An investigation of changes in physical properties of injectable calcium hydroxylapatite in a carrier gel when mixed with lidocaine and with lidocaine/epinephrine

INTRODUCTION As physicians incorporate calcium hydroxylapatite (CaHA) into their aesthetic treatment regimens, the question has arisen of whether the addition of anesthetic agents to prefilled CaHA syringes might provide sufficient anesthetic prophylaxis to warrant reduction in conventional anesthetic pretreatment procedures. STUDY DESIGN Investigators sought to determine changes in the physical properties of CaHA induced by the addition of lidocaine and lidocaine with epinephrine into the prefilled CaHA syringe. The CaHA and gel carrier (CHM) were mixed with varying amounts of lidocaine and lidocaine with epinephrine to measure the number of passes back and forth for optimal homogeneity of lidocaine and CaHA in syringes, changes in viscosity, extrusion force, needle jam rates, elasticity, and pH. RESULTS Ten mixing passes appeared sufficient for homogeneity. Viscosities and extrusion forces of CHM/lidocaine blends decrease with increasing amount of lidocaine. Needle jams do not increase. The pH and elasticity of the CHM/lidocaine blend are essentially equivalent to those of CHM alone. Epinephrine added to lidocaine did not alter the results enough to reach statistical significance. CONCLUSIONS Addition of lidocaine to original CHM can be safely added without harmful changes in physical properties of the original soft tissue filler. Further studies are required to explore whether the addition of lidocaine to CHM alters patient discomfort, durability, and efficacy.