Chronic toxicity of muroctasin in mice.

The chronic toxicity of N2-[(N-acetylmuramoyl)-L-alanyl-D-isoglutaminyl]-N6-stearoyl-L-lysine (MDP-Lys(L-18), muroctasin), a synthetic muramyl dipeptide, was investigated in mice. Leukocytosis and immunologically activated appearances of splenic white pulp and lung were seen in mice, when treated with MDP-Lys(L18) for 26 weeks. Furthermore, inflammation around the injection site and synovial epithelium hyperplasia of the tarsal joint occurred in higher incidence in the high dose group. These changes were similar to those seen in the subacute toxicity study with mice.