Pharmacokinetics of Low Dose Ketamine Infusion

Opioids, such as fentanyl, are commonly used in PICU patients to provide comfort and pain control. Opioid tolerance, the need to increase the dose of medication to achieve the same effect,is seen in PICU children who require opioid infusions. Animals and human studies have shown that activation of the N-methyl-D-aspartate (NMDA) receptor is involved in the development of opioid tolerance and that deactivation of this receptor can slow the development of tolerance. Ketamine, an NMDA receptor antagonists, turns off the NMDA receptor. Ketamine is used to provide sedation and anesthesia in children. Its use in inhibiting the development of opioid tolerance has not been tested in children. We aim to determine ketamine's effectiveness in the treatment of tolerance in PICU patients who require fentanyl infusions to treat pain and discomfort . Some physicians have reported using ketamine doses of 0.04mg/kg/hr to 0.5mg/kg/hr to inhibit opioid tolerance. We propose to study the sedative effect, and the metabolism of, three doses of ketamine, 0.1mg/kg/hr, 0.3mg/kg/hr, and 0.5mg/kg/hr. Patients admitted to the PICU, requiring a breathing machine and fentanyl infusion for discomfort or pain control will be enrolled. Patients' age three to eighteen years will be enrolled. Patients will receive a ketamine infusion once their COMFORT scores indicate an adequate sedation/comfort level on their current sedation regimen. The COMFORT score is a validated scale that measures distress in PICU patients. The COMFORT score will be continued for the twelve hours the patient receives the ketamine to test whether the ketamine adds to the level of sedation. Blood samples during and following the ketamine infusion will be taken to determine how ketamine and norketamine (one of ketamine's metabolites) are used in the body. To determine the effect of ketamine on tolerance it must be a ketamine dose that does not cause additional sedation. The goal of this study is to define a non-sedating dose