Oral bioavailability of a low molecular weight heparin using a polymeric delivery system

Abstract

Low molecular weight heparins (LMWHs) are the standards of anticoagulant for the prevention of deep vein thrombosis (DVT) in patients undergoing arthroplasty and abdominal surgery. However, LMWHs are so far only administered by parenteral route. Thus, they are usually replaced by oral warfarin for outpatient therapy. Since warfarin has a slow onset and high incidence of drug–drug interaction, there is a great need for the development of an oral LMWH formulation. LMWH (tinzaparin)-loaded nanoparticles prepared with a blend of a polyester and a polycationic polymethacrylate by the double emulsion method were administered orally in fasted rabbits. The plasma tinzaparin concentration was measured by a chromogenic anti-factor Xa assay. After oral administration of two doses of tinzaparin-loaded nanoparticles (200 and 600 anti-Xa U/kg), the oral absorption was observed between 4 and 10 or 12 h, with a delayed onset of action ranging from 3 to 4 h. Mean absolute bioavailabilities were 51% and 59% for the two tested doses. We now report that the encapsulation of tinzaparin into nanoparticles is likely to contribute to its oral efficacy with an anticoagulant effect prolonged up to 8 h.

Introduction

Heparin is safe and effective for thromboprophylaxis [1], but its poor oral bioavailability requires that it has to be administered by intravenous or subcutaneous injection [2]. Since many years, LMWH that does not necessarily require patient hospitalization tends to replace unfractionated heparin (UFH) in many countries, thus decreasing the cost in health care [3]. Moreover, LMWH have many other main advantages over UFH including a much-improved predictability of the pharmacodynamic effect and a lower risk of heparin-induced thrombocytopenia [4]. In addition, extended therapy with LMWH is increasingly considered as the anticoagulant of choice (i) for short anticoagulant treatment, (ii) in pregnant women [5], (iii) when the stabilization of the international normalized ratio within the desired therapeutic range is impossible [5], or (iv) to replace vitamin K antagonists. It would be consequently an important breakthrough in the care of such patients to administer LMWH orally. Non-parenteral heparin drug delivery systems have shown only limited gastrointestinal absorption with very low antithrombotic effect in animal models [6], [7], [8]. More recently, results with oral delivery agents based on N-acylated α- and non-α-amino acids have led to the development of a novel carrier, i.e., sodium N-[8(-2-hydroxybenzoyl)amino]decanoate (SNAD), which was designed to specifically facilitate the intestinal absorption of LMWH [9], [10] in similar fashion to N-[8(-2-hydroxybenzoyl)amino]caprylate (SNAC) with UFH [11], [12], [13]. The carriers SNAC and SNAD were identified as potent absorption enhancers, non-covalently bound to heparins, which dissociate from LMWH or UFH when the complex has crossed the intestinal barrier [14]. Another promising study was based on the synthesis of new heparin derivatives by coupling LMWH with deoxycholic acid (DOCA), which mediates also the intestinal absorption of LMWH [15]. Although these two most advanced studies show the oral absorption of LMWH in a dose-dependent manner in amounts that would provide prophylaxis against DVT, the anticoagulant activity did not last more than 4 h and high doses of LMWH were orally administered compared to the subcutaneous route. Moreover, SNAD is not yet accepted by health authorities and gives a bitter taste to the oral solution possibly involving compliance issues. As a consequence, many patients stopped the oral treatment during the clinical trial as reported by Emisphere [16]. Another absorption enhancer, labrasol, a pegylated triglyceride, showed in situ intestinal absorption of LMWH with the highest plasma anti-Xa activity after administration of LMWH and labrasol in jejunum compared to duodenum and ileum [17]. Thiolated polymers allowed also the oral absorption of LMWH due to their mucoadhesive properties [18], [19]. However, low oral bioavailability figures were obtained. Chitosan, a non-toxic biocompatible polymer, was also used as absorption enhancer for the oral delivery and intestinal absorption of low molecular weight heparin [20], [21]. Previous results obtained in our team with an oral delivery system of UFH and based on its encapsulation into polymeric particles have led to the GI absorption of heparin in rabbits, with doses that were similar to those administered by intravenous infusion or subcutaneous injection in humans [22].

We have pursued our research efforts by applying this polymeric system to the development of an oral LMWH (tinzaparin) formulation based on nanoparticles designed with a blend of poly(ε-caprolactone) and Eudragit® RS. Several LMWHs with different properties (e.g., elimination half-time) are currently marketed. It is well known that LMWHs are complex mixtures of different molecular weight species. In this study, we have selected tinzaparin (with an anti-Xa/anti-IIa ratio close to 2) and the results obtained after oral administration in rabbits of two different tinzaparin doses were reported.