FIELD OF THE INVENTION

The present invention generally relates to a method of preparing an ascorbic acid vial. The invention also relates to an ascorbic acid vial.

BACKGROUND OF THE INVENTION

Ascorbic acid has many industrial applications. However, it is known to be chemically unstable in solution. For example, aqueous ascorbic acid solutions (in the region of pH 2) turn yellow after several hours. Pharmacopoeias recommend only short-term storage of ascorbic acid solutions, ensuring protection from light, metal ions, and elevated temperatures. This means that it is typically necessary for aqueous ascorbic acid solutions to be prepared on the same day of use.

When ascorbic acid is used, for example, in pharmaceutical formulations, a sterile solution is required. According to ICH guidelines, the preferred method of sterilisation is terminal sterilisation, which uses heat or radiation on a product in its final container. Terminal sterilisation is lethal to microorganisms, simplifies the manufacturing process and increases sterility assurance. However, because ascorbic acid solutions degrade faster at high temperature, it is recommended that ascorbic acid solutions be prepared aseptically, i.e. using a process where separately sterilised components are combined under aseptic conditions.

One application of ascorbic acid is as a radiostabiliser. Radiostabilisers can be used in the manufacture of radiopharmaceuticals, pharmaceutical compounds that contain a radionuclide. Radiostabilisers are necessary because at relatively high concentrations the radiation can trigger decomposition of the radiopharmaceutical by radiolysis. To minimise radiolysis and improve process yields and radiochemical purity (RCP), radiopharmaceuticals can be stabilised with ascorbic acid.

Ascorbic acid solutions available on the market are aseptically prepared, contain metal-complexing agents, have a short shelf-life or require protection from light. In addition, these products have very high concentrations of ascorbic acid (more than 100 mg/mL) and are not ideal for use with radiopharmaceuticals, such as positron emission tomography (PET) products, without modification.

Accordingly, there is a need for pre-filled ascorbic acid solution vials which have a long shelf-life, can be terminally sterilised and do not require a metal-complexing agent or other stabilizing agent. SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a method of preparing a vial containing an ascorbic acid solution, the method comprising: providing an aqueous solution of ascorbic acid and a base, wherein the solution has a pH of 5.0 to 8.0; degassing the solution with an inert gas; dispensing the solution into a vial; degassing the vial headspace with an inert gas; and sealing the vial.

In a second aspect, the present invention provides a vial containing an ascorbic acid solution, obtainable by a process according to the first aspect.

In a third aspect, the present invention provides an ascorbic acid vial comprising: an aqueous solution of ascorbic acid and a base, wherein the solution has a pH of 5.0 to 8.0; and an inert gas.

FIGURES

Figure 1 shows an assay of ascorbic acid in solutions adjusted to pH 5.5, 5.8, 6.0 and 6.5 (using sodium hydroxide) after storage for 8 weeks at 50 °C. Autoclaved samples were autoclaved at a heat load of 121 °C Fo 22.4.

Figure 2 shows an assay of ascorbic acid as a function of heat load (121 °C Fo) (n=8). All the ascorbic acid samples autoclaved to Fo 18.7 were Y4 degree of yellow and samples autoclaved to Fo 32.5 were Y3.

Figure 3 shows the colour of 64 mg/ml_ ascorbic acid solutions before (1 : Y6) and after autoclaving with nitrogen (2-3: Y4) or air (4-5: Y3) as headspace gas.

DETAILED DESCRIPTION OF THE INVENTION

The term ‘radiopharmaceutical’ has its conventional meaning, and refers to a radioactive compound suitable for in vivo mammalian administration for use in diagnosis or therapy. A radiopharmaceutical as referenced herein may be a PET tracer.

By the term ‘radiostabiliser’ it is meant a compound that inhibits degradation reactions, such as redox processes, by trapping highly-reactive free radicals, such as oxygen-containing free radicals arising from the radiolysis of water. Radiostabilisers protect radio-labelled compound(s) from radiolysis and therefore lower / prevent a drop in the purity of the radio-labelled compound(s) over their shelf life. Reference herein to stabilising a radio-labelled compound refers to protecting a radio-labelled compound from radio lysis. The term ’comprising’ has its conventional meaning throughout this application and implies that the method, system, product or the like must have the components listed, but that other, unspecified components may be present in addition.

A ‘vial’ as referenced herein is a vessel that may be used to contain a liquid. A vial may be sealed using a cap, stopper or both. A vial may be made of glass or plastic and may be sealed with a plastic or rubber stopper, a metal cap, or a combination of both. Liquid contained within a vial may be extracted, for example, by means of syringing from the sealed vial (e.g. through a stopper). Vials may be formed of clear or non-clear (coloured) glass or plastic. A clear vial, which is transparent and non-coloured, allows the contents of the vial to be viewed, for example, to examine the colour of the solution. Non-clear (or coloured) vials can be used to shield the contents of a vial from light, for example in situations where this is necessary to prevent degradation by light. An ‘ampoule’ as referenced herein is a glass container sealed by melting of the top of the container to form a sealed neck, such that snapping of the neck is required to release contents of the ampoule.

An ‘inert gas’ as referenced herein may be, for example, nitrogen, argon, or a mixture thereof. The inert gas may be of European Pharmacopoeia quality.

In a first aspect, the present invention provides a method of preparing a vial containing an ascorbic acid solution, the method comprising: providing an aqueous solution of ascorbic acid and a base, wherein the solution has a pH of 5.0 to 8.0; degassing the solution with an inert gas; dispensing the solution into a vial; degassing the vial headspace with an inert gas; and sealing the vial.

The solution may be obtained by dissolving ascorbic acid in water; and adjusting the pH with a base. The water may be water for injection.

The method may comprise sealing the vial using a stopper and/or a cap. Vials sealed in this manner are more user-friendly than ampoules and can be used in automated systems because they do not require breaking of the glass to remove the contents. The vial is preferably not an ampoule.

The vial may be a clear plastic or glass vial, preferably a clear glass vial. A vial as described herein does not require the use of non-clear glass for protection from light. In addition, transparency allows the contents of the vial to be viewed, for example, to examine the colour of the solution.

The method may further comprise performing terminal sterilisation after sealing of the vial. The terminal sterilisation may be achieved by autoclaving. The autoclaving may be performed at 110 °C or higher, preferably not less than 121 °C. The autoclaving may be carried out to Fo of up to 25, for example, to Fo of 15 to 25 or 15 to 20. “Fo” represents the number of equivalent minutes of steam sterilisation at 121 °C delivered to a product. Accordingly, at an Fo value of 25 the sterilisation effectiveness is equal to 25 minutes at 121 °C.

In order to compensate for an average of 4% degradation of ascorbic acid during autoclaving (when carried out to Fo of 15 to 25), the target concentration of ascorbic acid in solution before manufacture may be 4% higher than the target concentration for the final product.

The pH of the solution may be from 5.5 to 7.5, preferably from 5.8 to 6.7, more preferably from 5.8 to 6.5, more preferably from 6.0 to 6.5. The pH of the solution may be from 6.6 to 8.0, preferably from 6.8 to 8.0, more preferably from 7.0 to 8.0.

The ascorbic acid concentration in the solution may be between 1 mg/ml_ and 100 mg/ml_. The concentration may be between 10 mg/ml_ and 100 mg/ml_. The concentration may be between 10 mg/ml_ and 30 mg/ml_.

The step of degassing the solution with an inert gas involves bubbling the solution through with an inert gas. Bubbling of an inert gas through the solution may be carried out while stirring the solution. This process is useful to remove undesired dissolved reactive gasses such as oxygen and carbon dioxide from the solution. The inert gas may be nitrogen, argon, or a mixture thereof. The inert gas may be nitrogen.

The step of degassing the vial headspace is useful to remove undesired reactive gasses such as oxygen and carbon dioxide from the vial headspace. The headspace of the vial refers to any space within a vial not occupied by the aqueous solution of ascorbic acid and a base. Degassing involves dispensing inert gas into the vial headspace to displace any other gases present therein. The presence of an inert gas in the vial headspace reduces discolouration during terminal sterilisation. The inert gas may be nitrogen, argon, or a mixture thereof. The inert gas may be nitrogen.

The base may be a metal hydroxide, a metal carbonate, or a mixture thereof. The base may be selected from sodium hydroxide, sodium carbonate, and mixtures thereof. The base may be sodium hydroxide.

The ascorbic acid solution in a vial of the present invention exhibits good stability from degradation without requiring the inclusion of any additional stabilizer or preservative. The solution may be free of a metal-complexing (chelating) agent. For example, the solution may be free of ethylenediaminetetraacetic acid (EDTA), sodium diethyldithiocarbamate, propyl gallate, dimercaptopropanol, 8-hydroxyquinoline and amino polycarboxylic acids (such as diethylenetriaminepentaacetic acid (DTPA), N-hydroxyethylethylenediaminetriacetic acid (HEDTA)), and salts thereof. The solution may consist essentially of ascorbic acid and base dissolved in water. It will be appreciated that within the solution, the ascorbic acid may exist as ascorbate, for example as sodium ascorbate if the base is sodium hydroxide or sodium carbonate. In a second aspect, the present invention provides a vial containing an ascorbic acid solution, obtainable by a process according to the first aspect.

In a third aspect, the present invention provides a vial containing an aqueous solution of ascorbic acid and a base, wherein the solution has a pH of 5.0 to 8.0; and an inert gas.

The pH of the solution may be from 5.5 to 7.5, preferably from 5.8 to 6.7, more preferably from 5.8 to 6.5, more preferably from 6.0 to 6.5. The pH of the solution may be from 6.6 to 8.0, preferably from 6.8 to 8.0, more preferably from 7.0 to 8.0.

The ascorbic acid concentration in the solution may be between 1 mg/ml_ and 100 mg/ml_. The concentration may be between 10 mg/ml_ and 100 mg/ml_. The concentration may be between 10 mg/ml_ and 30 mg/ml_.

The inert gas may be nitrogen, argon, or a mixture thereof. The inert gas may be nitrogen. The inert gas may fill the headspace of the vial. The presence of an inert gas in the vial headspace reduces discolouration during terminal sterilisation.

The base may be a metal hydroxide, a metal carbonate, or a mixture thereof. The base may be selected from sodium hydroxide, sodium carbonate, and mixtures thereof. The base may be sodium hydroxide.

The vial may be sealed using a stopper and/or a cap. Vials sealed in this manner are more user-friendly than ampoules and can be used in automated systems because they do not require breaking of the glass to remove the contents. The vial is preferably not an ampoule.

The vial may be a clear plastic or glass vial, preferably a clear glass vial.

The solution may be free of a metal-complexing (chelating) agent. For example, the solution may be free of ethylenediaminetetraacetic acid (EDTA), sodium diethyldithiocarbamate, propyl gallate, dimercaptopropanol, 8-hydroxyquinoline and amino polycarboxylic acids (such as diethylenetriaminepentaacetic acid (DTPA), N-hydroxyethylethylenediaminetriacetic acid (HEDTA)), and salts thereof.

Depending on factors such as Fo and the headspace gas, the solution as referenced in the first, second, and third aspect of the invention can be different degrees of yellow, wherein Yi represents the darkest and Y7 represents the lightest yellow (Ph. Eur. 2.2.2.). Preferably the solution disclosed herein is between Y7 and Y4 degrees of yellow. The vial containing the ascorbic acid solution does not require protection from light. As shown in example 5, the ascorbic acid solution does not degrade but becomes less yellow when exposed to UV-VIS light.

The vial containing the ascorbic acid solution may be stored for a period of at least 12 hours, at least 24 hours, at least 7 days, at least 6 months, at least a year, at least two years, or at least three years prior to use. The vial may exhibit good stability during storage, for example, with the degradation of ascorbic acid during storage being no more than 10%, preferably no more than 5% (based on the concentration of ascorbic acid in mg/mL). The vial may be stored at -20 °C to +5 °C.

The vials described in this invention are suitable for use with PET agents that require ascorbic acid as a radiostabiliser during purification or in the product formulation. Such pre-filled vials can now become available for use with PET products that require various ascorbic acid concentrations without the need for the PET manufacturing site or pharmacy to modify the vial content before use.

If the desired use (e.g. use as a radiostabiliser during purification) requires low pH, the pH of the ascorbic acid solution may be adjusted with an acid (for example, a mineral acid, such as phosphoric acid) at the point of use or shortly prior to use. This approach is useful, for example, in automated systems and processes requiring a low pH ascorbic acid solution (for example of pH 2-3). The vials described in this invention may be used with the FASTlab® system (GE Healthcare). There is practical and commercial benefit to such systems being able to utilise an ascorbic acid vial containing an ascorbic acid solution in a stable form.

Ascorbic acid is a more efficient radiostabiliser at low pH. However, low pH formulations can cause an undesirable reaction when administered to a subject. Therefore, if the ascorbic acid is to be used an a radiostabiliser in product formulation, pH adjustment prior to use may not be required.

The invention is further described with reference to the following non-limiting examples.

Examples

Example 1 : Manufacturing process for a typical 27.3 L batch of ascorbic acid (20.0 mg/mL) vials

For a typical batch of ascorbic acid vials, a process can be performed as outlined below.

1 . Dissolve 122.85 g sodium hydroxide in 3277.15 g water for injection on a magnetic stirrer for 10 minutes.

2. Dissolve 546.0 g L-(+)-ascorbic acid in 22.5 kg water for injection on a magnetic stirrer for 20 minutes. While mixing, bubble through the solution with nitrogen gas and protect from light.

3. Add the sodium hydroxide solution to the ascorbic acid solution. Start mixing immediately after combining the solutions, or preferably while combining the solutions. Mix for 10 minutes while bubbling through the solution with nitrogen gas. The solution no longer requires protection from light.

4. Measure the pH of the solution. The pH should be 5.8-6.5.

5. Adjust the final volume of the batch by adding water for injection, q.s. to 27.3 L.

6. Mix for 15 minutes while bubbling through with nitrogen.

7. Filter the solution through a 0.2 pm filter to reduce bioburden.

8. Dispense into 100 ml_ Type I glass vials: degas the empty vial with nitrogen until brimful with nitrogen (typically 2 seconds), dispense ascorbic acid (20.0 mg/ml_) into the vial, degas the vial headspace (typically 2 seconds), and add stopper and cap.

9. If a sterile product is required: autoclave at 121 °C to Fo of not more than 25.

Example 2: Assay of ascorbic acid in solutions stored for 8 weeks at 50 °C

Eight vials were prepared by a procedure corresponding to the general procedure described in example 1 , but adjusting the amounts to obtain solutions having an ascorbic acid content of 18 mg/ml_. The pH was adjusted using sodium hydroxide in order to obtain two vials of each of pH 5.5, 5.8, 6.0 and 6.5. One vial of each pH was autoclaved at a heat load of ¹²¹ ° ^c Fo 22.4. All vials were then stored for 8 weeks at 50 °C and ambient relative humidity, protected from light. After 8 weeks, an assay of ascorbic acid in these solutions was performed by redox titration. The results are provided in Figure 1 , with the assay % representing the percentage of the ascorbic acid concentration (mg/ml_) after storage by reference to the initial mg/ml_ ascorbic acid concentration.

Example 3: Assay of ascorbic acid as a function of heat load

Eight vials were prepared by the general procedure described in example 1 , but adjusting the amounts to obtain a solution having an ascorbic acid content of 74 mg/ml_. The pH of the solution was 5.8. The samples of ascorbic acid solution were then autoclaved. All the samples autoclaved to Fo 18.7 were Y4 degree of yellow and samples autoclaved to Fo 32.5 were Y3. An assay of ascorbic acid (% ascorbic acid concentration) was performed by redox titration at Fo 0, 18.7, and 32.5. The assay as a function of heat load is provided in Figure 2 and shows that pH 6 ascorbic acid solutions can be terminally sterilized at 121 °C to Fo 20 and ideally Fo 15-25.

Example 4: Effect of autoclaving and headspace gas on the colour of ascorbic acid solutions

Five vials were prepared by the general procedure described in example 1 , but adjusting the amounts to obtain a solution having an ascorbic acid content of 64 mg/ml_. The pH of the solution was 5.9. Vial 1 was not autoclaved, vials 2 and 3 were autoclaved. Vials 4 and 5 were also autoclaved, but the vial headspace was not degassed as part of the vial preparation process. Accordingly, vials 4 and 5 differed from vials 2 and 3 in that the headspace gas was air, not nitrogen. The colours of the solutions in the five vials are provided in Figure 3. The colour of solution in vial 1 was Y6, for vials 2 and 3 this was Y4 and for vials 4 and 5 this was Y3 (wherein Yi represents the darkest yellow and Y7 represents the lightest yellow (Ph. Eur. 2.2.2.)). This shows that the headspace of vials containing pH 6 ascorbic acid solution should ideally be degassed with inert gas (e.g. nitrogen) in orderto reduce discolouration during terminal sterilisation.

Example 5: Photostability of terminally sterilised pH 6 ascorbic acid solutions

Four terminally sterilised vials containing pH 6 ascorbic acid solutions were prepared by the general procedure described in example 1. The photostability of the solutions exposed to approximately 1.2 mill lux hours and 200 watt hours/m ² was investigated, in accordance with ICH Guideline Q1 B Option 2. The results (Table 1) show that the ascorbic acid solution does not degrade but becomes less yellow when exposed to UV-VIS light as according to ICH Q1B. Table 1

It will be readily understood by those persons skilled in the art that the embodiments of the inventions described herein are capable of broad utility and application. Accordingly, while the invention is described herein in detail in relation to the exemplary embodiments, it is to be understood that this disclosure is illustrative and exemplary of embodiments and is made to provide an enabling disclosure of the exemplary embodiments. The disclosure is not intended to be construed to limit the embodiments of the invention or otherwise to exclude any other such embodiments, adaptations, variations, modifications and equivalent arrangements. The scope of the invention is defined by the appended claims.