WO2010136818A2

WO2010136818A2 - Dry powder fibrin sealant

Info

Publication number: WO2010136818A2
Application number: PCT/GB2010/050909
Authority: WO
Inventors: Colin Dalton
Original assignee: Quadrant Drug Delivery Limited
Priority date: 2009-05-28
Filing date: 2010-05-28
Publication date: 2010-12-02
Also published as: WO2010136818A3; GB0909131D0

Abstract

A fibrin sealant powder comprises a mixture of first microparticles that comprise fibrinogen, second microparticles that comprise thrombin, and additional, relatively large carrier particles of a wound-compatible, water- absorbent material.

Description

DRY POWDER FIBRIN SEALANT

Field of the Invention

This invention relates to a dry powder fibrin sealant. Background of the Invention WO97/44015 describes a dry powder fibrin sealant based on micro- particles of fibrinogen and thrombin. In the Example, the components are prepared by spray-drying, fibrinogen with sucrose and thrombin with mannitol. Each product has a predominant particle size of less than 10 μm. The fibrin sealant, a blend of these components, has been demonstrated to be an easy-to- use, stable and efficacious topical haemostat. The product can be used immediately, without reconstitution. On contact with aqueous fluid such as blood, the exposed active thrombin converts the exposed fibrinogen into insoluble fibrin polymers. Summary of the Invention A novel fibrin sealant according to the present invention is of the general type described in WO97/44105, and additionally comprises relatively large particles of a wound-compatible, water-absorbent material. This addition of larger particles has the effect of increasing wettability of the powder and the rate that blood and/or body fluid are absorbed by the powder dose; hence the effectiveness of the fibrin sealant is improved as more of the fibrinogen and thrombin in the dose react to form fibrin. The invention provides a powder fibrin sealant product that has efficacy at low fibrinogen levels or lower powder doses, on bleeding wounds. Description of Preferred Embodiments Respective fibrinogen-containing and thrombin-containing soluble microparticles can be formulated together, with larger particles of water-soluble material, in stable, dry form. This formulation can be subsequently activated, as desired, to give a fibrin sealant that is useful in wound therapy and surgery. It can meet the primary objectives of increasing wettability leading to reduced efficacious dose, achieving good flow properties and reduced dusting.

The content of fibrinogen in the blended microparticles containing fibrogen may be about 0.1 to 50% w/w, preferably about 0.5 to 20 w/w. The content of thrombin in the microparticles containing it may be about 10 to 20,000 IU/g, preferably about 25 to 100 IU/g. Microparticles comprising fibrinogen or thrombin may be prepared by the procedures described in WO92/18164, WO96/09814 and WO96/18388. The content of each of these publications, and also of WO97/44015 and its equivalent US6113948, is incorporated herein by reference. These spray-drying and associated particle manipulation processes enable the production of soluble microcapsules with defined size distribution, e.g. of up to 50 μm in diameter. For example, as described in those documents, the microparticles may be produced reproducibly, e.g. with 90% or more (by volume) up to 30 μm, e.g. 10 to 20 μm, in size. Such microparticles of the invention are preferably prepared by spray- drying. Typically, a 2-fluid nozzle is used which utilises compressed air during the atomisation process; this results in the production of hollow microparticles. The maximum particle size (X50 as measured by Sympatec) of microparticles that can be manufactured using this atomisation system on the Niro Mobile Minor spray dryer is -30 μm. Preferred X50 values for the micoparticles of the invention are between 5 and 50 microns, most preferably between 10 and 20 microns.

Such microparticles of the invention may be prepared by separately spray-drying a solution of the each active component with an excipient alone, thus producing two powders which are subsequently blended together. An alternative procedure comprises co-spray-drying, in which fibrinogen or thrombin and another material are formulated and spray-dried, to give microparticles in which the active component is incorporated in the particle. The resultant powder is preferably amorphous or in the form of a glass, as measured by a suitable technique such as FTIR or DSC, with a glass transition temperature of at least 50 Celsius, most preferably at least 80 Celsius.

The fibrinogen or thrombin may be full-length or any active fragment thereof. Fragments are known; see Coller et al, J. Clin. Invest. 89:546-555 (1992). Fibrinogen raw material may be a frozen solution, although, lyophilised powder which requires reconstitution prior to spray-drying may be used.

Suitable excipients are proteins, which may be naturally occurring or recombinant. They may act as "wall-forming materials", as described in WO92/18164, where various examples are given or they may act to form a solid matrix. A preferred material is human serum albumin (HSA). For example, fibrinogen is spray-dried alone or in the presence of varying amounts of excipients such as HSA (e.g. fibrinogen: HSA ratios of 1:1 , 1 :3, 3:1) and trehalose. Other suitable substitutes for HSA include saccharides, including trehaolose, and surfactants, such as Tween 20, Tween 80, Poloxamer 407 or Poloxamer 188.

Calcium ion, e.g. as calcium chloride, may be incorporated in the thrombin feedstock. Alternatively, calcium chloride may be added to the microparticles after processing as a co-factor to aid fibrin formulation.

The additional particles used in the invention (described herein as "carrier particles") typically have a particle size of 50 to 1000 μm, e.g. 100 to 500 μm. They may comprise one material or a mixture.

Various materials are suitable for carrier particles. They include saccharides such as mono- and di-sacchaerides, including lactose, mannitol and trehalose. Cellulose products such as microcrystalline cellulose (Avicel range), methylcellulose, carboxymethyl cellulose, microfine cellulose or hydroxy propyl cellulose, and other materials such as cross-linked polyvinyl pyrrolidone (PVP), used singly or in admixture can be used for carrier particles. Also, suitable carriers particles include polyethylene glycol (PEG), preferably having a molecular weight of about 1000; polyvinylpyrrolidone (PVP), preferably having an average molecular weight of about 50,000; Poly(acrylic acid), PVA, Poly(methylvinylether co-maleic anhydride), Poly(ethyleneoxide), and dextran, typically having an average molecular weight of about 40,000.

Tablet disintegrants may also be used to make carrier particles. These materials will absorb moisture from the wound, expand rapidly and thereby enhance the wettability of the hemostatic components of the powder blend. Aqn example of such materials is sodium starch glycolate (Explotab or Primojel) that typically has an average particle size in the range of 35-55 μm and in which about 25% of the glucose units are carboxymethylated. Further examples are cross-linked polyvinyl pyrrolidone (polyplasdone), alginates, alginic acid and cross-linked sodium carboxymethylcellulose (Ac-Di-SoI).

Gums and gelling agents that can be used include, for example, tragacanth, karaya gum, soluble starch, gelatin, pectin, guar gum and gellan gum. One suitable material for making carrier particles is Emdex, i.e. a hydrated form of dextrates (spray-crystallized dextrose containing small amounts of starch oligosaccharides). It is a highly refined product composed of white, free-flowing, spray-crystallized macroporous spheres with a median particle size of 190-220 μm.

Another suitable material for making carrier particles is Non-Pareil Seeds® (Sugar Spheres). These are used in multiple drug units for improved content uniformity, consistent and controlled drug release and high drug stability, and have size ranges from 200 to 2000 mm. The carrier particles may also be made of the same materials as the microparticles. This has the advantage that no further toxicology is required.

The powder formulation of the invention may be sterilised. Sterile processing, electron bean irradiation, γ-irradiation and ethylene oxide are examples of suitable techniques. Although the components of the fibrin sealant of the invention are preferably water-soluble, and the particles are preferably obtained by spray- drying a suitable solution, the formulated power may be free-flowing and substantially dry and/or amorphous or glassy, with a residual moisture content preferably no greater than 5% w/w, most preferably no greater than 3% w/w. This means that the active components of fibrin sealant in accordance with this invention are not activated until they are wetted, e.g. by coming into contact with liquid at a wound site. The active components may therefore be delivered as a dry mixture, although separate application of the different particles is also envisaged. A dry powder fibrin sealant product may be of particular value where application to a large surface area is required. This includes surgery and repair of traumatic injuries to various organs such as the liver and spleen. A further advantageous application is in skin grafting for burns patients, and specifically where skin epidermal sheets are cultured in vitro and then transferred to the wound site. The use of a fibrin sealant powder in the latter indication may be particularly effective in patients with extensive burns, providing a biocompatible anchorage for skin grafts. It may also be suitable in the treatment of topical ulcers.

The following Example illustrates the invention. Example

A 30% w/v solution of trehalose dihydrate was spray dried on the Niro Mobile Minor configured with a stainless steel Newland Rotary Atomizer using the following operating parameters; Inlet temperature: 160⁰C

Feed rate: 8 g/minute

Atomizer voltage: 10.0 V

The resultant powder had a particle size (X50, geometric diameter) of 47 μm and a moisture content (Karl Fisher) of 5.9%. Dynanmic Vapour Sorption (DVS) Investigation

Powder was dried for 60 minutes at 0% RH then the RH was increased to 50% and held for 60 minutes. The rate of moisture uptake was plotted. This method has high reproducibility; however when using holding humidity above 50%, a decrease in reproducibility is observed. Filter Paper Experiments

Filter paper (Fischer cat no FDR-300-050J was found to be most suitable) was floated on the surface of a Petri dish filled with water. Water quickly wetted through the filter paper although it remained afloat. 100 mg of powder was sprinkled onto the filter paper. This mass allowed the powder to absorb water, but did not sink the filter paper. Results

Pure rotary-dried trehalose with a particle size of ca 47 microns is observed to wet completely quickly. Pure spray-dried trehalose wetted quickly, but any piles of powder that were more than approx 4 mm in height above the filter paper took much longer (~ 10 minutes) to become wet.

When a simple fibrin sealant comprising fibrinogen and thrombin microparticles was tested by this method, the bottom 2 mm of powder in direct contact with the filter paper wetted quickly. However, water did not penetrate beyond this height. It was found that, in order to improve the wettability of the simple fibrin sealant by this method, it was desirable to blend in rotary trehalose of ca 47 microns particle size at proportions of at least 50% w/w. The DVS trace suggests that although the fibrin sealant without carrier particles has a rapid uptake of moisture when exposed to 50% RH, it quickly reaches saturation point and does not continue to absorb water. The DVS traces for the rotary atomised trehalose carrier particles shows the same rapid uptake of water but this is sustained over a greater period of time leading to a greater uptake of water. In fact even after one hour, the formulation is still taking up water at a similar rate. When rotary atomised trehalose is added, the duration of water uptake is increased.

These finding show that wettability and likely fibrin formation are enhanced by the presence of the larger particles.

Claims

1. A fibrin sealant powder comprising a mixture of first microparticles that comprise fibrinogen, second microparticles that comprise thrombin, and additional, relatively large carrier particles of a wound-compatible, water- absorbent material.

2. A fibrin sealant as claimed in claim 1 , wherein said first microparticles contain 0.5 to 20% w/w fibrinogen.

3. A fibrin sealant as claimed in claim 1 or claim 2, wherein said second microparticles comprise 25 to 100 IU/g thrombin.

4. A fibrin sealant as claimed in any preceding claim, which comprises 30 to 70% w/w of the carrier particles.

5. A fibrin sealant as claimed in any preceding claim, wherein the carrier particles are saccharide.

6. A fibrin sealant as claimed in any preceding claim, wherein the carrier particles have a particle size of 50 to 1000 μm.

7. A fibrin sealant as claimed in claim 6, wherein said particle size is 100 to 500 μm.

8. A fibrin sealant as claimed in any preceding claim, for use in wound treatment.

9. A method of treating a wound in a patient in need of treatment, comprising administering to the wound a fibrin sealant as claimed in any of claims 1 to 7.