Soft tissue induration occurred following chronic pentazocine injection in three patients. Inflammatory nodules, cutaneous depression, and ulceration also developed in one or more of these three patients. However, in some cases, there may be incomplete absorption of the solution and precipitation due to the slightly alkaline pH of extracellular fluid. The precipitated crystals may initiate a chronic inflammatory response.
Schlicher JE, Zuehlke RL, Lynch PJ. Local Changes at the Site of Pentazocine Injection. Arch Dermatol. 1971;104(1):90-91. doi:10.1001/archderm.1971.04000190092016