Subcutaneous vs intramuscular botulinum toxin: split-face randomized study.

IMPORTANCE Much has been published regarding rejuvenation of the upper face with botulinum toxin A injection; however, the optimal target tissue layer has not been specifically examined. OBJECTIVE To seek a difference between subcutaneous (SC) and intramuscular (IM) administration. DESIGN, SETTING, AND PARTICIPANTS Prospective, randomized study at a tertiary care university facial plastic surgery practice. Nineteen patients who underwent botulinum toxin A treatment to the forehead were randomized so that each patient received IM injection on one side of the face and SC injection on the contralateral side. INTERVENTION Patients were assessed on the basis of eyebrow elevation before treatment, and at 2 weeks, 2 months, and 4 months following injection. Patients also completed a subjective questionnaire examining discomfort during injection, bruising, and tenderness, as well as their perception of their appearance after treatment. MAIN OUTCOME AND MEASURE Eyebrow height measurements between SC and IM techniques. RESULTS There was no difference in eyebrow height measurements between SC and IM techniques (0.00 [95% CI, -0.02 to 0.02]). Patients did report greater discomfort when receiving IM injections compared with SC injections (-0.76 [95% CI, -1.53 to 0.0005]). Patient satisfaction scores did not demonstrate a statistically significant difference between IM and SC techniques when measured on the first and second posttreatment visits; however, there was a trend toward significance on the final follow-up visit. CONCLUSIONS AND RELEVANCE Subcutaneous injection of botulinum toxin A is equally effective in achieving paralysis of the underlying frontalis muscle as IM botulinum toxin A administration. In addition, the SC route may result in less pain to patients receiving botulinum toxin A injection for rejuvenation of the upper face.