5-Fluorouracil (5FU) is a pyrimidine analogue, indicated for the therapy of proliferative skin diseases such as actinic keratosis (AK), superficial basal cell carcinoma and psoriasis. It has also been used for the treatment of solid tumours like colorectal, breast and liver carcinomas for nearly 40 years.
Although 5FU has always been administered parenterally and orally, metabolism is rapid and absorption is erratic. Several severe side-effects are also commonly associated with 5FU therapy, including myelosuppression, hand-foot syndrome and gastrointestinal effects. Seeing that 5FU is an important part of the treatment of several malignant and pre-malignant disorders, it would be advantageous to find a delivery route and delivery system that negate absorption and metabolic variation and decrease side-effects.
The transdermal route provides a promising alternative to the above-mentioned conventional delivery routes, solving most of the problems associated with parenteral and oral administration. That being said, the formidable barrier situated in the skin is not easily breached. The stratum corneum, the outermost skin layer, is mostly lipophilic in nature, preventing hydrophilic molecules such as 5FU from entering.
5FU-containing creams and lotions are currently commercially available, but absorption is still very limited. The transdermal absorption from these formulations has been compared to that obtained with the use of new transdermal delivery vehicles, with the newer formulations proving to be promising.
It was decided to entrap 5FU in a novel therapeutic system, in the form of the Pheroid™ system, to increase its transdermal penetration.
Pheroid™ vesicles are stable spherical structures in a unique, emulsion-like formulation, and fall in the submicron range. The main components of the Pheroid™ system are the ethyl esters of the essential fatty acids linoleic acid and linolenic acid, as well as the cys-form of oleic acid, and water. The formulation is saturated with nitrous oxide (N20).
Although Pheroid™ vesicles may resemble other lipid-based vehicles, such as liposomes and micro-emulsions, they are unique in the sense that they have inherent therapeutic qualities as well. The Pheroid™ formulation can be specifically manipulated to yield different types of vesicles, ensuring a fast transport rate, high entrapment efficiency, rapid delivery and stability of the delivery system for a specific drug.
In this study, 5FU was entrapped in the Pheroid™ formulation. Transdermal permeation studies were then performed to evaluate the influence of this delivery system on the transdermal flux of 5FU.
Vertical Franz diffusion cells were utilised to determine the transdermal penetration of 5FU. Only Caucasian female abdominal skin was used to minimise physiological variables. Diffusion studies were done over 12 hour periods, with the entire receptor phase being withdrawn at predetermined intervals. Samples were analysed using high performance liquid chromatography (HPLC), after which the cumulative concentration of active was plotted against time. The linear portion of this graph represents the flux of 5FU through the skin.
It was found that there were differences in the results between formulations containing 5FU in a phosphate buffer solution (PBS)-based Pheroid™ and water-based Pheroid™, though the difference was not statistically significant. The 0.5 % 5FU in water-based Pheroid™ resulted in a significantly bigger yield than the control (1 % 5FU in water) as well as a significant difference to the 1 % 5FU in PBS-based Pheroid™ formulation. In general the water-based Pheroid™ formulations had greater average cumulative concentrations, yields and fluxes than the other formulations.
The fluxes obtained with the water-based Pheroid™ formulations also correlated well with a previous study done by Kilian (2004).
Thus it can be concluded that the Pheroid™ therapeutic delivery system enhances the transdermal penetration of 5FU. Water-based Pheroid™ formulations proved to be more effective than PBS-based Pheroid™ formulations. It can also be concluded that a 0.5 % 5FU in water-based Pheroid™ formulation can be used instead of a 1 % formulation, because there were no statistically significant differences between the two formulations. This would be advantageous - patient compliance can be enhanced because of a more tolerable formulation with fewer side effects, while manufacturing cost is lowered by using a lower concentration of active.
It is recommended that some aspects of the study be investigated further to optimise the transdermal delivery of 5FU using the Pheroid™ therapeutic system. These aspects
include optimising the composition of the Pheroid formulation, investigating the entrapment process of 5FU within Pheroid™ spheres, the influence of PBS and water as basis of the Pheroid™ formulation and the amount of 5FU remaining in the epidermis after the 12 hour period of the diffusion study.
Keywords: 5-Fluorouracil, Franz diffusion cell, Heat separated epidermis, Skin penetration, Transdermal, Drug delivery system, Pheroid™ / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2008.
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/1905 |
| Date | January 2008 |
| Creators | Van Dyk, Christina Petronella |
| Publisher | North-West University |
| Source Sets | North-West University |
| Detected Language | English |
| Type | Thesis |
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