Magnesium levels after magnesium-containing cathartics

To determine the effect on serum Mg++ levels of oral Magnesium-containing cathartics (MgCC) used in the treatment of suspected drug overdose, a prospective, non-randomized study of 24 cases of suspected drug overdose was conducted. Ten cases admitted to the observation unit were assigned to the single dose MgCC group. Fourteen cases admitted to either the ICU or the observation unit were assigned to the multiple dose MgCC group. Single dose cases received 30 gm of magnesium sulfate (MgSO4) at 0 hours. Multiple dose cases received 3 30 gm doses of MgSO4 at 0, 4, and 8 hours. Mg++ levels were measured prior to each MgSO4 dose and 1 and 4 hours after the final dose in both groups. In the single dose group, there was no difference between baseline Mg++ levels and post MgSO4 levels, and only 2/10 developed slightly elevated levels (2.2, 2.3 mEq/L). In the multiple dose group, levels increased and remained significantly higher than baseline after the second MgSO4 dose, and 9/14 developed elevated levels (2.2 to 5.0 mEq/L). All patients who developed elevated Mg++ levels had normal BUN and creatinine values. When the single and multiple dose groups were compared, baseline Mg++ levels were no different (1.68 +/- 0.21 vs 1.69 +/- 0.24, p = 0.952), but peak Mg++ levels were significantly higher in the multiple dose group (1.80 +/- 0.31 vs 2.61 +/- 0.86, p = 0.004). Cases that developed hypermagnesemia had slightly higher baseline Mg++ levels (1.78 +/- 0.22 vs 1.60 +/- 0.19 mEq/L, p = 0.041). In the multiple dose group, higher peak Mg++ levels were noted in cases involving ingestions of anticholinergic or opioid drugs (2.83 vs 1.98, p = 0.025). Hypermagnesemia developed in some cases with normal renal function, blood pressure, and urine output. We conclude that significant hypermagnesemia can occur rapidly after use of multiple dose Mg++ cathartics in standard doses in patients with normal renal function.