MAGNESIUM Sulphate

1) Therapeutic drug action & mechanism(pharmacology)

• Magnesium supplement

• Antiarrhythmic

• Anticonvulsant

• Second most abundant intracellular cation

• Magnesium is a cofactor of membrane Na+-K+ —ATPase

• If enzyme activity is impaired due to low magnesium, intracellular potassium may decrease, leading to increased cellular excitability—in this setting, potassium supplements will not resolve the problem though magnesium supplements may

• Magnesium is a calcium antagonist, blocking slow calcium channels

• Magnesium deficiency may precipitate arrhythmias by enhancing early repolarisation

2) Indications

• Prophylactic or therapeutic treatment of magnesium depletion

• Ventricular tachycardia: monomorphic; polymorphic (torsade de pointes)

3) Effects on organs—side effects

• Coronary vasodilation

4) Toxic effects/ precautions with administration

• Vasodilation, hypotension

• Cardiac conduction defects/ cardiac arrest

• CNS depression

6) Reversal, antagonism or antidote

• Lasix; diuretics

• Calcium chloride to protect against the cardiac conduction defects effects of hypermagnesiumaemia

7) Loading dose, maintenance dose, frequency & method of administration

• Normal plasma level: 0.7 — 1.1 mmol/l

• Exists in 3 forms: ionised, protein bound & ion bound

8) Drug’s metabolism—Drug’s excretion—Half life

(pharmacokinetics)

• Cardiac patients are at high risk for hypomagnesaemia [decreased intake plus increased excretion (diuretics, diabetes, antibiotics)] or due to citrated blood products & albumen administration

• CPB further reduces Mg 2° administration blood products & dilution

• Calcium & magnesium are synergistic: low Mg can cause hypocalcaemia refractory to exogenous calcium administration