Relationship between concentrations and effects  Drowsiness, dissociative, and psychosis-like effects (e.g., hallucinations, delirium) are reported in patients treated with ketamine starting at circulating concentrations of around 50 to 200 ng/mL (210-841 nM), while analgesia begins at levels of approximately 100 to 200 ng/mL (421-841 nM). The typical intravenous antidepressant dosage of ketamine used to treat depression is low and results in maximal plasma concentrations of 70 to 200 ng/mL (294-841 nM). Circulating concentrations of around 2,000 to 3,000 ng/mL (8,413-12,620 nM) are employed during anesthesia, and patients may start to awaken once levels of ketamine have decreased to about 500 to 1,000 ng/mL (2,103-4,207 nM). There is wide variation in the peak concentrations of ketamine that have been reported in association with anesthesia in the literature, with values ranging from 2,211-3,447 ng/mL (9,300-14,500 nM) to as high as 22,370 ng/mL (94,100 nM). Biological activity concentrations of ketamine are lower than total plasma levels due to plasma protein binding, although plasma protein binding is relatively low with ketamine (approximately 12 to 47% protein-bound). Concentrations of ketamine in the brain have been reported to be several-fold higher than in plasma.. How many concentration levels start bellow 100 ng/ml?