<prompt> First sign of magnesium sulphate toxicity isLoss of deep tendon reflexesCardiac arrestRespiory depressionDecreased urinary output  <response>: Magnesium sulfate toxicity : Loss of deep tendon reflexes. - 7 mEqL Respiratory depression more than 10 meqL Cardiac arrest more than 25mEqL Ref: Dutta Obs 9e pg 222. 