First sign of magnesium sulphate toxicity is
Magnesium sulfate toxicity : Loss of deep tendon reflexes. - >7 mEq/L Respiratory depression more than 10 meq/L Cardiac arrest more than 25mEq/L Ref: Dutta Obs 9e pg 222.
Loss of deep tendon reflexes
Cardiac arrest
Respiory depression
Decreased urinary output
Medical, surgical and gynaecological illness complicating pregnancy