10% calcium gluconate solution (given intravenously) is the form of calcium most widely used in the treatment of hypocalcemia. This form of calcium is not as well absorbed as calcium lactate, and it only contains 0.93% (930 mg/dl) calcium ion (defined by 1 g weight solute dissolved in 100 ml solvent to make 1% solution w/v). Therefore, if the hypocalcaemia is acute and severe, calcium chloride is given instead.
It is also used to counteract an overdose of Epsom Salts magnesium sulfate, which is often administered to pregnant women in order to prophylactically prevent seizures (as in a patient experiencing preeclampsia). Magnesium sulfate is no longer given to pregnant women who are experiencing premature labor in order to slow or stop their contractions (other tocolytics are now used instead due to better efficacy and side effect profiles). Excess magnesium sulfate results in magnesium sulfate toxicity, which results in both respiratory depression and a loss of deep tendon reflexes (hyporeflexia). Calcium gluconate is the antidote for magnesium sulfate toxicity.
Calcium gluconate is also used as a cardioprotective agent in hyperkalemia. Though it does not have an effect on potassium levels in the blood, it reduces the excitability of cardiomyocytes thus lowering the likelihood of developing cardiac arrhythmias.
Historically, IV calcium gluconate was used as an antidote for black widow spider envenomation, often in conjunction with muscle relaxants. This therapy, however, has since been shown to be ineffective.
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