Metronidazole thermogel improves retention and decreases permeation through the skin

Metronidazole (MTZ) is widely used as the standard antibiotic for the treatment of rosacea and, more recently, is being used off label in Brazilian hospitals for the treatment of wounds. Following oral administration, minimal amounts of active agent reaches the skin and side effects are strongly induced. Consequently, MTZ is currently being applied topically in order to improve the therapeutic efficacy with reduced side effects, with Rozex(r) (RZ) (an MTZ gelled formulation) being the only marketed product. This study examined whether the use of MTZ 0.75% from thermogel formulations could improve drug retention and reduce dermal exposure compared to that by Rozex(r). Following a 21 h permeation study, the highest total amount of MTZ permeated through the rat healthy and disturbed skin was seen with Rozex(r), but similar to all formulations regardless of the skin condition. On the other hand, the amount retained in the epidermis/dermis was larger for thermogel formulations; at least 4 fold that of Rozex(r), when the stratum corneum was present as a barrier. In conclusion, thermogel formulations can be favorable alternatives to Rozex(r) for the topical application of MTZ with improved efficacy and reduced side effects

Topical bio(in)equivalence of metronidazole formulations in vivo

The topical bioavailabilities of metronidazole from a commercially available ‘reference’ product (Rozex®) and two extemporaneous test formulations were compared. With the reference drug product, a full skin pharmacokinetic profile, in vivo in human volunteers (following a 6-h uptake and clearance over the subsequent 22 h), was obtained using an improved stratum corneum (SC) sampling procedure. Then, a two-time point SC sampling method enabled the bio(in)equivalence of the test formulations to Rozex® to be evaluated. One test formulation was shown to be bioequivalent to Rozex®, both for uptake and clearance, whereas the other (more viscous and less spreadable) formulation was not. The delivery of metronidazole into the underlying viable epidermal tissue from Rozex® and from the equivalent test formulation was 2.5 to 3.5-fold higher than that from the inequivalent extemporaneous vehicle. The results highlight that the quantitative composition of a formulation, as well as its physical properties that influence events that take place at the vehicle-skin interface, can have a dramatic impact on the delivery of drug into the SC and subsequently to the viable skin layers below. The reproducible, sensitive and facile in vivo methodology employed may prove of particular value where regulatory approval of generic formulations lacks objective rigour.</p

Registro de medicamentos genéricos tópicos dermatológicos: cenário brasileiro e estudos para demonstração de bioequivalência | Registration of generic dermatologic topical medications: Brazilian scenario and studies to demonstrate bioequivalence

Comparando-se o número de registros concedidos para produtos tópicos pelo Food and Drug Administration (FDA) e pela Agência Nacional de Vigilância Sanitária (Anvisa) com o número de testes exigidos por essas e outras agências internacionais no momento do registro desses medicamentos, fica claro que a flexibilização das exigências regulatórias brasileiras vem proporcionando um maior número de medicamentos tópicos no mercado, sem que haja garantia da bioequivalência entre as diferentes formulações consideradas produtos genéricos. Diante disto, o objetivo deste trabalho é discutir, sob o ponto de vista do pesquisador brasileiro, as metodologias possíveis de serem utilizadas no Brasil para esta finalidade, considerando ser premente uma rediscussão da legislação brasileira no que concerne a bioequivalência destes produtos. Dentre as metodologias abordadas estão estudos de liberação e permeação in vitro, ensaio farmacodinâmico de branqueamento (exclusivo para os corticoides), dermatofarmacocinética e microdiálise dérmica. Concluímos que, inicialmente, baseados na simplicidade dos métodos, bem como na facilidade de implementação, parâmetros para a abordagem in vitro devem ser definidos. Posteriormente, uma discussão ampla envolvendo Anvisa, comunidade científica e segmento industrial deveria ser buscada, visando avaliar a viabilidade técnica e econômica de adequação à realidade brasileira, no emprego dos métodos in vivo, aqui discutidos. ============================================ Comparing the number of approvals granted for topical drug products by the FDA and by Anvisa, as well as the number of tests required by these and other international agencies at the time of registration, it becomes clear that the increased flexibility of the Brazilian regulatory requirements has resulted in a larger number of topical medicines on the market, without a guarantee of bioequivalence between the different formulations considered generic. For this reason, the aim of this study is to discuss, from the point of view of Brazilian researchers, the methodologies that could possibly be used in Brazil for the reasons mentioned above, the most urgent being a revaluation of Brazilian legislation concerning bioequivalence of these products. Among the approaches considered are: in vitro release test, in vitro permeation, pharmacodynamic test (only for corticoids), and dermatopharcokinetic and dermal microdialysis. We conclude that, firstly, based on the simplicity of the methods, as well as the ease for their implementation, parameters for the in vitro approach must be defined. Later, a wider discussion involving Anvisa, the scientific community and the industrial sector should be sought, aiming to assess the technical and economic viability of the adaptation to the Brazilian scenario in relation to the use of the in vivo methods discussed here