Safety and Efficacy of Adjuvant Low-Dose Ketamine Therapy for Patients with Sickle Cell Disease

Opioids are the mainstay of therapy for painful vasoocclusive crises (VOCs) in sickle cell disease (SCD). For some patients, opioid-induced hyperalgesia caused by activation of N-methyl-D-aspartate (NMDA) receptors has been considered to contribute to poor analgesia. Ketamine, an NMDA receptor antagonist, could be a useful adjunct therapy; however safety concerns remain with its use. We examined records of SCD patients at our institution who received ketamine as an adjuvant to opioids at the discretion of anesthesia pain services over the past 4 years. We sought to explore the safety of ketamine and determine its effect on daily opioid requirement in SCD patients hospitalized for VOCs.

The Institutional Review Board at Children's National Medical Center approved this study. A retrospective case-crossover study was conducted through review of the electronic medical record. For each patient we selected 2-paired hospitalizations occurring within 2 years of each other. One hospitalization where the patient received low-dose ketamine infusion in addition to opioid patient controlled analgesia (PCA), and a second hospitalization where the same patient received opioid PCA alone. We compared clinical characteristics of hospitalizations where patients did or did not receive ketamine. Exploratory bivariate analysis (paired t-test and McNemar's test) was used to compare variables between the pairs.

Thirty-three patients were identified to have at least 2 hospitalizations for VOC within 20 months of each other where they received adjuvant ketamine infusion during one, while not during the other. Average age was 15.6 ± 3.4 years, 67 % were females, and 36 % were on hydroxyurea therapy. SCD genotypes included homozygous SS 70%, SC 24 %, S-beta-zero thalassemia 3%, and S-beta-plus thalassemia 3%. Mean number of admissions in the 6 months prior to the ketamine hospitalization was 2 (range 0–5) and 64 % had ≥ 2 prior admissions within 6 months. Ketamine dose was 0.1 mg/kg/h for all patients except one who briefly received 0.15 mg/kg/hr. During the ketamine and opioid PCA hospitalization patients reported overall higher pain scores (6.53 vs. 5.94 out of 10; p = 0.0356), required higher doses of opioid (0.0395 mg/kg/hr vs. 0.0323 mg/kg/hr; p = 0.0038), and had a longer length of stay (LOS) (5.6 vs. 4.4 days; p =0.0148) as compared to the PCA alone hospitalization. Patients were more likely to have a diagnosis of acute chest syndrome (ACS) at some point during the ketamine and opioid PCA hospitalization (42% vs. 15 %; p = 0.0126) as compared to the opioid PCA alone hospitalization. Patients were more likely to be treated with additional adjuvant pain control agents (diazepam, lorazepam, gabapentin, pregabalin, amitripyline, or duloxetine) during the ketamine and opioid PCA admission as compared with opioid PCA alone admissions (45% vs. 9% p = 0.0013). Rates of red blood cell transfusion and ICU transfer were not different between the hospitalizations. In 3 patients ketamine was discontinued due to vivid dreams delusions, or dizziness. Nausea, pruritis, sedation, and use of complementary therapies were similar between hospitalizations.

We did not observe an opioid sparing effect of ketamine infusion as hypothesized in this group of frequently hospitalized patients. Low-dose ketamine is a safe adjuvant medication for SCD patients hospitalized for VOCs. Higher opioid use during ketamine and opioid PCA admissions is likely due to patients experiencing more severe VOCs as indicated by higher pain scores involving multiple sites, higher rates of ACS, and longer LOS. These severity measures may have contributed to the decision of the pain medicine service to add low-dose ketamine infusion to standard opioid PCA in this retrospective sample. Finally, VOCs in this group of frequently admitted individuals may represent chronic pain which is known to be minimally responsive to most pharmacologic therapies. Patients receiving ketamine appear to be using additional adjuvant pain agents and may be underutilizing hydroxyurea. Prospective randomized studies of adjuvant ketamine therapy in patients with SCD are warranted to determine true efficacy.

Off Label Use: Ketamine is a non-barbiturate phencyclidine derivative that is approved for use as a surgical anesthetic. It is not approved for use in pain management, however is commonly used in low-doses as an adjunct to traditional pain control therapies.