A study of 20 patient volunteers conducted by Shawn B. Allen, MD, and Neil A. Goldenberg, MD, PhD, found that reconstitution of abobotulinumtoxinA with preserved saline results in significantly less pain on injection than abobotulinumtoxinA reconstituted with preservative-free saline. The study—which was conducted in a private dermatology practice in Boulder, Colorado and appears in the Journal of Dermatologic Surgery (June 2012)—involved injecting one side of each patient’s face with abobotulinumtoxinA reconstituted with preservative-free saline and the other side of the face with abobotulinumtoxinA reconstituted with preserved saline. The patient volunteers reported their pain on a 10-point visual analogue pain scale after each side was injected and kept a diary for the first 48 hours after treatment to record onset of action, adverse events and any continued pain. The researchers report that 90% of patients reported 60% less pain on the side injected with preserved saline compared to the side injected with preservative-free saline. The patients and the investigators observed no difference in onset of action between the two sides.