Dunn 1993.

Methods	Double‐blind RCT of cross‐over design, carried out in 2 centres in the UK
Participants	28 participants (aged 51 to 82 years) selected from 2 general practices on the basis that they received regular repeat prescriptions for quinine
Interventions	Quinine sulphate 300 mg daily or placebo for a 30‐day treatment period, followed by a 3‐day washout period before cross‐over to a second 30‐day treatment period
Outcomes	Number of cramp nights, adverse events
Notes	Results were invalidated by a significant carry‐over effect due to a short washout period
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "...a randomised double blind cross‐over trial..." Comment: details of randomisation not provided
Allocation concealment (selection bias)	Unclear risk	No details regarding allocation concealment are provided
Blinding (performance bias and detection bias) All outcomes	Unclear risk	No details regarding methods of blinding are provided
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Of the 28 recruited, 25 completed the two parts of the trial and filled in diary cards successfully. Two of the three drop‐outs did so because of severe cramps during placebo period" Comment: 1 drop‐out not accounted for
Selective reporting (reporting bias)	Low risk	Both the intended outcome measures were addressed in the results and analysis
Other bias	High risk	Cross‐over trial with only 3 days allocated to washout period rendered a significant carry‐over effect of treatment