Stabilization of Interferon alpha-2b in a Topical Cream - Pharmaceutical Technology

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Stabilization of Interferon alpha-2b in a Topical Cream
The authors describe a proprietary process for producing a stable, topical interferon alpha-2b formulation that can deliver large drug molecules into the skin or mucosa.

Pharmaceutical Technology
Volume 33, Issue 7, pp. 80-86

Table II: Recovery of Component A from spiked placebo.
IFNα2b is present in very small amounts in the Interferon alpha-2b Cream (i.e., about 8 g/g, or 2MIU/g). The RP-HPLC method requires a sample size of approximately 200 mg for the extraction procedure to isolate IFNα-2b and IFNα-2b-related degradation products from the formulation. When a formulation was analyzed after five months in real-time storage, Component A was not identified (see Figure 1d). The same formulation was forced to degrade by adding 10L of 0.25% H2O2 and incubating at room temperature for 1, 3, 4, or 5 h. After 5 h, approximately 70% IFNα-2b was recovered while Component A was detected at approximately 22% peak area (see Figure 1e).

Table III. IFNα-2b content and potency after forced degradation with 3% hydrogen peroxide.
To force the degradation of IFNα-2b further, 30L of 3% H2O2 was added to 200 mg of cream, and the samples were left at room temperature for 1, 3, 4, or 5 h. The samples were analyzed using both the RP-HPLC and the AVA methods. Although the IFNα-2b content decreased significantly, the potency of the formulation remained unaffected (see Table III). As indicated in Figure 1f, the IFNα-2b content decreased to approximately 2% while Component A was the principal peak in the chromatogram after the sample oxidized for 5 h at room temperature.

As a result of this study, it was concluded that the oxidative degradation product of IFNα-2b, Component A, has a comparable potency to native IFNα-2b and contributes to the overall potency of IFNα-2b in the formulation. The AVA is therefore nonspecific and cannot differentiate between IFNα-2b and Component A. Consequently, the RP-HPLC assay used in conjunction with the AVA can be used to successfully monitor the stability of IFNα-2b in the cream.

Formulation development

The initial Interferon alpha-2b Cream formulation was prepared by mixing a proliposomal gel composed of phospholipid, an oil-in-water emulsion, and an aqueous solution of IFNα-2b. The IFNα-2b was highly unstable in this formulation and oxidized into various degradants although the biological activity of IFNα-2b was not affected (Data not shown).

Excipient selection

The oxidation rate of IFNα-2b in the formulation was controlled by adding antioxidants, protein stabilizers, chelating agents, and buffering agents. Processing conditions, such as temperature and the use of an inert environment and storage conditions, were also optimized.

Besides the IFNα-2b, the lipids present in Interferon alpha-2b Cream are also susceptible to oxidation; therefore, the addition of antioxidants was essential. Various antioxidants, including ascorbic acid, alpha-tocopherol, benzyl alcohol, butylated hydroxyanisole, butylated hydroxytoluene, and methionine, were screened for the ability to protect the components of the product from oxidation and also to prevent auto-oxidation of IFNα-2b .

The presence of small amounts of metal ions is known to catalyze oxidation reactions. Because trace amounts of metal ions are present in the excipients and equipment, the chelating agent ethylenediaminetetraacetic acid was added to the product. Methionine, which acts as an antioxidant, and glycine, a protein stabilizer, was also added to further inhibit IFNα-2b oxidation.

Oxidation is also dependent upon the pH of the environment. Different pH conditions using several buffers, such as citrate buffer and phosphate buffers, were explored. Rheological properties were controlled by varying the amounts of viscosity-imparting agents such as white wax, glycerol monostearate, and cetyl alcohol to achieve a desirable consistency and maximum physical stability.


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