The combination of dextromethorphan and quinidine is used to treat pseudobulbar affect (PBA; a condition of sudden, frequent outbursts of crying or laughing that can not be controlled) in people with certain conditions such as amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease; condition in which the nerves that control muscle movement slowly die, causing the muscles to shrink and weaken) or multiple sclerosis (a disease in which the nerves do not function properly and patients may experience weakness, numbness, loss of muscle coordination and problems with vision, speech, and bladder control). Dextromethorphan is in a class of medications called central nervous system agents. The way it works in the brain to treat PBA is not known. Quinidine is in a class of medications called antiarrhythmics. When combined with dextromethorphan, quinidine works by increasing the amount of dextromethorphan in the body.