C

In neonatal tetany the underlying emergency is symptomatic hypocalcaemia; the immediate measure is to raise serum calcium with intravenous calcium gluconate (10% solution, 1–2 mL/kg given slowly), while etiologic evaluation and longer-term therapy (e.g., vitamin D) follow [Vuralli, 2019, PMID 31320908; Haas et al., 1975, PMID 1104994].