Impact of manufacturing variables on product performance of contraceptive levonorgestrel intrauterine systems

Abstract

The development of Levonorgestrel Intrauterine Systems (LNG-IUSs) stands as a formidable challenge due to their intricate design and reliance on specialized manufacturing methods. Pharmaceutical manufacturers face a labyrinth of process variables that demand precise identification and comprehension to establish a robust product design to ensure consistent performance. The current manuscript navigates through this complexity, describing a small-scale processing method for LNG-IUSs via addition and condensation curing processes, as well as investigating the influence of key manufacturing variables on LNG-IUS product performance. Different mixing speeds and time exhibited distinct impact on drug content uniformity within the IUS drug-polymer reservoirs. Surprisingly, no variation in drug release rates were observed. Curing temperature and time were the critical processing parameters of IUSs which were dependent on the polymer type (polydimethylsiloxane, PDMS) and drug loading. At lower curing temperatures, crosslinking in PDMS remained relatively unaffected, irrespective of drug loading. By contrast, elevating curing temperatures resulted in a drastic reduction in PDMS crosslinking densities at higher drug loading. This was attributed to increased drug volume fraction within the matrix, impeding optimal prepolymer chain mobility and rearrangement which is crucial for complete crosslinking. Interestingly, rapid curing led to increased PDMS crystallinity, thereby retarding drug release rates while concurrently compromising mechanical properties. PDMS curing chemistry, such as condensation cure (no filler) and addition cure (cured at room temperature), did not affect drug release rates of the LNG-IUSs. In the condensation cure-based LNG-IUS, the formulations prepared without filler had higher drug release rates than those containing silica or diatomaceous earth fillers. Overall, the present study unravels the intricate interplay between PDMS characteristics, processing variables, and product performance, offering fundamental insights into product design and manufacturing of brand and generic LNG-IUS products.