SURFACTANT COMPOSITIONS

Abstract: It has been found that block copolymer surfactants can be stabilized by the presence of small quantities of certain metal ions and/or a polyalkyleneglycol. The metal ions afford block copolymer surfactant stability at very low concentration of metal ion and safety advantages over conventional stabilizing techniques. The present invention is all the more surprising in view of the prior art which clearly indicates that metal ions would be expected to accelerate autoxidative degradation.

Description: SURFACTANT COMPOSITIONS This invention relates to surfactants and in particular to block copolymer surfactants stabilized by the presence of metal ions. Block copolymer surfactants have a wide variety of uses in a number of industries. They are used as food additives, have applications in the cosmetic industry and have also been proposed as defoamers, anti-static agents, detergents, gelling agents, foam controllers, dispersants and dye levellers. However, due to their diversity and physiological safety for both external and internal administration, block copolymer surfactants are of particular importance in the pharmaceutical industry. The medical applications of block copolymer surfactants include many uses in drug delivery systems and formulations. For example, block copolymer surfactants are employed as emulsifying agents, e.g. in intravenous fat emulsions, wetting agents e.g. for antibiotics, thickening agents, coatings e.g. for tablets, solubilisers e.g. to maintain clarity in elixirs and syrups, dispersion enhancers and foaming agents. These polymers have also been used as bases for ointments and suppositories, as tablet binders, as lubricants for synthetic polyglycolic acid sutures as well as having a well known use in the stabilization of nanoparticle suspensions. In. many applications two or more functions of block copolymer surfactants may be utilised. A number of block copolymer surfactants have also been found to have their own therapeutic application. For example some block copolymer surfactants have been shown to act as adjuvants or hypolemic agents whilst Poloxa ers 182LF and F188 have therapeutic applications as a pharmaceutic aid and a cathartic respectively. F188 is also being investigated for its ability to improve blood flow in myocardial infarction and in sickle cell crisis and for potential application for the treatment of burns. A comprehensive discussion of medical applications of Poloxamers can be found in "Poloxamers in the Pharmaceutical Industry", Schmolka I.R., Polymers for Controlled Drug Delivery, Ed. Peter Tarcha, CRC Press, Boca Raton 1991, pages 189-214 which is incorporated herein by reference. Block copolymer surfactants are quite unstable undergoing degradation both in the solid phase and in aqueous or organic solutions. In solution, this degradation is faster under more neutral pH and is accelerated by high temperature and photoradiation. Solid phase degradation is also caused by light, thus further illustrating the photosensitivity of block copolymer surfactants. Block copolymer surfactant preparations also generally contain impurities along with degradation products which may also accelerate decomposition. Although it is possible to remove impurities such as aldehydes and peroxides from solution phase block copolymer surfactant compositions it would be highly advantageous if such procedures were not necessary. The degradation is believed to occur via a free-radical initiated autoxidative mechanism and its rate is dependent on the nature of the block copolymer surfactant. For example, oxidation is particularly significant in polymers containing tertiary hydrogen atoms and chain scission at weak links, such as those at branching sites, is a concern in some polymers. In McGary (Journal of Polymer Science, Vol. XLVI , pages 51-57, 1960) it is reported that iron, copper and silver salts, i.e. the type of metal salts typically found as impurities in block copolymer surfactant preparations, accelerate the degradation of poly (ethyleneoxide) and in general low valent metal ions are said to aid oxidative degradation. In Ray (Analytical Biochemistry, 146, 307-312,(1985)) it is disclosed that at micromolar levels, Fe 3+ and Cu 2+ cause substantial autooxidation in long-term studies. In Donbrow (Journal of Pharmaceutical Sciences, Vol. 67, No. 12, December 1978, pages 1676-1681) it is reported that the autoxidation of polysorbates, such as polyoxyethylene 20 sorbitan monolaurate, is catalysed by copper sulphate . There is therefore a specific need for a method of stabilizing block copolymer surfactant compositions to oxidative degradation. One method of stabilizing these compounds involves the addition of antioxidants to inhibit the radical decomposition reaction. However, it is not desirable to utilize an antioxidant, such as monothioglycerol, in a drug formulation as antioxidants are known irritants and are problematic in that they may cause adverse allergenic reactions in some patients. Moreover, protection from oxidation given by antioxidants is limited due to the finite supply of antioxidant material present in the formulation or other composition. Another method of stabilizing block copolymer surfactants may involve storing the compounds under an inert gas or in the absence of light, however these methods are undesirable and impractical for most block copolymer surfactant compositions. We have now surprisingly found, however, that block copolymer surfactants can be stabilized by the presence of small quantities of certain metal ions and/or a polyalkyleneglycol . The metal ions afford block copolymer surfactant stability at very low concentration of metal ion and safety advantages over conventional stabilizing techniques. The present invention is all the more surprising in view of the prior art which clearly indicates that metal ions would be expected to accelerate autoxidative degradation. It is envisaged that metal ions and/or a polyalkyleneglycol could be used to stabilise compositions intended for both medical and non-medical usage. Thus viewed from one aspect, the invention provides a composition comprising a block copolymer surfactant and a metal ion wherein said metal ion is present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant, particularly compositions which consist essentially of surfactant (and optionally impurities and degradation products conventionally associated with the particular surfactant), metal ions, optionally counter ions for the metal ions, and optionally a liquid solvent system, e.g. water or an organic solvent or a mixture of two or more solvents . Viewed from a further aspect the invention provides a process for the preparation of a stabilized block copolymer surfactant composition comprising adding a metal ion to a block copolymer surfactant composition in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant . Viewed from a yet further aspect the invention provides the use of a metal compound for the manufacture of a composition comprising a block copolymer surfactant wherein ions of said metal are present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant . Viewed from a yet further aspect the invention provides a method of therapy or diagnosis of a human or non-human animal (preferably a vascularised animal, e.g. a mammalian or avian animal) body, said method comprising administering to said body a therapeutically or diagnostically effective amount of a composition comprising a physiologically tolerable block copolymer surfactant and a physiologically tolerable amount of metal ion wherein said metal ion is present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant. In the present invention, the metal ion is used in a sufficient amount to achieve a stabilizing affect, e.g. a concentration sufficient to stabilize the composition for therapeutic or diagnostic administration. The quantity of metal ion used in the composition will depend on the nature and quantity of the block copolymer surfactant and other excipients present, the use of the composition, e.g. for therapy or diagnostic use or cosmetic use, the nature of the active agent and the like but the necessary amount may be readily determined by the person skilled in the art. In general, the concentration of metal ion employed relative to the block copolymer surfactant will be in the range 1 x 10 "6 M to 1 x 10 "3 M, preferably of the order of 10 "4 to 10 "5 M. The metal ions of the invention can be any ion which stabilizes a block copolymer surfactant. Particularly preferred metal ions include ions having stable lower valence states i.e. reducible ions such as transition metal ions, in particular ions of iron, zirconium, Nickel and cobalt, e.g. Fe 3+ , Zr 4+ , Ni 2+ and Co 2+ . The compositions of the present invention also encompass compositions utilising one or more metal ions to stabilise one or more block copolymer surfactants present in the same composition. Where the composition is for medical use the metal ion is present in a physiologically tolerable concentration. It is envisaged that the metal ions useful according to the invention can be bound to a chelating agent prior to administration although in view of the very low concentrations of metal ion required for stabilisation, this is not a necessity and this comprises a further advantage of the present invention. The block copolymer surfactants of the present invention are preferably non-ionic and may be for example block alkylene oxide copolymers, for example poloxamers such as the pluronics (e.g. Pluronic F68 and 108 which are block copolymer surfactants of ethyleneoxide and propyleneoxide) or poloxamines such as the tetronics . In general, the molecular weight of the block copolymer surfactants to be stabilised conveniently range from 1000 to 20,000, preferably 1550 to 15000, most preferably 2000 to 15000 atomic mass units. The block copolymer surfactants of the invention can be prepared by standard polymerisation procedures, e.g. under conditions of high temperature and pressure in an inert anhydrous atmosphere, but are readily available commercially. The quantity of block copolymer surfactant used in the composition will depend on the nature and quantity of the other excipients present, the use of the composition, e.g. for therapy or diagnostic use or cosmetic use, the nature of the active agent, the specific use of the block copolymer surfactant e.g. whether as an emulsifier or a coating agent, but the necessary amount may be readily determined by the person skilled in the art. It has also been surprisingly found that the addition of small amounts of a polyalkyleneglycol (i.e. polyalkyleneoxide) to a block copolymer surfactant composition may increase the stability of the composition. Thus, viewed from a still further aspect the invention provides a composition comprising a block copolymer surfactant and a polyalkyleneglycol wherein said polyalkyleneglycol is present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant . Viewed from a yet further aspect the invention provides the use of a polyalkyleneglycol for the manufacture of a composition comprising a block copolymer surfactant wherein the polyalkyleneglycol is present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant. Preferably the polyalkyleneglycol is used in conjunction with a metal ion and this forms a yet further aspect of the invention. The polyalkyleneglycol can be a block copolymer or a homopolymer, preferably having C 2 , C 3 or C 4 alkylene units especially C 2 or C 3 units. It is preferably a polyethyleneglycol . In general, the molecular weight of the polyalkyleneglycol ranges from 300 to 10,000 atomic mass units, preferably, 400 to 2000 atomic mass units. The quantity of polyalkyleneglycol used in the composition will depend on the nature and quantity of the block copolymer surfactant and other excipients present, the use of the composition, e.g. for therapy or diagnostic use or cosmetic use, the nature of the active agent and the like but the necessary amount may be readily determined by the person skilled in the art. In general , the amount of polyalkyleneglycol used ranges from 1 to 30%, preferably 5 to 20%, most preferably 10 to 20% by weight of the composition. Where the composition is for medical use, the polyalkyleneglycol will be present in a physiologically tolerable amount. The use of one or more polyalkyleneglycols to stabilise one or more block copolymer surfactants is also envisaged in the present invention. The polyalkyleneglycols of the invention are readily prepared by standard polymerisation techniques and are readily available commercially. The publications referred to herein are hereby incorporated by reference. The invention will now be described further by the following non-limiting Examples. Experimental Two size-exclusion HPLC methods were developed to analyze Poloxamer 338 using a refractive index detector. In the first method, a Superose 12 column (30 cm x 7.8 mm) from Pharmacia was used with a flow rate of 0.8 mL/min. The injection volume was 10 μl and the mobile phase contained 10% methanol and 25 mM NaCl . Solution samples were typically diluted with water to below 2% concentration before injection. In the second HPLC method, the samples were first dissolved in methanol and further diluted with 80% methanol to the appropriate concentration before injection. The method uses a TSK G2000SWXL column from Supelco (30 cm x 7.8 mm) and a mobile phase containing six parts methanol and four parts 62.5 mM NaCl . Figure la depicts typical chromatograms of the NF grade and purified Poloxamer 338. Poloxamer 338 as obtained from BASF showed a higher molecular weight (HMW) parent peak and a lower molecular weight impurity/degradant peak with nominal molecular weights of 14.6K and 3K respectively. As evident, the lower molecular weight peak was reduced significantly upon purification by membrane diafiltration. Figure lb shows typical chromatograms of poloxamer 338 samples in solution degraded under 40°C storage to different extents. Degradation of poloxamer 338 in solution manifested itself initially in a decrease of the parent peak and a corresponding increase of the lower molecular weight peak. No new peak was observed. Broadening of the lower molecular weight peak occurred only at a very late stage whereupon most of the parent peak had disappeared. Figure 2a shows the standard curve of Poloxamer 338 parent peak area versus concentration (% w/v) . Figure 2b shows the calibration curve of the SE- HPLC system for molecular weight determination using polyethylene glycol molecular weight standards and a Waters GPC software. Since the degradation of Poloxamer 338 is manifested in a gradual loss of the parent peak, the HPLC data of stability samples are expressed as percent of area under the parent peak. Steam Sterilization Steam sterilization was conducted with either a Castle M/C 3500 or an ETC Progenesis Lab ST-9-6 steam sterilizer using a "dry goods" cycle. The samples in either vials or ampules were placed in an aluminum basket to maintain the upright position. At temperatures above its cloud point of 106-108°C, Poloxamer 338 phase-separates from solution and precipitates to form a concentrated layer at the bottom of the vial. If allowed to cool without disturbance, the concentrated layer hardens into a gel-like layer. Therefore, immediately upon completion of the steam sterilization cycle, vials were gently shaken while still hot to redisperse the precipitated surfactant. Example 1 Stability of Poloxamer 338 in Solution The sample preparations in various solution stability studies were similar. About 1.5 mL of 3% w/v Poloxamer 338 solution was transferred into each 2-mL clear glass ampule (Kimble, treated and prewashed) . The ampules were sealed with oxygen flame. The nitrogen-flushed samples were sealed immediately after flushing the headspace and were stored in a vacuum oven at 40°C with a slow stream of nitrogen gas flowing through the chamber to assure no leakage of oxygen to the samples. At each time point, several vials were withdrawn and diluted with water, if necessary, prior to HPLC analyses. Samples were usually injected only once but some were injected twice and the results were averaged. The samples were also examined visually and the pH values were recorded. Solution Stability - pH Stability - Under 37 and 40°C 3% Poloxamer 338 solution samples at various pH's were analyzed after storage for two months at 40°C. The samples were initially passed through a 0.22 μm filter. The results, expressed as percent of parent peak, are listed below and plotted in Figure 3. Table 1 s seen from the data, Poloxamer 338 appears to be more stable under acidic (pH <4) and alkaline (pH >8) conditions and less stable at the pH region in between. Example 2 A study of the effect of metal ions on the stability of Poloxamer 338 was carried out with 3% aqueous solution Poloxamer 338 and 2 x 10 ~4 M (11-12 ppm) of metal ion. The samples, in duplicate, were buffered in 40 mM TRIS, pH 8, sterile filtered, and stressed at 40°C for one and two months. The SE-HPLC results are listed in the following table. Table 2 As seen, the control degraded significantly at 40°C after 1 month, Co +2 and Fe +3 ions were found to stabilize Poloxamer 338 in solution Example 3 To confirm the stabilization effect of Co +2 ions, another study was conducted with the same concentration of metal ions but with triplicate samples to increase the level of confidence. The samples were stressed at 40°C and the SE-HPLC results expressed as % parent peak area are listed in the following table. Table 3 Again, the results of this study confirmed that Fe +3 and Co +2 can stabilize Poloxamer 338 against degradation whereas Fe and Cu have no significant effect. Ni + 2 showed no stabilization effect in the previous study but a significant stabilization effect in this study. Example 4 The effect of zirconium ion on the stability of 3% (w/v) Poloxamer 338 aqueous solution was studied using ZrCl 4 salt along with Co +2 ions as a positive control . The samples were stressed at 40°C and the SE-HPLC results (triplicate samples) expressed as % parent peak area are listed in the following table. Table 4 The above data demonstrate that Zr +4 can also significantly improve the stability of Poloxamer 338 although its effect at 10 "5 M is not as strong as Co +2 . Example 5 Effect of PEG 1450 A stability study was conducted using purified Poloxamer 338 (95.5%) in aqueous solution at 50°C and under steam sterilization conditions. The following results were obtained after storing the samples at 50°C for 3 weeks. Table 5 As seen, the samples with 10% PEG 1450 showed better stability than the control . Example 6 Another stability study was conducted using Poloxamer 338 and storage at 50°C for 15 days, All samples were prepared in 40 mM TRIS, pH 9 buffer, The results are listed as follows: Table 6 Again, the sample with 10% PEG 1450 was slightly more stable than the control. PEG 1450 appeared to show some stabilization effect towards Poloxamer 338.

Claims: Claims 1. A composition comprising a block copolymer surfactant and a metal ion and/or a polyalkyleneglycol wherein said metal ion and/or polyalkyleneglycol are present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant. 2. A composition as claimed in claim 1 wherein the molecular weight of said block copolymer surfactant is between 1550 to 15000 atomic mass units. 3. A composition as claimed in either one of claims 1 or 2 wherein the block copolymer surfactant is a poloxamer or poloxamine. 4. A composition as claimed in any one of claims 1 to 3 wherein said metal ion is a transition metal ion. 5. A composition as claimed in claim 4 wherein said metal ion is a Zr, Co, Ni or Fe ion. 6. A composition as claimed in claim 5 wherein said metal ion is Zr 4+ , Co 2+ , Ni 2+ or Fe 3+ . 7. A composition as claimed in any one of claims 1 to 6 wherein the concentration of said metal ion relative to block copolymer surfactant is lxlO "6 M to lxlO "3 M. 8. A composition as claimed in any one of claims 1 to 7 wherein said polyalkyleneglycol comprises C 2 and/or C 3 units . 9. A composition as claimed in claim 8 wherein said polyalkyleneglycol is polyethylene glycol . 10. A composition as claimed in any one of claims 1 to 9 wherein said polyalkyleneglycol is present in an amount in the range of 10 to 20% by weight of the composition. 11. A composition as claimed in any one of claims 1 to 7 consisting essentially of a block copolymer surfactant, metal ions and counter ions thereof and optionally a solvent. 12. A composition as claimed in any one of claims 1 to 10 comprising a block copolymer surfactant, metal ions and a polyalkyleneglycol . 13. A process for the preparation of a stabilized block copolymer surfactant composition as claimed in any one of claims 1 to 12 comprising adding a metal ion and/or a polyalkyleneglycol to a block copolymer surfactant composition in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant. 14. The use of a metal compound and/or polyalkyleneglycol in the manufacture of a composition comprising a block copolymer surfactant wherein ions of said metal compound and/or polyalkyleneglycol are present in an amount sufficient to inhibit oxidative degradation of said block copolymer surfactant. 15. A method of therapy or diagnosis of a human or non- human animal, said method comprising administering to said body a therapeutically or diagnostically effective amount of a composition as claimed in any one of claims 1 to 12.

Inventors: NA GEORGE C, STEVENS HAROLD JACK, YUAN BARBARA O, NA, GEORGE, C., STEVENS, HAROLD, JACK, YUAN, BARBARA, O.
Applicants: COCKBAIN JULIAN, NA GEORGE C, NYCOMED IMAGING AS, STEVENS HAROLD JACK, YUAN BARBARA O, COCKBAIN, JULIAN, NA, GEORGE, C., STEVENS, HAROLD, JACK, YUAN, BARBARA, O.
Application year: 1998
Main classification: B01F17
IPC codes: B01F17