Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K49/00—Preparations for testing in vivo
  • A61K49/04—X-ray contrast preparations
  • A61K49/0433—X-ray contrast preparations containing an organic halogenated X-ray contrast-enhancing agent
  • A61K49/0447—Physical forms of mixtures of two different X-ray contrast-enhancing agents, containing at least one X-ray contrast-enhancing agent which is a halogenated organic compound
  • A61K49/0461—Dispersions, colloids, emulsions or suspensions
  • A61K49/0466—Liposomes, lipoprotein vesicles, e.g. HDL or LDL lipoproteins, phospholipidic or polymeric micelles

Definitions

• This invention relates to parenterally administrable particulate compositions, in particular contrast media, eg. MRI, X-ray, ultrasound, light imaging or nuclear imaging contrast media, especially X-ray contrast media and more particularly vesicle containing X-ray contrast media .
• contrast media eg. MRI, X-ray, ultrasound, light imaging or nuclear imaging contrast media
• X-ray contrast media especially X-ray contrast media and more particularly vesicle containing X-ray contrast media .
• Contrast media are widely used in a range of imaging modalities (eg. CT, MRI, ultrasound etc.) in order to improve the contrast in the images obtained, for example to assist in differentiation between different organs or between healthy and unhealthy tissue.
• imaging modalities eg. CT, MRI, ultrasound etc.
• insoluble inorganic heavy metal salts eg. barium sulphate
• soluble iodinated organic compounds usually triiodophenyl monomers and dimers, such as iohexol and iodixanol
• the soluble iodinated organic compounds have similar biodistribution and bioelimination patterns following parenteral administration, distributing into the extracellular fluid (ECF) compartment before relatively rapidly being renally excreted. Accordingly their clinical indications are similar although the non-ionic compounds (such as iohexol) are greatly preferred over the ionic compounds (such as metrizoate) for parenteral administration due to better patient comfort and tolerance.
• organ specificity for new contrast media and in particular there are demands for targetting agents which enhance contrast of specific organs such as the liver (liver agents) , the vasculature (blood pool agents) and the lymph nodes (lymphatic agents) .
• particulate X-ray contrast agents which, due to their particulate nature, are abstracted from the blood by the reticuloendothelial system and hence accumulate at the liver.
• iodophenyl contrast agents have been associated with macromolecular substrates or structures to extend their vascular half-lives.
• lymph node imaging attempts have been made to use local administration (eg. subcutaneous administration) of particulate contrast media.
• lymph node imaging following intravascular administration of particulate agents is also feasible.
• liver agents based on biodegradable particles see WO 89/00988 and WO 90/07491
• liposomes containing X-ray contrast agents see WO 95/26205
• emulsions see EP-A-294534
• Vesicle containing agents eg. liposomal agents, such as described in WO 95/26205 have shown promising liver imaging results in animal studies and acceptable safety profiles in pre-clinical trials. In trials on human volunteers at diagnostically desirable dosages, however, minor but uncomfortable adverse events have occurred.
• a liposomal contrast agent containing 80 mg I/mL of a water-soluble non-ionic X-ray contrast agent entrapped within phospholipid liposomes (having a mean (Z-average) particle size of about 350 nm, and constituting about 40% of the total composition volume) and dissolved in the aqueous suspension medium for the liposomes at substantially equal concentration caused side effects such as fever, chills, headache, nausea and vomiting. Investigations now indicate that these effects are related to the total particle count administered to the patient .
• This objective is met by the present invention by the reduction of the particle count/mg enclosed iodine in the composition, eg. by the use of higher entrapped iodine concentrations and/or by the use of higher volume vesicles .
• the invention provides a contrast agent composition, preferably an X-ray contrast medium, comprising vesicles (eg. micelles or liposomes) in suspension in an aqueous medium, said vesicles and optionally also said aqueous medium containing an iodinated X-ray contrast agent, characterised in that a dose of said composition containing 100 mgl entrapped in said vesicles contains no more than 8xl0 12 vesicles (preferably less than 6xl0 12 , especially preferably less than 4xl0 12 , particularly preferably less than 2xl0 12 , and more especially less than 10 12 , eg.
• vesicles eg. micelles or liposomes
• an iodinated X-ray contrast agent characterised in that a dose of said composition containing 100 mgl entrapped in said vesicles contains no more than 8xl0 12 vesicles (preferably less than 6xl0 12 , especially preferably less
• the weight ratio of encapsulated iodine to vesicle membrane material is at least 1.8:1, eg. at least 2:1, for example 2-5:1, more preferably 2.5 to 4.8:1, especially preferably 3.0 to 4.5:1.
• the encapsulated iodine content is at least 30 mg/mL (of total composition) , more preferably at least 60 mg/mL and particularly preferably at least 100 mg/mL.
• the invention also provides a method of generating a contrast enhanced image, eg. an X-ray image, comprising parenterally (eg. intravenously or intraarterially) administering a contrast agent composition according to the invention to a human or non-human animal (preferably mammal) body and generating an image, preferably an X-ray (eg. CT) image, of at least part of said body, preferably at least of the liver.
• parenterally eg. intravenously or intraarterially
• administering a contrast agent composition according to the invention to a human or non-human animal (preferably mammal) body and generating an image, preferably an X-ray (eg. CT) image, of at least part of said body, preferably at least of the liver.
• the vesicles may be unilamellar or multilamellar; preferably the composition has a high degree of bi or trilamellar liposomes and/or unilamellar vesicles.
• the iodine may be entirely or substantially entirely associated with the vesicles, eg. by encapsulation within the vesicle core and/or by incorporation within the vesicle membrane .
• the aqueous medium within which the vesicles are suspended will contain a dissolved iodinated organic contrast agent, especially at or near the iodine concentration within the vesicle core.
• the contrast medium has a three-fold contrast effect - the vesicles providing blood pool and RES (eg. liver and lymph node) contrast enhancement and the iodinated agent in the aqueous suspension medium providing blood pool and other ECF contrast .
• RES eg. liver and lymph node
• the iodine concentration in the composition as a whole is conveniently 100 to 500 mgl/mL, especially 100 to 460 mgl/mL, more especially 150 to 420 mgl/mL, particularly 200 to 400 mgl/mL, and more particularly 225 to 370 mgl/mL.
• the concentration of vesicle encapsulated contrast medium is preferably at least 40 mgl/mL (eg. 40 to 160 mgl/mL) , especially preferably at least 40 to 100 mgl/mL relative to the volume of the overall composition.
• the dosage is preferably 60-600 mgl (in total) per kg bodyweight, preferably 150 to 500 mgl/kg, more preferably 200 to 400 mgl/kg.
• injection or infusion, and in particular bolus injection of the contrast medium provides particularly diagnostically effective iodine concentrations within the vasculature.
• Having substantially similar iodine concentrations within and surrounding the vesicles has further advantages in terms of simplicity of production and sterilization, particularly autoclave sterilization, of the contrast medium since removal of non-entrapped iodine is not required and since diffusion over time (and hence storage) will not radically change the iodine distribution.
• the particle count eg. number of vesicles per mL, in the contrast medium of the invention is not in itself a critical parameter. What is critical, and therefore characteristic of the compositions of the invention, is the number of particles per dose (or more particularly in the dose per kg bodyweight of the patient) .
• the present inventors surmise that the adverse effects and the lower imaging effects of the prior art parenteral particulate X-ray contrast media arise from overloading of the particle uptake system of the liver and that therefore what is critical is to deliver to the liver an iodine dose which is diagnostically effective for liver contrast enhancement without causing a level of uptake saturation sufficient to provoke the unacceptable side effects.
• the X-ray contrast agent used in the compositions of the invention is preferably a triiodophenyl compound and more especially a non-ionic compound. Both monomers (such as iohexol) and dimers (such as iodixanol) may be used.
• Suitable X-ray contrast agents include the compounds of WO-A-96/09282 and WO-A-96/09285 as well as compounds such as iodixanol, iopentol, iohexol, metrizamide, metrizoate, ioversol, ioxilan, ioxaglate, iopamidol, iotrolan, ioglicate, iomeprol, iophendylate, iopromide, iosimide, iotasul, iothalamate, iotroxate and ioxitalamate .
• Non-ionic monomers such as iohexol, iopamidol and iopentol and non-ionic dimers such as iodixanol and iotrolan are however most preferred.
• the vesicles used in the compositions of the invention as the vehicles for transporting encapsulated iodine to the liver, may be produced by conventional means using vesicle membrane forming agents, preferably phospholipids .
• vesicle membrane forming agents preferably phospholipids .
• suitable membrane forming materials are set out in WO 95/26205 the disclosure of which is incorporated herein by reference.
• the membrane preferably comprises both a neutral phospholipid and a charged phospholipid.
• both phospholipids are substantially saturated.
• the neutral phospholipid preferably comprises at least one substantially saturated fatty acid residue.
• the number of carbon atoms in such fatty acid residues is preferably at least 15 or more, preferably at least 16. Where the number of carbon atoms in a fatty acid residue is less than 14, the ability of liposomes to hold the internal aqueous phase is low and the stability of liposomes in blood after administration is low. On the other hand, where the number of carbon atoms in a fatty acid residue is 28 or more, biocompatibility becomes low, and very high temperature is necessary during production of liposomes.
• substantially saturated means that fatty acid residues of the neutral and charged phospholipids are fully saturated (i.e. contain no C-C double bonds) or that the extent of their unsaturation is very low, e.g. as shown by an iodine value of no more than 20, preferably no more than 10 most preferably 5 or less. Where the extent of unsaturation is too high, the liposomes are easily oxidized.
• the vesicle membrane advantageously comprises a charged phospholipid, eg. one comprising at least one substantially saturated fatty acid residue.
• the number of carbon atoms in such a fatty acid residue is usually at least 14, preferably at least 15 and more preferably at least 16, for the reasons set out above.
• the absolute value of the zeta potential of the vesicles in the compositions of the invention is preferably less than -50 mV, particularly less than -58 and especially less than -60, eg. -50 to -70 mV.
• Neutral phospholipids useful in the present invention include, for example, neutral glycerophospholipids, for example a partially or fully hydrogenated naturally occurring (e.g. soybean- or egg yolk-derived) or synthetic phosphatidylcholine, semi-synthetic or synthetic dipalmitoyl phosphatidylcholine (DPPC) or distearoyl phosphatidylcholine (DSPC) .
• neutral glycerophospholipids for example a partially or fully hydrogenated naturally occurring (e.g. soybean- or egg yolk-derived) or synthetic phosphatidylcholine, semi-synthetic or synthetic dipalmitoyl phosphatidylcholine (DPPC) or distearoyl phosphatidylcholine (DSPC) .
• DPPC dipalmitoyl phosphatidylcholine
• DSPC distearoyl phosphatidylcholine
• Charged phospholipids useful in the present invention include, for example, positively or negatively charged glycerophospholipid ⁇ .
• Negatively charged phospholipids include, for example, phosphatidylserine, for example a partially or fully hydrogenated naturally occurring (e.g. soybean- or egg yolk-derived) or semi-synthetic phosphatidylserine, particularly semi-synthetic or synthetic dipalmitoyl phosphatidylserine (DPPS) or distearoyl phosphatidylserine (DSPS) ; phosphatidylglycerol, for example a partially or fully hydrogenated naturally occurring (e.g.
• soybean- or egg yolk-derived or semi-synthetic phosphatidylglycerol, particularly semi-synthetic or synthetic dipalmitoyl phosphatidylglycerol (DPPG) or distearoyl phosphatidylglycerol (DSPG) ; phosphatidylinositol, for example a partially or fully hydrogenated naturally occurring (e.g.
• soybean- or egg yolk-derived or semi- synthetic phosphatidylinositol, particularly semi- synthetic or synthetic dipalmitoyl phosphatidylinositol (DPPI) or distearoyl phosphatidylinositol (DSPI) ; phosphatidic acid, for example a partially or fully hydrogenated naturally occurring (e.g. soybean- or egg yolk-derived) or semi-synthetic phosphatidic acid, particularly semi-synthetic or synthetic dipalmitoyl phosphatidic acid (DPPA) or distearoyl phosphatidic acid (OSPA) .
• DPPA dipalmitoyl phosphatidic acid
• OSPA distearoyl phosphatidic acid
• both the charged phospholipids are positively charged, or both the charged phospholipids are negatively charged, in order to prevent aggregation.
• Positively charged lipids include, for example, an ester of phosphatidic acid with an aminoalcohol, such as an ester of dipalmitoyl phosphatidic acid or distearoyl phosphatidic acid with hydroxyethylenediamine .
• the ratio of the neutral phospholipid to the charged phospholipid is usually 200:1 to 3:1, preferably 60:1 to 4:1, and more preferably 40:1 to 5:1 by weight, e.g. about 10:1.
• the mean vesicle size is preferably in the range 50 to 4000 nm, especially 100 to 3000 nm particularly 150 to 2000 nm.
• the upper size limit is dictated partially by the size constraints of the capillaries and may be exceedable for vesicles with particularly flexible membranes.
• the lower size limits are dictated by the desire according to the invention to minimize the number of vesicles required to deliver a diagnostically effective iodine dosage to the liver and other parts of the RES. Size discrimination of vesicles may be achieved by extrusion of larger vesicles through filters of appropriate pore sizes (see Biochem Biophys Acta 557:9 (1979)), or by gravitational or centrifugal separation techniques .
• the contrast agent compositions of the invention may contain various optional components in addition to the membrane forming agents and the X-ray contrast agent.
• vitamin E ⁇ -tocopherol
• vitamin E acetate ester as an antioxidant may be added in an amount of 0.01 to 2 molar %, preferably 0.1 to 1 molar % relative to total amount of lipids .
• sorbitol is preferably included as a tonicity adjusting agent (particularly important where a non-ionic dimer is used as the X-ray contrast agent) .
• the concentration of total lipid is generally 10 mg/ml to 100 mg/ml, preferably 15 mg/ml to 90 mg/ml, and more preferably 20 mg/ml to 80 mg/ml, in order to enhance encapsulation of contrast agent in the vesicles.
• contrast agents are preferably encapsulated in the vesicles in the form of an isotonic solution or suspension (relative to physiological osmotic pressure in the body) in an appropriate medium so that the vesicles are stably maintained in the body after administration.
• an isotonic solution or suspension relative to physiological osmotic pressure in the body
• an appropriate medium water, buffer solution such as TRIS-HC1 buffer, phosphate buffer, citrate buffer or the like may be used.
• a preferred pH range at room temperature is 4.5-8.5, more preferably 6.8-7.8.
• the contrast agent is a non-ionic X-ray contrast agent carrying multiple hydroxyl groups, e.g. iohexol, iodixanol or iopamidol
• the buffer is preferably one having a negative temperature coefficient, as described in US-A-4278654.
• Amine buffers have the required properties, particularly TRIS. This type of buffer has a lower pH at autoclaving temperatures, which increases the stability of the X-ray contrast agent during autoclaving, while returning to a physiologically more acceptable pH at room temperature.
• the contrast agent is dissolved or suspended in a medium at a concentration which provides an isotonic solution.
• a contrast agent alone cannot provide an isotonic solution because, for example, solubility of the contrast agent is low
• other non-toxic water soluble substances for example salts such as sodium chloride or sugars such as mannitol, glucose, sucrose, sorbitol or the like may be added to the medium so that an isotonic solution is formed.
• compositions of the invention which are also in accordance with WO 95/26205 is their ability to withstand autoclaving. They also have a high encapsulation capacity and encapsulation ratio by virtue of their lipid composition.
• the vesicles can be produced by conventional procedures used for formation of multilamellar liposomes. These procedures include the Bangham method (J. Mol . Dial. 13 , 238-252, 1965), the polyvalent alcohol method (Japanese Examined Patent Publication (Kokoku) No. 4-36734) , the lipid-solution method (Japanese Examined Patent Publication (Kokoku) No. 4-36735), and the mechanochemical method (Japanese Examined Patent Publication (Kokoku) No. 4-28412) .
• desired multilamellar vesicles can be prepared by dissolving the above-mentioned phospholipids in a volatile organic solvent such as chloroform, methanol, dichloromethane, ethanol or the like, or a mixed solvent of said organic solvent and water, removing said solvent, mixing the resulting residue with an aqueous phase containing a contrast agent, and shaking or stirring the mixture.
• a volatile organic solvent such as chloroform, methanol, dichloromethane, ethanol or the like
• a mixed solvent of said organic solvent and water removing said solvent, mixing the resulting residue with an aqueous phase containing a contrast agent, and shaking or stirring the mixture.
• Bangham 1 s method uses evaporation, but spray- drying or lyophilization also can be used.
• the amount of the solvent used relative to lipid is not critical, and any amount which allows dissolution of lipid is acceptable. Removing solvent from the resulting mixture of lipid and solvent by evaporation can be carried out according to conventional procedure,

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• 1996
  • 1996-11-29 GB GBGB9624918.0A patent/GB9624918D0/en active Pending
• 1997
  • 1997-11-28 EP EP97945974A patent/EP1009445A2/de not_active Withdrawn
  • 1997-11-28 AU AU51293/98A patent/AU5129398A/en not_active Abandoned
  • 1997-11-28 JP JP52444098A patent/JP2001504837A/ja active Pending
  • 1997-11-28 WO PCT/GB1997/003283 patent/WO1998023297A2/en not_active Application Discontinuation

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