Criteria for the bioanalytical method and its application in dermatopharmacokinetic (DPK) study in pig skin (ex vivo) using metronidazole

Conventional pharmacokinetic profiles of drugs are described mainly by plotting drug plasma concentration versus time. However, topical drugs are designed to target local tissue and, as such, have limited systemic absorption. For these drugs, the pharmacokinetic measurements in the local tissue (skin) are of more importance than systemic measurements. In this context, this study aims to develop and discuss the appropriate bioanalytical methodology by high performance liquid chromatography (HPLC) and application to ex vivo DPK metronidazole (MTZ) study based on the resolution - RE no. 899/2003 and Collegiate Board Resolution – RDC no. 27/2012 guidelines from the National Health Surveillance Agency of Brazil (ANVISA) and the FDA Guidance for Industry Bioanalytical Method Validation (2013). The average of recovery was 98.71% in a linear range from 0.1 to 20 μg/mL. The intraday and interday precision and accuracy were within specified limits to bioanalytical methods. MTZ was not detected in the receptor solution after 6 h, demonstrating that during this time, the drug is not able to cross the skin at a flow, resulting in a concentration higher than 0.1 μg/mL, which is the lower limit of quantification of this method. The amount of MTZ found in the pig SC was 20.91±7.02 µg/cm2 (n=14). Based on these results, it can be concluded that the validation of the drug dosage methodology described here was sensitive, precise and accurate and was successfully applied to analyze ex vivo DPK samples and is an important step for ensuring the reliability of these analyses.   Key words: Bioanalytical method, dermatopharmacokinetic (DPK), metronidazole, tape stripping.