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

Abstract

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).

Keywords: Intrauterine device; lidocaine; pain; pharmacokinetics; topical anesthetic.