Reduction of the lethality and the nephrocalcinotic effect of single fluoride doses by magnesium in rats.

Magnesium chloride, administered by gavage to fasting young rats, 30 min prior to sodium fluoride, elevated the LD50 for fluoride from 76 to 104 mg/kg body wt. The LD50 was elevated to greater than 180 mg/kg when magnesium was given in a dose equivalent to 2 or 3 times that of fluoride. In two experiments, a dose of 50 mg F/kg caused a mean 14- and 19-fold increase above the level of the control animals in the renal calcium content. The nephrocalcinotic effect of fluoride was nearly completely prevented by administering magnesium in a dose which is 3-fold the equivalent of the fluoride dose 30 min prior to fluoride.