It is used as a cough suppressant, although it can sometimes be used, medicinally, as a pain reliever, and is also used as a recreational drug.Quinidine sulfate affects the way the heart beats, and is generally used in people with certain heart rhythm disorders. It is also used to treat malaria. Quinidine sulfate, as a metabolic inhibitor, "increases plasma levels of dextromethorphan by competitively inhibiting cytochrome P450 2D6, which catalyzes a major biotransformation pathway for dextromethorphan," enabling therapeutic dextromethorphan concentrations.Dextromethorphan/quinidine is a combination of these two generic drugs, and is the first FDA-approved drug for the treatment of PBA, approved on October 29, 2010.For this multicenter study, the "Objectives...[were] to evaluate the safety, tolerability, and efficacy of two different doses of AVP-923 [Dextromethorphan/quinidine combination]...when compared to placebo." The conditions and results of that study are as follows:

At one study site, a total of 326 participants received one of three dose options. "METHODS: In a 12-week randomized, double-blind trial, ALS and MS patients with clinically significant PBA" were given a twice-daily dose of one of the following:
placebo (N=109)
dextromethorphan hydrobromide 30 mg/quinidine sulfate 10 mg (N=110)
Nuedexta – dextromethorphan hydrobromide 20 mg/quinidine sulfate 10 mg (N=107)283 patients (86.8%) completed the study. The number of PBA episodes (laughing, crying or aggressive outbursts) were 47% and 49% lower (based on the trials outcome measures), respectively, for the drug-combination options than for the placebo. The "mean CNS-LS scores" decreased by 8.2 points for both drug-combination options, vs a decrease of 5.7 points for the placebo.
The clinical effect of PBA can be severe, with unremitting and persistent symptoms that can be disabling to patients, and may significantly affect quality of life for caregivers. Social impact
While not as profoundly disabling as the physical symptoms of these diseases, PBA may significantly influence individuals social functioning and their relationships with others. Such sudden, frequent, extreme, uncontrollable emotional outbursts may lead to social withdrawal and interfere with activities of daily living, social and professional pursuits, and reduce overall healthcare. For example, patients with ALS and MS are often cognitively normal. However, the appearance of uncontrollable emotions is commonly associated with many additional neurological disorders such as attention deficit/hyperactivity disorder, Parkinsons disease, cerebral palsy, autism, epilepsy, and migraines. This may lead to avoidance of social interactions for the patient, which in turn impairs their coping mechanisms and their careers. Depression
PBA may often be misdiagnosed as clinical depression or bipolar disorder; however, many clear distinctions exist. In depressive and bipolar disorders, crying, anger or laughter are typically indicative of mood, whereas the pathological displays of crying which occur in PBA are often in contrast to the underlying mood, or greatly in excess of the mood or eliciting stimulus. In addition, a key to differentiating depression from PBA is duration: PBA episodes are sudden, occurring in an episodic manner, while crying in depression is a more sustained presentation and closely relates to the underlying mood state.