Category: Formulation and Quality
Purpose: Arsenic is a toxic metalloid and a human carcinogen available in plenty in the earth’s crust. It affects various cellular processes in a time and dose dependent manner1. Organic arsenicals have been used for chemical warfare, affecting thousands of people during World War I/II. Lewisite is one such example in this category of warfare chemicals. Exposure to lewisite results in painful inflammatory blistering of the skin, lung and eye2. Human skin shows signs of erythema, swelling and pain within minutes of exposure to these toxic arsenicals. Nordihydroguaretic acid (NDGA), is a lignan found in Larrea tridentate. Commonly known as Mascoprocol, its treatment is effective in reducing UVB-induced solar keratosis3. We found that its topical application suppresses cutaneous inflammatory response. In this study, we are attempting to develop a formulation for a quick delivery of NDGA in skin, that will help mitigate the early symptoms of vesicant action of arsenicals. NDGA being highly prone to oxidation, N-acetyl cysteine (NAC) was used as an anti-oxidant to protect NDGA from oxidation. NAC helps attenuate arsenic toxicity4, thus serving as a functional excipient.
Methods: NDGA and NAC were procured from TCI America (Tokyo Chemical Industry, USA) and Sigma Aldrich, USA respectively. Solutions of 1%, 2%, 3%, 4% and 5%w/v concentrations were made by dissolving NDGA in a homogenous mixture of DMSO: IPA: PG: Water (20: 15: 10: 55) containing 0.2% NAC. A concentration study was carried out to find the minimum concentration delivering maximum drug. Once the concentration was established, a time-dependent and multi-dose study were performed to define the delivery of NDGA in skin at a specific time interval. Three time-dependent studies were carried out for a time of 2hr, 4hr and 8hr respectively. The multi-dose study was carried out for 8hrs with a dosing at 0hr, 2hr and 4hr.
Dermatomed human skin was mounted on Franz diffusion cells to carry out permeation studies. The receptor solution contained PEG: 1XPBS in the ratio of 30: 70 to maintain sink conditions. The receptor solution also contained 0.2% NAC. Donor contained 12.5µL of the NDGA solution. Skin concentration of drug was calculated by subjecting epidermis and dermis samples to an extraction using of methanol: water solution (ratio 90:10) containing 0.2% NAC. Samples were analyzed using a High Performance Liquid Chromatography (HPLC) system connected to a Photodiode array detector.
Results: There was no significant difference in the amount of drug delivered by 5%w/v (31.327±2.466), 4%w/v (30.532±3.173) and 3%w/v (37.449±4.321) formulations. Hence, 3%w/v was the concentration chosen for the time and multi-dose studies. There was no significant difference in the amount of drug delivered in 2hr, 4hr and 8hr. However, the epidermal concentration of the multi-dose group that was carried out for 8hrs was significantly higher (20.692±1.850) as compared to the 2hr study (4.097±0.506) as shown in Fig. 1. There was no significant difference in the amount of drug delivered at the end of 24hrs (single dose) and 8hr (multi dose) groups. No significant difference was found in the amount of drug delivered to the dermis in any of the groups.
Conclusion: Oxidation of NDGA was successfully prevented by adding NAC. A minimum dosing concentration of 3% was established for topical delivery of NDGA. Quick delivery of NDGA was achieved, thus, immediate application of NDGA may help people get a relief from the symptoms of toxicity of arsenicals.