This invention relates to a process for the enhancement of the stability of gelatin products against higher storage temperatures, humidity and/or chemically influenced crosslinking, as well as suitable gelatin compositions and their use in capsule manufacturing or as coating or binding agents of tablets and casing materials.

Gelatin is widely used in the pharmaceutical industry as well as in the health food supplement market to manufacture capsules as containers or as coating agents for the capsules or other dosage forms, or as adjuvants or excipients in pharmaceutical preparations like tablets. A primary objective of these dosage forms is to have a good disintegration after being administrated in order to enable a fast dissolution of the active substances in the appropriate digestive organ. Any delay of the disintegration would consequently retard or even reduce the effect of the drug. Consequently, this disintegration characteristic has to remain unchanged over time when finished products are stored prior to use. Extensive dissolution stability testing has been conducted to assess this stability.

Unfortunately, as has been widely described in the literature, the risk for the gelatin product to exhibit a delay in disintegration over time is high. A primary cause of the problem, exposure to certain aldehydes contained in the capsules content at the initial stage or originating from the decomposition of the drug or one of the excipients over time, has been reported in many references as a cause. The mechanism of this chemical interaction named "crosslinking" has been well understood as action of the aldehyde on the free amino groups of the amino acids and especially the lysine and arginine (G. Digenis & al, to be published in J. of Pharm. Sci.). It has also been used further in the sense that overcrosslinking of the gelatin would make it totally insoluble and inappropriate for an enteric dosage form (G. Gutierrez, FR-8201127).

Various patents have been published which deal with this issue. The resistance to crosslinking by formaldehyde can be obtained by chemically modifying the gelatin (succinylated gelatin: Toyo Jozo Co, JP 61/186315 Nippon Elanco Co, JP-61/186314), by adding ions in it (Sanofi, FR-8708828) or silicones (R.P. Scherer, FR-2346/69) or peptides (NITTA, EP-0 335 982).

Another procedure to protect gelatin from crosslinking is to include in the formulation of the drug a formaldehyde scavenger (Teikoku Hormone Mfg Co, JP-168874/1989 and Lion Corporation EP-0 242 855).

Some literature references have also reported that exposure or storage to/under hot and humid conditions is another reason for the delay in the disintegration of gelatin products. These conditions were reported in a temperature range of 25 to 55°C and a humidity range of 40% to 90% relative humidity. This appears to be very important for most of the pharmaceutical applications of the gelatin where a stability is requested for storage at 40°C with 75% RH over 3 to 6 months without significant delay in drug dissolution.

This phenomenon was described extensively in the literature, but no proposal has been made to explain the mechanism of the chemical reactions involved in responsible for the poorer dissolution performance of the gelatin: H.W. GOUDA & al., Intl. Jour. Pharmaceutics, 18, 1984, 213-215; S.A. KHALIL & al., Pharmazie, 29 H1, 1974, 36-37; T.C. HAHL & al., Drug Dvpt Industr. Pharmacy, 17 (7), 1991, 1001-1016; M. DEY & al., Pharmaceutical Res., 10 (9), 1993, 1295-1300; K.S. MURPHY & al., Pharm. Techno., March, 1989, 74-82. In the state of the art, no method is known for increasing the resistance of the gelatin to storage at hot and humid conditions as described before.

In JP-A-53091118 a lyophilised stable antigen composition is described which consists of a mixture of sodium chloride, magnesium chloride, calcium chloride, gelatin, saccharose and an antigen.

The present invention relates to a process for the manufacturing of gelatin products which have improved stability against storage under hot and humid conditions and/or aldehydes in order to improve the dissolution of the gelatin products comprising incorporating additives into the gelatin solution and forming the final product as usual. A further aspect of the invention is the gelatin compositions used for the gelatin products prepared by the process.

The gelatin to be used with the present invention may be from acid processed pork skin known as A gelatins, from lime processed bones known as B gelatins, from calf skin known as C gelatins, acid processed bones known as AB gelatins or from a combination of two or more of these gelatins.

The additives are selected from the group consisting of sodium sulfate, sodium chloride, potassium sulfate, potassium chloride, lithium sulfate, lithium chloride, calcium sulfate, calcium chloride, magnesium sulfate, magnesium chloride, iron (II) sulfate, iron (II) chloride, iron (III) sulfate, iron (III) chloride, manganese (II) sulfate, manganese (II) chloride, glutamic acid, aspartic acid, asparagine, lysine, tryptophane, arginine, guanidine, ascorbic acid, ethylenediamine tetraacetate, nitrilotrismethylene phosphonic acid.

The amount of additives is up to 25%, preferably 0.1 to 10% by weight of the dry gelatin. Each additive can be added alone or in combination with one or more additive.

Two types of storage conditions were studied:

• 1) Hot and humid conditions: temperature varied between 20 and 55°C and humidity between 40% and 95% RH.
• 2) Formaldehyde:
  • a. Capsules were filled with lactose contaminated by formaldehyde with levels varying between 0-200 ppm, preferably between 1 and 60 ppm. These capsules were either stored in closed bottles at 50°C up to 2 months or in the open at hot and humid conditions up to 6 months.
  • b. Gelatin films were stored in lactose powder contaminated by formaldehyde with level between 0 and 200 ppm, preferably between 1 and 50 ppm. Films are dipped in the contaminated lactose powder in a closed plastic box and kept at 50°C up to 1 month.

The dissolution measurements were made with the apparatus described in USP XXII, method II (paddle 50 rpm). The medium was demineralized water at 37°C ± 0.5°C and two procedures were used one for the capsules and one for the gelatin films. The samples are added in the media in a special sinker which prevents them from floating.

The capsules are previously stored under one or both of the storage conditions described before. The capsules were filled with Acetaminophen and dissolved in water at 37°C under agitation (paddle 50 rpm). The percentage of dissolved Acetaminophen is determined by UV spectrophotometry at 300 nm. The required level of dissolved Acetaminophen is higher than 80% at 45 min.

Films of gelatin are casted on glass plates. These films are stored at one or both of the conditions described before. The films are then added in demineralized water at 37°C under agitation (paddle 50 rpm) and the percentage of dissolution is determined by UV spectrophotometry at 217 nm. Uncrosslinked films have a dissolution of more than 90% at 6 min.

The following examples will demonstrate how the addition of inventive compounds increases the resistance of gelatins to crosslinking by hot and humid storage and/or formaldehyde.

The effect of addition of nitrilotrismethylene phosphonic acid (AMP, Masquol® P320) on the dissolution of gelatin films stored in presence of formaldehyde is studied. The films were prepared by casting a gelatin solution (30% w/w water) containing Masquol® P320 (1% w/w gelatin on glass plate and drying at room conditions for 24 hours.

The dissolution samples were then prepared and stored dipped in formaldehyde contaminated lactose in a closed plastic box for 1 week at 50°C prior to dissolution measurements.

The dissolution results are shown in the following table 2. Gelatin AMP Dissolution 3 min 6 min 9 min 12 min 15 min A 240 0% 0% 3% 10% 16% 21% 1% 3% 15% 26% 41% 52% B 200 0% 8% 42% 70% 84% 87% 1% 8% 77% 89% 93% 94%

Here the beneficial effect of the addition of an additive, Masquol® P320, on the resistance of gelatin films to formaldehyde crosslinking is clearly demonstrated.

Effectively, a significant increase in the dissolution of gelatin films was observed for both A 240 films (+150% at 15 min) and B 200 films (+85% at 6 min).

Gelatin films with amino acids as additives were prepared and stored at hot and humid conditions prior to dissolution measurements. Gelatin films were casted from 30% w/w solution containing either 1% Tryptophan or 1% Glutamic acid. Gelatin films of A 240 and of B 200 were prepared. Films were dried at room conditions for 24 hours prior to sample preparation. The samples were stored at 50°C and 80% RH for 3 (A240) or 4 months (B 200) prior to dissolution measurements. The results are shown in table 3 in comparison with gelatin without additives stored at room temperature (Ref.). Gelatine Additive Dissolution (%) after minutes 3 6 9 12 15 A 240 0% 6% 8% 14% 36% 67% 1% Glu 6% 50% 92% 99% 100% 1% Trp 10% 87% 97% 99% 100% B 200 0% 3% 76% 92% 98% 98% 1% Glu 54% 92% 97% 99% 100% 1% Trp 59% 97% 100% 100% 100% A 240 0% Ref. 72% 96% 99% 100% 100% B 200 0% Ref. 96% 100% 100% 100% 100%

The dissolution results, compared with reference tests, demonstrate that the addition of amino acids, specifically Glutamic acid and Tryptophan at 1% level (in respect of dry gelatin) increases the dissolution of gelatin films especially at 3 min for B 200 and 9 min for A 240 gelatins.

In both cases, we reached the total dissolution of gelatin films (100% dissolution) more rapidly with additives than with reference films stored at the same conditions.

Gelatin films with salts or organic compounds were prepared as in example 2. The following product were added at 1% level compared to dry gelatin weight: Masquol® P320 (AMP).

The dissolution measurements were performed as for example 3 and results are summarized in following table 4: Gelatine Additive Dissolution (%) after minutes 3 6 9 12 15 A 240 0% 6% 8% 14% 36% 67% 1% Glu 10% 92% 99% 100% 100% 1% AMP 94% 97% 100% 100% 100% B 200 0% 3% 76% 92% 98% 98% 1% AMP 77% 94% 99% 100% 100% A 240 0% Ref. 72% 96% 99% 100% 100% B 200 0% Ref. 96% 100% 100% 100% 100%

The addition organic compounds (Masquol® P320) increased significantly the dissolution of gelatin films of both type A 240 and B 200.

For A 240 the 100% dissolution is obtained at about 6 min compared to only 8% dissolution for gelatin films without additives. This result is comparable to reference films (Ref.) stored at normal conditions. The dissolution is higher than 75% for B 200 gelatin after only 3 min (3% for B 200 films without additives). These results are comparable to reference B 200 films (Ref.) stored at normal conditions.

As demonstrated from these examples, the incorporation of selected additives into the gelatin films increases the resistance of gelatin films and capsules to crosslinking in presence of aldehydes or when stored in hot and humid conditions.

The dissolution of capsules containing additives and filled with lactose contaminated by formaldehyde (5ppm or 20 ppm) and stored at 50°C in closed bottles for 1 or 2 months was studied. The results are expressed as the level of dissolution of acetaminophen filled in the capsules and measured according to the USP XXII Method 2. Test Additive Dissolution (%) after minutes 15 30 45 60 75 A 0% 12% 40 57% 71% 79% B 0% 24% 50% 66% 78% 88% 1% (II) 39% 79% 95% 100% 100% C 0% 43% 79% 94% 98% 99% Test A: Storage 4 weeks at 50°C, 20 ppm formaldehyde

Test B: Storage 2 months at 50°C, 5 ppm formaldehyde

Test C: Reference storage at room conditions

Additive (II): Aspartic acid

The dissolution of capsules containing additives is better than the reference one. This dissolution is equal to the dissolation of standard capsules stored at room conditions.