The most readily detected clinical sign of hypermagnesemia is-

Hypermagnesaemia This is a much less common abnormality than hypomagnesaemia. Predisposing conditions include acute kidney injury, chronic kidney disease and adrenocoical insufficiency. The condition is generally precipitated in patients at risk from an increased intake of magnesium, or from the use of magnesium-containing medications, such as antacids, laxatives and enemas. Clinical features include bradycardia, hypotension, reduced consciousness and respiratory depression. Disappearance of deep tendon reflexes Management involves ceasing all magnesium-containing drugs and reducing dietary magnesium intake, improving renal function if possible, and promoting urinary magnesium excretion using a loop diuretic with intravenous hydration, if residual renal function allows. Calcium gluconate may be given intravenously to ameliorate cardiac effects. Dialysis may be necessary in patients with poor renal function. Ref Davidson 23rd edition pg 368