Kalla 2011.

Methods	Pharmacological interventions for acquired downbeat nystagmus Allocation: double‐masked Masking: double‐masked Exclusions: 0 Losses: 0 Design: cross‐over RCT
Participants	Country: Germany Number of participants randomised: 8 Age: mean 68 years ± 5.93, 58‐76 years Gender: 6 females, 2 males Aetiologies: degeneration (2), Arnold‐Chiari malformation (1), cryptogenic cerebellar ataxia (4), inflammation (1) Ocular motility condition: downbeat nystagmus Inclusion criteria: adult nystagmus Exclusion criteria: not specified
Interventions	Intervention 1: 4‐aminopyridine Dose: 10 mg Intervention 2: 3,4‐diaminopyridine Dose: 10 mg Duration: 1 day for intervention with 6‐day wash‐out period between interventions
Outcomes	Measurements: 3D video‐oculography, drug effects by participant recall Adverse events: Mild paraesthesia
Notes	Health economic costs: not reported Quality of life measures: not reported Funding: German Ministry of Education and Research Declaration of interests: authors declare no conflicts of interest Dates of study: not specified Trial registration ID: not specified
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomly assigned capsules of 10 mg of 3,4‐DAP or 4‐AP; they received 1 single capsule of either substance. There was a washout period of 6 days when no medication was given. One week later, the treatment was switched (i.e., they received a single capsule of the other substance)." Judgement comment: it was not reported how the allocation sequence was generated.
Allocation concealment (selection bias)	Low risk	Judgement comment: study was described as "double‐blind" and identical single 10 mg doses used so we judge it was likely that the allocation was concealed.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "...identical single 10‐mg doses of both aminopyridines were compared in our double‐blind study with crossover design" Judgement comment: although this information was only provided in the discussion section of the article we judge that masking of participants was likely to have been done with identical tablets.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "...identical single 10‐mg doses of both aminopyridines were compared in our double‐blind study with crossover design" Judgement comment: although this information was only provided in the discussion section of the article we judge that masking of outcome assessors was likely to have been done with identical tablets and description of the study as double‐masked.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Judgement comment: the article describes a study of 8 patients. Loss to follow‐up was not mentioned.
Selective reporting (reporting bias)	Unclear risk	No access to study protocol or trials registry entry.
Other bias	High risk	Additional 'Risk of bias' assessment for cross‐over study Was the cross‐over design suitable: probably Was there a carry‐over effect: uncertain, no analysis done. Was only first period data are available: no, first period data not available Was the analysis correct: unclear, no estimates of effect reported Comparability of results with those from parallel‐group trials: no parallel group trials