Fifty-two TRD subjects received an open-label infusion of ketamine ( 0.5 mg/kg over 40 minutes ) , and , four to six hours post-infusion , were randomized to either flexible-dose ( 100-200mg / day ) riluzole or placebo in the following proportions : Family History Positive ( FHP ) riluzole ( n = 10 ) , FHP placebo ( n = 9 ) , Family History Negative ( FHN ) riluzole ( n = 16 ) , and FHN placebo ( n = 17 ) .