Manufacturing and characterization of long-acting levonorgestrel intrauterine systems

Mirena® is long-acting (5 years) contraceptive intrauterine device. It is composed of a hollow cylindrical drug reservoir (containing Levonorgestrel and polydimethylsiloxane), which is covered with a release rate controlling silicone membrane. This structure presents a manufacturing challenge and to date, there have been no literature reports on the manufacturing, product design and quality evaluation of these hollow cylindrical intrauterine devices. It is vital to develop a reproducible and robust manufacturing process for these long-acting intrauterine devices or systems to obtain an understanding the in vitro and in vivo performance of such drug-device combinations. In this study, a twin-syringe method with a customized mold was developed to manufacture hollow cylindrical polydimethylsiloxane (PDMS)-based levonorgestrel intrauterine systems (LNG-IUSs). Different mold materials, curing temperatures and times were screened to fabricate PDMS-drug reservoirs with good quality characteristics (easy demolding, good appearance and appropriate physicochemical characteristics). The prepared PDMS-drug reservoirs were covered with the release rate controlling membrane to fabricate the LNG-IUSs. Physicochemical characterization (drug content and content uniformity, powder X-Ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) of the PDMS-drug reservoirs with different drug loadings (10%, 25% and 50% w/w) was conducted. Real-time in vitro drug release testing of LNG-IUSs with different drug loading was performed in normal saline (0.9% w/v NaCl) at 37 °C using a water bath shaker rotating at 100 rpm. The prepared PDMS-drug reservoirs demonstrated good and reproducible quality characteristics including appearance (smooth surfaces), targeted drug loading and good drug content uniformity in the PDMS matrix. The PXRD showed that the crystallinity of the API was maintained inside the PDMS matrix. DSC, TGA and FTIR confirmed the structure of the drug and the PDMS, indicating no interaction between the drug and the PDMS matrix in the prepared LNG-IUSs. Real-time in vitro drug release from the LNG-IUSs with different drug loadings showed zero-order release kinetics, and the drug release rate (based on daily release percentage) was inversely proportional to the drug loading.