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