Magnesium plays many important roles in structure, function, and metabolism and is involved in numerous essential physiologic reactions in the human body. Supplemental magnesium has been used extensively by patients for cardiovascular disease, diabetes, osteoporosis, asthma, and migraines, although most individuals consume adequate levels in their diet (Institute of Medicine 2001). Patients with a history of these illnesses may be supplementing with magnesium and therefore should be questioned.
The most obvious pain-related consideration in treating a patient taking magnesium supplements has to do with its effect on muscle relaxants in the operating room. The mineral can potentiate the effects of non-depolarizing skeletal muscle relaxants such as tubocurarine. Therefore, it may be advisable to ask patients about their magnesium usage preoperatively to avoid complications during certain interventional procedures performed in the operating room (Hendler and Rorvik 2001).
It should be noted that when caring for obstetrical patients (typically out of the realm of pain practitioners), one must be aware of the effects of magnesium sulfate in the patient undergoing cesarean section. Literature suggests that the duration of action of relaxant anesthetics, such as mivacurium, may be affected by subtherapeutic serum magnesium levels (Hodgson et al. 1998).
Magnesium may also interfere with the absorption of antibiotics such as tetracyclines, fluoroquinolones, nitrofurantoins, penicillamine, angiotensin-converting enzyme (ACE) inhibitors, phenytoin, and histamine (H2) blockers. Absorption problems can be ameliorated by not taking doses of magnesium within 2 h from these other medications (Tatro 1999, Shiba et al. 1995, Naggar and Khalil 1979, Osman et al. 1983). The mineral may also make oral hypoglycemics, specifically sulfonylureas, more effective when used, thus increasing the risk of hypoglycemic episodes (Kivisto and Neuvonen 1992).
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