<prompt> MagnesiumIs essential for efficient secretion and peripheral action of PTHIs essential for efficient secretion and peripheral action of calcitoninIs cofactor for vitamin D in boneCompetitively occupies calcium slots in bone  <response>: It is uncommon and always due to excessive intake either orally antacids, rectally enema or parenterally. Causes of hypermagnesemia are listed in Box 35.19. Magnesium intoxication causes depression of neuromuscular system, causing lethargy, hypotension, respiratory depression, brady- cardia and weak tendon reflexes. In severe conditions, acute rhabdomyolysis results. Hypermagnesemia induces decrease in serum calcium by inhibiting PTH secretion, which in turn will have deleterious effects.Ref: DM Vasudevan, page no: 412 