Zaleplon nanospanlastics loaded transdermal patches: formulation, optimization, ex-vivo permeation, and in-vivo studies

Zaleplon (ZLP) is a commonly used sedative-hypnotic drug that has low oral bioavailability because of its poor water solubility and extensive hepatic metabolism. This study aimed to encapsulate ZLP into spanlastic nanovesicles to enhance its bioavailability via transdermal delivery. Using Span 60 and Tween 80, ZLP-loaded spanlastics were fabricated using thin film hydration technique according to 3² full factorial design. In the applied design, the influence of formulation variables on vesicle size, entrapment efficiency, and cumulative drug amount released over 24 h was investigated, leading to the identification of the optimal formulation. The optimized spanlastics were nanosized, spherical vesicles measuring 297.2 ± 8.17 nm, with an encapsulation efficiency of 65.75 ± 3.28% and a 24-hour drug release rate of 76.44 ± 5.66%. FT-IR studies revealed no significant chemical interactions between ZLP and the excipients used. HPMC K100M transdermal patches loaded with the optimized ZLP-spanlastics were formulated utilizing solvent casting technique. The patches were smooth and elastic with uniform drug content, ranging from 92.65 ± 2.54 to 96.12 ± 1.57%. The steady-state flux (Jss) of the spanlastic transdermal patch (ZLP-SP1) across rabbit skin was over 3.62 times higher than that of the control transdermal patch, indicating a significant enhancement in drug permeation. The investigated transdermal patches were stable under accelerated conditions with non-irritating properties. The <i>in-vivo</i> studies have shown that the pharmacokinetic parameters of ZLP oral suspension and ZLP-SP1 are significantly different, with the relative bioavailability of ZLP-SP1 being 2.681%. Therefore, these fabricated transdermal patches could be effectively used to treat insomnia.