HYPERMAGNESAEMIA

    DEFINITION

    A serum magnesium concentration above the normal range (typically 0.8
    to 1.2 mmol/L, 1.6 to 2.4 mEq/L, 2.0 to 2.6 mg/dL).

    TOXIC CAUSES

    States of magnesium excess usually result from overzealous therapeutic
    administration of magnesium or from conventional doses in the presence
    of impaired renal function.

    NON-TOXIC CAUSES

    Adrenal insufficiency
    End-stage renal disease
    Familial benign hypocalciuric hypercalcaemia.
    Rhabdomyolysis

    CLINICAL FEATURES

    Magnesium reduces neuromuscular transmission and acts as a central
    nervous system depressant.  Nausea usually appears at 3 to 5 mEq/L. 
    Sedation, hypoventilation with respiratory acidosis, decreased deep
    tendon reflexes and muscle weakness appear at 4 to 7 mEq/L. 
    Hypotension, bradycardia and diffuse vasodilatation appear at 5 to 10
    mEq/L. Respiratory paralysis occurs at 10 to 15 mEq/L.

    DIFFERENTIAL DIAGNOSIS

    Bradycardia due to other causes (e.g. beta-adrenoceptor antagonists,
    digoxin, myocardial infarction).
    Disturbance of consciousness due to other causes (e.g. drug overdose).
    Muscle weakness due to other causes (e.g. muscular dystrophies). 

    RELEVANT INVESTIGATIONS

    Serum electrolytes, blood urea, creatinine, glucose and arterial blood
    gases are helpful in determining the diagnosis and in evaluating the
    severity of this disorder.  An ECG may be indicated to assess any
    cardiac dysrrhythmias.

    TREATMENT

    Treatment of hypermagnesaemia is directed firstly at removal of the
    source of magnesium and secondly at enhancing removal if the serum
    concentration of magnesium poses a threat to survival.  Infusion of
    calcium will produce a rapid but short-lived reduction in the serum
    magnesium and often dramatic improvement in the patient's clinical
    condition.  High serum concentrations of magnesium in the presence of
    impaired renal function may require haemodialysis.

    CLINICAL COURSE AND MONITORING

    Magnesium concentrations should be monitored during therapeutic
    intervention.  If the concentration does not return to the normal
    range, further correction may be necessary.  Fluid balance,
    electrolytes, cardiac status and acid-base balance should also be
    monitored.

    LONG-TERM COMPLICATIONS

    None.

    AUTHOR(S)/REVIEWERS:

    Authors:       Tim Meredith and Yeong-Liang Lin
                   Center for Clinical Toxicology
                   Vanderbilt University Medical Center
                   Nashville, USA.

    Reviewers:     Rio de Janeiro  9/97:  J.N. Bernstein, E. Birtanov,
                   R. Fernando, H. Hentschel, T.J. Meredith, Y. Ostapenko,
                   P. Pelclova, C.P. Snook, J. Szajewski.