Prolonged apnea due to repeated dosing with succinylcholine is due to it entering phase 2 block. Phase I depolarizing block is preceded by muscle fasciculation. During paial neuromuscular block, phase I depolarizing block is characterised by: No fade during repetitive stimulation (tetanic or TOF) No post tetanic facilitation (potentiation) Rapid hydrolysis by butyrylcholinesterase (plasma cholinesterase) terminates phase I depolarizing blockade of succinylcholine. Phase II block resembles non depolarizing block, is characterised by: Fade during repetitive stimulation (tetanic or TOF) Post tetanic facilitation (potentiation) Phase II block can be antagonized by administering a cholinesterase inhibitor like neostigmine.