Fig. 3. Meta-analytical calculations comparing the blood levels of ketamine (pg/ml) and norketamine (pg/ml) in responders and non-responders to ketamine (n = 286, 9 studies).
*Responder = participant with at least 50% improvement in depression scores. **Blood levels of ketamine and norketamine were measured at the same timepoint for responders and non-responders in individual studies. However, the timepoints were not the same across all studies (varied from during the infusion to 24 h post-infusion). The specific timepoints were: Andrashko et al. (2020) = immediately post-infusion; Chen et al. (2021) = 200 min post-infusion; Diazgranados et al., (2010) = 190 min post-infusion; Farmer et al. (2020) = 190 min post-infusion; Grunebaum et al., (2017) = immediately post-infusion; Grunebaum et al., (2019) = immediately post-infusion; Lenze et al. (2016) = 24 h post-infusion; Milak et al. (2020) = area under the curve calculated as the sum of the blood levels at 50 and 80 min post-infusion; Siegel et al. (2021) = 24 h post-infusion.