Infraorbital Nerve Blockade and Cytotoxicity Study of a Long-Acting Nanoparticulate Injectable Formulation of a Local Anesthetic Agent: Statistical Optimization Using a 3² Full Factorial Design

We sought to overcome the systemic toxicity induced by ropivacaine (RPV) and to enhance its duration of action. Nanoparticles (NPs) were manufactured using a high-speed homogenization method. Phosphate-buffered saline (PBS; pH 7.4) was used to study encapsulation efficiency with HPLC (High Performance Liquid Chromatography). The surface morphology, observed using TEM (Transmission electron microscopy), showed NPs of a spherical nature with non-adherent properties. Photon correlation spectroscopy using a laser light-scattering instrument was used to assess the mean diameter of NPs. A cytotoxicity study was performed using 3T3 cells cultured in Dulbecco's modified Eagle's medium (DMEM), supplemented with 10% fetal bovine serum. A rat infraorbital nerve blockade study demonstrated local anesthetic activity. Overall encapsulation efficiency, when evaluated statistically, ranged from 74.51% (F2) to 89.20% (F13). The mean diameter and zeta potential of the NPs were 102.27±8.5 nm and –38.90±2.5 mV, respectively, with a polydispersity index of 0.18±0.002. The sustained release of drug from the NPs explained the reduced cytotoxic effect. Statistical analysis of F13 NPs revealed a prolonged recovery time and an enhanced local anesthetic effect of RPV at 0.20 (p < 0.02) and 0.40 (p < 0.05) mg/mL. The experimental and statistical results confirmed the sustained release formulation with reduced systemic toxicity.