RP-HPLC Method Development, Validation and Application for Quantification Assay and Release Kinetics of Etonogestrel from Contraceptive Subdermal Implant

Abstract

Etonogestrel (ENG), a biologically active metabolite of desogestrel and a synthetic progestin, is administered via a single-rod implant that represents one of the most effective long-acting reversible contraceptives (LARCs) with minimal side effects. It was aimed to develop and validate a robust method for quantifying ENG and to evaluate its release kinetics from an ENG-releasing single-rod LARC implant, Implanon, using a reversed-phase high-performance liquid chromatography (RP-HPLC) technique. An RP-HPLC method was developed for the quantitative analysis of ENG using Waters C₁₈ column (250 × 4.6 mm, 5 μm) where the mobile phase consisted of water and acetonitrile (50:50, v/v), with a flow rate of 1.0 mL/min at room temperature. The injection volume was 50 μl and detection was carried out at a wavelength of 250 nm. All validation parameters of the developed method met the acceptance criteria in accordance with ICH Q2(R1) USP guidelines. The total chromatographic run time was 12 min, with ENG eluting at retention time of 5.5 (± 0.03) min. The method showed linearity over the concentration of 80-120% with a correlation coefficient (r²>0.998). The limits of detection (LOD) and quantification (LOQ) were 0.08 μg/mL and 0.24 μg/mL, respectively. Accuracy values ranged between 99% and 101%, while precision studies demonstrated %RSD values of <2%. The method remained robust under deliberate variations in chromatographic parameters. In vitro release study revealed an initial release of ENG, followed by a gradual decline consistent with sustained diffusion-controlled release. The release profile showed the best fit to the Higuchi model (R²>0.98), suggesting diffusion as the primary release mechanism. The validated method is suitable for routine quality control, stability assessment, and release profiling of ENG-containing implants.

Bangladesh Pharmaceutical Journal 29(2): 246-253, 2026 (July)