Defibrotide for the treatment of severe hepatic veno-occlusive disease and multiorgan failure after stem cell transplantation: a multicenter, randomized, dose-finding trial

Therapeutic options for severe hepatic veno-occlusive disease (VOD) are limited and outcomes are dismal, but early phase I/II studies have suggested promising activity and acceptable toxicity using the novel polydisperse oligonucleotide defibrotide. This randomized phase II dose-finding trial determined the efficacy of defibrotide in patients with severe VOD following hematopoietic stem cell transplantation (HSCT) and identified an appropriate dose for future trials. Adult and pediatric patients received either lower-dose (arm A: 25 mg/kg/day; n = 75) or higher-dose (arm B: 40 mg/kg/day; n = 74) i.v. defibrotide administered in divided doses every 6 hours for > or =14 days or until complete response, VOD progression, or any unacceptable toxicity occurred. Overall complete response and day +100 post-HSCT survival rates were 46% and 42%, respectively, with no significant difference between treatment arms. The incidence of treatment-related adverse events was low (8% overall; 7% in arm A, 10% in arm B); there was no significant difference in the overall rate of adverse events between treatment arms. Early stabilization or decreased bilirubin was associated with better response and day +100 survival, and decreased plasminogen activator inhibitor type 1 (PAI-1) during treatment was associated with better outcome; changes were similar in both treatment arms. Defibrotide 25 or 40 mg/kg/day also appears effective in treating severe VOD following HSCT. In the absence of any differences in activity, toxicity or changes in PAI-1 level, defibrotide 25 mg/kg/day was selected for ongoing phase III trials in VOD.

Study on pharmacokinetics of radioactive labelled defibrotide after oral or intravenous administration in rats

Defibrotide (D) was labelled with 125I or with 32P. The radiolabelled compounds ([125I]-Defibrotide ([125I]-D), [32P]-Defibrotide ([32P]-D) retained the same profibrinolytic activity, in vitro, as the parent drug, suggesting that the labelling procedures had not modified the pharmacological properties of D and hence that its chemical structure was not affected significantly. After single intravenous or oral administration of [125I]-D or [32P]-D the pharmacokinetic parameters for the two labels were generally in good agreement (75%). t 1/2 alpha was in the range of minutes while t 1/2 beta was in the range of hours. Bioavailability, following single oral administration of [125I]-D or [32P]-D, was in the range of 58-70%. These data suggest that D, in spite of its macromolecular nature, is absorbed, after oral administration, fairly well.

Renal uptake of an 18-mer phosphorothioate oligonucleotide

Renal uptake of a 35S labeled 18-mer phosphorothioate oligodeoxynucleotide (molecular wt approximately 6,000) was evaluated following intravenous infusion into rats. The kidneys contained 21 +/- 3% of the infused dose at five hours after infusion and 3 +/- 1% of the infused dose at four days after infusion. The concentration of oligonucleotide was greater in the kidney than in the liver, spleen, or plasma at both intervals. Urine excretion of oligonucleotide label averaged 17 +/- 1%, 35 +/- 5%, and 64 +/- 3% of the infused dose at five hours, one day, and four days after infusion. Electrophoresis (PAGE) showed that oligonucleotide was retained in the kidney was the intact 18-mer at both five hours and four days after infusion, while full size oligonucleotide was not found in the urine at either interval. Light microscopic autoradiography showed that oligonucleotide uptake was most prominent in the early proximal tubule. Electron microscopic autoradiography indicated that oligonucleotide was not confined to the brush border or endocytic-lysosomal pathway. Micropuncture studies showed that the tubule fluid to plasma concentration ratios of oligonucleotide label averaged 7 +/- 3% in Bowman's space and 6 +/- 2% in the distal tubule. Despite restriction of filtration by plasma protein binding, as indicated by the low Bowman's space to plasma concentration ratio, the calculated tubular reabsorption rate for oligonucleotide was sufficient to account for the large amount of oligonucleotide found in the kidney after intravenous infusion. These results indicate that the proximal tubule plays a prominent role in the disposition of intravenously infused oligonucleotide, and raise the possibility that oligonucleotides could exert antisense effects in this nephron segment.

Pharmacokinetics, absorption, distribution and disposition of [125I]-defibrotide following intravenous or oral administration in the rat

Defibrotide (D) was labelled with 125I. The radiolabelled compound ([125I]-Defibrotide ([125I]-D)) retained the same profibrinolytic activity as the parent drug. Following single intravenous administration of [125I]-D the half lives of radioactivity associated with D components in plasma were 9.45 min and 11.27 h for alpha and beta phases respectively. Following single oral administration of [125I]-D the half life of radioactivity associated with D components in plasma was 12.83 h for the elimination phase. Bioavailability was apparently 58%. The areas under plasma total radioactivity versus time curves were dose-dependent following both intravenous and oral administration. No significant accumulation of total radioactivity in plasma was observed following multiple oral administration of [125I]-D. Following single intravenous administration of [125I]-D a larger proportion of administered radioactivity was excreted via urine than faeces while following single oral administration excretion via urine and faeces accounted for similar proportions of administered radioactivity. Following both single and oral administration the levels of total radioactivity in tissues and organs examined were generally highest in highly perfused organs and were very high in the thyroid despite pretreatment with non-radiolabelled potassium iodide. Radioactivity was also found to be associated with the aorta wall.

Defibrotide. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in vascular disorders

Defibrotide is a deoxyribonucleic acid derivative extracted from mammalian organs, which has been developed for the treatment of a number of vascular disorders. It appears to increase fibrinolysis and may possess antithrombotic, antiatherosclerotic and anti-ischaemic actions, probably due to its ability to selectively increase prostaglandin I2 and E2 levels and to increase tissue plasminogen activator and decrease plasminogen activator inhibitor function. Defibrotide is available as an intravenous and intramuscular preparation, and also as an oral formulation for long term use. Trials performed to date have provided initial evidence that defibrotide is effective in the treatment of peripheral obliterative arterial disease and acute thrombophlebitis, while preliminary data suggest possible use in preventing fibrin deposition in the circuitry of renal haemodialysis equipment. Efficacy in preventing deep vein thrombosis after surgery has been demonstrated but defibrotide does not appear to offer any therapeutic advantage over heparin. Further clinical experience is required in other disorders, including acute myocardial infarction, Raynaud's phenomenon, renal thrombotic microangiopathy and renal transplant rejection, before adequate assessment of efficacy in these areas can be made. Defibrotide is well tolerated, as assessed in trials of up to 6 months duration, with a low global incidence of adverse events (< 1 to 9%). Mild allergic reactions and gastrointestinal disturbances have occasionally been described, and a hypotensive effect has also infrequently been observed. Thus, available data suggest that defibrotide is a well tolerated agent with little or no anticoagulant activity, which is conveniently available in both parenteral and oral formulations. Initial data indicate that the drug may be a useful alternative in the treatment of peripheral obliterative arterial disease and thrombophlebitis, while its therapeutic potential in other vascular disorders and efficacy relative to established agents remains to be fully determined.

High-performance liquid chromatography determination of polydeoxyribonucleotides in plasma: its application to the determination of defibrotide's pharmacokinetics in the rabbit

We describe an HPLC method for the determination of whole polydeoxyribonucleotides in animal plasma. This method was compared to a colorimetric method, which evaluates the sugar moiety of polydeoxyribonucleotides, and to an agarose gel electrophoresis method, which evaluates the whole polydeoxyribonucleotides as does the HPLC method, and was found to give results very close to those obtained with these two other methods. A pharmacokinetic study of the antithrombotic, profibrinolytic, polydeoxyribonucleotidic drug defibrotide was carried out by evaluating the plasma drug levels by these three methods. The pharmacokinetic parameters calculated from the data are very similar.

Conjugation of benzo(a)pyrene 7,8-dihydrodiol-9,10-epoxide in infant Swiss-Webster mice

Benzo(a)pyrene 7,8-dihydrodiol-9,10-epoxide (BPDE), accepted as the ultimate carcinogen of benzo(a)pyrene, has a very short half-life in aqueous solutions yet induces lung tumors when injected into infant mice. To evaluate the possibility that metabolites of BPDE, principally in the form of stable conjugates, contribute to binding to DNA in peripheral tissues, infant mice were injected i.p. with 39 nmol (+/- ) anti-BPDE. One h after injection, 5% of the dose was recovered in serum and appeared mostly as conjugated metabolites (54% as glucuronides and 16% as glutathione conjugates). Amounts of direct acting electrophiles in serum estimated by trapping with DNA comprised less than 0.02% of the injected dose. No more than 10% of the radioactivity in extracts of liver, lung, and kidney was recovered as BPDE. Glutathione conjugates predominated in the liver and lung, whereas glucuronides were the major metabolites in kidney. Radioactivity bound to DNA in liver, lung, and kidney was 21.5, 42.7, and 7.8 pmol/mg, respectively. Despite the rapid conversion of BPDE to stable conjugates, 32P-postlabeling profiles of DNA adducts in lung closely resembled that noted after addition of BPDE directly to lung homogenate. Thus, the reactive intermediate as well as stable conjugates of BPDE may be transported to target tissues where they initiate tumors.

[Pharmacokinetics of defibrotide in uremic patients undergoing hemodialysis]

Defibrotide pharmacokinetics were studied in 6 voluntary healthy subjects and in 10 uremic patients undergoing dialysis during which (instead of heparin) defibrotide was administered to prevent fibrino-formation in the circuit. Blood concentrations of the drug were assessed (expressed with reference to the residual glycidic deoxyribose) during a standard dialysis using defibrotide, 3.5, 15, 30, 45, 60 and 90 minutes after the defibrotide bolus (200 mg) had been injected into the arterial channel. The half-lives of the alpha and beta plasmatic phases were found to be equal at 3.79 and 41.4 min in dialysed subjects and at 1.13 and 16.54 in healthy volunteers. These results indicate that in uremic patients undergoing dialysis at intervals using defibrotide, a longer time is required to eliminate the drug from the circulation. This variation does not however appear to be significant in terms of the therapeutic use of the drug during dialysis.

Absorption through the peritoneum of the macromolecular profibrinolytic drug defibrotide in the rabbit

Defibrotide is the sodium salt of a polydeoxyribonucleotide extracted from mammalian lungs by controlled depolymerization. This macromolecular compound (mean molecular weight 20,000 d) has profibrinolytic activity. It also is antithrombotic after both intravenous and oral administration. The purpose of this study was to see whether defibrotide could activate the fibrinolytic system after intraperitoneal administration, because it has been observed that in ascitic patients treated intraperitoneally with defibrotide, no occlusion of the peritoneal-jugular catheter valve draining the ascitic fluid (according to LeVeen et al.) occurred. The profibrinolytic activity of defibrotide and its plasma levels were dose dependent, with a statistically significant correlation between the fibrinolytic activities and the AUC of the plasma levels of defibrotide. No rebound effect was observed during the duration of the experiments (24 hours). We hypothesize that the fibrinolytic activity elicited by defibrotide prevented the deposition of fibrin in the catheter valve, enabling normal drainage of the ascitic fluid. The lack of rebound makes defibrotide a safe drug. The mechanism by which this macromolecular compound is absorbed is still unknown.