Study limitations
Sex, age, and other demographic characteristics did not predict response or remission, but suicide planning trended toward higher response rates (P = .083). This suggests that a more depressed subgroup can achieve greater benefit from the treatment than can less symptomatic patients, the investigators note.
A history of psychosis also trended toward better response to treatment (P = .086) but not remission.
The researchers note that study limitations include that it was retrospective, lacked a control group, and did not require patients to be hospitalized – so the study sample may have been less severely ill than in other studies.
In addition, most patients paid out of pocket for the treatment at $495 per infusion, and they self-reported their symptoms.
As well, the researchers did not assess adverse events, although nurses made follow-up calls to patients. Dr. Oliver noted the most common side effects of ketamine are nausea, vomiting, and anxiety.
Previous research has suggested that ketamine therapy is not linked to long-term side effects, such as sexual dysfunction, weight gain, lethargy, or cognitive issues, said Dr. Oliver.
The investigators point out another study limitation was lack of detailed demographic information, such as race, income, and education, which might affect its generalizability.
Concerns and questions
Pouya Movahed Rad, MD, PhD, senior consultant and researcher in psychiatry, Lund (Sweden) University, noted several concerns, including that the clinics treating the study participants with ketamine profited from it.
He also speculated about who can afford the treatment because only a few patients in the study were reimbursed through insurance.
Dr. Movahed Rad was not involved with the current research but was principal investigator for a recent study that compared intravenous ketamine to ECT.
He questioned whether the patient population in the new study really was “real world.” Well-designed randomized controlled trials have been carried out in a “naturalistic setting, [which] get closer to real-life patients,” he said.
He also noted that the median dose after clinician titration (0.93 mg/kg over 40 minutes) “may be considered very high.”
With regard to doses being titrated to achieve symptoms of partial dissociation, “there is no obvious evidence to my knowledge that patients need to develop dissociative symptoms in order to have antidepressant effect,” said Dr. Movahed Rad.
Finally, he noted that the finding that 28% of the participants were using illegal drugs “is worrying” and wondered what drugs they were taking; he also questioned why 81% of the study population needed to take antidepressants.
The study did not receive outside funding. Dr. Oliver is the founder of MindPeace Clinics, which specialize in ketamine therapeutics. Dr. Movahed Rad has reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.