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Hypermagnesemia

By

Allison J. Stewart

, BVSC (Hons), MS, DACVIM-LA, DACVECC, The University of Queensland

Last full review/revision Sep 2013 | Content last modified Sep 2013

Hypermagnesemia (plasma Mg concentration >2 mg/dL [1.1 mmol/L]) is a rare condition reported only in monogastric animals. Horses show signs of sweating and muscle weakness within 4 hr of receiving excessive oral doses of magnesium sulfate administered as a cathartic for treatment of large-intestinal impactions. This is followed by recumbency, tachycardia (120 bpm), and tachypnea (60 breaths/min). Signs subside after treatment with slow IV infusion of calcium gluconate (23% solution). Hypermagnesemia has been reported in cats with renal failure that were receiving IV fluid therapy. As plasma Mg concentrations exceed 2.5 mmol/L, there may be ECG changes with prolongation of the PR interval; at 5 mmol/L, deep tendon reflexes disappear, followed by hypotension and respiratory depression. Cardiac arrest may occur with blood Mg levels >6.0–7.5 mmol/L.

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Disorders of Calcium Metabolism
Parturient paresis, also called milk fever, can cause flaccid paralysis and circulatory collapse in dairy cows during or soon after parturition. Serum calcium levels must be corrected as soon as possible by administering intravenous calcium gluconate slowly over 10-20 minutes. Which of the following signs is most consistent with too-rapid administration of intravenous calcium administration? 
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