Mag-SR Disease Interactions

The parenteral administration of magnesium is contraindicated in patients with heart block or heart damage from myocardial infarction. These conditions may be exacerbated during magnesium infusion. High serum levels of magnesium (> 4.5 mEq/L) can cause sinus bradycardia, AV block, nodal rhythms, and bundle branch block, which can progress to asystole and cardiac arrest at magnesium levels of approximately 14 mEq/L to 15 mEq/L. If parenteral magnesium is used in patients with preexisting conduction disturbances, it should be infused at a slower rate, and cardiac function and serum magnesium level should be closely monitored. The usual precautionary measures should be observed to prevent hypermagnesemia, and IV calcium salts (e.g., calcium gluconate), pressors, cardiac pacemakers, and equipment for supportive care should be immediately available in case of acute magnesium intoxication.

Magnesium is eliminated by the kidney. The serum concentration of magnesium is increased in patients with renal impairment. Magnesium toxicity includes CNS depression, muscular paralysis, respiratory depression, hypotension and prolonged cardiac conduction time. Disappearance of the patellar reflex is a useful clinical sign of magnesium intoxication. Therapy with magnesium should be administered cautiously and dosages should be modified in patients with compromised renal function. Clinical monitoring of serum magnesium levels is recommended.