REAGENT FOR MAKING TECHNETIUM-99M LABELLED TIN COLLOID FOR BODY SCANNING

Abstract: A packaged reagent for making Technetium-99m labelled tin colloids comprises 0.75 to 750 µg stannous tin, 50 to 7000 µg sodium, potassium or ammonium ion, 40 to 5000 µg fluoride ion, 50 to 10,000 µg of a non-toxic non-ionic surface-­ active agent based on poly(alkylene oxide) glycol and a con­ tainer aseptically enclosing said reagent. The presence of the surface-active agent, preferably one of the Pluronic types, results in smaller sized particles being produced on addition of pertechnetate to the reagent. This results in a higher liver/spleen biodistribution ratio.

Description: British Patent Specification 1535847 describes a Technetium-99m labelled tin colloid for body scanning, particularly liver scanning. In the preparation of this colloid, an aqueous solution of a stannous salt is mixed with an excess of sodium, potassium or ammonium fluoride and the mixed solution freeze-dried. It is believed that there is formed a fluoro-stannite complex which is stabilised by excess fluoride. When the freeze-dried mixture is reconstituted by the addition of water or isotonic saline containing pertechetate ion, the complex is hydrolysed and there occurs simultaneous reduction and co-precipitation of the technetium with the colloidal tin hydrate. By this method, the tin colloid is formed only at the time of labelling, so the labelled colloid can be stored only for a maximum of eight hours. This is an advantage over pre-formed tin colloids which may have to be stored for months but which are prone to deterioration. A liver scanning kit based on the invention of British 1535847 has been marketed and has achieved widespread commercial success. Uniform dispersion of the colloid particles in the aqueous medium has been achieved without the need to include a wetting agent or to take any other precautions. However, this commercial kit does suffer from some disadvantages. The particle size is typically 1 to 3 µm, and might usefully be rather smaller. Occasionally, oversize particles are taken up in the lungs. Uptake by the spleen is higher than desired. The biodistribution of the colloid depends on the time between reconstitution and injection, and is somewhat less good after storage for 6 hours. It is an object of the present invention to overcome these disadvantages, but without at the same time increasing the blood retention or reducing hepatic uptake of the colloid. This object is achieved by the use of a surface-active agent based on poly(alkylene oxide) glycol and typified by those sold under the Trade Mark Pluronic®. The use of Pluronic® F-68 in Technetium-99m labelled body scanning agents is not new. British Patent Specification 1343154 describes a lung-scanning agent made by labelling pre-formed micro-particles with Technetium-99m, and uses Pluronic® F-68 as a wetting agent to help suspending the particles. As is well-known, particles smaller than 5 to 8 µm do not become located in the lungs, so particles for lung scanning have a size range typically of 8 to 60 µm. It is natural that such pre-formed particles might need a wetting agent to prevent aggregation during storage and to assist suspension at the time of use. US-A-4337240 and FR-A-2512031 describe scanning agents made by labelling pre-formed denatured albumin-reducing metal complex colloidal particles with Technetium-99m. The pre-formed colloidal particles may be stored prior to labelling as a lyophilisate and a surfactant (e.g. a Pluronic® type surfactant) may be incorporated in the lyophilisate to aid redispersion (reconstitution) of the pre-formed complex colloidal particles in a pertechnetate solution at the time of labelling. These prior art documents are not concerned with the preparation of labelled hydrous tin oxide colloids which are formed at the time of labelling. The present invention provides in one aspect a method of making a Technetium 99m labelled tin colloid, which method comprises adding Technetium-99m, as an aqueous solution of pertechnetate ion, to a reagent comprising from 1 to 1000 µg of stannous fluoride and from 0,1 to 10 mg of a fluoride salt selected from sodium fluoride, potassium fluoride and ammonium fluoride, characterized in that the reagent further comprises from 0.05 to 10 mg of a non-toxic non-ionic surface-active agent based on poly(alkylene oxide) glycol. Preferably, the reagent used in the method of the invention comprises 1 part by weight of sodium, potassium or ammonium fluoride, from 0.001 to 1 part by weight of stannous fluoride and from 0.05 to 10, more preferably from 0.1 to 5.0, parts by weight of a non-toxic non-ionic surface active agent based on poly(alkylene oxide) glycol. The reagent may be in aqueous solution but is preferably used as a freeze-dried solid. Suitably the solution of pertechnetate may be in water or in saline such as may conveniently be obtained by elution of a Technetium-99m generator; when the eluate is sterile, it is desirable that the reagent to which it is added should also be in a sterile state. There will normally be a large stoichiometric excess of stannous and fluoride ions over pertechnetate. The absolute amount of reagent used is governed by two parameters at different ends of the scale of use, i.e. at the lower end of the scale there must be sufficient reagent to reduce the Technetium-99m, whilst at the upper end of the scale toxicity of fluoride could become a limiting factor. Conveniently, from 2 to 200 mCi of Technetium-99m may be added to an amount of the above reagent containing 1mg. of sodium, potassium or ammonium fluoride. In another aspect, the present invention provides a packaged reagent for making Technetium-99m labelled tin colloids comprising from 1 to 1000µg of stannous fluoride and from 0.1 to 10mg of a fluoride salt selected from sodium fluoride, potassium fluoride and ammonium fluoride, and a container aseptically enclosing said reagent characterized in that the reagent also contains from 0.05 to 10mg of a non-toxic non-ionic surface active agent based on poly(alkylene oxide) glycol. Preferably, the packaged reagent contains from 0.1 to 5mg of the surface active agent. The reagent may be in aqueous solution, but is conveniently in freeze-dried from. The reagent may be prepared by providing in the container an aliquot of aqueous solution containing from 1 to 1 000 µg of stannous fluoride from 0.1 to 10 mg of sodium, potassium or ammonium fluoride and from 0.05 to 10, preferably 0.1 to 5.0 mg of the surface-active agent; freeze-drying the solution; sealing the container, preferably under a nitrogen atmosphere; the whole preparation being performed aseptically. Alternatively, terminal sterilization of the container and contents, e.g. by exposure to gamma radiation, may be performed. The Pluronic® series of surface-active agents are marketed in Europe by Pechiney Ugine Kuhlmann and manufactured by BASF/Wyandotte Chemicals. They are block copolymers having the general formula HO - (CH₂CH₂O) a - (CH(CH₃)CH₂O) b -(CH₂CH₂O) c -H where a and c are statistically equal. Variation of a, b, and c leads to a family of polymers, the molecular composition and physical form of the polyol being indicated by the number and prefix letter. Pluronic® Surface-active agents Pluronic® No. %C₂H₄O M.W.(C₃H₆O) b L-31 10 950 L-35 50 950 F-38 80 950 L-42 20 1200 L-44 40 1200 L-61 10 1750 L-62 20 1750 L-64 40 1750 F-68 80 1750 L-72 20 2050 P-75 50 2050 F-77 70 2050 L-81 10 2250 P-85 50 2250 F-88 80 2250 P-94 40 2750 F-98 80 2750 L-103 30 3250 P-105 50 3250 F-108 80 3250 The amount of surface-active agent used is not very critical as far as particle size reduction is concerned. Amounts of as little as 0.1 mg per vial are effective in reducing the particle size of the formed tin colloid by a substantial factor. However, the liver/spleen bio distribution ratio and the liver/background ratio are both critically dependent on the amount of surface-active agent, used. For instance, if too little surface-active agent is used, the liver/spleen biodistribution ratio is not stable whereas if too much is used, too much non-target activity is distributed around the body thus causing a reduction in the liver/background ratio. The use, in the present invention, of from 0.05 to 10 mg of surface-active agent therefore represents a convenient compromise between these two requirements. Preferably, however, the amount of surface-active agent is in the range of from 0.1 to 5.0 mg, particularly about 0.5 mg, per vial. In the present invention, liver/spleen biodistribution ratios can be selected by use of the appropriate surface-active agent quantity. A variety of additives has been tried in place of surface-active agents based on poly(alkylene oxide) glycol but have been found not to give the same improvements. These include:- a) Polyethylene glycol and polyvinyl acetate exhibited no major effect on particle size or stability. b) Gelatin, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide and acacia satisfactorily reduced particle size but biodistribution in rats indicated that increased blood background resulted. c) Sodium lauryl sulphate gave rise to satisfactory particle size and blood background levels but reduced hepatic uptake. Examples In these examples, the test formulations were freeze-dried mixtures of 125 µg of stannous fluoride, 1.0 mg of sodium fluoride and the stated amount of Pluronic® surface-active agent F38, F68 and F108. These vials were not sterilized by gamma-radiation but were manufactured aseptically. The mixture was reconstituted by the addition of 5-6 ml of pertechnetate eluate from a technetium generator in isotonic saline. The reconstitution of the solution was performed with gentle handling although, by employing the present invention, reconstituted solutions are generally less sensitive to rough handling than existing products. Unless otherwise stated, the reconstituted solution was used immediately. The test animals in these examples were rats. The results are set out in Tables 1 to 4. Clinical trials are now being performed on humans. Satisfactory results have so far been obtained in these.

Claims: A method of making a Technetium-99m labelled tin colloid which method comprises adding Technetium-99m, as an aqueous solution of pertechnetate ions, to a reagent comprising from 1 to 1,000 µg of stannous fluoride and from 0.1 to 10 mg of a fluoride salt selected from sodium fluoride, potassium fluoride and ammonium fluoride characterised in that the reagent further comprises from 0.05 to 10 mg of a non-toxic non-ionic surface active agent based on poly(alkylene oxide) glycol. A method according to claim 1, wherein the reagent comprises 1 part by weight of sodium, potassium or ammonium fluoride, from 0.001 to 1 part by weight of stannous fluoride and from 0.05 to 10 parts by weight of a non-toxic non-ionic surface active agent based on poly(alkylene oxide) glycol. A method according to either claim 1 or claim 2, wherein the non-toxic non-ionic surfce active agent comprises one or more non-toxic compounds having the general formula HO(CH ₂ CH₂O) a (CH(CH₃)CH₂O) b (CH₂CH₂O) c H wherein a, b and c are integers and a and c are statistically equal. A method according to any one of claims 1 to 3, wherein the aqueous solution of pertechnetate is a solution in isotonic saline. A method according to any one of claims 1 to 4, wherein the solution of pertechnetate and the reagent are both sterile. A method according to any one of claims 1 to 5, wherein from 2 to 200mCi of Technetium-99m are used per 1mg of sodium, potassium or ammonium fluoride in the reagent. A packaged reagent for making Technetium-99m labelled tin colloids comprising from 1 to 1,000 µg of stannous fluoride and from 0.1 to 10mg of a fluoride salt selected from sodium fluoride, potassium fluoride and ammonium fluoride, and a container aseptically enclosing said reagent characterized in that the reagent further comprises from 0.05 to 10mg of a non-toxic non-ionic surface active agent based on poly(alkylene oxide) glycol. A packaged reagent according to claim 7, wherein the reagent is a lyophilisate. A packaged reagent according to either claim 7 or claim 8 wherein the non-toxic non-ionic surface active agent comprises one or more non-toxic compounds having the general formula. HO(CH₂CH₂O) a (CH(CH₃)CH₂O) b (CH₂CH₂O) c H wherein a, b and c are integers and a and c are statistically equal. A packaged reagent as claimed in any of claims 7 to 9, wherein the surface active agent is present in an amount of from 0.1 to 5.0mg.

Inventors: HARRISON, ROGER CHARLES
Applicants: AMERSHAM INTERNATIONAL PLC
Application year: 1984
Main classification: A61K49
IPC codes: A61K51