D-Arginine is the D-isomer and inactive form of L-Arginine.D-Arginine is an endogenous metabolite and inhibitor of EC 4.1.1.19 (arginine decarboxylase), has broad-spectrum toxicity to microorganisms, and acts as a regulator of microbial subpopulations.

In male albino mice, D-Arginine was administered via intraperitoneal injection (700–1400 mg/kg; single dose) to evaluate the effects on the central nervous system and toxicity. At 700 mg/kg, D-Arginine exhibited central excitatory effects, while at 1400 mg/kg, D-Arginine produced central depressant effects, including prolonged barbiturate-induced sleep and significant anticonvulsant activity against pentylenetetrazole-induced seizures. The LD₅₀ was determined to be 2800 mg/kg, and pretreatment with propranolol (2 mg/kg) or betamethasone (0.5 mg/kg) increased the LD₅₀ to 3600 mg/kg and 3300 mg/kg, respectively. [1]