To improve the transdermal bioavailability and safety of alendronate (ALN), a nitrogen-containing bisphosphonate, we developed self-dissolving microneedle arrays (MNs), in which ALN is loaded only at the tip portion of micron-scale needles by a dip-coating method (ALN(TIP)–MN). We observed micron-scale pores in rat skin just after application of ALN(TIP)–MN, indicating that transdermal pathways for ALN were created by MN. ALN was rapidly released from the tip of MNs as observed in an in vitro release study. The tip portions of MNs completely dissolved in the rat skin within 5 min after application in vivo. After application of ALN(TIP)–MN in mice, the plasma concentration of ALN rapidly increased, and the bioavailability of ALN was approximately 96%. In addition, the decrease in growth plate was effectively suppressed by this efficient delivery of ALN in a rat model of osteoporosis. Furthermore, no skin irritation was observed after application of ALN(TIP)–MN and subcutaneous injection of ALN, while mild skin irritation was induced by whole-ALN-loaded MN (ALN–MN)—in which ALN is contained in the whole of the micron-scale needles fabricated from hyaluronic acid—and intradermal injection of ALN. These findings indicate that ALN(TIP)–MN is a promising transdermal formulation for the treatment of osteoporosis without skin irritation.
Interferon alpha (IFNα) is one of the most famous drugs for the treatment of chronic hepatitis C and various types of human malignancy. Protein drugs, including IFNα, are generally administered by subcutaneous or intramuscular injection due to their poor permeability and low stability in the bloodstream or gastrointestinal tract. Therefore, in the present study, novel IFNα-coated polyvinyl alcohol-based microneedle arrays (IFNα-MNs) were fabricated for the transdermal delivery of IFNα without the painful injection. IFNα was rapidly released from MNs in phosphate buffered solution and these MNs presented piercing ability in the rat skin. Slight erythema and irritation were observed when MNs were applied to the rat skin, but these skin damages completely disappeared within 24 h after removing the IFNα-MNs. Furthermore, the pharmacokinetic parameters of IFNα-MNs were similar to those of IFNα subcutaneous administration. Finally, IFNα-MNs showed a significant antitumor effect in tumor bearing mice similar to that of IFNα subcutaneous administration. These results indicate that IFNα-MNs are a useful biomaterial tool for protein drug therapy and can improve the quality of life in patients by avoidance of painful injections.
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