Relationships between levels and effects
Dissociation and psychotomimetic effects are reported in people treated with ketamine at plasma concentrations of approximately 100 to 250 ng/mL (0.42–1.1 μM). 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 (0.29–0.84 μM). At similar plasma concentrations (70 to 160 ng/mL; 0.29–0.67 μM) it also shows analgesic effects. In 1–5 minutes after inducing anesthesia by a rapid intravenous injection of ketamine, its plasma concentration reaches as high as 60–110 μM. When the anesthesia was maintained using nitrous oxide together with continuous injection of ketamine, the ketamine concentration stabilized at approximately 9.3 μM. In an experiment with purely ketamine anesthesia, people began to awaken once the plasma level of ketamine decreased to about 2,600 ng/mL (11 μM) and became oriented in place and time when the level was down to 1,000 ng/mL (4 μM). In a single-case study, the concentration of ketamine in cerebrospinal fluid, a proxy for the brain concentration, during anesthesia varied between 2.8 and 6.5 μM and was approximately 40% lower than in plasma. Pharmacokinetics
Ketamine can be absorbed by many different routes due to both its water and lipid solubility. Intravenous ketamine bioavailability is 100% by definition, intramuscular injection bioavailability is slightly lower at 93%, and epidural bioavailability is 77%. Subcutaneous bioavailability has never been measured, but is presumed to be high. Among the less invasive routes, the intranasal route has the highest bioavailability (45–50%) and oral – the lowest (16–20%).
During about the sixth month of fetal life, two centres make their appearance in the base of this process: they are placed laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece of cartilage. The base of the process is separated from the body by a cartilaginous disk, which gradually becomes ossified at its circumference, but remains cartilaginous in its center until advanced age. In this cartilage, rudiments of the lower epiphyseal lamella of the atlas and the upper epiphyseal lamella of the axis may sometimes be found. The apex of the odontoid process has a separate centre that appears in the second and joins about the twelfth year; this is the upper epiphyseal lamella of the atlas. In addition to these, there is a secondary centre for a thin epiphyseal plate on the undersurface of the body of the bone. Clinical significance
Fracture of dens
Fractures of the dens, not to be confused with Hangmans fractures, are classified into three categories according to the Anderson Alonso system:

Type I fracture - Extends through the tip of the dens. This type is usually stable. Type II fracture - Extends through the base of the dens. It is the most commonly encountered fracture for this region of the axis. This type is unstable and has a high rate of non-union. Type III fracture - Extends through the vertebral body of the axis.