Dexamethasone and Pain Following Total Knee Arthroplasty

This is a Phase IV single center, prospective, randomized, double-blind, dose response study designed to evaluate the optimum dose of dexamethasone to administer as an analgesic in total knee arthroplasty surgery. Randomization will be performed using computer software and the randomization order will be written and enclosed in envelopes in the study office. A total of 40 patients will be randomized to receive different doses of dexamethasone intravenously at induction of anesthesia with the same dose repeated 24 hours later. The dose groups are: 0mg, 6mg, 12mg, 24mg. The groups will be evenly divided into 10 subjects in each group. Patients will be cared for using established standard of care anesthetic and multi modal analgesia pathway used clinically at Duke University Medical Center. Knee arthroplasty generally occurs in patients over 65 years of age and an inclusion criteria is age 55 years or older is included in the study. Regional anesthesia is more technically challenging in morbidly obese patients. Because of an increased failure rate of regional anesthesia in morbidly obese patients an upper limit BMI of 40 is included in the study design.

Anesthetic regime. The anesthesia will be standard of care apart from the administration of the study drug.

Study Drug. After randomization the first dose of intravenous dexamethasone will be administered by the anesthesia care team immediately before surgery. The subject and study personnel will be blinded to the dose. The patient will be sedated and the study personnel will not be in the operating room. The dose will be recorded on the anesthesia record.

The second dose of dexamethasone will be prescribed by the PI. This will be prescribed electronically to be administered to the subject on the floor 24 hours after the first dose.

Surgery The surgery will proceed normally with no difference for the study.

Postoperative Pain Management Patients in all groups will receive standard of care postoperative analgesic regimen.

Blood Samples Blood will be drawn in preop holding (Time 0) for Interleukin 6, Interleukin10 and for macrophage sorting.

Blood samples will be repeated for Interleukin 6 and Interleukin10 at 10-14, 22-26 and 33-39hours after surgery.

Blood samples for macrophage sorting will be repeated at 33-39hours. The total blood collected will be 30ml on the day of surgery and 10 ml post operative day 1 for an overall total of 40cc.

Inclusion criteria

• Patients scheduled to undergo unilateral total knee arthroplasty.
• American Society of Anesthesiology (ASA) Physical Class 1-3.
• BMI <40 kg/m2

Exclusion criteria

• Revision surgery.
• Bilateral total knee arthroplasty.
• Unicompartmental knee arthroplasty.
• Patients with a contraindication to regional anesthesia. This includes abnormal clotting, skin infection in groin or near the back, the presence of neurological disorders or anatomical abnormalities of the vertebral column.
• Contraindications or known drug interactions with dexamethasone.
• Use of any of the following medications within the times specified before surgery:

• Long-acting opioid medication within 3 days.
• Any opioid medication within 24 hours.
• Body weight less than 50 kilograms (~110 pounds).
• Planned administration of another investigational product or procedure during the subject's participation in this study.
• Suspected, or known addiction to or abuse of illicit drug(s), prescription medicine(s), or alcohol within the past 2 years.
• Uncontrolled anxiety, schizophrenia, or other psychiatric disorder that, in the opinion of the Investigator, may interfere with study assessments or compliance.
• Current or historical evidence of any clinically significant disease or condition that, in the opinion of the Investigator, may increase the risk of surgery or complicate the subject's postoperative course.
• Significant medical conditions or laboratory results that, in the opinion of the Investigator, indicate an increased vulnerability to study drugs and procedures, and expose the subject to an unreasonable risk as a result of participating in this clinical trial, such as: debilitating diseases, acute illnesses, hypotension, partial or complete conduction block, impaired cardiac function (Ejection fraction under 35%), epilepsy, myasthenia gravis), severe renal impairment (creatinine > 1.8), comorbid conditions associated with an immunocompromised status, such as blood dyscrasias, HIV/AIDS, or recent chemotherapy.