Nitrous oxide as an adjunctive therapy in major depressive disorder: a randomized controlled double-blind pilot trial

This double-blind placebo-controlled between-subjects study (n=23) tested the antidepressant efficacy of inhaled nitrous oxide (50% N₂O|50% O₂ versus 100% O₂) in patients diagnosed with major depression (MDD). Across multiple treatment sessions administered across a period of 4 weeks, there were significant reductions in depressive symptoms in the acute response to treatment and accumulatively across sessions.

Abstract

“Objective: Major depressive disorder (MDD) is related to glutamatergic dysfunction. Antagonists of glutamatergic N-methyl-D-aspartate receptor (NMDAR), such as ketamine, have antidepressant properties. Nitrous oxide (N₂O) is also a NMDAR antagonist. Thus, this study aimed to evaluate the effects of augmenting antidepressant treatment with N₂O.

Methods: This double blind, placebo-controlled randomized parallel pilot trial was conducted from June 2016 to June 2018 at the Hospital das Clínicas, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo. Twenty-three subjects with MDD (aged 18 to 65, on antidepressants, with a score > 17 on the 17-item-Hamilton Depression Rating Scale [HAM-D₁₇]) received 50% N₂O (n=12; 37.17±13.59 years) or placebo (100% oxygen) (n=11; 37.18±12.77 years) for 60 minutes twice a week for 4 weeks. The primary outcome was changes in HAM-D₁₇ from baseline to week 4.

Results: Depressive symptoms improved significantly in the N₂O group (N₂O: from 22.58±3.83 to 5.92±4.08; placebo: from 22.44±3.54 to 12.89±5.39, p < 0.005). A total of 91.7% and 75% of the N₂O group subjects achieved response (≥ 50% reduction in HAM-D₁₇ score) and remission (HAM-D₁₇ < 7), respectively. The predominant adverse effects of N₂O treatment were nausea, vomiting, and headache.

Conclusion: N₂O treatment led to a statistically significant reduction in HAM-D₁₇ scores compared to placebo.”

Authors: Mara C. Guimarãe, Tiago M. Guimaraes, Jaime E. Hallak,  João Abrão & João P. Machado-de-Sousa

Summary

Introduction

Major depressive disorder (MDD) is the fifth leading cause of disability worldwide and the second leading cause of disability taking into account only non-communicable diseases. It causes a high economic burden, reduced quality of life, increased mortality and morbidity associated with other chronic medical conditions, as well as increased suicide rates.

In animal models of depression, antagonists of N-methyl-D-aspartate subtype receptors of glutamate reversed the behavioral inhibition induced by depression. In pre-clinical studies, ketamine had rapid-onset antidepressant effects.

Ketamine may also act on other mechanisms beyond its action on NMDAR, including the mammalian target of rapamycin pathway, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and glycogen synthase kinase 3.

Nitrous oxide (N2O) is an anesthetic that acts as an NMDAR antagonist, which indicates a possible antidepressant effect. It also has analgesic and anxiolytic effects through activation of gamma-aminobutyric acid type A receptors and inhibition of pre-synaptic 5-HT1A serotonin autoreceptors.

In 2015, Nagele et al.23 published a proof-of-concept trial evaluating the effect of N2O inhalation in treating treatment-resistant depression. N2O was superior to placebo in improving depressive symptoms and was associated with a response rate of 20%.

The available data suggest that glutamatergic modulators have antidepressant potential, and a randomized controlled pilot trial was conducted to investigate the efficacy of N2O in reducing depressive symptoms.

Methods

To increase the number of eligible subjects, the eligibility criteria were adjusted to include subjects on any class of antidepressant, alone or in combination.

Participants were men and women aged 18 to 65 years with MDD who were on antidepressant treatment without dose adjustments for at least 4 weeks. Exclusion criteria included being bipolar, psychotic, or substance use disorder, and having chronic lung diseases.

Interventions

Subjects were randomly allocated to receive either N2Oor placebo and were given N2O inhaled through a disposable nasal mask coupled to a portable device for nitrous oxide/oxygen sedation and analgesia.

A 3 hour session was performed with 100% oxygen inhalation or N2O inhalation. Physiological parameters were continuously monitored during the session as a safety measure.

Outcomes

Changes in HAM-D17 and BDI-II scores, therapeutic response and remission at the end of the trial, effects on suicidal ideation, manic symptoms, and adverse effects were assessed.

Randomization and blinding

Subject allocation was done using a randomization plan generated at Randomization.com. Two collaborators were responsible for setting the equipment parameters to provide 50% N2O or 100% oxygen according to the randomization plan.

Statistical analysis

We performed repeated measures analysis of variance for HAM-D17 scores considering the factors time, drug, and time-drug interaction, and applied independent sample t-tests where significant time-drug interactions were detected.

We used Z partial square (Z2 p) tests to assess the effect size of the differences found between the two groups, and classified values according to Maroco’s method.

We calculated the rate of remission and therapeutic response in each group at the end of the trial and compared the rates of both groups using Fisher’s exact test.

Ethics statement

The subjects gave written informed consent to participate in the study, which was approved by the HCFMRP-USP board of ethics.

Results

The trial was conducted between August 2016 and June 2018. Eleven subjects were randomly allocated to the placebo group and 12 were randomly allocated to the N2O group.

The 21 subjects who completed the eight sessions were included in the analysis of outcome measures.

Demographic and clinical characteristics

There were no significant differences between the two groups regarding age, sex, and severity of symptoms.

HAM-D17

The time-drug interaction effect was significant, with the greatest effect in the N2O group. The post-inhalation assessment showed a significant difference with the placebo group, but this effect disappeared in sessions 5 and 6 until reappearing in the final two sessions.

Within each session, both groups showed significant reductions in post-vs. pre-inhalation scores, but only the N2O group reached the remission range. Likewise, only the N2O group reached means within the therapeutic response range compared to baseline scores.

BDI-II

Significant reductions in BDI-II scores occurred in both groups, with greater reductions in the N2O group. There were no time-drug interaction effects, and 66.7% of subjects in the N2O group reached remission criteria vs. 33.3% of subjects in the placebo group.

YMRS

There were no significant differences in YMRS variation over time in either group, and no subject had a total YMRS score of 4 12.

Adverse effects

The mean inhalation time per session in the N2O group was 59.164.93 minutes, and four subjects required temporary inhalation interruptions in 12 different sessions due to nausea, vomiting, emotional discomfort, and regurgitation.

In the placebo group, 78 sessions were performed with a mean inhalation time of 59.9660.34 minutes. One subject had increased blood pressure in one session.

Discussion

In this preliminary study, the antidepressant effect of N2O was superior to placebo based on HAM-D17 scores. The antidepressant effect of N2O was evident in 91.7% of the patients in the N2O group and 75% of the patients in the N2O group who achieved remission.

The antidepressant effect of N2O was acute and cumulative. The effects of N2O were greater than those of the placebo group in all sessions, but only statistically significant in the fourth, seventh, and eighth sessions.

Other glutamatergic modulators, such as memantine, have shown no antidepressant effects. Ketamine and N2O may differ in their actions because they increase concentrations of nitric oxide, a messenger that has been linked to antidepressant, anxiolytic, and analgesic effects.

The BDI-II score decreased in the N2O and placebo groups, but did not reflect the same intensity of symptom improvement as the HAM-D17 score. This might be because the BDI-II is a self-rating inventory, and patients may perceive their symptoms as more severe than clinicians.

The placebo group showed similar results to the active drug group in terms of improvement in depressive symptoms, although there was no significant difference between groups. The placebo effect may have been due to the care and attention received by the participants.

Although clinical evaluation and subjective reports indicated that dissociative and psychotomimetic effects were neither frequent nor intense among participants, no standardized tests were used for this purpose.

Regarding drug tolerability, subjects who received N2O reported tranquility, relaxation, and a ”sense of well-being”. Only one subject required temporary interruption or early discontinuation in most sessions due to adverse effects (nausea and vomiting), and the remaining five discontinued inhalation in less than half of the sessions.

Our study has certain limitations, including the small sample size, short duration, lack of post-treatment assessments and intention-to-treat analysis, and the use of active drug controls. Long-term follow-up trials are needed to establish whether the potential benefits of N2O for depression persist over time.

The most commonly used depression rating scales were not appropriate to detect changes in symptom severity that occurred within hours or a few days. A visual analogue scale or even the 6-item-Hamilton Depression Rating Scale might have been more appropriate.

We did not find any data in the literature about the best concentration of N2O to be used in patients with depressive disorders. Future studies should assess the effects of different concentrations and should also determine the frequency of N2O administration.

This trial of N2O as a treatment for depression is the second to apply semiweekly doses for a month in only non-treatment-resistant patients.

In patients with persistent symptoms of depression, 50% N2O administered twice a week for one month led to reductions in depressive symptoms, but not the BDI-II.