Dual-responsive lidocaine in situ gel reduces pain of intrauterine device insertion.

The most effective and safe contraceptive method, intrauterine devices (IUDs), is still underutilized due to the pain barrier during IUD insertion. Lidocaine, a well-known local anesthetic, can be used to relieve IUD insertion pain. This study aimed at formulation, in vitro, in vivo and clinical evaluation of a novel lidocaine dual-responsive in situ gel. Pluronic and Gelrite were used as thermosenstive and ion-activated polymers, respectively. In situ gels containing 2% lidocaine, pluronics and/or Gelrite were prepared. The optimized dual-responsive formula (F) was clear, with 95% drug content, free flowing at room temperature and gel at vaginal temperature (T of 28 °C). This optimized dual-responsive in situ gel was found to be superior to single-responsive one due to presence of Gelrite, imparting resistance to dilution effect of simulated vaginal fluids. DSC thermograms revealed no interaction between formulation components. Biocompatibility study showed no degeneration, necrosis or inflammation. Optimized dual-responsive in situ gel was further evaluated for pain reduction efficiency via a pilot randomized, double-blinded, placebo-controlled clinical trial showing ease of self-administeration by patients and significant pain reduction induced at all steps of IUD insertion. In conclusion, lidocaine dual-responsive in situ gel can be effectively used in prevention of pain during IUD insertion.