Formulation, in vitro release and transdermal diffusion of salicylic acid and topical niacinamide
Acne affects as many as 80% of young adults and adolescents all over the world. This detrimental condition can be classified into four stages: (a) open comedo (blackhead), (b) closed comedo (whitehead), (c) papule and (d) pustule (Russell, 2000:357-366). There are various factors that can lead to acne outbreaks which include: (a) hormone level changes during the menstrual cycle in women, (b) certain drugs (i.e. lithium), (c) certain cosmetics and (d) environmental conditions such as humidity (University of Maryland, 2009:1). The skin performs a variety of functions which include the two major functions: (a) the containment and (b) the protection of the internal organs of the body. The containment function relates specifically to the ability of the skin to confine the underlying tissues and restrain their movement from place to place. The protective function, on the other hand, relates to the ability of the skin to act as a microbiological barrier to most micro-organisms; a chemical barrier to exogenous chemical compounds; barrier to radiation and electrical shock; and mechanical barrier to impact (Danckwerts, 1991:315). Niacinamide and salicylic acid were chosen in combination, due to the beneficial effects that they have on acne. Niacinamide has an anti-inflammatory action on acne; which reduces redness, dryness and irritation caused by Propioni-bacterium acnes that live in the clogged pores of pimples (Acnetreatmentlab, 2008:1). Salicylic acid is a keratolytic and keratoplastic agent. It is used in combination with other ingredients to enhance the shedding of corneocytes. This causes penetration into the skin to be very difficult (SAMF, 2005:177). The solubility of niacinamide and salicylic acid in PBS (pH 7.4 at 32°C) were 212.95 mg/ml and 4.07 mg/ml, respectively. The log D values of niacinamide and salicylic acid were determined to be -0.32 and 0.33, respectively. According to the solubility of niacinamide and salicylic acid it was expected that both of the active ingredients would permeate through the skin. However, it is expected that niacinamide will depict enhanced permeation with respect to salicylic acid. The results of the log D for both of the active ingredients indicate that there would not be optimal permeation. This study involved the formulation of four different acne preparations (Pheroid™ cream, Pheroid™gel, cream and gel), combining niacinamide and salicylic acid. The evaluation of stability parameters for the different formulations indicated that none of the formulations was stable under the different storage conditions determined by the Medicines Control Council. Nevertheless, the cream and gel were the most stable of the four formulations. Visual assessment of the Pheroid™ formulations with the confocal laser scanning microscopy (CLMS) was conducted and inconclusive evidence to whether the active substances were entrapped within the Pheroids™, was obtained. Franz cell diffusion studies indicated that the cream (in the case of niacinamide) and gel (in the case of salicylic acid) depicted the highest average and median flux from hours 6 to 12. Results of the tape stripping studies showed that with the gel formulation, concentrations of 2.060 µg/ml and 44.749 µg/ml niacinamide were obtained in the epidermis and dermis respectively. After the Pheroid™ gel was applied, tape stripping depicted only 1.587 µg/ml niacinamide in the epidermis with respect to 22.764 µg/ml niacinamide in the dermis. The cream formulation, on the other hand, showed niacinamide concentrations of 2.001 µg/ml in the epidermis and 13.363 µg/ml in the dermis, whereas with the Pheroid™ cream formulation, concentrations of 1.097 µg/ml and 18.061 µg/ml were obtained in the epidermis and dermis respectively. Tape stripping results depicted that with the gel formulation, concentrations of 2.113 µg/ml and 49.519 µg/ml salicylic acid were obtained in the epidermis and dermis respectively, whereas the Pheroid™ gel formulation showed salicylic acid, concentrations of 1.114 µg/ml in the epidermis and 95.360 µg/ml in the dermis. The cream formulation, however, depicted salicylic acid concentrations of 0.758 µg/ml in the epidermis and 44.729 µg/ml in the dermis. Lastly, after the Pheroid™ cream was applied, salicylic acid concentrations of 0.411 µg/ml and 48.424 µg/ml in the epidermis and dermis respectively, were measured. It could, therefore, be concluded that both niacinamide and salicylic acid tend to concentrate more in the dermis, irrespective of the formulation. This may be an advantage since acne is usually targeted in the dermis and epidermis.
- Health Sciences