Oral Ketamine for Acute Pain Management After Amputation Surgery

Intravenous ketamine has been shown to provide postoperative analgesia in many clinical trials, in particular to reduce opioid consumption. The primary objective of this pilot study is to determine if multiple dosing over a three-day perioperative period with oral ketamine is a safe treatment method for acute pain after amputation surgery.

Three consented subjects (age 57-60 years) undergoing elective amputation of the lower extremity were included in the study (Institutional Review Board and Food and Drug Administration Investigational New Drug approved). An analgesic dose of oral ketamine (1.0 mg/kg) was administered one hour before surgery. Eight hours after the preoperative dose, a second dose was given. On the first postoperative day, subjects received oral ketamine (1.0 mg/kg) three times per day; and on the second postoperative day, this dose was reduced to 0.5 mg/kg three times per day. The primary outcome measure was the incidence of adverse events.

No serious and unexpected adverse events occurred; therefore, no subject required a dose reduction. The numerical rating score for postoperative pain of the body part adjacent to the amputation site ranged from 0.5-4.0. Morphine milligram equivalent opioid doses were in the range of 0-17.5 mg on the first postop day and 1.0-4.0 mg on the second postop day.

Our pilot study suggests that oral ketamine is safe to use at 1 mg/kg three times per day, as well as convenient for hospital floor and potential home use. Future studies will determine if the perioperative oral ketamine also reduces the incidence of chronic stump or phantom limb pain.