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transportII research

transportII research - 1988 Biol Pharm Bull 33(12...

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Recently much attention has been paid to a new approach for enhancing transdermal drug delivery employing needles in micron scale, termed microneedles. Such a technique combines the concepts of the user-friendly delivery of trans- dermal patches and the broad effectiveness of hypodermic in- jections. Several studies have established the increasing effi- cacy of microneedle-assisted transdermal delivery for a vari- ety of compounds, 1—4) especially for high molecular weight hydrophilic compounds. 5—7) Microneedles are also expected to be safe, because they are minimally invasive and do not typically cause bleeding or any severe pain at the injection site. 8) Although microneedles assist in penetrating the stratum corneum (SC) barrier and offer several microchannels facili- tating drug transport across the skin, the release of macro- molecular drugs at the desired therapeutic rate might not be achieved by only (enhanced) passive diffusion from the patch-based drug reservoir due to the small diffusional area produced by needles. 9) It is necessary to further improve the transdermal delivery of drugs of large molecular weight by contributing push pressure to propel the drug toward the skin, similar to conventional topical injection. Wu et al. re- ported that the combination of solid microneedle pretreat- ment and subsequent iontophoresis significantly enhanced FD flux compared with microneedle pretreatment alone or iontophoresis alone. 9) It is difficult, however, to determine the penetration-en- hancing effect as well as the parameters affecting the deliv- ery efficiency produced by each enhancing technique and also by each individual microneedle. Yoshida et al. carried out a study to investigate the dermatopharmacokinetics (DPK) and systemic drug disposition after topical (intracuta- neous (i.c.)) injection of sodium salicylate and concluded that the injection volume was one of the factors which can be utilized to control the drug migration rate from the injection site. 10) Al-Qallaf et al. found that different surface areas of the hollow microneedle array-patch system affected the blood concentration of human growth hormone (hGH). 11) Moreover, information on the effect of several factors related to the delivery efficiency of hollow microneedles, for in- stance, various needle parameters, including injection condi- tions ( e.g. length of microneedle/injection depth, needle numbers, distance between each needle, hollow size, pressure of injection, etc. ), physicochemical properties of drugs ( e.g. molecular weight, lipophilicity, etc. ), and formulations must be considered for designing the optimum device. In this study, we therefore concentrated only on the influ- ence of variables related to the hollow microneedle system on in vitro drug release behavior from skin. A single 33- gauge hypodermic needle, where the diameter was almost the same to the arrayed microneedles recently reported, 2,7,9,12,13) was used as a single type hollow microneedle in order to re- duce the effect of needle parameters. The effects of injection
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