Toxicity of diclofenac sodium salt after two weeks of daily intramuscular administration in cynomolgus monkeys

Diclofenac sodium salt (DSS) has been extensively studied in pharmacological research to better understand its pain relief and inflammation-reducing properties. However, it is crucial to evaluate the safety profile of this non-steroidal anti-inflammatory drug, particularly in nonhuman primates (NHPs), such as cynomolgus monkeys. Understanding the potential adverse effects and toxicity of DSS in NHP is critical for determining their overall safety and use in clinical settings. Further investigation into its toxicity to NHPs would provide valuable information for developing and using this drug in medical practice. Our aim was to evaluate the toxicity of DSS administered repeatedly to cynomolgus monkeys to identify its safety profile in NHPs. The general toxicity of DSS was established using a 2-week repeated-dose toxicity test. Twenty-four cynomolgus monkeys were intramuscularly injected with 0, 0.33, 1, and 3 mg/kg of DSS each day. This study assessed the potential adverse effects and toxicity of DSS in these monkeys, providing valuable data for understanding its safety in clinical settings. The 2-week repeated-dose toxicity study of DSS revealed no treatment-related changes in body weight, food consumption, ophthalmology, or general symptoms. Furthermore, no significant changes were observed in hematological, clinical chemistry, or urinalysis data. Histopathological examination revealed decreased cellularity (lymphocytes) in both the thymus and spleen (white pulp). The sternal bone marrow had a higher cell count than usual. Furthermore, mixed cell and mononuclear cell infiltration, inflammation, myofiber degeneration, and muscle fiber necrosis were observed at the injection site (skin), but these findings were not considered adverse effects. Notably, the no observed adverse effect level of DSS was estimated to be greater than 3 mg/kg in both males and females. Therefore, this study established a non-toxic dose of DSS, laying the groundwork for further nonclinical studies to assess the safety of DSS using NHP.