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. 2012 Sep 12;2012(9):CD009402. doi: 10.1002/14651858.CD009402.pub2

Frusso 1999.

Methods Double‐blind RCT of cross‐over design
Participants 45 non‐pregnant rest cramp sufferers > 18 years (mean age 61.6 years) having a normal neurologic exam and at least 6 leg cramps in a 4‐week placebo run‐in. Recruitment from a single large university‐based Argentinean family practice clinic.
Interventions Magnesium citrate 900 mg pill (approx. 100 mg elemental magnesium) twice daily or similar tasting and appearing placebo, each for 4 weeks. Four‐week placebo run‐in and 4‐week washout between treatments.
Outcomes Primary: Number of cramps in treatment period. Secondary: Cramp duration by 4 ordinal categories (< 5 minutes, 5 to 10 minutes, 10 to 30 minutes, > 30 minutes). Cramp intensity by “analog scale”. Sleep disturbance on a 0 to 10 scale with 0 = “no sleep disturbance” and 10 = “could not sleep because of the cramps”. Adverse events.
Notes Published. Independent funding. The 4‐week placebo run‐in was pre‐randomization. Unclear what the range for the analog scale of intensity is (assumed 0 to 10). Cramp duration was recorded by ordinal category but reported with a mean and standard deviation in minutes.
Risk of bias
Bias Authors' judgement Support for judgement
Random sequence generation (selection bias) Unclear risk Quote: “Patients randomly received magnesium or placebo...”
Comment: unclear how randomization was performed
Allocation concealment (selection bias) Unclear risk Quote: “The codes were inside a sealed envelope opened at the end of the analysis.”
Comment: Unclear who allocated subjects and maintained the blinding
Blinding (performance bias and detection bias) 
 All outcomes Low risk Quote: “Each pill contained 900 mg of magnesium citrate or matched placebo (same appearance and taste).”
Comment: Satisfactory blinding
Incomplete outcome data (attrition bias) 
 All outcomes Low risk 3/45 subjects withdrew with reasons given. It is not stated which intervention they were receiving at the time or how their data were dealt with.
Comment: Probably satisfactory as the number of dropouts was small.
Selective reporting (reporting bias) Unclear risk No indication of selective reporting for clinical endpoints (although urine for magnesium was collected and not reported). Duration of cramps was measured on a 4‐point ordinal scale but results were reported with the mean duration and standard deviation measured in minutes as though they were a continuous variable
Cramp diary (recall bias) Low risk Diary used
Other bias Low risk No obvious other bias