Development of a Novel Self-Dissolving Microneedle-Assisted Percutaneous Delivery System of Diacerein through Solid Dispersion Gel: Solubility Enhancement, Proof of Anti-inflammatory Activity and Safety

Diacerein, an osteoarthiritis drug, experiences slow topical permeation due to limited solubility. Additionally, it shows a laxative effect due to acid/base hydrolysis of the drug in the colon.Diacerein solubility was improved to increase percutaneous drug delivery.To improve saturation solubility of the drug, Diacerein was pre-treated with Polysorbate 80 aqueous solution (1% v/v) to obtain lyophilized powder after wet milling or formulated as solid dispersion using PEG 4000 by fusion method. The lyophilized Diacerein in hydroxypropyl methylcellulose (HPMC 8% w/w) and polyvinyl pyrrolidone (PVP 30% w/w) matrix, with PEG 400 as co-solvent, provided an optimized array. The solid dispersion was loaded in the CMC based gel for subsequent administration on dissolving microneedle-treated skin.The addition of PEG 400 increased Diacerein loading in microneedles to 390.35±4.28 μg per array. The lyophilized drug displayed amorphous characteristics in the dissolving microneedles as per XRD analysis. SEM photographs showed uniformity in the surface topology of microneedles. The needles showed rapid polymer dissolution within 5 minutes, whereas methylene-blue distribution confirmed the formation of microcavities in excised rat skin. The drug-loaded arrays showed better permeation (74.39%) and skin deposition (15.75%) after 24 hours, however, ⁓12% of Diacerein remained in the baseplate. This led to the tailoring of CMC-based gel (3% w/v) containing 0.4% solid dispersion of Diacerein. When compared to untreated skin, the gel improved permeation rate by 2.43 folds through aqueous microchannels generated by dissolving microneedle pre-treatment and allowed 98% drug permeation. The quasi-Fickian diffusion mechanism was found to drive ex vivo release kinetics, with a shorter lag time (0.88 h) and higher flux (26.65 μg/sq.cm.h). Microneedle-assisted Diacerein gel showed a positive anti-inflammatory effect in the paw edema model and reduced diarrheal episodes in comparison to the marketed oral formulation. The gel showed desired characteristics at 5°C±2°C when tested under accelerated stability conditions.The present study reports for the first time the verification of efficacy and safety to advocate the suitability of Diacerein for percutaneous delivery through dissolving microneedle-treated skin.