Novel topical formulation of lidocaine provides significant pain relief for intrauterine device insertion: pharmacokinetic evaluation and randomized placebo-controlled trial

Objective To investigate the pharmacokinetics, safety, and analgesic efficacy of a novel topical formulation of lidocaine at insertion of an intrauterine device (IUD). Design Randomized controlled trial; phase-I and phase-II studies. Setting University and public hospitals. Patient(s) Women aged ≥18 years who wanted to receive an IUD. Four women were parous in phase I; all in phase II were nulliparous. Intervention(s) A single, 8.5-mL dose of lidocaine formulation (SHACT) was administered (to the portio, cervix, and uterus) with a specially designed applicator. Main Outcome Measure(s) The phase-I study (single-arm) was designed for pharmacokinetic assessment; the phase-II study (randomized) was intended for investigation of efficacy and safety. Result(s) From the phase-I study (15 participants), mean pharmacokinetic values were: maximum plasma concentration: 351 ± 205 ng/mL; time taken to reach maximum concentration: 68 ± 41 minutes; and area under the concentration–time curve from 0 to 180 minutes: 717 ± 421 ng*h/mL. Pain relief was observed with lidocaine vs. placebo in the phase-II study (218 women, randomized). Mean visual analog scale score for maximum pain during the first 10 minutes after IUD insertion was 36% lower with lidocaine than with placebo (28.3 ± 24.6 vs. 44.2 ± 26.0). Pain intensity was also significantly lower in the lidocaine group at 30 minutes. On average, 3 of 4 patients will have less pain with lidocaine than with placebo. Adverse events were similar in the placebo and lidocaine groups. No serious adverse events were reported. Conclusion(s) Lidocaine provides pain relief lasting for 30–60 minutes for women undergoing IUD insertion, without any safety concerns. Further studies of this lidocaine formulation, for IUD insertion and other clinical applications, are planned. Clinical Trial Registration Number 2011-005660-18 and 2011-006220-20 (EudraCT).