Development of a naproxen and gaultheria oil based topical nanoemulsion for the amelioration of osteoarthritis†

Osteoarthritis (OA) is a chronic degenerative condition characterized by the wearing down of the articulating surfaces of the tibia–femoral joint. It involves the breakdown of cartilage, leading to a reduction in joint space, primarily affecting the medial aspect of the joint. Treatment options for OA include oral and topical medications, as well as chemical and surgical interventions. Among potential treatments, naproxen (NAP) and gaultheria oil (GO) have shown promising anti-inflammatory effects. However, NAP's distribution is hindered by its limited solubility and poor penetration. Additionally, there is no marketed product or published report of any combination product of GO with any synthetic drug. Hence a novel nanoemulsion (NE) based gel has been developed. For NE development, Tween 80 and PEG 400 were selected as the surfactant and co-surfactant, respectively. The particle size, polydispersity index (PDI) and zeta potential were found to be 209.2 nm, 0.2119, and −24.7 mV respectively. In vitro cumulative drug release in the initial 24 h was 95.64 ± 0.75% for NE and 87.44 ± 0.84% for NEG. Similarly, in vitro drug permeation after 24 h was 17.447 μg cm⁻² and 9.3287 μg cm⁻², respectively. The rheological behavior, skin irritation, and stability of the NEG were also evaluated.