Acute Toxicological Profile of Pharmaceutical-Grade Nicotinamide Riboside: A Route-Dependent Assessment Across Intravenous, Intramuscular, and Subcutaneous Administration

Nicotinamide riboside chloride (NR-Cl) has been studied predominantly by the oral route, while information regarding its toxicity following parenteral administration is limited. To characterize route-dependent acute toxicity and estimate median lethal doses (LD50), pharmaceutical-grade NR-Cl was evaluated following bolus intravenous (IV), intramuscular (IM), and subcutaneous (SC) administration in female Sprague Dawley rats, in three independent studies. All studies were conducted using an adapted OECD Guideline 425 Up-and-Down procedure, modified for parenteral administration, in the absence of standardized route-specific OECD guidance. Animals received a single dose of NR-Cl via the respective administration route and were monitored for mortality, clinical signs, bodyweight changes, and gross pathological findings over a 14-day observation period. Following IM and SC administration, no mortalities were observed at doses up to 2000 mg/kg, and LD50 values for both routes were determined to be greater than 2000 mg/kg. In contrast, IV administration yielded an estimated LD50 of approximately 2000 mg/kg. These findings demonstrate that the acute toxicity of NR-Cl differs by route of administration and establish foundational safety benchmarks to support future research.