In 2013, Drs. Jaime Hallak, Joao Paulo Maia-de-Oliveira and associates in Ribeirao Preto, Brazil, published results from a randomized controlled trial of intravenous nitroprusside in schizophrenia. Two Canadian researchers from the University of Alberta collaborated on the trial. This study was the first to find that sodium nitroprusside, a treatment for hypertensive crises, has a rapid and prolonged effect on both positive and negative symptoms in patients with acute psychosis. The presumed mechanism is enhancement of nitric oxide in the central nervous system, which may modulate the NMDA receptor-cGMP pathway. In normotensive patients, nitroprusside has minimal effect on blood pressure, and cyanide accumulation is a theoretical concern but occurs only after 72 hours or more of continuous infusion. In treating schizophrenia, the infusion dose is 0.5 mg/kg/minute for four hours.
In the initial trial published in JAMA Psychiatry, Hallak’s team used the Brief Psychiatric Rating Scale and the negative subscale of the Positive and Negative Syndrome Scale (PANSS) as outcome measures. A significant effect on certain components occurred within the first two to three hours of treatment, and improvement endured for four weeks. All the patients were also receiving an antipsychotic other than clozapine.
I met with Jaime, Joao Paulo and their team at the University of Sao Paulo Hospital in Ribeirao Preto and was able to observe a treatment. When I first met the patient, whose infusion had begun 10 minutes before, she appeared anxious and tended to avoid eye contact. When I returned 90 minutes later, she was engaged in an art activity and was eager to show me what she had created. She smiled broadly and even tested her English vocabulary a little. The researchers said that they often see an improvement in the patients’ affect over the course of the infusion, and they are trying to find ways to measure this more objectively. Although data are still limited, the effect in treatment-resistant patients tends to be more delayed.
Further studies of nitrous prusside in Ribeiroa Preto are underway, including for treatment-resistant patients, some on clozapine, and on neurophysiologic effects as detected with fMRI and event-related potential. Because the benefits of the treatment begin to wane after four weeks, they are planning a controlled trial of weekly nitrous prusside infusions for four weeks followed by 60 days of observation.