Intravenous ketamine is effective for treatment-resistant bipolar depression, with dosing typically based on actual body weight. In a retrospective analysis of 22 inpatients, doses recalculated using formulas for lean body mass, ideal body weight, and body surface area were compared between responders and nonresponders. Body surface area-normalized doses ranged from 17.63 to 23.09 mg/m² in nonresponders and 15.73 to 23.89 mg/m² in responders. Lean body mass and ideal body weight recalculations at 0.5 mg/kg yielded lower relative doses, especially among nonresponders, suggesting potential underdosing. These preliminary findings do not support alternative dosing formulas over actual body weight, but replication in larger controlled studies is warranted.
Impulsive behaviors are common in major depressive disorder and bipolar disorder, raising suicide risk and mood instability. Ketamine, an NMDA receptor antagonist, can produce rapid antidepressant and antisuicidal effects, and magnesium given with low-dose NMDA antagonists reduces anxiety- and depression-like behaviors in animals. This observational study of 49 inpatients with treatment-resistant mood disorders measured impulsivity with the Barratt Impulsiveness Scale (BIS-11) and magnesium levels before and during a four-week course of eight ketamine infusions. Magnesium ion concentration during treatment was not associated with changes in BIS-11 scores. The findings provide no evidence for a relationship between magnesium levels and impulsivity during ketamine therapy.