Transungual Delivery of Antifungal Agents in Onychomycosis: Application of Chemical Penetration Enhancers, Nanotechnology and Hypobaric Pressure

Abstract

Onychomycosis is one of the highly prevalent nail disorders and constitute about 50% of nail diseases. Topical treatment for onychomycosis is hampered due to the thickness and hardness of the nail resulting in poor permeation of the antifungal agents. The current study was designed for transungual delivery of terbinafine HCl (TBN) and antifungal nitric oxide (NO) gas. Optimum chemical penetration enhancer (PE) was selected utilizing hydration enhancement factor (HEF). Cold method was modified to prepare selected PE containing TBN loaded poloxamer 407 (TBN-P407) gel for transungual delivery of antifungal lipophilic drug i.e., TBN with enough drug loading and gel strength. Functional additives were utilized for improvement of drug loading and gel strength i.e., thioglycolic acid (TGA) as PE and ethanol as cosolvent. Face centred central composite design (FCCCD) was employed to optimize P407 gel formulation with enough loading of lipophilic drug i.e., TBN without compromising on gel strength. TBN loaded chitosan nanoparticles (TBN-CSNP) were prepared by nanoprecipitation method, optimized in terms of size and entrapment efficiency (EE) using FCCCD and further characterized for different physicochemical properties. Optimized TBN-CSNP formulation was incorporated to P407 gel (already optimized above). Both developed TBN-P407 gel and TBN-CSNP loaded P407 gel was evaluated for different physicochemical characteristics. Transungual delivery of NO was investigated utilizing S-nitrosothiols i.e., S-nitrosoglutathione (GSNO), S-nitroso N-acetyl-D-penicillamine (SNAP) and S-Nitroso-N-acetyl-L-cysteine (SNAC) as NO donor molecules. Hypobaric pressure and metallic iron oxide nanoparticle (IONP) was evaluated for its ability to stimulate the release of NO from donor molecules. Finally, the potential of NO for transungual delivery was evaluated using rhino horn model. TGA was selected as optimum PE because of highest HEF value i.e., 2.73±0.43. SEM analysis showed that TGA has significant effect as nail PE to disturb the integrity of the nail plate. Increase in concentration of P407 and TGA significantly reduced gelation temperature and increased the gel strength of TBN-P407 gel. Optimized TBN-P407 gel prepared with modified cold method showed a gelation temperature of 8.7±0.16 °C, gel strength of 122±7.5s and drug loading of 1.27±0.1% w/w, which was four times more than the drug loading in the P407 gels prepared with conventional cold method. Optimized TBN-P407 gel showed pseudoplastic rheological behaviour and gel erosion of 47.75±3.48% after 12 washings and drug release of 67.21±2.16% after 12h. viii Cumulative amount of TBN permeated from TBN-P407 gel and TBN-P407 gel (without TGA) after 24 h was 27.30±4.18 and 16.69±2.31 µg/cm2, respectively. The particle size of the optimized TBN-CSNP formulation was 229.47±5.37nm having zeta potential, polydispersity index (PDI), EE and % yield of 37.03±1.48 mV, 0.39±0.09, 75.15±2.16 %, and 64.40±5.06% respectively. SEM analysis confirmed spherical shape. X-ray diffractometry (XRD) and Fourier transform infra-red (FTIR) analysis confirmed reduced crystallinity of TBN in the TBN-CSNP and no significant interactions between drug and formulation ingredients respectively. Rheological behaviour of TBN-CSNP loaded P407 gel was pseudoplastic and showed 39.8±2.03% of gel erosion after 12 washings and good spreadability of 10.52±1.79 g.cm/second. Drug release from TBN CSNP and TBN-CSNP loaded P407 was 84±4.86% and 56.74±3.24% respectively after 12h and demonstrated good stability for storage period of 6 months. Cumulative quantity of drug permeated from TBN-CSNP loaded P407 gel was 25.41±8.1µg/cm2. Nail uptake study showed that uptake of RHO into the nail following 2h application of TBN-CSNP loaded P407 gel and TBN-P407 gel was 3.6±0.71 and 2.1±0.27µg, respectively. NO release from GSNO, SNAP and SNAC solution was 4.35±0.37, 2.13± 0.1, and 0.65±0.15% respectively at 0 psi, which increased to 7.43± 0.75, 2.74±0.51, and 1.12±0.05% at -20 psi for GSNO, SNAP and SNAC respectively. The extent of decomposition for GSNO, SNAP and SNAC solution in the absence of IONP was 22.67±5.9, 20.06±1.76 and 18.81±1.72% respectively, which increased to 36.62±1.72, 35.9±2.58 and 23.15±7.2% in the presence of IONP. NO permeated from GSNO, SNAP and SNAC solution was 29.47±10.52, 54.38±9.59, and 38.84±3.54 μM/cm2. which increased to 66.5±15.05, 67.04±7.46 and 47.12±16.19 μM/cm2. when GSNO, SNAP and SNAC solutions were applied in the presence of IONP. TGA showed the potential to enhance both the transungual delivery of TBN and gel strength of P407 gel. Modification in cold method enhanced loading of lipophilic drug into P407 gel. Developed TBN-P407 and TBN-CSNP loaded P407 gel formulation demonstrated improved transungual delivery of TBN with TBN-CSNP loaded P407 showing enhanced uptake in to nail even after application for limited time. Further, NO gas showed rapid permeation across rhino horn and can be used in combination with TBN loaded formulations for enhanced effect.