title: Effect of chlorzoxazone in patients with downbeat nystagmus: a pilot trial.
abstract: OBJECTIVE
  Downbeat nystagmus (DBN) is the most frequent form of acquired persisting fixation nystagmus with different symptoms such as unsteadiness of gait, postural instability, and blurred vision with reduced visual acuity (VA) and oscillopsia. However, different symptomatic therapeutic principles are required, such as 3,4-diaminopyridine and 4-aminopyridine, that effectively suppress DBN. Chlorzoxazone (CHZ) is a nonselective activator of small conductance calcium-activated potassium (SK) channels that modifies the activity of cerebellar Purkinje cells. We evaluated the effects of this agent on DBN in an observational proof-of-concept pilot study.
  
  
  METHODS
  Ten patients received CHZ 500 mg 3 times a day for 1 or 2 weeks. Slow-phase velocity of DBN, VA, postural sway, and the drug's side effects were evaluated. Recordings were conducted at baseline, 90 minutes after first administration, and after 1 or 2 weeks.
  
  
  RESULTS
  Mean slow-phase velocity significantly decreased from a baseline of 2.74°/s ± 2.00 to 2.29°/s ± 2.12 (mean ± SD) 90 minutes after first administration and to 2.04°/s ± 2.24 (p < 0.001; post hoc both p = 0.024) after long-term treatment. VA significantly increased and postural sway in posturography showed a tendency to decrease on medication. Fifty percent of patients did not report any side effects. The most common reported side effect was abdominal discomfort and dizziness.
  
  
  CONCLUSIONS
  The treatment with the SK-channel activator CHZ is a potentially new therapeutic agent for the symptomatic treatment of DBN.
  
  
  METHODS
  This study provides Class IV evidence that CHZ 500 mg 3 times a day may improve eye movements and visual fixation in patients with DBN.
authors: From the Department of Neurology and German Center for Vertigo and Balance Disorders, University Hospital Munich, Campus Grosshadern, Munich, Germany.
authors: Katharina
authors: K
authors: Feil
authors: Jens
authors: J
authors: Claaßen
authors: Stanislavs
authors: S
authors: Bardins
authors: Julian
authors: J
authors: Teufel
authors: Siegbert
authors: S
authors: Krafczyk
authors: Erich
authors: E
authors: Schneider
authors: Roman
authors: R
authors: Schniepp
authors: Klaus
authors: K
authors: Jahn
authors: Roger
authors: R
authors: Kalla
authors: Michael
authors: M
authors: Strupp
mesh_terms: D000368:Aged; D016009:Chi-Square Distribution; D002753:Chlorzoxazone / Q000627:therapeutic use*; D005133:Eye Movements / Q000187:drug effects; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009125:Muscle Relaxants, Central / Q000627:therapeutic use*; D009759:Nystagmus, Pathologic / Q000188:drug therapy* / Q000503:physiopathology*; D010865:Pilot Projects; D004856:Postural Balance / Q000187:drug effects; D018709:Statistics, Nonparametric; D016896:Treatment Outcome; D014792:Visual Acuity / Q000187:drug effects
chemical_list: D009125:Muscle Relaxants, Central; D002753:Chlorzoxazone