The effect of magnesium infusion on rest cramps: randomized controlled trial.

This was a double-blind randomized placebo-controlled trial in independent, community-dwelling older adults with rest cramps. For the magnesium infusion arm, 24 participants were randomized; 22 participants were randomized to placebo. Participants were recruited in the Greater Vancouver area of British Columbia, Canada, and were selected to be free of major kidney or heart disease and able to complete cramp diaries.

Intravenous magnesium sulfate was given as 20 mmol (5 g) per infusion in 250 mL D5W over 4 hours on 5 consecutive days (Monday to Friday), compared with placebo infusion. The active regimen tested was magnesium sulfate, not oral supplementation.

Intravenous magnesium did not reduce rest cramp frequency versus placebo, so the intervention was not effective for cramp prophylaxis in this geriatric population. The primary outcome changed by -2.4 cramps per week in the magnesium group versus -1.7 in the placebo group (p = .51; 95% CI for the difference -3.1 to 1.7). Percentage change in cramps was also similar (-26.8% vs -21.3%; p = .71; 95% CI difference -35.0 to 23.9). Magnesium retention did not predict response, with no correlation between percent retention and change in cramp rate. Reported adverse events included infusion-site burning, facial flushing, and transient hypotension/lightheadedness in some magnesium recipients.

The trial was small and had limited power to detect modest benefits. Follow-up was short, centered on a 30-day pre- and post-infusion window, and results come from relatively healthy, independent older adults in one Canadian region, which limits generalizability. The diary-based cramp outcome and infusion tolerability issues also affect interpretation.