Myoclonic movements and pain on injection are common problems during induction of anesthesia with etomidate (Amidate®, Bedford Labs). Researchers from Turkey, investigating ways to pre-treat the pain, randomly assigned 100 patients to four groups: ketamine 0.2 mg/kg, ketamine 0.5 mg/kg, magnesium sulfate 2.48 mmol, and normal saline.
Pre-treatment with magnesium sulfate reduced the incidence and intensity of myoclonic movements; 19 patients (76%) had none. By contrast, 18 patients (72%) in the 0.5-mg ketamine group, 16 (64%) in the 0.2-mg ketamine group, and 18 (72%) in the control group had myoclonic movements.
After magnesium treatment, 64% of patients experienced mild-to-moderate pain associated with the etomidate injection. However, both doses of ketamine provided better pain relief; at the lower dose, 44% of the patients experienced pain, and at the higher dose, only 28% of patients had pain.
Despite the better analgesia, however, ketamine did not effectively reduce myo-clonus. At the higher dose, it caused mild-to-severe sedation in all patients and respiratory depression in 80% of patients.
The researchers say that this is the first reported clinical study showing that pre-treatment with magnesium reduces myoclonic muscle movements without any adverse effects.