MLX-NLC gel stored under different temperature and humidity conditions (Table 1) was evaluated for any changes in particle size, l 'IP, zeta potential and drug content at 30, 60-90 day time points to assess the effect of storage conditions on stability as a function of time. Particle size was monitored at regular intervals during storage to assess particle aggregation. Nanoparticles are a thermodynamically unstable system and for their stability, a zeta potential value between –30 mV and –60 mV is desirable to avoid particle aggregation (Muller et al., 2000). Thus, measuring the zeta potential gives us the evaluation of the storage stability of the nanoparticles. Furthermore, Tween 80 could improve the stability of the system thanks to its steric effect which increases the repulsion between particles and prevents their aggregation (Lim and Kim 2002). The stability of the MLX-NLC gel was evaluated in terms of its MLX entrapment efficiency. Log (EE%) was plotted against time and slopes (m) were calculated by linear regression. The slopes (m) were then substituted into the following equation for determining the k values: k " = m × 2.303 " The shelf life values ​​(the time for 10% loss, i.e. t90) were then calculated by the following equation: t90 " = 0.105/k » In the case of MLX-NLC gel, no significant change (p>0.05) in particle size, IP, zeta potential and Drug entrapment efficiency was observed at 4 ± 2 °C over a period of 90 days (Table 3). Decrease in zeta potential and drug entrapment efficiency were observed with storage duration at 25 ± 2 °C/60% ± 5% RH and 40 ± 2 °C/75 ± 5% RH Increase. of particle size and polydispersity index, as well as the decrease in zeta potential and drug entrapment...... middle of paper ...... The degree of itation was classified as negligible ( PII = 0-0.4), mild (PII = 0.5-1.9), moderate (PII = 2-4.9) or severe (PII = 5-8) (Manosroi et al., 2013). The study indicated that MLX-NLC gel had no significant effect on animal weight at all time points (P > 0.05). MLX-NLC gel showed no erythema or edema on rabbit skin with a PII of 0.0. However, 20% SLS treatment resulted in moderate skin irritation with a PII value of 2.33 and 2.0 after 1 h and 24 h, respectively. This established the skin tolerance and safety of MLX-NLC gel for topical application. This could be because entrapment of MLX in a nanoparticle-based gel would have resulted in the prevention of direct contact of the drug with the skin and thus avoided drug-related local side effects. Thus, the MLX-NLC gel formulation would prove very advantageous for topical use with an improved safety profile...