Which of the following is the earliest sign of magnesium toxicity in a patient with eclampsia on treatment with magnesium sulphate?

Throughout the administration of magnesium, the patient needs continuous clinical monitoring for magnesium toxicity. Toxicity is manifested by loss of deep tendon reflexes (patellar), decrease in respiratory rate, oliguria and altered mental status. Comparatively, loss of deep tendon reflexes appears to be the earliest of all the signs and it occurs when the magnesium level exceeds 5 mmol/L. Ref: 'John Hopkins' Textbook of Obstetrics 2nd edition, Page 20; Core Topics in Critical Care Medicine By Fang Gao, Page 345; Danfoh's obstetrics and gynecology By Ronald S. Gibbs, David; Newton Danfoh, Beth Y. Karlan, Ahur F. Haney, Page 270 - 271