometamorphosis. Such an evolution is observed in Ambystoma mexicanum too. Then, a significant increase occurs during metamorphosis. In contrast, calmodulin level in P. waltlii cardiac ventricular muscle increases continuously from hatching to the end of metamorphic climax. Thyroxine treatment which promotes precocious metamorphosis in P. waltlii and experimental metamorphosis in neotenic A. mexicanum, induces a rapid and significant increase in muscle calmodulin concentration.

Double-blind crossover trial of progabide versus placebo in severe epilepsies

In this double-blind, two-period, crossover trial with randomized treatment assignment, progabide (+/- 30 mg/kg/day) and placebo were compared as add-on to standard therapy in 20 "therapy-resistant" epileptic patients (11 males, nine females; age range, 7-47 years). The duration of each treatment period was 6 weeks. Crossover was performed gradually over 3-4 days. Twenty-four patients entered the study: three dropped out for reasons unrelated to progabide effects; one dropped out during the placebo period because of increased seizure frequency. Of the 20 patients who completed the study, 14 had partial, two partial plus secondary generalized, and four generalized seizures. Preexisting antiepileptic treatment consisted of one antiepileptic drug (AED) in three, two AEDs in eight, three AEDs in five, and four AEDs in four patients (mean, 2.5 AEDs/patient). The following parameters were recorded at biweekly intervals: (a) efficacy parameters--total seizure count, counts of each seizure type, and global clinical judgment; (b) safety parameters--adverse drug effects, brief clinical and neurological examinations, and laboratory tests; and (c) plasma concentrations of progabide and of the associated AEDs. Twelve patients were considered to be improved (p less than 0.01) with progabide by global clinical judgment compared with two patients improved with placebo. Nine patients of 20 had a 48-100% reduction of total seizure count in the verum period, leading to a significant reduction of total seizure number and of complex partial seizures in the verum period as compared with the placebo period (p less than 0.05). Adverse effects were reported or observed in 10 patients during the progabide period and in five patients in the placebo period. The side effects were generally mild and consisted of somnolence in four cases and of tremors, dry mouth, troubles of equilibrium, anorexia, euphoria, depression, and anxiety in individual patients; a 15-20% reduction of the progabide dose was required in two cases only. No treatment-related alterations in results of laboratory tests were observed.

No effect of food intake on clobazam absorption

The kinetics of clobazam taken 3 h before, during, and 3 h after a standard hospital meal were studied in six healthy volunteers. Peak plasma levels were significantly lower when the drug was taken with or after meals suggesting that the rate of absorption was reduced by food. The mean area under the concentration vs time curve was not affected by the time of drug administration indicating that the meal had no effect upon the extent of absorption.