RESUMEN
BACKGROUND: The commonality between chronic conditions that are treated with low-dose ketamine, such as specific chronic pain conditions, depression, and post-traumatic stress disorder, can be found in relation to the stress system, particularly the hypothalamus-pituitary-adrenal axis. In this study we assess the effect of ketamine on the stress system by measuring plasma and saliva cortisol production during and following exposure to low-dose ketamine. METHODS: In a double-blind, randomized, placebo-controlled study, the influence of subanaesthetic ketamine (0.29 mg kg(-1) h(-1) for 1 h, followed by 0.57 mg kg(-1) h(-1) for another hour) was studied with repeated plasma and saliva cortisol samples in 12 healthy male volunteers. A pharmacokinetic-pharmacodynamic model was used to describe the circadian rhythm-dependent ketamine-induced production of cortisol. RESULTS: The endogenous mean baseline cortisol production was 7.9 (SE 1.5) nM min(-1). Consistent with the circadian rhythm, cortisol production decayed by 1.25 nM min(-1) h(-1). Ketamine doubled the cortisol production at a concentration of 165 (SE 35) ng ml(-1). The salivary cortisol concentration closely mirrored the plasma concentration and was exponentially related to the plasma concentration with, at 100 ng ml(-1) ketamine, a saliva:plasma ratio of 0.036 (se 0.006). CONCLUSIONS: Ketamine has an appreciable effect on cortisol production. This may impact on critical physiological and psychological functions. CLINICAL TRIAL REGISTRATION: This study was registered in the Dutch Trial Register under number NTR2717 at www.trialregister.nl.