Abstract

Background/Objectives: Drug administration by microneedle patch (MNP) offers advantages over conventional dosage forms as a painless, self-administered skin patch for parenteral delivery. Dissolvable MNPs are typically manufactured by casting an aqueous formulation containing dissolved active pharmaceutical ingredient (API) and excipients into a mold and allowing it to dry. This process can be detrimental to APIs that are sensitive to dissolution and drying during the casting process. Methods: This study presents a MNP fabrication process in which drug particles are suspended in an organic solvent carrier without being dissolved in the solvent. Results: We started with drug particles either as pure API or formulated with excipients to stabilize them. We then screened nine organic solvents, ranging from high (methanol) to low (toluene) polarity, to identify those that suspend the drug particles without dissolution or damage to the API. To guide formulation of stabilized drug particles, we generated a companion database of 16 common stabilizing excipients and measured their solubility in our panel of organic solvents to identify excipient–solvent combinations that did not lead to excipient dissolution. We generated a second database of 14 water-soluble polymers to serve as the microneedle matrix material and determined their solubility in our panel of solvents to identify solvents that enabled polymer dissolution. Using these data, we designed casting solutions that suspended particles of API (and excipients) in an organic solvent that dissolved a matrix polymer. Casting and drying these solutions on molds produced MNPs for delivery of three model compounds: lyophilized tetanus toxoid (i.e., a vaccine), methotrexate (i.e., a small molecule drug), and insulin (i.e., a biologic). Conclusions: We conclude that this fabrication method, guided by the excipient and polymer solubility databases, offers a novel method to produce MNPs by suspension casting of drugs in organic solvents.

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