WO2025053806A1

WO2025053806A1 - Sapropterin soluble tablet composition

Info

Publication number: WO2025053806A1
Application number: PCT/TR2023/050934
Authority: WO
Inventors: Hatice ONCEL; Onur Pinarbasli; Hande GAYRETLI; Bahar KOKSEL OZGEN; Nurdan ATILGAN; Asuman AYBEY DOGANAY; Nagehan SARRACOGLU
Original assignee: Ilko Ilac Sanayi ve Ticaret AS
Current assignee: Ilko Ilac Sanayi ve Ticaret AS
Priority date: 2023-09-08
Filing date: 2023-09-08
Publication date: 2025-03-13
Anticipated expiration: 2026-03-08

Abstract

The invention relates to develop a soluble tablet composition comprising sapropterin hydrochloride that is highly stable during storage and can administer sapropterin hydrochloride, an effective therapeutic agent for the treatment of tetrahydrobiopterin-responsive hyperphenylalaninemia, to patients of a wide range of ages, ranging from infants to adults, in a single preparation.

Description

SAPROPTERIN SOLUBLE TABLET COMPOSITION

Technical field:

The present invention relates to develop a soluble tablet composition comprising pharmaceutically effective amount of sapropterin or a salt thereof and one or more pharmaceutically acceptable excipients, wherein the said composition comprises mannitol having average mean particle diameter 100 pm. It is used for the treatment of tetrahydrobiopterin-responsive hyperphenylalaninemia, to patients of a wide range of ages, ranging from infants to adults, in a single preparation.

Prior Art:

Sapropterin is a synthetic formulation of the naturally-occurring 6R-diastereomer of tetrahydrobiopterin (‘BH4’), an endogenous compound which is a co-factor of phenylalanine hydroxylase, the enzyme responsible for phenylalanine metabolism. BH4 is a biogenic amine of the naturally-occurring pterin family that is a cofactor for a number of different enzymes, including phenylalanine hydroxylase (PAH), tyrosine hydroxylase, tryptophan hydroxylase and nitric oxide synthase. Pterins are present in physiological fluids and tissues in reduced and oxidized forms, however, only the 5, 6, 7, 8, tetrahydrobiopterin is biologically active. It is a chiral molecule and the 6R enantiomer of the cofactor is known to be the biologically active enantiomer while the 6S form may cause inactivation of phenylalanine hydroxylase, thus inhibiting the effects of the 6R form.

Sapropterin dihydrochloride is a crystalline powder. It is hygroscopic and very soluble in water (> 1 g/ml). Its chemical name is (6R)-2-amino-6-[(1 R,2S)-1 ,2-dihydroxypropyl]- 5,6,7,8-tetrahydro-4(1 H)-pteridinone dihydrochloride, the molecular formula is C9H15N5O3 2HCI with a molecular weight of 314.17. It exhibits polymorphism and many crystalline forms have been identified; among all the polymorphic forms, Form B was identified to be thermodynamically stable crystalline anhydrate form. The structure of sapropterin is shown below:

Sapropterin

Phenylketonuria (PKU, also known as phenylalanine hydroxylase (PAH) deficiency) is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. Phenylalanine is a protein building block (an amino acid) that is obtained from eating certain foods (such as meat, eggs, nuts, and milk) and in some artificial sweeteners. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

PKU can often be managed by following a diet that is low in phenylalanine. Since phenylalanine is found in all proteins, the PKU diet consists of avoiding meat, dairy, nuts, tofu, and other foods that are high in protein. Infants with PKU need to be fed with a low- protein formula. Affected individuals are often limited to certain fruits and vegetables and foods containing fats and sugars (such as butter, jelly, pasta, and potato chips). The artificial sweeter aspartame, which is found in diet soda and many other low-calorie items, should be avoided as it contains high amounts of phenylalanine. The amount of phenylalanine that is safe to consume is different for each person. Affected individuals should work with a health care professional to develop an individualized diet.

Babies born to mothers who have PKU and are not following a low-phenylalanine diet have a significant risk of intellectual disability because they are exposed to very high levels of phenylalanine before birth. These infants may also have a low birth weight and grow more slowly than other children. They may also have heart defects or other heart problems, an abnormally small head size (microcephaly), and behavioral problems. Women with PKU who are not following a low-phenylalanine diet (and may have high levels of phenylalanine) also have higher risk of pregnancy loss. The occurrence of PKU varies among ethnic groups and across geographic regions worldwide. In the United States, PKU occurs in 1 in 25,000 newborns. Most cases of PKU are detected shortly after birth by newborn screening, and treatment is started promptly. As a result, the severe signs and symptoms of classic PKU are rarely seen. The main treatments for PKU include a lifetime diet with very limited intake of foods with phenylalanine and medications. However, such a dietary regimen, apart from providing low phenylalanine, eliminates many other sources of other essential amino acids, vitamins and minerals. Consequently, such a diet provides inadequate protein, vitamins and minerals thereby hindering normal growth and development. Apart from adults, for babies too infant formulae which have low phenylalanine content are the primary food source. The phenylalanine-free protein formulae that are available are mostly bitter tasting making the food unpalatable. Further the strict regimen of dietary protein is practically impossible for patients of all ages to adhere to in daily life.

The U.S. Food and Drug Administration has approved the medicine sapropterin dihydrochloride (Kuvan). The product is used for the treatment of hyperphenylalaninemia (HPA) in adult and paediatric patients with phenylketonuria (PKU) or tetrahydrobiopterin (BH4) deficiency. It is marketed by BioMarin in the US and Merck Serano in Europe. It has been designated as an orphan medication since hyperphenylalaninemia is a rare disease. Kuvan can help the body break down phenylalanine. Although PKU is characterized by a defect in the PAH (phenylalanine hydroxylase) enzyme, residual enzymatic activity may be present in some patients. Thus, sapropterin may act like a chemical chaperone to promote the normal metabolism of Phe (Phenylalanine) and lower its concentration in the blood in a subset of patients who are BH4 responsive. Sapropterin may be used to assist in the control of Phe concentrations.

EP0191335B1 (Shiratori Pharmaceutical) discloses a process for the preparation of (6R)-tetrahydro-L-biopterin firstly.

US7727987B2 (Merck) discloses crystal forms of (6R)-L-erythro-tetrahydrobiopterin dihydrochloride, hydrates and solvates and processes for their preparation. These crystal forms are either intermediates for the preparation of stable polymorphic form B or are suitable for solid formulations.

Polymorph B is a slightly hygroscopic anhydrate with the highest thermodynamic stability above about 20°C. Furthermore, form B can be easily processed and handled due to its thermal stability, possibility for preparation by targeted conditions, its suitable morphology and particle size.

EP1757293B1 (Daiichi Sankyo) discloses a therapeutic agent for tetrahydrobiopterin- responsive hyperphenylalaninemia provided in the form of granules, fine granules, or dry syrups containing sapropterin hydrochloride as an active ingredient. It also provides an effective sapropterin hydrochloride preparation that is highly stable during storage and can administer sapropterin hydrochloride, an effective therapeutic agent for the treatment of tetrahydrobiopterin-responsive hyperphenylalaninemia, to patients of a wide range of ages, ranging from infants to adults, in a single preparation. The stability of the finished products were tested for appearance (especially for discoloration) and percent amount sapropterin remained in the product.

W02006/055511 (BioMarin Pharmaceutical) discloses stable tablet formulations of tetrahydrobiopterin or precursors, derivative or analogs thereof for the treatment of humans. Compositions of the invention may comprise a stable, crystalline form of BH4 that is stable at room temperature for more than 8 hours and a pharmaceutically acceptable carrier, diluent or excipient. Exemplary stable tablets of the invention have been prepared using a dry tableting process and have been shown to have a shelf-life of at least 6 to 9 months at room temperature.

WO2012/117362A1 (Rubicon Research) discloses stable pharmaceutical compositions of tetrahydrobiopterin and processes for producing such compositions. Particularly the present invention relates to stable pharmaceutical compositions comprising tetrahydrobiopterin and at least one stabilizing agent. Antioxidants that stabilize tetrahydrobiopterin; with the weight ratio of the antioxidant to active ranging from 0.2 - 1 .5.

CN104257623A (Guangdong Zhongsheng) discloses an effervescent tablet containing sapropterin dihydrochloride.

A significant problem with BH4 is that it is unstable and readily undergoes aerobic oxidation at room temperature (Davis et al., Eur. J. Biochem., Vol 173, 345-351 , 1988; U.S. Patent No. 4,701 ,455) and has a shelf-life of less 8 hours at room temperature (Berneggar and Blau, Mol. Genet. Metabol. 77:304-313, 2002). It also undergoes autooxidation in aqueous solutions at pH 7.4 to form 7, 8-dihydrobiopterin (BH2) (Thony et al., 2000). Tetrahydrobiopterin is also very hygroscopic. Therefore the development of stable composition comprising tetrahydrobiopterin that is prone to degradation at accelerated temperature is a challenging task.

As a result of the aforementioned issues, there is a need for development of novel pharmaceutical formulations of sapropterin. The instability of such BH4 compositions is commercially undesirable and significant degradation due to improper storage could hinder therapy of patients. Also there is no information at prior documents about the degradation behaviour related to impurities formed in the storage conditions.

Thus, there remains a need for a stable solid formulation of tetrahydrobiopterin and processes for manufacturing such stable formulations. The present invention is directed to addressing such a need.

Description of the Invention:

It is an object of the present invention to provide pharmaceutically effective amount of sapropterin preparation that is highly stable during storage and can administer sapropterin, an effective therapeutic agent for the treatment of tetrahydrobiopterin- responsive hyperphenylalaninemia, to patients of a wide range of ages, ranging from infants to adults, in a single preparation.

Another aspect of the invention provides a stable pharmaceutical soluble tablet composition comprising pharmaceutically effective amount of sapropterin or a salt thereof and one or more pharmaceutically acceptable excipients, wherein the said composition comprises mannitol having average mean particle diameter 100 pm.

Another aspect of the invention provides a stable pharmaceutical soluble tablet composition, a dry granulation process for preparing final sapropterin containing granule mix ready for the compression having particle size distribution (D50) between 100 pm to 300 pm, preferable between 100 pm to 200 pm (measured by the method of laser diffraction in a dry method (Malvern Mastersizer, general purpose mode, refractive index: 1.55, air pressure: 0.5 atm- 1.5 atm, obscuration rate: 0.5%-10.0%, feed rate 30%-40%)), comprising pharmaceutically effective amount of sapropterin hydrochloride and one or more pharmaceutically acceptable excipients, wherein the said composition comprises mannitol having average mean particle diameter 100 pm.

Another aspect of the invention provides a stable pharmaceutical soluble tablet composition comprising pharmaceutically effective amount of sapropterin hydrochloride, mannitol as a filler/diluent, ascorbic acid as an axtioxidant, crospovidone as a disintegrant, dibasic calcium phosphate as a binder.

Another aspect of the invention provides a stable pharmaceutical soluble tablet composition comprising a dose of 100mg sapropterin hydrochloride, mannitol is present in an amount of 52 to 58% by weight of total formulation, ascorbic acid is present in an amount of 1 to 3% by weight of total formulation, crospovidone is present in an amount of 2 to 5% by weight of total formulation, dibasic calcium phosphate is present in an amount of 2 to 3% by weight of total formulation. The soluble tablet composition can be applicable to patients of all ages, ranging from infants, who are incapable of swallowing, to elderlies, who are having difficulty swallowing, so as to deliver the drug in a wide range of doses required by the different age groups.

Thus, though researchers have developed compositions of sapropterin comprising stabilizers in variety of ratios, the stability of these compositions is low at room temperature or 40°C/75% relative humidity and need to be stored under refrigeration. Low stability of such tetrahydrobiopterin compositions is commercially undesirable and significant degradation due to improper storage could hinder therapy. Need therefore, exists for preparations of tetrahydrobiopterin that are more stable and retain desired amount of active over a longer time even when not refrigerated.

The stable solid formulation preferably contains one or more of the following additional ingredients that improve stability or other characteristics of the formulation: lubricants, binders, antioxidants, filler/diluents, disintegrants and coloring agents or mixtures thereof. One exemplary preferred composition includes anhydrous dibasic calcium phosphate, crospovidone, ascorbic acid, stearyl fumarate, mannitol and optionally riboflavin. The stable solid formulation may optionally include other therapeutic agents suitable for the condition to be treated, e.g. folates, including folate precursors, folic acids, or folate derivatives; and/or vitamins such as vitamin C and/or vitamin B 12; and/or neurotransmitter precursors such as L-dopa or carbidopa; and/or 5- hydroxytryptophan; and/or arginine. Compositions comprising tetrahydrobiopterin (or a precursor or derivative or analog) and a folate, and optionally further comprising arginine, are particularly contemplated.

Further tetrahydrobiopterin also decomposes in the presence of moisture and it may also react with reducing sugars or may cause discoloration of some excipients due to its strong reducing power. The stability of sapropterin also needs to be ensured during the process of preparation of compositions thereof.

The term "active ingredient" or "active pharmaceutical ingredient" means any component that is intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body of man or other animals. In the present invention, the active ingredient is sapropterin or an acceptable salt thereof, namely sapropterin dihydrochloride. The term "pharmaceutically effective amount" refers to an amount that is effective to achieve therapeutic and/or beneficial effect. In one embodiment the compositions of the present invention may administer a dose of about 100mg tetrahydrobiopterin.

The term ‘BH4’ as used herein is also to be understood to optionally mean a pharmaceutically acceptable salt of 6R-(L-erythro)-5,6,7,8-tetrahydrobiopterin.

The term "stabilizer" and "stabilizing agent" for the purpose of the present invention has been used interchangeably and refers to compounds that stabilize tetrahydrobiopterin and compositions thereof. The stabilizing agents employed in the compositions of the present invention include, but are not limited to, antioxidants, chelating agents, disaccharides or higher polyols, cyclodextrins, moisture retaining agents, hydrophobic agents and the like or any combinations thereof. In the present invention ascorbic acid is used as an antioxidant.

The term "composition" or "formulation" or "dosage form" has been employed interchangeably for the purpose of the present invention and mean that it is a pharmaceutical composition which is suitable for administration to a patient.

The term “shelf life” means the storage period during which an active pharmaceutical ingredient (API) in a pharmaceutical formulation has minimal degradation when the pharmaceutical formulation is stored under specified storage conditions, for example, room temperature at normal humidity.

The term “comprising” is used to mean including but not limited to. Thus, other nonmentioned substances, additives, carriers, or steps may be present.

In addition to the active or therapeutic ingredients, the composition may contain a number of inert materials known as excipients. The pharmaceutical compositions described herein can, if desired, include one or more pharmaceutically acceptable excipients. The term "excipient" herein means any substance, not itself a therapeutic agent, which may be used as a carrier or vehicle for delivery of a therapeutic agent to a subject or combined with a therapeutic agent (e.g., to create a pharmaceutical composition) to improve its handling or storage properties or to permit or facilitate formation of a dose unit of the composition

The pharmaceutically acceptable excipients that may be present in the stable pharmaceutical compositions of the present invention include, but are not limited to, lubricants, binders, antioxidants, filler/diluents, disintegrants, coloring agents, artificial and natural sweeteners or mixtures thereof. Filler/ diluents are added to increase the bulk weight of the blend resulting in a practical size for compression. Filler/ diluents that may optionally be incorporated in the compositions of the present invention include, but are not limited to, talc, mannitol, xylitol, sucrose, sorbitol, microcrystalline cellulose, silicified microcrystalline cellulose dibasic calcium phosphate, starch, maize starch, pregelatinized starch, partially pregelatinized starch and the like, and combinations thereof. In the present invention mannitol is used as a filler/diluent.

Mannitol is widely used in pharmaceutical formulations and food products. In pharmaceutical preparations it is primarily used as a diluent (10-90% w/w) in tablet formulations, where it is of particular value since it is not hygroscopic and may thus be used with moisture-sensitive active ingredients. Mannitol is commonly used as an excipient in the manufacture of soluble/ chewable tablet formulations because of its negative heat of solution, sweetness, and mouth feel.

Mannitol is available in various mean particle size grades (25 pm to 500 pm). In the present invention three different grades of mannitol were used. Namely: Mannitol having average mean particle diameter 25 pm (Mannitol 25C); mannitol having average mean particle diameter 100 pm (Mannitol 100SD); mannitol having average mean particle diameter 200 pm (Mannitol 200SD).

Binders are agents, which impart cohesive qualities to the powdered material. Binders employed in the compositions of the present invention include, but are not limited to, microcrystalline cellulose, calcium hydrogen phosphate, polyethylene glycol, polyvinylpyrrolidone, maize starch, pregelatinized starch, partially pregelatinized starch, hydroxypropyl methylcellulose, hydroxypropyl cellulose and the like, or combinations thereof. In the present invention dibasic calcium phosphate is used as a binder.

Disintegrants are often included to ensure that the tablet has an acceptable rate of disintegration. Disintegrants employed in the compositions of the present invention include, but are not limited to, sodium starch glycolate, sodium carboxymethyl cellulose, croscarmellose sodium, crospovidone, polyvinylpyrrolidone, methyl cellulose, starch, pregelatinized starch, partially pregelatinized starch and the like or combinations thereof. In the present invention crospovidone is used as a disintegrant.

Lubricants are typically added to prevent the tableting materials from sticking to punches, minimize friction during tablet compression, and allow for removal of the compressed tablet from the die. Lubricants that may be employed in the compositions of the present invention include, but are not limited to, magnesium stearate, calcium stearate, zinc stearate, sodium stearyl fumarate and the like, or combinations thereof. Suitable glidants include but are not limited to, colloidal silica, silica gel, precipitated silica, and the like or combinations thereof. Suitable anti-adherents employed include, but are not limited to, talc, magnesium stearate or finely divided silica, and the like or combinations thereof. Suitable pH adjuster or buffer employed include, but are not limited to, sodium citrate, citric acid and the like or combinations thereof. Suitable acidulants employed include, but are not limited to, citric acid, malic acid, tartaric acid, fumaric acid, succinic acid, glycolic acid, oxalic acid, mandelic acid, phosphoric acid, aspartic acid, glutamic acid and salts thereof and the like or combinations thereof. Further anti-caking agents that may be optionally incorporated include, but are not limited to, colloidal silicon dioxide, tribasic calcium phosphate, powdered cellulose, magnesium trisilicate, starch, and mixtures thereof. In the present invention, sodium stearyl fumarate is used as a lubricant.

In one embodiment the stabilizing agent employed in the compositions of the present invention is at least one antioxidant. Antioxidants are included in the compositions of the present invention to prevent degradation of the active from oxidation. Antioxidants employed in the compositions of the present invention include, but are not limited to, organic antioxidants and inorganic antioxidants or any combinations thereof.

The organic antioxidants employed in the compositions of the present invention include, but are not limited to, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tert-butyl-hydroquinone (TBHQ), 4-hydroxymethyl-2,6-di-tert-butylphenol (HMBP), 2,4,5- trihydroxybutyrophenone (THBP), alkylgallates, propyl gallate, octyl gallate, dodecyl gallate, ethoxyquin, gallic acid, nordihydroguaiaretic acid, glycine, ascorbic acid, fatty acid esters of ascorbic acid such as ascorbyl palmitate and ascorbyl stearate, and salts of ascorbic acid such as sodium, calcium, or potassium ascorbate; erythorbic acid, L- carnitine, acetyl L-carnitine, thioglycerol, thioglycolic acid (TGA), cysteine, N-acetyl cysteine, methionine, glutathione, citric acid, tartaric acid, fumaric acid, succinic acid, glycolic acid, oxalic acid, malic acid, ellagic acid, tocopherols such as, but not limited to, alpha tocopherol, delta tocopherol; lipoic acid, thiolated polymers such as, but not limited to, polycarbophil-cysteine, polymethacrylic-SH, carboxy methylcellulose-cysteine, betacarotene, carotenoids, flavonoids, flavones, isoflavones, flavanones, catechins, anthocyanidins, chaicones, vitamins, amino acids; enzymes such as, but not limited to, superoxide dismutase; and the like or any combinations thereof. In one embodiment the organic antioxidant may be acidic, non-acidic or any combination thereof. In the present invention, ascorbic acid is used as an antioxidant for the purpose of stabilizing agent. The following examples represent various embodiments of the present invention. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention.

Example 1. Production Methods - Selection of Production Method

In the formulation, the reference product produced by Biomarin under the trademark Kuvan® Soluble Tablets was referenced. The formulation development studies started with the investigation of the physical properties, chemical properties, solubility and pharmacokinetic properties of the active ingredients. The properties of the finished product were determined by taking into account the content, in-vitro release of the formulation of the reference product.

Firstly, the unit formula was tested with two different granulation methods. The same formulation was studies with wet granulation method (F-wet) and dry granulation method (F-dry).

In the production method selection study, the water dissolving time of the finished products prepared by wet granulation was longer than the expected time for soluble tablets. Tablets prepared by wet granulation method were dissolved longer than 15 minutes in water, whereas tablets prepared by dry granulation method were dissolved lower than 15 minutes in water as expected.

According to the production method selection study, dry granulation was selected for the production hereafter.

Example 2. Production Methods - Selection of Unit Formula with Different Excipients

Different formulation trials with different mannitol types were studied for the exact formulation. Table 1 : Formulation trials with different mannitol grades

Ratio

F-01 F-02 F-03

Sapropterin Dihydrochloride 32-35 32-35 32-35

Mannitol 25C* 52-58

Mannitol 100 SD* - 52-58

Mannitol 200 SD* - - 52-58

Ascorbic acid 1-3 1-3 1-3

Riboflavin 0.01 0.01 0.01

Crospovidon 2-5 2-5 2-5

Sodium Stearyl Fumarate 1-3 1-3 1-3

Dibasic Calcium Phosphate 2-3 2-3 2-3

*Mannitol 25C: Mannitol having average mean particle diameter 25 pm; Mannitol 100SD: Mannitol having average mean particle diameter 100 pm; Mannitol 200SD: Mannitol having average mean particle diameter 200 pm.

Required amounts of Sapropterin dihydrochloride, ascorbic acid, riboflavin, mannitol and crospovidone (kollidon CL) are mixed for 10 minutes. Then, sodium stearyl fumarate is added and mixed for 10 minutes. The resulting powder mixture is passed through the compactor for dry granulation. The structure taken from the compactor should be in the form of thin wafers, strips that do not break easily when handled, are hard but can be broken with a little pressure (with a hardness above medium). The granules passed through the compactor are ground, and the required amount of mannitol, crospovidone (kollidon CL) and dibasic calcium phosphate are added to the granules obtained as a result of grinding and mixed for 5 minutes. Finally, sodium stearyl fumarate is added and mixed for 10 minutes. The final sapropterin containing granule mix is compressed in soluble tablet specifications.

In the studies, adhesion was observed in the granulation step of the F-01 formula. It is predicted that this is due to the small particle distribution of the excipient mannitol 25 SD. In addition to adhesion, the tablets prepared by F-01 were dissolved longer than 15 minutes in water. The products obtained with the F-01 formula were not taken into the dissolution and stability stage due to the problem of sticking to the punch surfaces and capping, both during granulation and during tablet compressing.

No adhesion problems were experienced in F02 and F03 formulations. The dissolving test in water, appearance, assay and degradation results of the products obtained with the F02 and F03 formulas were evaluated in the initial conditions and were taken to the stability stage as they were found appropriate.

Example 3. Dissolution Profiles

Comparative dissolution tests were conducted based on proposed FDA dissolution methods for sapropterine dihydrochloride tablet. An in-vitro comparative dissolution test was performed for the test (Formulations F02 and F03) and the reference products (Kuvan®), in accordance to the Guideline on Investigation of Bioequivalence, was performed using the chosen dissolution conditions (500 mL dissolution medium, paddle at 50 rpm at 37°C ±0.5°C) at three different pHs (pH 1.2, pH4.5 acetate buffer having 0.1% ascorbic acid and pH 6.8 phosphate buffer having 0.1% ascorbic acid), releasing minimum 80% sapropterin within 30 minutes. The above exemplified compositions (Formulations F02 and F-03) comprising sapropterin hydrochloride were tested in vitro and they were compared with a commercial reference product Kuvan®.

The dissolution profiles were compared; the dissolution profiles obtained were evaluated by similarity factor (fp) (Helmy & Bedaiwy, 2013). An f2 value between 50 and 100 suggests that the two dissolution profiles are similar (EMEA Guideline on the Investigation of Bioequivalence, 2010). The similarity factor (fp) values of test products (Formulations F-02 and F-03) and reference product (Kuvan® 100 mg Soluble Tablet) for the different pH media are found between 50 and 100.

Example 4. Stability Studies

The stability of a drug substance is an important factor in the manufacture of safe and effective pharmaceutical products. Stability studies are required to be submitted by any applicant seeking approval for a new pharmaceutical product. The rules in force (e.g. "Note for Guidance on Impurities in New Drug Products" CPMP/ICH/2738/99, issued by EMEA, European Medicines Agency) provide strict limitations for impurities, nevertheless it is better to prevent or reduce as possible the degradation to avoid the exposure of patients to substances.

The stability of a pharmaceutical dosage form is related to maintaining its physical, chemical, microbiological, therapeutic, and toxicological properties when stored, i.e., in a particular container and environment.

It is known that many drugs exhibit poor or modest shelf stability. The presence of degradation products of these drugs can give rise to efficacy or toxicity issues, but even if they do not, the diminution of the concentration of a drug as a result of its degradation is inherently undesirable, as it makes therapy with the drug less certain. Stability issues can be caused by environmental factors such as humidity, temperature and the like. However, degradation may result from, or be accelerated by, interactions of drug substances with pharmaceutical excipients such as fillers, binders, lubricants, glidants and disintegrating agents or impurities contained in any of these excipients.

Accelerated stability tests are performed by storing a product in stress conditions. These tests allow predicting the shelf life of the product over the years when it will be stored in normal storage conditions. The accelerated stability test in this case was performed according to the EMEA Guideline on Stability Testing (CPMP/QWP/122/02, rev 1), i.e. by maintaining the product in its container at a temperature of 40°C ± 2°C and 75% ± 5 %RH (Relative Humidity) for six months.

Table 2. Stability results (assay) for Test products and reference product (Kuvan®) initially and after 6 months at 40°C±2°C/ 75%±5 %RH and 25°C±2°C/ 60±5% Relative Humidity, RH±5% storage conditions.

Assay (%)

According to the stability studies, the reference product (Kuvan® 100 mg Soluble Tablet) and test products (Formulations F-02 and F-03) gave appropriate results for assay test under 6-month stability conditions. In addition, no change was observed in the appearance tests between the initial conditions and the 6-month stability conditions.

While stability conditions were examined in prior art documents, only the appearance and quantity determination tests of the products were compared. However, it is also very important to examine the degradation products formed for active substances that are prone to degradation. In this regard, impurity tests were carried out on both the reference product (Kuvan® 100 mg Soluble Tablet) and the test products (Formulations F-02 and F-03) under initial and stability conditions. Table 3. Stability results (degradation products) for Test products and reference product (Kuvan®) initially and after 6 months at 40°C±2°C/ 75%±5 %RH and 25°C±2°C/ 60±5% Relative Humidity, RH±5% storage conditions.

Degradation Product (%)

*Max Unk.: Maximum unknown impurity

Claims

1. A stable pharmaceutical soluble tablet composition comprising pharmaceutically effective amount of sapropterin or a salt thereof and one or more pharmaceutically acceptable excipients, wherein the said composition comprises mannitol having average mean particle diameter 100 pm.

2. The soluble tablet composition according to claim 1 , wherein the active substance is sapropterin dihydrochloride.

3. The soluble tablet composition according to claim 1 , wherein sapropterine containing granules are obtained by using dry granulation method.

4. The soluble tablet composition according to claim 1 , wherein one or more pharmaceutically acceptable excipients is selected from the group comprising, lubricants, binders, antioxidants, filler/diluents, disintegrants and coloring agents or mixtures thereof.

5. The soluble tablet composition according to claim 3, wherein particle size distribution (D50) of final sapropterin containing granule mix ready for the compression, measured by the method of laser diffraction in a dry method (Malvern Mastersizer, general purpose mode, refractive index: 1.55, air pressure: 0.5 atm- 1.5 atm, obscuration rate: 0.5%-10.0%, feed rate 30%-40%), is between 100 pm to 300 pm.

6. The soluble tablet composition according to claim 5, wherein particle size distribution (D50) of final sapropterin containing granule mix ready for the compression, measured by the method of laser diffraction in a dry method (Malvern Mastersizer, general purpose mode, refractive index: 1.55, air pressure: 0.5 atm- 1.5 atm, obscuration rate: 0.5%-10.0%, feed rate 30%-40%), is between 100 pm to 200 pm.

7. The soluble tablet composition according to claim 4, wherein filler/diluent used in the composition is mannitol.

8. The soluble tablet composition according to claim 7, wherein mannitol is present in an amount of 52 to 58% by weight of total formulation.

9. The soluble tablet composition according to claim 4, wherein antioxidant used in the composition is ascorbic acid.

10. The soluble tablet composition according to claim 9, wherein ascorbic acid is present in an amount of 1 to 3% by weight of total formulation.

11. The soluble tablet composition according to claim 4, wherein disintegrant used in the formulation is crospovidone.

12. The soluble tablet composition according to claim 11 , wherein crospovidone is present in an amount of 2 to 5% by weight of total formulation.

13. The soluble tablet composition according to claim 4, wherein binder used in the composition is dibasic calcium phosphate.

14. The soluble tablet composition according to claim 13, wherein dibasic calcium phosphate is present in an amount of 2 to 3% by weight of total formulation.

15. The soluble tablet composition according to claim 1, wherein the composition comprises a dose of 100mg tetrahydrobiopterin.