• Change in the frequency of leg cramps per week (active versus placebo) over the first 30 days post infusions compared to the 30 days prior to randomization (as recorded in patient diaries). [ Time Frame: See above ] [ Designated as safety issue: No ]
  

• Assessment of magnesium status at trial entry as determined by 24 hour fractional excretion of magnesium on day 1 of infusions. [ Time Frame: Unspecified ] [ Designated as safety issue: No ]
  
• Subjective assessment as to whether cramps were unchanged, more, or less frequent /painful/"bothersome" over the 3 months. following infusions. [ Time Frame: See above ] [ Designated as safety issue: No ]
  
• Overall quality of life changes as measured by an SF36 questionnaire. [ Time Frame: Unspecified ] [ Designated as safety issue: No ]
  

Drug: Intravenous Infusion of Magnesium Sulfate
See Detailed Description.

Subjects will be randomized to receive 5 days of 4 hour IV infusions of D5W either with or without 20 mmol magnesium sulfate added. Twenty four hour urinary excretion of magnesium will be determined on the first day of infusions to assess whether magnesium deficiency is present. Ten normal controls will also undergo a single infusion and collection of urine to serve as a comparison group for the urinary excretion data.

Inclusion Criteria:

• ≥2 leg or foot cramps per week in a 4 week run-in diary

Exclusion Criteria:

• eGFR<50
• Neurologic disease
• Pregnancy
• Heart block
• Bradyarhythmia without pacemaker
• Digoxin use
• Liver disease
• Addison's disease
• History of MI
• CHF
• Absence of detectable reflexes