Garrison 2011a.

Study characteristics
Methods	Double‐blind, parallel‐group RCT
Participants	46 non‐pregnant rest cramp sufferers (mean age 69.3 yrs) with at least 8 cramps in a 30 day baseline diary. Recruitment from posters and pamphlets in 21 Canadian (Richmond, British Columbia) family practitioner offices and also by newspaper advertisement
Interventions	5 days consecutive 4‐hour IV infusions of 250 ml 5% dextrose in water either with 20 mmol of magnesium sulphate (treatment group) (n = 24) or without magnesium sulphate (control group) (n = 22) (20 mmol magnesium sulphate = 486 mg elemental magnesium)
Outcomes	Primary: Change in the number of cramps per week from baseline at 30 days Secondary: Change in the number of cramps per week from baseline at 90 days Percentage change in cramps per week. Cramp pain (1 to 10 interval scale) Cramp duration on a 3‐point ordinal scale (1 = < 1 minute, 2 = 1 to 5 minutes, 3 = > 5 minutes) 24‐hour urinary magnesium on days 1 and 5 to determine % retention of infused magnesium
Conflicts of interest	No mention of conflict of interest
Funding	Independent funding
Notes	Published. Conducted from January 2007 to October 2008
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Randomization, using a computer generated random allocation sequence without any blocking or stratification was carried out by the hospital pharmacist dispensing the study drugs according to a series of opaque allocation envelopes kept in the pharmacy." Comment: satisfactory randomization
Allocation concealment (selection bias)	Low risk	Quote: "All investigators, study nurses and subjects were blinded as to treatment allocation." Comment: satisfactory allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: 1) "Active and Placebo solutions were indistinguishably clear and colorless." 2) "Subjects had been told that IV site discomfort was possible with both placebo and Mg infusions. While generally it was considered that blinding was reasonable, the sensation of burning at the IV site, coupled with the additional saline dilution in some Mg participants, could have compromised the blind to some extent (presumably favouring the intervention)."
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Diary completed by participants blinded to the intervention but blinding to the intervention was at an unclear risk of bias. To avoid compromising the blind, all participants underwent urine collection identically, and results of urine testing (along with baseline serum Mg) were sequestered from investigators until trial completion.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts or losses to follow‐up. ITT analysis
Selective reporting (reporting bias)	Low risk	Did not process urine samples for magnesium of those getting placebo (although did a reasonable job collecting urine samples from all participants to make sure the blinding was not broken). Report described severity and duration of cramps only as not being different (i.e. no numbers given); however, trial authors made these data available.
Cramp diary (recall bias)	Low risk	Diary used
Other bias	Low risk	No obvious other bias