Percutaneous delivery of methotrexate in the absence and presence of natural permeation enhancers
Pretorius, Mariska Heleen
MetadataShow full item record
The transdermal delivery of drugs has a lot of advantages above other routes of delivery, such as the avoidance of first-pass hepatic and intestinal metabolism, the non-invasive infusion of drugs, etc. However, the transdermal delivery of drugs, especially hydrophilic drugs, is limited due to the lipophilic nature of the stratum corneum. Methotrexate is a folic acid antagonist with antineoplastic activity and is used for the treatment of psoriasis and Kaposi's sarcoma. The permeation of methotrexate through the skin for systemic use is however limited due to its high molecular weight, the fact that it is mainty dissociated at physiological pH and its hydrophilic nature (Alvarez-Figueroa et al.. 2001). Thus the aim of my study was to enhance the permeation of methotrexate with the use of terpene. Terpenes are lipophilic in nature and have Log P values of around 2-4 (Godwin & Michniak, 1999). These characteristics make them excellent candidates as penetration enhancers. Terpenes are not only used for penetration enhancers, but in a huge number of other products, such as aromatherapeutic oils. For this reason the permeation of the terpenes through human skin and the effect of methotrexate on this permeation were also determined. The following enhancers were used in this study: menthol, menthone. isomenthol, limonene, B-myrcene, a-pinene and 1,8-cineole Five different sets of experiments were done in this study: a) a control experiment with methotrexate in the absence of the terpenes without ethanol; b) a control experiment with methotrexate in the absence of the terpenes with ethanol: c) experiments with methotrexate in the presence of the terpenes; d) control experiments with the terpenes in the absence of methotrexate and e) experiments with tile terpenes in the presence of methotrexate. For this study only human female abdominal skin was used. A saturated solution of methotrexate in water:propylene glycol (50:50) with a pH between 4 and 5 (Vaidyanathan et al., 1985) was used as the model drug and the receptor phase was PBS-buffer (pH=74) and water:ethanol (50:50) for HPLC and GC analysis respectively. The dilfusion apparatus used consisted of Vertical Franz diffusion cells with a capacity of 2 ml and a diffusion area of 1.075 cm2. The cells were placed in a water bath (+- 37 "C) on magnetic stirrers for the duration of the experiment. After the receptor phase was placed in the receptor compartment the cells were equilibrated for an hour before putting 25 ul of a 5% terpene solution in absolute ethanol on the skin in the donor compartment. This was left for half and hour to allow evaporation of the ethanol. The saturated solution of the methotrexate was now placed on the skin in the donor compartment. The experiments for methotrexate stretched over a period of 12 hours and samples were collected every 2 hours. The terpene experiments were performed over a 24-hour period and samples were taken at 2,4,6,12 and 24 hours. The concentration methotrexate permeated was determined by using HPLC-analysis and terpenes by using GC-analysis. The flux (ug/cm2/h), kp(cm/h), lag time (h) and enhancement ratio were calculated to compare the methotrexate permeation in the control and actual experiments. The results showed that a-pinene, B-myrcene and isomenthol enhanced the permeation of methotrexate most, although all the terpenes had an enhancing effect. They produced a 4- fold increase in the flux values of methotrexate. Due to the fact that the terpene experiments were only a semi-quantitative evaluation only the percentage terpenes that permeated was calculated. The experiments were done on all the terpenes except apinene. All the terpenes permeated the skin with menthol having the highest permeation. The results also showed that methotrexate did have an effect on the terpene permeation. Menthone and menthol's permeation was higher in the presence of methotrexate, while the other terpenes had a higher permeation in the absence of methotrexate. The reason for this is not clear. In conclusion, the study revealed that the enhancers used did have an enhancing effect on methotrexate permeation. This could be due to the extraction or disruption of lipids by the terpenes (Zhoa & Singh, 2000) or an increase in diffusivity and partitioning. The terpene experiments also showed that the terpenes do permeate the skin and that methotrexate does have an effect on this permeation.