Are marketed topical metronidazole creams bioequivalent? Evaluation by in vivo microdialysis sampling and tape stripping methodology.
ABSTRACT To evaluate the bioequivalence of 3 marketed topical metronidazole formulations by simultaneous dermal microdialysis and stratum corneum sampling by the tape stripping methodology, and to compare the techniques as tools for the determination of bioequivalence.
Nine microdialysis probes were inserted in the volar aspect of the left forearm of 14 healthy volunteers and, following application of the 3 metronidazole creams, microdialysis samples were collected for 5 h. On the right forearm, tape strip sampling was performed 30 and 120 min after product application. At the end of the experiment, ultrasound scanning measurements confirmed that all probes were placed inside the dermis.
There was no statistical difference in penetration of the 3 topicals as determined by microdialysis. However, their bioequivalence could not be determined due to intersubject variability exceeding the criteria for bioequivalence evaluation. Tape strip sampling established a bioequivalence between 2 of the creams, but rejected any bioequivalence between these 2 formulations and the third. The third formulation was a generic formulation approved despite containing a lower concentration of metronidazole (0.75%) than the innovator formulation (1.0%). The result of the bioequivalence evaluation depends on the methodology employed.
Whenever the dermis is the target tissue, microdialysis provides the most relevant information on drug bioavailability.
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ABSTRACT: The efficacy of topically applied drugs is determined by their action mechanism and their potential capacity of passing the skin barrier. Nanoparticles are assumed to be efficient carrier systems for drug delivery through the skin barrier. For flexible nanoparticles like liposomes, this effect has been well demonstrated. The penetration properties of solid nanoparticles are currently under intensive investigation. The crucial advantage of nanoparticles over non-particulate substances is their capability to penetrate deeply into the hair follicles where they can be stored for several days. There is no evidence, yet, that solid particles ≥40 nm are capable of passing through the healthy skin barrier. Therefore and in spite of the long-standing research efforts in this field, commercially available solid nanoparticle-based products for drug delivery through the healthy skin are still missing. Nevertheless, the prospects for the clinical use of nanoparticles in drug delivery are tremendous. They can be designed as transport systems delivering drugs efficiently into the hair follicles in the vicinity of specific target structures. Once deposited at these structures, specific signals might trigger the release of the drugs and exert their effects on the target cells. In this article, examples of such triggered drug release are presented. © 2013 S. Karger AG, Basel.Skin pharmacology and physiology 01/2013; 26(4-6):227-33. DOI:10.1159/000351940 · 2.89 Impact Factor
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