**4. Danaparoid**

Danaparoid sodium is a mixture of linear glycosaminoglycuronans (GAGs) with a MWave of 4500 Da (range 2500–10,000 Da). It is extracted from porcine mucosa

after heparin removal and ultrafiltration. The final product consists of heparan sulphate (HS) 85% with about 12% dermatan sulphate (DS) and traces of chondroitin sulphates 4 and 6 (CS). The HS appears to be more concentrated in the lower MWave chains and the DS and CS in the longer chains. The main structural difference between danaparoid and the heparins is the presence of glucuronic acid in place of iduronic acid. Enzyme degradation of danaparoid GAG chains produces disaccharides (see **Figure 1**) with a low degree of sulphation and acidification. Hence the GAG chains in danaparoid a low overall negative charge density compared with the heparins [unfractionated (UFH) and the fractionated low molecular weight heparins (LMWHs)]. However, about 5% by weight of the HS fraction of danaparoid [the so-called high affinity HS (HA-HS)] consists of more highly sulphated chains because like those of UFH they contain an antithrombin (AT) binding pentasaccharide sequence that includes a triple sulphated glucosamine residue. Only this specific AT binding site possesses a higher overall negative surface charge density than the rest of danaparoid chains that do not bind AT.

Danaparoid is an antithrombotic that inhibits thrombin generation by both AT mediated inhibition of factor Xa by the HA-HS subfraction and direct inhibition of thrombin activation of factor IX by the major non AT binding HS. In addition, a minor inhibition of thrombin activity is produced by the HA-HS, mediated via AT, and by the DS fraction mediated via heparin-cofactor II.

Danaparoid is not a heparin but a heparinoid and further, unlike the heparins, it is not an anticoagulant because the recommended therapeutic dose regimen hardly affects the routine clotting tests (aPTT, PT, ACT and TT). A lack of spontaneous platelet activation and the weak inhibition of thrombin-induced platelet activation is associated with virtually normal primary haemostasis and hence low bleeding risk.

Three biological effects of danaparoid can be assayed—its anti-Xa activity, anti-thrombin activity and TGI. These have plasma half-lives of 24.7, 2.0 and 6.7 h respectively. However, the anti-thrombin activity is too weak for monitoring and at the time of its clinical development (1980s) there was no simple TGI assay. Hence the pharmacokinetics of danaparoid was based on the effect of the smallest subfraction

**Figure 1.**

*Comparison of heparin and danaparoid disaccharide structures.*

#### *Danaparoid Sodium: A Review of Its Use in Hepatic Thrombotic Disorders DOI: http://dx.doi.org/10.5772/intechopen.103851*

of danaparoid (HA-HS) that represents only 5% by weight of the total product and is responsible for only half of its anti-thrombotic activity.

Plasma anti-Xa activity measurements have shown that at least the HA-HS subfraction is cleared via the kidneys and that the liver plays no role in its elimination from the blood. In the absence of overall labelling studies it is assumed that the remaining fractions of danaparoid undergo a similar fate. Although useful for estimating plasma levels of danaparoid the anti-Xa activity shows poor correlation with bleeding or thrombotic events reflecting the fact that this assay, unlike thrombin generation inhibition (TGI), does not measure all actions contributing to danaparoid's effect on haemostasis.

Only 5% of the HS chains in danaparoid contain the trisulphated disaccharide required for AT binding. The remaining chains are low in both sulphate and acidic groups hence the overall negative charge density of danaparoid is low compared with the heparins (see **Figure 1**). Thus danaparoid is unable to bind to the many positively charged 'heparin-binding' proteins in the circulation and without this 'neutralising effect' danaparoid is 100% bioavailable for antithrombotic activity compared with 30% for UFH and about 80% for the LMWHs. This is also the reason why the anti-Xa activity units (U) of danaparoid are not equivalent to the IU of the heparins.

Clinical development of danaparoid led to widespread approval for deep venous thrombosis (DVT) prophylaxis hip following hip orthopaedic and general cancer surgery and in Japan for the treatment of disseminated intravascular thrombosis (DIC). The absence of heparin making it unlikely to cross-react with the specific antiplatelet antibody led to its approval for the treatment of heparin-induced thrombocytopenia (HIT), including the prevention or treatment of thrombosis in patients with renal failure requiring use of an extracorporeal circuits, in children and in pregnancy, if these patients also have HIT or other forms of heparin intolerance. **Table 3** compares some PK and PD aspects of danaparoid with those of the heparins.

Apart from its antithrombotic activity, animal and isolated tissue experiments revealed that like heparin danaparoid has both immune-modulatory and anti-inflammatory activities [32], with both similarities and differences from the heparins (see **Table 4**).

The first indication of this came when danaparoid prevented heparin from activating platelets in the presence of plasma from patients with HIT [33]. In addition, it was found that while the isolated HA-HS subfraction (4% by weight of danaparoid) showed 100% cross reactivity with the specific HIT antibody this was totally prevented by addition of the remaining 96% of danaparoid with no affinity for AT [34]. Finally it was shown that danaparoid is unique among currently available antithrombotics in interfering with the interactions of the specific HIT antibody with heparin and its platelet and monocyte targets [35]. In addition, it was shown that danaparoid is unable complex with platelet factor 4 (PF4, a platelet derived cytokine to which heparin binds to induce HIT) to form the ultra-high molecular weight complexes with neo-antigenic sites [36] required to induce the specific antiplatelet antibody underlying the pathogenesis of HIT. Other experiments [37–49] (summarised in **Table 4**, where it is compared with the effects of the heparins) have shown that danaparoid inhibits or attenuates anti-inflammatory effects induced by various triggers, including endotoxin, ischaemia, reduction of ischaemia/reperfusioninduced hepatic injury in animals and a pilot endotoxin study in volunteers. Many of these actions occurred at the equivalent of its usual therapeutic dosing intensities. They appear to be independent of danaparoid's antithrombotic activity, since they occur in the absence of AT or other clotting cascade constituents. From independent studies of synthetic GAGs or chemically modified heparin the resultant chemical structure of its oligosaccharide chains is of great importance. The low degree of sulphation with fewer acid groups and

#### *Anticoagulation - Current Perspectives*


*[ ] square brackets indicates action greatly reduced or virtually absent, APC = activated protein C. 1 Roman numerals refer to clotting factors.*

*2 aPTT, PT and TT measure residual thrombin activity, the HepT (Heptest) measures anti-Xa and anti-IIa activities. 3 Increases plasmin access.*

*4 Only to its specific targets: AT and HCoII.*

*5 One study of PVT treatment [31] found less efficacy of dan if AT <50%.*

#### **Table 3.**

*The heparins and danaparoid, modes of action, pharmacokinetics and pharmacodynamics compared.*

the absence of the 2-O sulphate group on the glucosamine (see **Figure 1**) appear to be responsible for many of the immune-modulatory/anti-inflammatory activities summarised in **Table 4** [31, 32, 50–53].

Thus fine structural differences between the many HSs within the body are responsible for myriad interactions that are site-specific with roles in haemostasis, inflammation, leukocyte transmigration, immune homeostasis, lipid metabolism, cell attachment, angiogenesis, migration, invasion and cell differentiation.

Based on the combination of antithrombotic activity and immune/modulatory actions danaparoid has been successfully used to treat patients with sepsis, DIC and HIT. In addition its low bleeding inducing capacity has led to off label use to prevent post-HSCT SOS and TA-TMA and to treat patients with PVT.


### *Danaparoid Sodium: A Review of Its Use in Hepatic Thrombotic Disorders DOI: http://dx.doi.org/10.5772/intechopen.103851*

*HIT = heparin-induced thrombocytopenia, HMGB-1 is a chromatin protein and cytokine mediator of inflammation, NET = neutrophil extracellular trap, PF4 = platelet factor 4.*

*1 However highly dependent on the specific annexin and degree of sulphation of the GAG involved. 2 Single report using recombinant adeno-associated virus- type 24 .*

*nd—no data, brackets indicate action is weaker or only occurs under certain circumstances.*

#### **Table 4.**

*GAG immune-modulatory effects at therapeutic dose levels.*

#### **4.1 Danaparoid treatment of portal vein thrombosis**

#### *4.1.1 Population exposure*

Danaparoid exposure in relation to PVT is available for 559 patients. Five retrospective comparative studies treated 177 patients with danaparoid only v UFH [54], v danaparoid + AT [55, 56] or v danaparoid + AT and AT only [57] and danaparoid + AT v AT only [58]. In addition, 383 patients received danaparoid in reports of retrospective case series and single case reports [57, 59–91] in which danaparoid was used alone or combined with AT and finally 2 single case reports of danaparoid administered with UFH [92] or urokinase [93]. Danaparoid was given to treat the PVT in 41 of the 43 reports. In the remaining 2 it


*AT = Antithrombin.*

*1 Not all studies had complete information hence the different denominator.*

*2 Danaparoid was compared in most studies with danaparoid + AT. In Ref. [31] the number receiving dan alone or + AT is only specified in an interim analysis for 28 of the final 55 patients. Three additional case reports of dan + UK, dan + UFH and dan + warfarin are not included in table but are discussed in text.*

#### **Table 5.**

*General characteristics of PVT of danaparoid treated patients and non-danaparoid controls.*

was given for PVT prophylaxis. **Table 5** shows some patient characteristics that could be identified with the treatment given.

Hepatic PVT was present in 524 of the 558 patients exposed to danaparoid (including those receiving AT and the 3 receiving concomitant antithrombotics— UFH, warfarin or a thrombolytic). In 33 patients thrombus was also present in the splenic vein and in 33 in the superior mesenteric vein, but only 11 single case reports stated the exact distributions when 2 or more sites were implicated, i.e. PV + SMV 6 cases, PV + SV 1 case, PV + SV and SMV 3 cases and PV + B-Ch 1 case and one publication mentioned that in 16 of 41 patients the PVT was present in more than 1 site.

The frequencies of some relevant presenting parameters were inconsistently provided in the study reports, e.g. hepatic failure was hardly mentioned but one study [60] reported a mean MELD score of 8.6, encephalopathy was only mentioned in four reports, the Child-Pugh status was provided for 10 comparative studies and 6 case reports as either scores (range 5–12) or classes A, B and C—118, 166 and 49 respectively, bleeding (in all cases gastrointestinal, 3 due to varices) was only mentioned in 6 single case reports and severe infection in only 3 reports, mean plasma AT levels available in only 8 publications were low normal or <60% of normal levels in 7 and platelet counts provided in only 5 single case reports and 4 comparative studies or case series were a median 80 G/L (range 17–655). It is not known if these parameters were therefore normal, absent or not considered, hence their absence from the pooled overview shown in **Table 5**.

Patients were followed-up after danaparoid discontinuation for at least 3 months and in some studies events up to 2 or 3 years were recorded. During this follow-up period at least 210 patients had been transitioned to a warfarin to continue anticoagulation. One study [66] found that long-term edoxaban succeeded but warfarin failed to sustain successful initial danaparoid treatment of PVT.

#### *4.1.2 Danaparoid dosing for PVT*

All studies, apart from three single cases [72, 81, 94], were performed in Japan. In two cases, HIT [72, 81] was also present and in three cases the PVT was accompanied by hepatic vein thrombosis (HVT, Budd-Chiari syndrome) [72, 81, 87]. Because treatment and prevention of PVT is an off label indication for danaparoid the dosing regimen used in Japan was that approved for DIC treatment, i.e. 1250–2500 U/day as 1 or 2 i.v. bolus

### *Danaparoid Sodium: A Review of Its Use in Hepatic Thrombotic Disorders DOI: http://dx.doi.org/10.5772/intechopen.103851*

injections (or short infusions) respectively. For most patients the higher dose 1250 U b.d., i.v. was chosen. In the three non-Japanese single case reports [72, 81, 91] the danaparoid regimen was 'therapeutic' (i.e. >2250 U/day) to treat HIT resulting from initial use of a heparin for the PVT and/or the HVT. In one of these patients it was used safely up to and after orthotopic liver transplant and to anticoagulate the cell saver during surgery [81]. For the other HIT patient no precise dosing information is available and for the third non-Japanese patient [93], the dose was also not mentioned but it was administered with warfarin until the patient could be discharged on warfarin only. Danaparoid exposure lasted a median 14 days (range 4 days to 2 months). In addition, sporadic reports state its successful re-use when PVT recurred during long-term warfarin use [55, 59, 67, 70].

Fifteen reports showed that AT was used concomitantly with danaparoid in 180 patients and in 2 studies AT was used alone as a comparator in 93 patients. In some studies comparing danaparoid alone with danaparoid + AT the AT was only used in patients presenting with plasma levels below 60%. The AT regimen was usually 1500 U daily for 3 days, but in one comparative study [56] and one case report [88] it was administered for 5 days. Administration of AT was often dependent upon the patient's AT status but in two studies danaparoid alone was compared with danaparoid + AT.

#### *4.1.3 Results*

The efficacy of danaparoid treatment assessed as complete, ≥70%, 50%–70%, <50% recanalisation/no change or as a new/progressive thrombosis, are summarised in **Table 6**.

Danaparoid treatment was associated with complete recanalisation in 46% of the patients and clinically significant thrombosis management in 72.6% (i.e. ≥70% PVT resolution) of the patients (although some investigators considered >50% reduction as clinically significant). An ineffective outcome was recorded in 10.7% of the patients including one with progression of thrombosis. Two studies assessed vessel volume reduction as a measure of recanalisation. One [61], involving 41 patients treated with danaparoid only, expressed the result as the mean reduction of 55.1% ± 40.2% at


#### **Table 6.**

*Pooled outcomes of PVT treatment.*

2 weeks, the other [66], involving 55 patients also treated with danaparoid only, found a reduction from median 3.43 cm3 to 1.42 cm3 , also at 2 weeks. Incidental presenting thromboses were: SSST and ovarian vein in one patient and two PEs, all resolved during danaparoid treatment, but only one of the three concomitant hepatic vein thromboses responded favourably to danaparoid. In all reports providing data on coagulation markers d-dimer, TAT and fibrinogen the plasma levels normalised by 2 weeks. All platelet counts (including the two patients with HIT) also increased to normal except for one patient, but no reason was given. In addition, plasma AT levels, whether above 60% before danaparoid treatment initiation or supplemented with injected AT, did not deteriorate during danaparoid use. The only study with a group of non-anticoagulated controls showed.

Three bleeding events (0.8%) developed, one each in three patients, during danaparoid treatment initiation: two from varices (one following endoscopic ligation), and one peritoneal haemorrhage. Danaparoid was restarted in one. No problem was recorded during the transition from danaparoid to warfarin.

No patient death was reported within 3 months of stopping danaparoid treatment. Other adverse events reported were the development of ascites in two patients (one with diarrhoea) and one case of thrombocytopenia that was not considered serious but no other details were provided. Despite one investigator [56] calculating that warfarin doubled the time of PVT recurrence from 1 to 2 years, eight others [55–59, 61, 66, 67] reported that follow-up treatment with warfarin failed to maintain PVT reductions achieved when danaparoid was discontinued.

#### *4.1.4 Indirect comparison of danaparoid with other anticoagulants*

Due to the lack of adequate non danaparoid and or AT controls an indirect comparison of pooled PVT treatment outcomes with various other drug treatment strategies has been made in **Table 7**. These data [95–107], however, lack consistency in describing PVT treatment outcomes. Hence it was necessary to express the results as complete and ≥50%. Despite this restriction it appears that clinically relevant PVT resolution, i.e. complete or ≥70% recanalisation, occurred in 73% of danaparoid treated patients compared with <42% for no treatment, <62% for sulodexide and <67% for the LMWH. It is not possible to calculate for warfarin but it is also in likely to be in the region of 70%. Thus the efficacy of danaparoid is at least as good as warfarin and the LMWH. However the frequencies of no change or progression of the PVT and bleeding was much lower with danaparoid.

Comparison with non-danaparoid controls other than AT is confounded by: the fact that only two small studies [54, 58] used such controls. One study tested danaparoid prophylaxis and found that no PVTs in the 11 danaparoid treated patients but 2 in the 32 patients receiving AT only. The two PVTs and seven from a prior 'testing' cohort in this study were successfully treated with danaparoid. In a study of cirrhosis related PVT [54] danaparoid successfully managed all eight PVTs in its treatment group but of the seven UFH + Urokinase controls only five (71.4%) responded favourably and the two non-responders died of liver failure within 3 months of treatment. While there is little evidence from non-danaparoid controls in the danaparoid studies there is evidence based on the use of the heparins and VKA that anticoagulation increases the chance of recanalisation of PVT. However if recurrences are to be prevented it is also necessary to follow-up with long term outpatient anticoagulation. This has largely been left to the VKAs but more recently the oral direct oral anticoagulants (DOACs) have also become available.

*Danaparoid Sodium: A Review of Its Use in Hepatic Thrombotic Disorders DOI: http://dx.doi.org/10.5772/intechopen.103851*


*nc = no change, TE = thrombi, LMWHs = low molecular weight heparins.*

*1 in many reports PVT resolution expressed only as complete or ≥50%.*

*2 LMWH unspecified, enoxaparin and nadroparin.*

*3 only >50% resolution data for all studies.*

*4 in one study of 20 patients data for <50% resolution and recurrence were combined (12 = 60.0%) hence the study has been excluded from the calculation.*

#### **Table 7.**

*Comparison of pooled published non-danaparoid PVT outcomes with pooled danaparoid outcomes.*
